Acid Sulfate Soils Centre

Acid Sulfate Soils Centre

RW Fitzpatrick, P Shand, AKM Baker, S Grocke and BT Thomas Acid Sulfate Soils Centre Report: ASSC_067 (V4) 12th March, 2015

Dry C reek S alt F ields : As s es s ment of Ac id S ulfate S oil environments in S ec tion 2 for ponds (PA3 to PA12) and drains

Enquiries should be addressed to: Professor Rob Fitzpatrick: Acid Sulfate Soils Centre, The University of Adelaide, Private Bag No 2, Glen Osmond, South Australia

Email: [email protected] Phone: 08 8303 8511; Mobile: 0408 824 215

Citation: RW Fitzpatrick, P Shand, AKM Baker, S Grocke and BT Thomas (2015) Dry Creek Salt Fields: Assessment of Acid Sulfate Soil environments in Section 2 for ponds (PA3 to PA12) and drains. Acid Sulfate Soils Report No ASSC_067, 12th March 2015.

Copyright and Disclaimer To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of The University of Adelaide.

Disclaimer The University of Adelaide advises that the information contained in this publication comprises general statements based on scientific research. The results and comments contained in this report have been provided on the basis that the recipient assumes the sole responsibility for the interpretation and application of them. The author gives no warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or use of the results and comments contained in this report by the recipient or any third party.

Cover image Aerial photograph of the series-flow salt field at the Dry Creek Salt fields showing: (i) a portion of the impounded salt ponds extending south from the road connecting St Kilda, which is located on the coast adjacent to mangrove swamps, (ii) the series of salt concentrating ponds with gypsum crusts near St Kilda, to the final concentrators and crystallisers at Dry Creek (southernmost ponds) where common salt (Halite) precipitates and (iii) a soil profile (inset) near St Kilda showing a pink coloured gypsum layer underlying a thick black gypseous layer with high concentrations of iron monosulfides, pyrite and carbonate (shell grits)

Photographs: Aerial photograph obtained from Mr Nick Withers Ridley Corporation Limited. Inset soil profile: Rob Fitzpatrick @ 2014 Acid Sulfate Soils Centre, The University of Adelaide

mailto:[email protected]�

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C ontents E XE C UTIVE S UMMAR Y .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

1. INTR ODUC TION .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.1 Overview and purpose ............................................................................................ 10 1.2 Aims and scope of work .......................................................................................... 11 1.3 Acid sulfate soil materials ....................................................................................... 12 1.4 Acid sulfate soil types and subtypes ....................................................................... 13 1.5 Review of previous acid sulfate soils investigations ............................................... 13

2. F IE L D AND L AB OR AT OR Y ME THODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.1 Field sampling of soils ............................................................................................ 18 2.2 Laboratory soil analysis methods ........................................................................... 18 2.3 Acid Volatile Sulfur .................................................................................................. 23 2.4 Total carbon and nitrogen ....................................................................................... 23 2.5 Rapid metal release test methods .......................................................................... 24 2.6 Mineralogical analyses by x-ray diffraction ............................................................. 24 2.7 Water analyses ....................................................................................................... 25

3. S OIL P R OF IL E AS S E S S ME NT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1 Ponds PA3 to PA12 ................................................................................................ 27 3.1.1 Background ............................................................................................................. 27 3.1.2 Reconnaissance survey: soil acidity ....................................................................... 27 3.1.3 Detailed survey: soil acidity and acid-base accounting .......................................... 31 3.1.4 Soil Mineralogy ....................................................................................................... 43 3.1.5 Organic carbon and nitrogen .................................................................................. 43 3.1.6 Classification and acidification and deoxygenation/smell hazard assessment ...... 44 3.2 Drains ...................................................................................................................... 47 3.2.1 Background ............................................................................................................. 47 3.2.2 Reconnaissance survey: soil acidity ....................................................................... 47 3.2.3 Detailed survey: soil acidity and acid-base accounting .......................................... 48 3.2.4 Soil Mineralogy ....................................................................................................... 50 3.2.5 Classification and acidification and deoxygenation/malodour hazard assessment 52 3.2.6 Organic carbon and nitrogen .................................................................................. 53

4. R AP ID ME T AL R E L E AS E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 4.1 Introduction ............................................................................................................. 54 4.2 Methodology and analytical techniques .................................................................. 55 4.3 Soil extraction data ................................................................................................. 56

5. S OIL -R E G OL ITH HY DR O-TOP OS E QUE NC E MODE L S TO E XP L AIN AND P R E DIC T C HANG E S IN S OIL S OVE R T IME AND S P AC E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 5.1 Soil-regolith hydro-toposequence models .............................................................. 64 5.2 Ponds PA3 to PA12 ................................................................................................ 65 5.3 Degree of external and internal factors controlling pedogenic processes in salt

pond evolution and rehabilitation for western and eastern segments .................... 68

6. AC ID S UL F AT E S OIL C L AS S IF IC ATION MAP S AND HAZAR D R ATING MAP S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 6.1 Construction of acid sulfate soil classification maps .............................................. 72

6.2 Acid sulfate soil classification maps for ponds PA3 to PA12 .................................. 77 6.3 Acid sulfate soil classification maps for pond PA7a................................................ 77 6.4 Acid sulfate soil classification maps for drains ........................................................ 78 6.5 Acid sulfate soil hazard ratings for acidity and deoxygenation/smell...................... 79 6.5.1 Hazard or risk evaluation ........................................................................................ 79 6.6 Acidification hazard ................................................................................................. 82 6.7 Soil deoxygenation/malodour hazard ..................................................................... 82 6.8 Sodicity hazard........................................................................................................ 83

7. S UMMAR Y .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 1.1 Brief summary ......................................................................................................... 84 1.2 Communication Activities ........................................................................................ 85

8. R E F E R E NC E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

9. Appendix 1 – Aus tralian ac id s ulfate s oil identification key . . . . . . . . . . . . . . . . . . . . . . . . 91

n-Value or Index of S quis hines s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

10. Appendix 2 –F ield photographs (electronic file) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

11. Appendix 3 – Mineralogy: X-ray diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12. Appendix 4 – pH incubation data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

13. Appendix 5 – Ac id B as e Accounting, AVS , Total Organic carbon and Nitrogen data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

14. Appendix 6 – Metal E xtraction Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

L is t of F igures Figure 1-1 Aerial photograph of the series-flow salt field at the Dry Creek Salt fields showing: (i)

a portion of the impounded salt ponds extending south from the road connecting St Kilda, which is located on the coast adjacent to mangrove swamps, (ii) the series of salt concentrating ponds with gypsum crusts near St Kilda, which is host to brine shrimp, to the final concentrators and crystallisers at Dry Creek (southernmost ponds) where common salt (NaCl or Halite) precipitates, which contain mostly plankton and archeobacteria and (iii) a soil profile (inset) near St Kilda showing a pink coloured gypsum layer underlying a thick black gypseous layer with high concentrations of iron monosulfides, pyrite and carbonate (shells grits). ......................................................................................................................... 11

Figure 1-2 Barker Inlet tidal estuary showing the original major vegetation types, physiographic settings and two study areas located at St Kilda (“natural” mangrove woodlands with acid sulfate soil profiles 600 and 2610 located in this area) and Gillman. The Gillman site is predominately vacant, consisting of open grasslands, samphire shrub lands and salt and sand flats. It is bordered by urban and industrial development to the south, and abuts tidal mangrove woodland along North Arm. The Gillman area has been progressively reclaimed from the intertidal and supratidal environments of Barker Inlet since the 1930s by construction of a series of bund walls that prevent tidal inundation for agriculture and industry. The land at Gillman was soon abandoned due to severe acidification, salinity and stormwater ponding (From Fitzpatrick et al. 2008b,c; Thomas 2010). ................................ 15

Figure 1-3: Schematic cross-section from Le Fevre Peninsula to the Mount Lofty Ranges, showing relationships between Quaternary coastal marine and continental facies of the St Vincent Basin. The St Kilda Formation (Holocene sands and clays) overlay the Glanville Formation (Pleistocene clays), and they together on-lap the thick alluvial Hindmarsh Clay Formation (after Belperio & Rice 1989; Belperio 1995; and Thomas 2010). ....................... 16

Figure 3-1 NearMap (http://www.nearmap.com/) aerial image of the Ridley Dry Creek Salt Field ponds PA3 to PA12 showing distribution of: (i) soil profiles sampled during the walkover reconnaissance survey of all sites (yellow dots: Profiles DPA3-01 to DPA12-01; Profile DPAD-01 = drain) in December 2013, and (ii) representative soil profiles sampled during the detailed sampling campaign in March/April 2014 (green star symbols; profiles DPA3d-01 to DPA12d-01; Profile DPADd-01 = drain for incubation experiments, laboratory pH, peroxide pH; full acid base accounting; analysis for AVS, selected mineralogy and metal availability testing). ............................................................................................................... 28

Figure 3-2 Initial pH and incubation pH (16 weeks) plotted against depth for each DPA profile collected ............................................................................................................................... 29

Figure 3-3 Photograph of profile DPA6-02 collected in December 2013 showing wide range of acid sulfate soil materials and related features (e.g. gypsum crusts and shell grit layers) . 32

Figure 3-4 pH, acid base accounting, total organic carbon and total nitrogen data plotted against depth for each DPAd soil profile collected in March/April 2014 .............................. 33

Figure 3-5 Profile DAP7A-01 photographed and sampled 16th December, 2013 following an extensive DRY PERIOD ...................................................................................................... 40

Figure 3-6 Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014 ...................................................................... 40

Figure 3-7 Profile DAP7A-01 photographed and sampled 16th December, 2013 following an extensive DRY PERIOD ...................................................................................................... 41

Figure 3-8 Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014 ...................................................................... 41

Figure 3-9 Profile DAP7A-01 photographed and sampled 16th December, 2013 – following an extensive DRY PERIOD showing a hard continuous gypsum crust ranging from 3cm to 10cm thick ............................................................................................................................ 42

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Figure 3-10 Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014 showing a fragile discontinuous gypsum layer ranging from 3cm to 10cm thick ........................................................................................... 42

Figure 3-11 Close-up views of sections of Profile DAP7A-01 photographed and sampled 16th December, 2013 – following an extensive DRY PERIOD showing a hard continuous gypsum crust ranging from 3cm to 10cm thick .................................................................... 42

Figure 3-12 Close-up views of sections of Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014 showing a fragile discontinuous gypsum layer ranging from 3cm to 10cm thick ............................................. 42

Figure 3-13 Initial pH and incubation pH (16 weeks) plotted against depth for drain DPAD-01 profile collected .................................................................................................................... 47

Figure 3-14 pH, acid base accounting, total organic carbon and total nitrogen data plotted against depth for each drain profile collected ...................................................................... 48

Figure 3-15 Selected range of photographs in drain DPADd-2 showing profile of the sulfuric soil DPADd-2.1 (top two photo’s), white surface salt efflorescences (middle two photo’s illustrating field measurement of low acidity: pH <1.5) and iron precipitates (bottom left hand side photo) and a remnant of an aluminium drink can that has been dissolved by the extreme acidic conditions (bottom right hand side photo) .................................................... 51

Figure 4-1 Surface of soil at contaminated site showing bright yellow efflorescences of ammonium carnallite, halite, and epsomite (see section 3.2.4 for more details and soil characteristics). .................................................................................................................... 55

Figure 4-2 Plots of pH, SEC, Eh and alkalinity, comparing data from sampled soils with the same soils incubated for 8 weeks. ....................................................................................... 57

Figure 4-3 Piper plot showing the relative proportions of major elements in soil extractions ..... 58

Figure 4-4 Depth profile of PA 6.2 showing depth trends of pH, Eh and SEC ............................ 59

Figure 4-5 Depth profile for major elements, Sr and TOC .......................................................... 60

Figure 4-6 Depth profile for trace elements ................................................................................. 61

Figure 4-7 Plots of trace elements plotted against pH highlighting the different behaviour of these elements. .................................................................................................................... 62

Figure 5-1 Representative soil-regolith hydro-toposequence model for section 2 based largely on the soil features for pond PA6 in autumn (March/April, 2014) showing the spatial distribution of: (i) water levels from West to East (horizontal scale less exaggerated), (ii) topography, including salt ponds, bund walls, tidal creek in mangrove swamp and AHD levels, (iii) vegetation (mangroves and samphire), (iv) major acid sulfate soil materials: monosulfidic, hypersulfidic and hyposulfidic (vertical scale exaggerated) and (v) soil horizons (gypsum crusts / fragments =- Gypsic horizons; halite crusts = salic horizons) and sediment layers based on (colour and texture (light brown clay / shell grit). ....................... 67

Figure 5-2 Predictive soil-regolith model for Salt Ponds PA3 to PA 12 western segments illustrating the dominant pedogenic pathways and processes ............................................. 70

Figure 5-3 Predictive soil-regolith model for Salt Ponds PA3 to PA 12 eastern segments illustrating the dominant pedogenic pathways and processes ............................................. 71

Figure 6-1 Acid sulfate soil classification and acidification hazard rating map for ponds PA3 to PA12 (using legend in Table 6-2) ......................................................................................... 78

Figure 6-2 Acid sulfate soil classification and deoxygenation/malodour hazard rating maps for ponds PA3 to PA12 (using legend in Table 6-3 ) ................................................................. 78

Figure 6-3 Acid sulfate soil classification and acidification hazard rating maps for pond PA7a (using legend in Table 6-4) .................................................................................................. 78

Figure 6-4 Acid sulfate soil classification and deoxygenation/malodour hazard rating maps for pond PA7a (using legend in Table 6-5 ) ............................................................................ 78

Figure 6-5 Acid sulfate soil classification and acidification hazard rating maps for drains DPAD-01, 02, 03 and 04 (using legend in Table 6-6) ..................................................................... 78

Figure 6-6 Acid sulfate soil classification and deoxygenation/malodour hazard rating maps for drains DPAD-01, 02, 03 and 04 (using legend in Table 6-7) ............................................... 78

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L is t of T ables Table 2-1 List of methods for field data collection. ..................................................................... 19

Table 2-2 List of methods for laboratory analysis conducted. ..................................................... 21

Table 2-3: Criteria indicating the need for an ASS management plan based on texture range and chromium reducible sulfur concentration and amount of soil material disturbed (Dear et al. 2002). .............................................................................................................................. 22

Table 2-4 Methods used for analyses of water .......................................................................... 25

Table 3-1 Mineralogical composition of selected soil samples from ponds PA6, PA7a and PA9 .............................................................................................................................................. 43

Table 3-2 Samples from section 2 ponds: summary of ASS material classification, ASS subtype soil profile classification, other major soil morphology features used to determine acidification hazard ratings (where a sulfuric soil** has a high rating, hypersulfidic soil* has medium rating and hyposulfidic soil has a low rating) .......................................................... 45

Table 3-3 Mineralogical composition of soil sample from drain DPADd-02 sampled in April, 2013 .............................................................................................................................................. 50

Table 3-4 Mineralogical composition of soil samples from drain PAD-02 sampled in December, 2013 ...................................................................................................................................... 50

Table 3-5 Samples from section 2 drains: summary of ASS material classification, ASS subtype soil profile classification, other major soil morphology features used to determine acidification hazard ratings (where a sulfuric soil** has a high rating, hypersulfidic soil* has medium rating and hyposulfidic soil has a low rating) .......................................................... 52

Table 4-1 Concentrations of selected contaminants in sample DPAD-02.2 for t0 and t8 water extractions. ........................................................................................................................... 63

Table 6-1. Map Legend showing potential soil map units ordered by landscape (ponded water level) and then acid sulfate soil class and texture. ............................................................... 73

Table 6-2. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for ponds PA3 to PA12 with acidification hazard ratings ..................................... 74

Table 6-3. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for ponds PA3 to PA12 with Deoxygenation/malodour hazard ratings .............. 74

Table 6-4. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for pond PA7a with acidification hazard ratings .................................................. 75

Table 6-5. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for pond PA7a with Deoxygenation/malodour hazard ratings ............................ 75

Table 6-6. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for drains DPAD-01, 02, 03 and 04 with acidification hazard ratings .................. 76

Table 6-7. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for drains DPAD-01, 02, 03 and 04 with deoxygenation/malodour hazard ratings

.............................................................................................................................................. 76

Table 6-8: Standardised table used to determine the consequence of a hazard occurring. ....... 80

Table 6-9: Likelihood ratings for the disturbance scenario (from MDB 2010). ............................ 80

Table 6-10: Risk assessment matrix (Standards Australia/Standards New Zealand, 2004). ..... 81

Table 6-11: Salinity hazard as defined by the electrical conductance of a saturation extract (ECse) and 1:5 soil:water extract (i.e. soil is extracted with distilled water)1 ....................... 83

Ac knowledgments We would like to acknowledge the support, comments and project management provided by Nick Withers from Ridley Corporation Limited (Ridley). This work was jointly funded by Ridley and various agencies in the South Australia State government with co-investment from CSIRO.

The following staff are thanked for analytical and logistical support: Greg Rinder in preparing some figures; Mark Raven (CSIRO Land and Water) for X-ray diffraction analyses; John Gouzos and team for anion analyses; and Chad Jarolimek for ICP analyses.

0BEXECUTIVE SUMMARY

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E XE C UT IV E S UMMAR Y

Acid sulfate soils (ASS) are soils that are either acidic (due to the generation of sulfuric acid forming sulfuric material), or have the potential to generate sulfuric acid when exposed to oxygen because of the presence of sulfide minerals (sulfidic material). The prime objective of this report is to:

• Verify the presence (or absence) of the four main types of ASS materials (hypersulfidic, hyposulfidic, sulfuric and monosulfidic materials) in ponds PA3 to PA12 and adjacent drains in Section 2 of the Dry Creek salt fields, and assess the potential acidification and deoxygenation/malodour hazards.

• Identify various subtypes of ASS (e.g. hypersulfidic subaqueous clayey soils or sulfuric clayey soils) present, and provide predictive capability of current and potential acidification and deoxygenation/ malodour hazards of ASS present when the salt ponds continue to drain and/or subsequently re-flood.

Key findings Sampling was followed by quantitative laboratory analyses of soil samples to develop a better understanding of the temporal and spatial changes in Acid Sulfate Soils caused by rapid drying and inundation/reflooding in ponds PA3 to PA12 and adjacent drains.

The study provides a spatial dataset for the soil condition at the times of sampling (summer, December 2013 and autumn, March/April 2014) from which conceptual models and maps were generated to show the presence and spatial heterogeneity of acid sulfate soil properties in ponds PA3 to PA12.

Soil maps, showing acid sulfate soil sub-types, were produced that allowed integration of additional information to be incorporated such as soil characteristics with depth, water depth, identification of monosulfidic material and knowledge about the location of underlying clay layers/horizons. These maps provide a detailed overview of acid sulfate soil variation that occurred when ponds PA3 to PA12 were surveyed in March/April 2014 (detailed investigation). The high concentrations and distribution of iron monosulfides in ponds PA3 to PA12 have been promoted by:

• the dominantly depositional environment (closed evaporation ponds), • high organic matter, • low Fe and very high carbonate concentrations (precipitated early in the salt

production process), and • low re-suspension (due to very slow seawater inflow/throughflow velocities and

more sheltered nature of the bunded ponds).

Acid sulfate soil acidification and deoxygenation/ malodour hazard ratings were assigned to the ASS maps, with polygons rated as high (yellow coloured map unit), medium (brown coloured map unit) and low (blue coloured map unit). This assessment was based on field and laboratory data, particularly the detailed information obtained during the March/April, 2014 field survey.

A number of contaminants were identified as being potentially mobile using a simple batch water extraction, including As, Cr, Cu, U and especially Mo. A highly contaminated site contained very high concentrations of a number of metal contaminants. Their mobility is related to a number of factors such as source which varies with depth, soil pH, Eh, mobility of dissolved organic matter.

0BEXECUTIVE SUMMARY

Summary The acid sulfate soil maps, in combination with soil-regolith toposequence models, present an understanding of ASS distribution in three dimensions. A generalized temporal soil-regolith model has been constructed to describe the current understanding of complex ASS distribution and to demonstrate predictive scenarios for changes occurring over time (i.e. progression from being mostly drained and dry in summer (December 2013) to wet and re-flooded in autumn (March/April 2014).

Ponds PA3 to PA12 A generalised conceptual soil-regolith hydro-toposequence model in the form of cross-sections was constructed for both the western and eastern segments of ponds PA3 to PA12 to explain the spatial and temporal heterogeneity of: (i) acid sulfate soil properties comprising a range of ASS materials and subtypes, (ii) ground/surface water interactions and (iii) salt efflorescences and gypsum crusts.

The conceptualised temporal soil-regolith model was used to describe the current understanding of acid sulfate soil distribution and to demonstrate predictive scenarios for possible changes occurring over time (e.g. progressive drying to depth). Two temporal overall predictive models were constructed for the western and eastern segments of ponds PA3 to PA12 to illustrate and explain the various pedogenic rate processes for pond origin and change over time.

Acidification hazard: Medium for western segments of ponds Low for eastern segments of ponds (no treatment required)

Deoxygenation/malodour hazard: Medium for western and eastern segments of ponds

Predicted future soil sodicity hazard: Low.

Pond PA7a Complex soil, hydrological and biogeochemical interactions have led to the following changes in properties of the gypsum crust in the northern segment of the pond:

(i) hard crust in December 2013 following a dry period and

(ii) friable and soft in March/April 2014 following an extreme high rainfall event in February, 2014.

Acidification hazard: Low

Deoxygenation/ malodour hazard: Medium for southern segments of ponds Low for northern segments of ponds

Predicted future soil sodicity hazard: Low

Drain adjacent to pond PA10 (DPAD-02): Acidification hazard: High

Occurrence of sulfuric clayey soils with a high acidification hazard rating.

Deoxygenation/ malodour hazard: Low

Predicted future soil sodicity hazard: Medium

Drains adjacent to ponds PA3 to PA12 (DPAD-01, 03 and 04) Acidification hazard: Low

Deoxygenation/ malodour hazard: Medium (mostly) to high

Predicted future soil sodicity hazard: Medium:

1BINTRODUCTION

10 Assessment of Acid Sulfate Soil environments in Section 2, Dry Creek Salt works

1. INT R ODUC T ION

Summary This section gives a brief and selective historical background to the Dry Creek salt fields with emphasis on the soil drying processes during the closure of the Dry Creek salt fields - as background to defining the aims and scope of this project. It also briefly defines Acid Sulfate Soils (ASS), the criteria used for the classification of sulfuric, sulfidic, hypersulfidic, hyposulfidic and monosulfidic materials and ASS Sub-types.

This section also provides a brief synopsis of previously published ASS work within, and adjacent to, the Dry Creek salt fields. These historical case studies describe how sulfides in anthropically modified environments are oxidised to form sulfuric acid, iron-oxide minerals and salts by processes such as draining due to the construction of bund walls. They illustrate the complexities and importance of understanding specific sites (e.g. Gillman site with major bund wall structures) to assess particular ASS processes, implications and suitability of the different management options.

1.1 Overview and purpos e

The Dry Creek salt fields (4,000 ha) are located on the coast, 12 km NW of Adelaide, South Australia (Figure 1-1). Salt has been produced at this site the late 1930’s by evaporating seawater pumped into a series of concentrating ponds to the point where common salt (NaCl or halite) precipitates. The less soluble salts, iron oxide and calcite, followed by gypsum, are precipitated out during passage and evaporation of seawater through the chain of ponds (Figure 1-1). According to Peri Coleman (personal communication) during a series of expansions of the salt fields (6 in 65 years) the ponds were maintained at a stable depth and the brine moved slowly through them as it concentrated. This means that conditions in any specific pond “remained the same, with the salinity gradient arranged spatially across the landscape, instead of changing temporally”. As a consequence, substantial amounts of pyrite, metastable iron monosulfides and gypsum have progressively built-up in these permanently saturated sediments or subaqueous soils (Figure 1-1) in the ponds (i.e. the permanently saturated sediments did not dry out to oxidise pyrite and iron monosulfides). The ponds extend about 35 km from Dry Creek (Section 1) to St Kilda (Section 2) to Port Gawler (Section 3) to Middle Beach (Section 4).

The salt production operation is now being ceased with the goal to close and rehabilitate the site. Several environmental challenges exist, which include draining numerous hypersaline ponds, potential dust and malodour impacts, maintaining the sites value for migratory bird species, and re-establishing vegetation (e.g. mangroves, salt marsh). An excellent opportunity exists to assess and characterise in detail not only the wide range of subaqueous acid sulfate soils present, but also to investigate the soil drying processes during the closure of the Dry Creek salt fields. This information will be used to investigate and advise on the acid sulfate soil hazards from a) the temporary holding pattern in which designated ponds are drained while investigations are conducted to design closure works and b) the permanent closure works, to help the design of these. The holding pattern is temporary and reversible. Closure is not, and is part of the pathway to future uses of the site. The advice on the soil hazards will be used by Ridley and Government agencies to assess and prioritise risks for prevention, mitigation and management.

1BINTRODUCTION

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1.2 Aims and s c ope of work

The Acid Sulfate Soils Centre (ASSC) was commissioned by Ridley Land Corporation Limited (Ridley) and several South Australian State Government agencies (DMITRE, EPA, SA Water) to characterise the properties of the potential Acid Sulfate Soil (ASS) hazards and the potential imminent or longer term risks to the environment inside and outside PA3 to PA12 salt ponds and adjacent drains in Section 2 from the drying being undertaken (i.e. December, 2013) and planned within the salt fields.

Figure 1-1 Aerial photograph of the series-flow salt field at the Dry Creek Salt fields showing: (i) a portion

of the impounded salt ponds extending south from the road connecting St Kilda, which is located on the coast adjacent to mangrove swamps, (ii) the series of salt concentrating ponds with gypsum crusts near St Kilda, which is host to brine shrimp, to the final concentrators and crystallisers at Dry Creek (southernmost ponds) where common salt (NaCl or Halite) precipitates, which contain mostly plankton and archeobacteria and (iii) a soil profile (inset) near St Kilda showing a pink coloured gypsum layer underlying a thick black gypseous layer with high concentrations of iron monosulfides, pyrite and carbonate (shells grits).

The aims of this investigation were to undertake: (i) a brief review of previous Acid Sulfate Soils work conducted in Barker Inlet and the Dry Creek Salt fields, (ii) a reconnaissance (walkabout survey) Acid Sulfate Soil (ASS) survey of PA3 to PA12 salt ponds and adjacent drains in December, 2013 so as to ascertain the need for a more detailed systematic assessment in March/April 2014 involving quantitative laboratory analyses in order to:

• Assess acidification and deoxygenation/malodour hazards caused by ASS sub-types (i.e. with sulfuric, hypersulfidic, hyposulfidic & monosulfidic materials) using reliable interpretation methods.

1BINTRODUCTION


• Determine the potential, available and retained acidity to provide more confidence in the drying action currently underway.

• Assess (if possible) the spatial and temporal extent/variations of ASS subtypes caused by drying and/or reflooding of ponds PA3 to PA12 and adjacent drains.

• Provide regular verbal and written briefings to Ridley Land Corporation (Ridley) and agencies in the Government of South Australia.

1.3 Ac id s ulfate s oil materials

Acid Sulfate Soils (ASS) are those soils in which sulfuric acid may be produced, is being produced, or has been produced in amounts that have a lasting effect on main soil characteristics (Pons 1973). This general definition includes: (i) potential, (ii) actual (or active), and (iii) post-active ASS, three broad generic soil types that continue to be recognised (e.g. Fanning 2002). However, definitions of these broad generic types of ASS can be confusing and the Acid Sulfate Soil Working Group of the International Union of Soil Sciences agreed to adopt changes to the classification of ASS materials (Sullivan et al. 2010), which was also adopted by the Scientific Reference Panel of the Murray-Darling Basin Acid Sulfate Soils Risk Assessment Project for use in detailed assessment of acid sulfate soil in the Murray-Darling Basin. This report follows these recommendations. Acid sulfate soils are essentially soils containing detectable sulfide minerals, principally pyrite (FeS2) or monosulfides (FeS). The definitions used in this report are:

Sulfuric material: Soil material that has a pH less than 4 (1:1 by weight in water, or in a minimum of water to permit measurement as currently defined by the Australian Soil Classification, Isbell 1996).

Sulfidic materials* – soil materials containing detectable sulfide minerals. The intent is for this term to be used in a descriptive context (e.g. sulfidic soil material or sulfidic sediment) and to align with general definitions applied by other scientific disciplines such as geology and environment science (e.g. sulfidic sediment). The method with the lowest detection limit is the Cr-reducible sulfide method, which currently has a detection limit of 0.005%; other methods (e.g. X-ray diffraction, visual identification, Raman spectroscopy or infra red spectroscopy) can also be used to identify sulfidic materials.

*This term differs from previously published definitions in various soil classifications (e.g. Isbell 1996) Hypersulfidic material – (adapted from (e.g. Isbell 1996) with modifications to inter alia account for recent improvements to the incubation method ( Sullivan et al. 2009). Hypersulfidic material is a sulfidic material that has a field pH of 4 or more and is identified by experiencing a substantial** drop in pH to <4 (1:1 by weight in water, or in a minimum of water to permit measurement) when a 2 - 10 mm thick layer is incubated aerobically at field capacity. The duration of the incubation is either: a) until the soil pH changes by at least 0.5 pH unit to below 4, or b) until a stable*** pH is reached after at least 8 weeks of incubation.

Hyposulfidic material - (adapted from Isbell (1996) with modifications to inter alia account for recent improvements to the incubation method (Sullivan et al. 2009): Hyposulfidic material is a sulfidic material that (i) has a field pH of 4 or more and (ii) does not experience a substantial** drop in pH to <4 (1:1 by weight in water, or in a minimum of water to permit measurement) when a 2 - 10 mm thick layer is

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incubated aerobically at field capacity. The duration of the incubation is until a stable*** pH is reached after at least 8 weeks of incubation.

**A substantial drop in pH arising from incubation is regarded as an overall decrease of at least 0.5 pH unit.

***A stable pH is assumed to have been reached after at least 8 weeks of incubation when either the decrease in pH is < 0.1 pH unit over at least 14 day period, or the pH begins to increase.

Monosulfidic materials - soil materials with an acid volatile sulfide content of 0.01%S or more. Monosulfidic materials are subaqueous or waterlogged organic-rich materials that contain appreciable concentrations of monosulfides. Monosulfidic black oozes are specific materials characterised by their gel-like consistence.

Non-Acid Sulfate Soil materials In addition, the Scientific Reference Panel of the Murray-Darling Basin Acid Sulfate Soils Risk Assessment Project agreed to identify “other acidic soil materials” arising from the detailed assessment of wetland soils in the Murray-Darling Basin even though these materials may not be the result of acid sulfate soil processes (e.g. the acidity developed during ageing may be the result of Fe2+ hydrolysis, which may or may not be associated with acid sulfate soil processes). The acidity present in field soils may also be due to the accumulation of acidic organic matter and/or the leaching of bases. Of course, these acidic soil materials may also pose a risk to the environment.

The definition of these other acidic soil materials for the detailed assessment of acid sulfate soils in the Murray-Darling Basin is as follows:

1. Other acidic soil materials – either:

a. non-sulfidic soil materials that acidify by at least a 0.5 pHw unit to a pHw of <5.5 during moist aerobic incubation, or

b. soil materials with a pHw ≥ 4 but < 5.5 in the field.

2. Other soil materials – soils that do not have acid sulfate soil (or other acidic) characteristics.

1.4 Ac id s ulfate s oil types and s ubtypes

Acid sulfate soil profiles are allocated (or classified) an acid sulfate soil type and subtype according to the Acid Sulfate Soil Identification Key (Fitzpatrick et al., 2010; Fitzpatrick 2013; Appendix 1). The Key was designed for people who were not experts in soil classification systems, assisting them to easily identify five acid sulfate soil types (subaqueous, organic, cracking clay, sulfuric and hypersulfidic soils) and 18 sub-types based on the occurrence of sulfuric, hypersulfidic, hyposulfidic, or monosulfidic material, and clayey or sandy layers.

1.5 R eview of previous acid s ulfate s oils inves tigations

The following brief review of previous Acid Sulfate Soils (ASS) investigations in the Dry Creek Salt fields and adjacent Barker Inlet (Figure 1-2) is largely derived from information described by: Fitzpatrick et al. (2008a,b) and supplemented by observations and studies performed by Fitzpatrick (1991; 2012), Fitzpatrick et al. (1993; 2008b,c), Fitzpatrick & Self (1997), Merry et al. (2003), Poch et al. (2009); Thomas et al. (2003a, b; 2004), Thomas (2010) and AECOM (2013).

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Soil horizons that contain sulfides are called sulfidic material (previous definition of sulfidic: Isbell 1996; Soil Survey Staff 2003) or hypersulfidic material (new definition replacing sulfidic of Isbell 1996: see Sullivan et al. 2010), and can be environmentally damaging if exposed to air by disturbance. Exposure results in the oxidation of pyrite, with each mole of pyrite yielding 4 moles of acidity (i.e. 2 moles of sulfuric acid). This process transforms sulfidic or hypersulfidic material to sulfuric material when, on oxidation, the material develops a pH of 4 or less (Isbell 1996); note that a sulfuric horizon has a pH of 3.5 or less according to Soil Survey Staff (2003), the USDA soils classification.

Acid Sulfate Soils form in the coastal, estuarine and mangrove swamp environments of Barker Inlet and the Gulf St Vincent, because these waterlogged or highly reducing environments are ideal for the formation of sulfide minerals, predominantly iron pyrite (FeS2). Soil horizons that contain sulfides are called sulfidic material (Soil Survey Staff 2003) or hypersulfidic material (Sullivan et al. 2010; Isbell 2014 – revised 2nd edition), and can be environmentally damaging if exposed to air by disturbance. Exposure results in the oxidation of pyrite, with each mole of pyrite yielding 4 moles of acidity (i.e. 2 moles of sulfuric acid). This process transforms sulfidic or hypersulfidic material to sulfuric material when, on oxidation, the material develops a pH of 4 or less (Isbell 1996; note that a sulfuric horizon has a pH of 3.5 or less according to Soil Survey Staff 2003). When ASS become strongly acidic, acid drainage water is produced. This acid together with toxic elements that are leached from soils and sediments can kill fish and shellfish and contaminate groundwater, and can corrode concrete and steel in homes, underground pipes and buildings. These impacts can be measured in terms of:

• poor water quality with loss of amenity, damage to estuarine environments and reduction of wetland biodiversity,

• the need for rehabilitation of disturbed areas to improve water quality and minimise impacts,

• loss of fisheries and agricultural production, and

• additional maintenance of community infrastructure affected by acid corrosion.

The distribution, processes, environmental hazards and remediation options of these coastal ASS in Barker Inlet Mediterranean climate have been described in several case studies, which covers an area of about 25 km2 immediately adjacent the Dry Creek Salt Fields (Figure 1-2).

These investigations were concentrated mainly at: (i) St Kilda, which comprised a transect through tidal and intertidal mangrove woodland and salt marshes, and (ii) Gillman, which is a highly degraded wetland adjacent to the city of Port Adelaide (Figure 1-2). Over 50 years ago, ~1 000 ha of coastal wetland were drained for urban and industrial development by the construction of a levee bank, a network of drains and tidal floodgates. Construction of the levee bank subdivided the intertidal environment and initially conditions were similar on both sides of the levee bank. Subsequently, within the bunded area, drainage and acidification degraded about 325 ha (e.g. Harbison 1986; Fitzpatrick 1991; Fitzpatrick et al. 1992; Thomas et al. 2003a), while outside the levee bank the undrained soils are approximately in their original condition, and now provide a baseline for the assessment of environmental change. Consequently, these changes to Barker Inlet, have allowed several investigations of drainage-induced changes in ASS from a series of drained and undrained sites at Gillman and St Kilda (Fitzpatrick 1991; Fitzpatrick & Self 1997; Poch et al. 2009; Thomas et al. 2003a,b; 2004; 2010; Thomas 2010).

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The recent geological evolution of Barker Inlet has largely been controlled by global sea level fluctuations (Edmonds 1995). Two million years ago sea level was 45 m lower than at present and Gulf St Vincent was dry land. Alluvial fans formed as rivers and streams drained from the higher land inland, depositing sands, gravels and particularly the thick Hindmarsh Clay (Figure 1-2) that underlies Barker Inlet, the Dry Creek Salt Fields and Adelaide.

Figure 1-2 Barker Inlet tidal estuary showing the original major vegetation types, physiographic settings and two study areas located at St Kilda (“natural” mangrove woodlands with acid sulfate soil profiles 600 and 2610 located in this area) and Gillman. The Gillman site is predominately vacant, consisting of open grasslands, samphire shrub lands and salt and sand flats. It is bordered by urban and industrial development to the south, and abuts tidal mangrove woodland along North Arm. The Gillman area has been progressively reclaimed from the intertidal and supratidal environments of Barker Inlet since the 1930s by construction of a series of bund walls that prevent tidal inundation for agriculture and industry. The land at Gillman was soon abandoned due to severe acidification, salinity and stormwater ponding (From Fitzpatrick et al. 2008b,c; Thomas 2010).

About 9000 years ago sea level rose. The Le Fevre peninsula (Figure 1-2 and Figure 1-3) was built between 6000 years ago and the present, by sand building up as a result of wave and wind action. The reworking of coastal sediments since sea level stabilisation about 7,500 BP resulted mostly in the northerly extension of sand ridges on Le Fevre Peninsula and the Port River outlet (Figure 1-2 and Figure 1-3).

The establishment of extensive sea-grass meadows led to the rapid accumulation of marine and estuarine sediments resulting in coastal land progradation throughout the late Holocene (Edmonds 1995). Progradation led to the simultaneous back-barrier development of marshes and mangrove swamps parallel to the shoreline. The Barker Inlet embayment is now mostly in-filled except for the Port River estuary.

Seagrass banks developed in shallow water, but this gradually became enclosed and estuarine mangroves took over in the intertidal zones. Then the early settlers arrived and the area became severely modified by human activities. The Gillman area has

1BINTRODUCTION


been progressively reclaimed from the intertidal and supratidal environments of Barker Inlet by construction of a series of bund walls for agriculture and industry that prevented tidal inundation (Figure 1-2 and Figure 1-3).

Subsidence rates of 1 mm per year have been documented in the Barker Inlet area (Belperio 1993), and are attributed to movement along the Para Fault, ground water extraction and consolidation of inter-tidal soils after drying due to construction of levee banks (Figure 1-2 and Figure 1-3). The presence of “sulfide-rich sediments

” in the Gillman area was identified firstly by Harbison (1986), and observed in later investigations (Belperio & Rice 1989, Belperio & Harbison 1992, Belperio 1993; 1995).

Figure 1-3: Schematic cross-section from Le Fevre Peninsula to the Mount Lofty Ranges, showing relationships between Quaternary coastal marine and continental facies of the St Vincent Basin. The St Kilda Formation (Holocene sands and clays) overlay the Glanville Formation (Pleistocene clays), and they together on-lap the thick alluvial Hindmarsh Clay Formation (after Belperio & Rice 1989; Belperio 1995; and Thomas 2010).

In 1991, CSIRO was contracted to conduct an urgent investigation of the Gillman area for the proposed construction of a multi-function-polis (Fitzpatrick, 1991). The MFP was a concept for a high technology community comprising housing, education and leisure facilities, and high-tech industries to provide employment. Fitzpatrick (1991) alerted the promoters to the problem of acid sulfate soils, and for this and other reasons the project was eventually abandoned.

Prior to 1991, no specific soil investigations had been conducted to identify and characterise types of Acid Sulfate Soils and their extent in the Barker Inlet area. However, based on several later investigations (e.g. Fitzpatrick 1991, Fitzpatrick et al. 1992, 1993, 1996; 2008b,c; Fitzpatrick & Self 1997, Thomas et al. 2004, 2003a,b; 2010; Poch et al. 2009; Thomas 2010), the properties, formation and distribution of the following 6 major types of ASS materials that commonly occur as layers in soil profiles in the wide range of physiographical environments in Barker Inlet, are summarised in discussions below:

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• Contemporary tidal zones with hypersulfidic material (mangrove and samphire marshes).

• Disturbed tidal zones with sulfuric material (drained tidal, intertidal or supratidal mangrove or samphire marshes, particularly near Gillman).

• Disturbed tidal zones with hypersulfidic material (drained tidal, intertidal or supratidal mangrove or samphire marshes, particularly in disturbed salt evaporation ponds).

• Sand plains and dunes overlying relict buried layers of hypersulfidic material.

• Anthropogenic fill materials overlying buried hypersulfidic and sulfuric materials.

• Subaqueous soils below the low tidal mark with hypersulfidic and monosulfidic materials beneath shallow, stagnant water bodies (e.g. poorly flushed or blocked estuaries, rivers, river tributaries, salt evaporation seeps and seagrass mud flats associated with Barker Inlet Estuary and Port Adelaide River).

AECOM (2013) developed a preliminary generalized conceptual site model for occurrence of “Potential Acid Sulfate Soil” in the Dry Creek salt fields and indicated that “there is potential for some inland ponds in Sections 3 and 4 to contain non-acid sulfate soils (NASS)” because they may sit on Quaternary and Pleistocene aged Pooraka Formation. They also emphasised that the boundary of the two formations had not been determined. Their model also indicated that “ASS hazard exists mostly in Holocene aged material, which contained “Potential Acid Sulfate Soil” materials (PASS; i.e. hypersulfidic material) across the entire site and may generate sulfuric acid as a result of oxidisation”.

Based on limited desktop survey information and field / laboratory data, AECOM (2013) allocated “acid sulfate soil hazard ratings” to each pond. As a consequence, they also produced hazard rating maps (Low with blue colour; Medium with orange colour and High with red colour) for each pond. However, they stipulated that as further site detail and information is obtained, their “definitions for ASS hazard ratings may be further refined”.

2BFIELD AND LABORATORY METHODS


2. F IE L D AND L AB OR AT OR Y ME T HODS

Summary This section outlines the methods used to survey, sample and analyse representative Acid Sulfate Soil samples from soil profiles and surface salt efflorescences in drains in crusts on ponds from Section 2 at the Dry Creek Salt fields.

2.1 F ield s ampling of s oils

Representative soil profiles within similar geomorphic areas were identified, described and sampled in the Ridley Dry Creek Salt Field ponds PA3 to PA12 and adjacent drains during the two field survey campaigns conducted in: (i) summer: December, 2013 (i.e. the walkover reconnaissance survey of all sites) and (ii) autumn March/April 2014 (i.e. detailed survey and samples collected from selected sites only). A summary of methods for field data collection is presented in Table 2-1. Sample site location coordinates were obtained using a GPS, using the WGS 84 Datum: Zone 54 South (Easting’s and Northing’s; Table 2-1).

Photographs were taken of the soil profile sites and soil profiles in: (i) soil pits, (ii) cores or (iii) shovels for each site (see electronic data base of photographs). In the field, each soil profile was photographed with a scale and horizons were sub-sampled. Soil material was described and physical properties such as colour, consistency, structure and texture follow McDonald et al. (1990) (Appendix 2). The presence of ‘sulfidic’ smells (e.g., H2S – rotten egg gas and methyl thiols) as well as oxidising odours (SO2) were recorded.

Representative sub-samples were collected in chip trays for: (i) soil morphological study/ description and (ii) incubation tests. For the autumn March/April 2014 detailed sampling campaign, additional sub-samples were placed in plastic jars for acid-base accounting, electrical conductivity and pH measurements. Air was excluded as far as possible when samples were collected in the plastic bottles. The analytical data for these analyses are appended to this report.

2.2 L aboratory s oil analys is methods

A summary of methods for laboratory analyses conducted is presented in Table 2-2. Following sampling, the soils were kept cool at 4°C until analysed. Samples for acid-base accounting were air dried at 80°C. Moisture contents were recorded and bulk densities estimated. Samples for sulfur suite analysis were sent to the Environmental Analysis Laboratory of Southern Cross University. Samples were also stored in chip trays to conduct incubation tests to follow the course of potential acidification and confirm ASS status. Oven and air dried/moist samples and chip tray samples were kept for long-term storage to allow for future re-sampling and analyses, if required.


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Table 2-1 List of methods for field data collection. Data and Analysis Objective Method

Field Data

Site number uniquely identifies the site Unique alpha numeric code (e.g. DXF2-01): D – project name; XF2 pond ID

Site location (Zone, easting, northing coordinates)

accurately places the sample site within the study area

Global positioning system (GPS) + or – 1 meters, locate to the WGS 84 Z 54S Grid.

Depth of water or depth to water table below soil surface

Current status of water level relative to the soil surface

Tape measure (National Committee on Soil and Terrain 2009)

Site description Places the sample site within the landscape and surrounding environment, to enable extrapolation of the profile information and to estimate the proportion that it represents in study area

Refer for guidance to National Committee on Soil and Terrain (2009).

Sample depth (upper and lower)

Estimating the layer thickness and position in the profile of the soil sample

Tape measure (National Committee on Soil and Terrain 2009)

Soil Morphology Description: field texture, consistence, structure, moisture status, and other diagnostic features if present, such as mottling (redoximorphic features), odour, organic material, shell fragments, minerals such as jarosite, crystals, coarse fragments)

For characterisation and classification of the soil. To facilitate understanding of soil variability and transfer of quantitative data between profiles and layers that appear similar through this qualitative description

National Committee on Soil and Terrain (2009); Schoeneberger et al. (2002) – for redoximorphic features

As discussed previously, sulfide minerals are generally stable under reducing conditions, however, on exposure to the atmosphere the acidity produced from sulfide oxidation can impact on water quality, crop production, and corrode concrete and steel structures (Dent 1986). In addition to the acidification of both ground and surface waters, a reduction in water quality may result from low dissolved oxygen levels (Burton et al. 2006; Sammut et al. 1993; Sullivan et al. 2002a), high concentrations of aluminium and iron (Ferguson and Eyre 1999; Ward et al. 2002), and the release of other potentially toxic metals (Burton et al. 2008a; Preda and Cox 2001; Sullivan et al. 2008; Sundstrom et al. 2002).



In nature, a number of oxidation reactions of sulfide minerals (principally pyrite: FeS2) may occur which produce acidity, including:

2FeS2 + 7O2 + 2H2O ---> 2Fe2+ + 4SO42- + 4H+

4FeS2 + 15O2 + 10H2O ---> 4FeOOH + 8H2SO4

A range of secondary minerals, such as jarosite, sideronatrite and schwertmannite may also form, which act as stores of acidity i.e. they may produce acidity upon dissolution (e.g. during rewetting).

Acid-base accounting (ABA) Acid-base accounting (ABA) is used to assess both the potential of a soil material to produce acidity from sulfide oxidation and also its ability to neutralise any acid formed (e.g. Sullivan et al. 2001; Sullivan et al. 2002b).

The standard ABA applicable to acid sulfate soil is as described in Ahern et al. (2004) and summarised here. The equation below shows the calculation of Net Acidity (NA).

Net Acidity = Potential Sulfidic Acidity + Existing Acidity – ANC*/Fineness Factor *ANC = Acid Neutralising Capacity The components in this ABA are further discussed below and by Ahern et al. (2004).

Potential Sulfidic Acidity (PSA) The potential sulfidic acidity is most easily and accurately determined by assessing the chromium reducible sulfur (SCr). This method was developed specifically for analysing acid sulfate soil materials (Sullivan et al. 2000) to, inter alia, assess their potential sulfidic acidity (PSA) also known as the ‘acid generation potential’ (AGP). The method is also described in Ahern et al. (2004), which includes the chromium reducible sulfur method (SCr or CRS: Method Code 22B) and its conversion to PSA.

Existing Acidity Existing acidity is the sum of the actual acidity and the retained acidity (Ahern et al. 2004). Titratable actual acidity (TAA) is a measure of the actual acidity in acid sulfate soil material that has already oxidised. TAA measures the sum of both soluble and exchangeable acidity in acid sulfate soil material and non-acid sulfate soil material. The retained acidity (RA) is an operational term used to estimate the acidity ‘stored’ in minerals such as jarosite, schwertmannite and other hydroxysulfate minerals. Although these minerals may be stable under acidic conditions, they can release acidity to the environment when these conditions change. The methods for determining both TAA and RA are given by Ahern et al. (2004).

Acid Neutralising Capacity (ANC) Soils with pHKCl values > 6.5 may potentially have ANC in the form of (usually) carbonate minerals, principally of calcium, magnesium and sodium. The carbonate minerals present are estimated by titration, and alkalinity present is expressed in CaCO3 equivalents. By accepted definition (Ahern et al. 2004), any acid sulfate soil material with a pHKCl < 6.5 has a zero ANC. The methods for determining ANC are given by Ahern et al. (2004).

Fineness Factor (FF) This is defined by Ahern et al. (2004) as “A factor applied to the acid neutralising capacity result in the acid base account to allow for the poor reactivity of coarser carbonate or other acid neutralising material. The minimum factor is 1.5 for finely divided pure agricultural lime, but may be as high as 3.0 for coarser shell material”.


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Fine grinding of soil materials may lead to an over-estimate of ANC when carbonates are present in the form of hard nodules or shells. In the soil environment, they may provide little effective ANC when exposure to acid may result in the formation of surface crusts (iron oxides or gypsum), preventing or slowing further neutralisation reactions. For reasons including those above, the use of the “Fineness Factor” also applies to those naturally occurring alkalinity sources in soil materials as measured by the ANC methods.

Table 2-2 List of methods for laboratory analysis conducted.

Data and Analysis Objective Method

Laboratory Analysis

pHwater Measures the current sampled status of the soil acidity or alkalinity

pH meter; 1:1 soil:water (Rayment and Higginson 1992)

pHperoxide Measures the potential end oxidized status of the soil pH

pH meter; Method 4E1 (Rayment and Higginson 1992)

pHincubation Represents a scenario for soil sample on exposure to air (oxygen) for a specified period of time

Fitzpatrick et al. 2008

Electrical conductivity Measure of the soil salt content (Rayment and Higginson 1992)

Soil texture Assessment of texture to assist with interpretation of acid base accounting results

Hand texture determination placed into 3 classes – coarse, medium, fine

pHKCl pH value. Provides trigger value (pHKCL >6.5) for deciding to test for acid neutralising capacity.

pH meter. Method 23A (Ahern et al. 2004)

Chromium reducible sulfur (SCR)

Identifies presence of sulfides. For acid base accounting

Method 23B (Ahern et al. 2004)

Titratable actual acidity (TAA)

Identifies soil acidity. For acid base accounting.

Method 23F (Ahern et al. 2004)

Acid neutralising capacity (ANC) (where pHKCl >6.5)

Identifies neutralising capacity of soil. For acid base accounting.

Method 19A2 (Ahern et al. 2004)

Retained acidity (RA) Identifies stored soil acidity. For acid base accounting.

Method 20J (Ahern et al. 2004)

Net acidity (NA) Identifies the soil acidity (or alkalinity) Calculated (Ahern et al. 2004)



pH testing after peroxide treatment Hydrogen peroxide (H2O2) is a strong oxidising agent and is used to encourage the oxidation of sulfide minerals (principally pyrite: FeS2) and the subsequent production of acidity. Since peroxide is a strong oxidising agent, it can be argued that the resultant pH measured is a worst-case scenario. In nature, the presence of carbonate minerals such as calcite (CaCO3) may neutralise acid produced, however, in some cases the carbonate may not fully dissolve due to slow dissolution rates (reaction kinetics). The dissolution rates of individual minerals may be controlled by a number of factors, hence additional tests based on measuring the carbonate content are recommended. Acid-base accounting Acid-base accounting is a technique, which balances the potential acid generated from the sum of sulfide-S (SCR or chromium-reducible S) and the titratable actual acidity (TAA) of the soil (AGP) with the total amount of potential alkalinity/acid neutralising capacity (ANC) generated. Details of the chemical methods used are given in Ahern et al. (2004). The ANC is usually only routinely measured when soil pHKCl (measured in a high ionic strength KCl solution) is greater than pH 6.5. When pHKCl is less than 4.5, this indicates that secondary less soluble acid-producing minerals such as jarosite are present. This is measured as retained acidity. The net acid generating potential (NAGP) is the acid generating potential (AGP) plus retained acidity minus ANC, which gives an indication of acid generation if all components react fully. Arguments against this technique include the fact that the form of carbonate may not be available to soil solutions (e.g. if it is coated and protected with organic material or iron oxides) or if it is in a form that is not particularly reactive (e.g. iron carbonates and dolomite (CaMgCO3) have much slower reaction kinetics than calcite). Net acidity aims to take this into account by introducing a “fineness factor”, whereby net acidity is calculated by dividing the ANC by a factor of 1.5. However, the oxidation of pyrite may also cause pyrite to not react fully if it becomes coated with protective secondary minerals. Thus, it may be difficult to assess acidification scenarios effectively.

For coastal and inland acid sulfate soils in Australia, the action criteria or trigger values for the preparation of an ASS management plan are shown in Table 2-3. Table 2-3: Criteria indicating the need for an ASS management plan based on texture range and chromium reducible sulfur concentration and amount of soil material disturbed (Dear et al. 2002).

Texture range SCR (%S)

<1000 t disturbed soil >1000 t disturbed soil

Coarse: Sands to loamy sands 0.03 0.03

Medium: Sandy loams to light clays

0.06 0.03

Fine: Medium to heavy clays 0.10 0.03 Incubation (ageing) experiments The third method used, which is often considered to represent a more realistic scenario for ASS testing is based on the ‘incubation’ of soil samples. A number of specific techniques are employed, but all are based on keeping the sample moist for a specified period (usually a number of weeks or months), which allows a more realistic oxidation of sulfide minerals to occur than that produced during peroxide testing.


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Although this may mimic nature more closely and does not force reactions to occur (as in the peroxide test) or rely on total ‘potential’ reaction, it can be argued that the complex processes occurring in the field are not represented e.g. exchange with sub-surface waters (containing ANC) or biogeochemical reactions. These should also be assessed, where possible, but often require a thorough understanding of water movement (e.g. groundwater) which, is often scenario specific.

The current practice in CSIRO Land and Water/ Acid Sulfate Soil Centre (ASSC) is to use all of the above techniques and, where possible, to monitor changes in the field during periods of drying to assess the most likely scenarios of acid generation and neutralisation.

This test used for these acid sulfate soil protocols is a modification of this incubation procedure which involves the following steps:

• Incubate mineral or organic soil materials, which have a natural pH (1:1 soil:water) value > 4, as a layer ca. 1 cm thick under moist conditions, while maintaining contact with the air at room temperature.

• Measure the pH and observe whether there is a drop in pH of 0.5 units or more to a value of 4.0 or less, including wetting and drying cycles.

• The duration of incubation shall continue for a minimum of 8 weeks until a stable pH is reached (differs from the fixed 8 weeks in the formal Australian Soil Classification definition) as described in Sullivan et al. 2009.

• Collection and storage of moist samples in plastic chip trays produces similar conditions, and thus chip trays are suitable for incubation testing as described and used in Fitzpatrick et al. (2008, 2009a; 2010).

2.3 Ac id V olatile S ulfur

Iron-monosulfides, defined operationally as acid-volatile sulfur (AVS) is readily extracted by the diffusion method described by Hsieh et al. (2002) using a modified apparatus (Burton et al. 2006; 2007). Approximately 2 g of wet sample is equilibrated (orbital shaking at 150 rpm for 18 hrs) with 10 ml of 6M HCl/0.1M ascorbic acid in gas-tight 55 cm3 polypropylene reactors. The evolved H2S(g) is trapped in 7 ml of 3% Zn acetate in 2 M NaOH, and subsequently quantified via iodometric titration. The quantitative recovery of acid volatile sulfur using this method is 96 ± 4%. Pyrite-S is not extracted by the acid volatile sulfur analytical method employed here (Hsieh et al. 2002). The slurry remaining after acid volatile sulfur extraction is diluted to 50 ml with deionised water and centrifuged (4000 g, 10 minutes).

2.4 T otal c arbon and nitrogen

Samples were analysed by the Environmental Analysis Laboratory, Southern Cross University for total carbon and nitrogen using a high temperature combustion method (LECO CNS2000 Analyser) described in Rayment and Lyons (2010). Electrical Conductivity (1:5, soil:water) was determined using the standard method described in Rayment and Lyons (2010).



2.5 R apid metal releas e tes t methods

All soil samples, whether they were dry, moist or water-logged when collected, were dried before use in the rapid (acid, metal and nutrient) mobilisation tests. Slow drying of soils in slightly humid conditions best resembles what may occur naturally in the field, however, for the purpose of this study the soils were dried in an oven at 80 ºC for three days.

All samples were handled using appropriate measures to avoid sample contamination. This included the wearing of clean powder-free vinyl gloves for the handling of all sample bottles and sampling equipment.

Soil samples collected from the surveys were air dried at 40 0Celcius to resemble drying as it would occur in the field. 25g of each sample was weighed into clean acid washed 250mL Nalgene extraction bottles and resuspended in 250 mL of deionised water for a total period of 24 hours by an end over shaker. Water blanks were run with the batch extraction to monitor water quality throughout the experiment. At 1 hour a 25ml aliquot was sampled to measure water quality at the start of the extraction, with the measurements repeated at the end of extraction (24 hours). Water quality measurements included dissolved oxygen, pH, alkalinity/acidity, redox potential (Eh), and specific electrical conductance (SEC).

At the completion of the extraction phase the samples were centrifuged to settle solids and allow the supernatant to be filtered for analytical chemistry using Millex 0.45 micron PVDF syringe filters. Analyses for a suite of metals and metalloids plus nutrients were run on the filtered water extracts to provide a detailed profile of each sample’s chemistry. The metal release batch experiment was run at time zero and eight weeks incubation to compare the variability in each soil sample over the standard ph incubation period.

A comprehensive suite of inorganic analyses on water samples at the end of the tests comprised (i) alkalinity (ii) dissolved organic carbon, (iii) the major anions/nutrients (Cl, NO2, NO3, NH4, TN, TOC, PO4, SO4 and total N), (iv) the major cations Na, K, Ca, Mg, and (v) trace metals and metalloids.

2.6 Mineralogic al analys es by x-ray diffrac tion

The soil samples (bulk and <2µm fractions), gypsum crusts and salt efflorescences were ground in an agate mortar and pestle The resulting fine powders were either gently back pressed into stainless steel sample holders or lightly front pressed onto silicon low background holders for X-ray diffraction analysis (XRD) analysis. XRD patterns of samples were collected with a PANalytical X'Pert Pro Multi-purpose Diffractometer in “standard” configuration mode using iron filtered Co Kα radiation, automatic divergence slit and X'Celerator Si strip detector. The diffraction patterns were recorded in steps of 0.017° 2 theta with a 0.5 second counting time per step.

Analysis of the XRD patterns were performed using in-house developed XPLOT software and commercial software, HighScore Plus from PANalytical. Mineralogical phase identification were made by comparing the measured XRD patterns with the International Centre for Diffraction Data (ICDD) database of standard diffraction patterns using computer aided search/match algorithms.


25

2.7 Water analys es

Various methods were used for water analyses as shown in Table 2-4.

Table 2-4 Methods used for analyses of water Analyte Method

Dissolved metals by ICP-AES

Dissolved metals were measured by ICP-AES (CIROS, SPECTRO). The sample is converted to an aerosol and transported into the plasma. Atoms and ions of the plasma are excited and emit light at characteristic wavelengths. The light emitted by the sample passes through the entrance slit of the spectrometer. The different wavelengths are measured and converted to a signal and quantified by comparison with standards.

Dissolved metals by ICP-MS

Dissolved metals were measured by ICP-MS (Agilent 7500 CE). Analyte species originating in a liquid are nebulised by a Micromist nebuliser and a cooled double-pass spray chamber. The ions are detected by an electron multiplier. The ions are quantified by comparison with prepared standards.

Alkalinity and Acidity as calcium carbonate

APHA 21st ed., 2320 B This procedure determines alkalinity by both manual measurement and automated measurement (PC Titrate) using pH 4.5 for indicating the total alkalinity end-point. Acidity is determined by titration with a standardised alkali to an end-point pH of 8.3.

Major anions - filtered APHA 21st ed., 4500 Cl - B. Automated Silver Nitrate titration.

Chloride APHA 21st ed., 3120; USEPA SW 846 - 6010 The ICP-AES technique ionises filtered sample atoms emitting a characteristic spectrum. This spectrum is then compared against matrix matched standards for quantification.

Nitrite and nitrate as N APHA 21st ed., 4500 NO3- I. Nitrate is reduced to nitrite by way of a cadmium reduction

column followed by quantification by FIA. Nitrite is determined separately by direct colourimetry and result for Nitrate calculated as the difference between the two results.

Reactive phosphorus - filtered

APHA 21st ed., 4500 P-E Water samples are filtered through a 0.45um filter prior to analysis. Ammonium molybdate and potassium antimony tartrate reacts in acid medium with orthophosphate to form a heteropoly acid -phosphomolybdic acid - which is reduced to intensely coloured molybdenum blue by ascorbic acid. Quantification is achieved by FIA.

Total organic carbon (TOC)

APHA 21st ed., 5310 B, The automated TOC analyzer determines Total and Inorganic Carbon by IR cell. TOC is calculated as the difference.

Moisture content A gravimetric procedure based on weight loss over a 12-24 h drying period at 110±5ºC.

Paste pH, conductivity Paste pH (USEPA 600/2-78-054): pH determined on a saturated paste by ISE. Electrical Conductivity of Saturated Paste (USEPA 600/2-78-054) - conductivity determined on a saturated paste by ISE.

3BSOIL PROFILE ASSESSMENT


3. S OIL P R OF IL E AS S E S S ME NT

Summary This section presents the soil profile assessment data from the two field survey campaigns conducted in: (i) summer, December, 2013 – involving a reconnaissance soil survey by sampling 17 soil profiles and 106 soil layers/horizons) and (ii) autumn March/April 2014 – involving a detailed soil survey by sampling 37 selected soil profiles and 98 soil layers/horizons.

The baseline maps used in the field to conduct the “walkover reconnaissance survey” in summer was a NearMap (http://www.nearmap.com/) aerial image taken in early November, 2013 (i.e. electronic/digital and hardcopy formats: Figure 3-1 for ponds PA3 to PA12 and adjacent drains). The targeted sampling locations were initially based on: (i) contrasting patterns observed in the aerial image and (ii) the following surface features observed in the field during the walkover soil survey such as: ponded water, colour of soil (e.g. reddish-brown, grey or black), presence or absence of soil surface salt efflorescences, presence or absence of soil surface salt crusts (e.g. gypsum or halite), presence or absence of shells or mussels, presence or absence of flocculated or dispersed clay (e.g. fluffy or hard surface), soil texture (sandy, clayey or loamy), presence or absence of desiccation cracks (pattern, depth and width), topography (e.g. mounds, depressions, flat areas or sand drift) and smell. Most of these features were identified to specifically address key characteristics of interest on aerial image maps and in the field of factors informing possible ASS hazards.

The reconnaissance/ walkover field survey of all sites was conducted on 16th to 20th December, 2013. During this investigation 17 soil profile sites were investigated and 106 soil layers/horizons were described, sampled in chip trays and subjected to laboratory pH incubation analyses. The distribution of these site locations is shown in Figure 3-1 for ponds PA3 to PA12 and adjacent drains. Sample site location coordinates were obtained using a GPS, using the WGS 84 Datum: Zone 54 South (Easting’s and Northing’s).

The approach adopted was to resample the ponds after a 3 month period following extensive reflooding and drying events (Figure 3-1) in March/April 2014 to help understand changes associated with seasonality and water level fluctuation following reflooding. Sample selection was based on the field observations and pH incubation data from the reconnaissance/ walkover field survey investigation.

On the second sampling occasion in March/April 2014, the selected soil profile sites were re-sampled within a few metres of the original reconnaissance/ walkover field survey soil pit or auger hole. During this investigation 37 soil profile sites were investigated and 98 soil layers/horizons were described, sampled in chip trays and subjected to laboratory pH incubation analyses. A GPS was used to re-locate sample sites on the second monitoring occasion. It should be noted that soil profile sampling was carried out by observable horizon and not fixed sampling depths and was achieved using digging with a spade/shovel and a soil augers.

Selected samples were also taken of salt efflorescences, salt crusts, hardpans and shells/mussels for X-ray diffraction analysis (Appendix 3). pH peroxide testing was done on all samples the laboratory.

http://www.nearmap.com/�


27

3.1 P onds PA3 to PA12

3.1.1 B ac kground

Ponds PA3 to PA12 (Profiles DPA3-01 to DPA12-01) are situated in the southern part of the Ridley Dry Creek Salt Field (see Figure 1-1 and Figure 3-1). All of these ponds are mostly covered by a gypsum crust of varying thickness. They are bounded to the north by Section 3 ponds, which mostly do not have gypsum surface crusts and are permanently ponded with saline water and hence comprise dominantly subaqueous ASS. They are bounded to the west by the coast with mangrove swamps and native samphire. In some locations, there are low-lying areas (dark areas in Figure 3-1) where water has remained or the soil is mostly saturated. To the east, the ponds are adjacent to shallow drains often with sporadic native samphire and salt bush.

At the time of the reconnaissance/walkover survey between 16th to 20th December 2013, the pond surfaces were generally dry with some wetter areas, mostly on the western boundary due to seepage from the tidal Mangrove swamp areas – especially in: (i) the excavated areas used to construct the bund walls along the western border between ponds PA3 to PA12 and (ii) previous low-lying natural stream channels (Figure 3-1).

The first phase (DPA3-01 to DPA12-01) of soil sampling in ponds PA3 to PA12 (Figure 3-1) was carried out between 16th and 20th December 2013, when 17 soil profiles (106 samples of soil horizons/layers) were sampled. During the second phase of sampling in March/April 2014 (“d”, DPA3d-01 to DPA12d-01; and DPADd-1 to DPADd-4), 37 soil profiles with 98 samples were sampled (see site map Figure 3-1; and Appendix 2 and for electronic profile descriptions).

3.1.2 R ec onnais s anc e survey: soil ac idity

As shown in Figure 3-2, the pH (T=zero) data confirmed the identification of mostly hyposulfidic materials with a pH(T=zero) >4 for all sites (DPA3 to DPA12). Only one profile, namely sample DPA6-02.5 (see Figure 3-3) out of 37 soil profiles comprising 98 samples contained hypersulfidic material (i.e. 1 sample out of 98 samples). This site is adjacent to mangrove swamps and the associated areas have a medium hazard of acidification. As a consequence, this site was included for detailed investigations and sampling and laboratory analyses (Figure 3-3). Detailed profile descriptions are presented in Appendix 2 with accompanying soil profile photographs located in a separate electronic data base.

Samplings in both December and March/April encountered thick (0-30 cm) black, organic-rich monosulfidic black ooze in all the wetter areas, which mostly occurs on the western boundary due to seepage from the ocean.



Figure 3-1 NearMap (http://www.nearmap.com/) aerial image of the Ridley Dry Creek Salt Field ponds

PA3 to PA12 showing distribution of: (i) soil profiles sampled during the walkover reconnaissance survey of all sites (yellow dots: Profiles DPA3-01 to DPA12-01; Profile DPAD-01 = drain) in December 2013, and (ii) representative soil profiles sampled during the detailed sampling campaign in March/April 2014 (green star symbols; profiles DPA3d-01 to DPA12d-01; Profile DPADd-01 = drain for incubation experiments, laboratory pH, peroxide pH; full acid base accounting; analysis for AVS, selected mineralogy and metal availability testing).



29

Figure 3-2 Initial pH and incubation pH (16 weeks) plotted against depth for each DPA profile collected

DPA3-01

pH2 4 6 8 10

0-1

1-5

5-15

15-35

35-80 pH 0pH inc

DPA4-01

pH2 4 6 8 10

0-1

1-2

2-4

4-10

10-20

20-30

30-35

35-80pH 0pH inc

DPA4-02

pH2 4 6 8 10

0-10

pH 0pH inc

DPA5-01

pH2 4 6 8 10

0-2

2-15

15-30

30-50

50-90 pH 0pH inc

DPA6-01

pH2 4 6 8 10

0-2

2-10

10-20

20-40

40-60

60-90

90-100 pH 0pH inc

DPA6-02

pH2 4 6 8 10

0-2

2-4

4-15

15-25

25-55

55-70

70-80

80-150

pH 0pH inc

DPA7-01

pH2 4 6 8 10

0-10

10-20

20-50

50-60

60-100

100-150 pH 0pH inc

DPA7-02

pH2 4 6 8 10

0-3

3-8

8-20

20-30

30-40

40-55

55-90

90-150pH 0pH inc

DPA7a-01

pH2 4 6 8 10

0-1

1-20

20-40

40-50

50-65

65-100 pH 0pH inc



Figure 3-2 continued: Initial pH and incubation pH (16 weeks) plotted against depth for each DPA profile collected

DPA8-01

pH2 4 6 8 10

0-2

2-5

5-10

10-20

20-60

60-80

80-90

90-120pH 0pH inc

DPA8-02

pH2 4 6 8 10

0-3

3-5

5-20

20-40

40-50

50-80

80-95

pH 0pH inc

DPA9-01

pH2 4 6 8 10

0-2

2-5

5-10

10-20

20-50

50-70

70-100

100-110pH 0pH inc

DPA9-02

pH2 4 6 8 10

0-3

3-15

15-50

50-60

60-85

85-110 pH 0pH inc

DPA10-01

pH2 4 6 8 10

0-2

2-5

5-10

10-25

25-55

55-100 pH 0pH inc

DPA11-01

pH2 4 6 8 10

0-15

15-20

20-50

50-80

80-100

100 -110

pH 0pH inc

DPA12-01

pH2 4 6 8 10

0-2

2-5

5-30

30-50

50-80 pH 0pH inc

DPAD-01

pH2 4 6 8 10

0-3

3-10

10-30

30-80

80-100 pH 0pH inc


31

3.1.3 Detailed s urvey: s oil ac idity and ac id-bas e ac c ounting

Acid-base accounting was carried out according to the methods described in Section 2.2 and comprised analyses for sulfide-S (SCR or Cr-reducible S), Retained Acidity (RA), Titratable Actual Acidity (TAA), Acid Neutralising Capacity (ANC) and Net Acidity (NA). Acid-base accounting and pH data (pHW and pHINC) for each soil layer are presented in Figure 3-4. These data were used to inform the acidification hazard assessment that is presented in Table 3-2. The total amount of non-organic reduced-S (or reduced inorganic sulfur – RIS), contained mainly within sulfide minerals (SCR), is determined by the Cr-reducible S technique (Ahern et al. 2004). The total amount of acid generated, assuming complete oxidation, can be quantified, usually in mol H+ tonne-1, or taking into account the bulk density, as mol H+ m-3. However, shielding of sulfide minerals by Fe-(oxy)-hydroxide minerals, may limit sulfide oxidation, in effect decreasing the amount of potential acid available for reaction. As well as potential acidity, the amount of acidity already present in the soil can be quantified as titratable actual acidity (TAA).

In sulfuric materials, retained acidity may form a major component of stored acid (e.g. stored in mineral phases such as jarosite and schwertmannite). The sum of acidity generated by SCR, TAA and retained acidity represents the acid generating potential (AGP) of the sample. As well as taking into account the total acid potential of the sample, acid generated post-sampling and prior to analysis is included as part of total potential of the sample.

Most soil profiles in ponds PA3 to PA12 that were sampled in December 2013 were re-sampled in March/April 2014. The pH before incubation (time zero) and after 16 weeks incubation did not change significantly (i.e. materials were not re-classified) with low acidification hazard (Table 3-2). The net acidity values exceeded zero for only three (3) soil layers in two (2) out of 37 sites sampled (Figure 3-4), namely at sites DPA 11-01 and DPA12-01 and in some cases was high (maximum of 580 moles H+/tonne). Values decreased towards the soil surface and in most cases at depth (Figure 3-4). There was generally high ANC in the subsoil layers where calcite, Mg-calcite and aragonite (shell fragments) have been identified by X-ray diffraction (Table 3-1; Appendix 3).

Generally there was no significant changes noted between pH values in samplings in March/April 2014 (pH decrease) compared to December 2013.



Figure 3-3 Photograph of profile DPA6-02 collected in December 2013 showing wide range of acid sulfate soil materials and related features (e.g. gypsum crusts and shell grit layers) Profile DPA6-02 (Figure 3-3) collected in December 2013 and profiled DPA6d-02 re-sampled in March/April 2014 were both classified as a Hypersulfidic subaqueous sandy/shell grit soil with monosulfidic material (i.e. medium to low acidification hazard rating and medium deoxygenation/malodour hazard) (Table 3-2). During the reflooding condition, the upper portion of this profile (between 0 to 80 cm) was subaqueous and comprised hyposulfidic material (Figure 3-4). Acidity comprised a combination of mainly SCR and some TAA (Figure 3-4). At depth, the soil profile comprised hypersulfidic material with high organic carbon (14% organic carbon), which classified as sapric material with small negative net acidity and moderate levels of ANC and no TAA and minor SCR (Figure 3-4).


33

Figure 3-4 pH, acid base accounting, total organic carbon and total nitrogen data plotted against depth for each DPAd soil profile collected in March/April 2014

DPA03-01

Net acidity (mol H+/tonne)

-1500 -1000 -500 0 500 1000

Layer Depth (cm)

0-20

20-45

45-50

50-100

TAA Scr ANC RA Net Acidity

pH2 4 6 8 10

pH 0pH incpH KCl

DPA03-02


-12000 -10000 -8000 -6000 -4000 -2000 0 2000

Layer Depth (cm)

0-15

15-25

25-30

30-90

90-110

TAARISANCRANet Acidity

pH2 4 6 8 10

pH 0pH incpH KCl

DPA04-01


-5000 -4000 -3000 -2000 -1000 0 1000

Layer Depth (cm)

0-15

15-35

35-45

45-100


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0.0 0.5 1.0 1.5 2.0

TN (%)

0.00 0.05 0.10 0.15 0.20 0.25

TOCTN

TOC (%)0 2 4 6 8 10 12 14

TN (%)

0.0 0.2 0.4 0.6 0.8

TOCTN

TOC (%)0.0 0.5 1.0 1.5 2.0

TN (%)

0.00 0.05 0.10 0.15 0.20 0.25

TOCTN



Figure 3-4 continued: pH, acid base accounting, total organic carbon and total nitrogen data plotted against depth for each DPAd soil profile collected in March/April 2014

DPA04-02


-1200 -1000 -800 -600 -400 -200 0 200

Layer Depth (cm)

2-7

7-15


pH2 4 6 8 10

pH 0pH incpH KCl

DPA05-01


-8000 -6000 -4000 -2000 0

Layer Depth (cm)

0-10

10-25

25-45

45-75

75-100


pH2 4 6 8 10

pH 0pH incpH KCl

DPA06-01


-8000 -6000 -4000 -2000 0 2000

Layer Depth (cm)

0-30

30-55

55-80

80-90


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0 1 2

TN (%)

0.0 0.1 0.2 0.3

TOCTN

TOC (%)0 1 2 3 4 5 6

TN (%)

0.00 0.05 0.10 0.15 0.20 0.25

TOCTN

TOC (%)0.0 0.5 1.0 1.5 2.0

TN (%)

0.00 0.04 0.08 0.12 0.16

TOCTN


35


DPA06-2


-12000 -10000 -8000 -6000 -4000 -2000 0 2000

Layer Depth (cm)

0-35

35-50

50-80

80-85

85-100


pH2 4 6 8 10

pH 0pH incpH KCl

DPA07-1


-8000 -6000 -4000 -2000 0

Layer Depth (cm)

0-30

30-48

48-70

70-80


pH2 4 6 8 10

pH 0pH incpH KCl

DPA07-2


-12000 -10000 -8000 -6000 -4000 -2000 0 2000

Layer Depth (cm)

0-30

30-45

45-55

55-90

90-100


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0 2 4 6 8 10 12 14

TN (%)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

TOCTN

TOC (%)0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8

TN (%)

0.00 0.02 0.04 0.06 0.08 0.10

TOCTN

TOC (%)0 1 2 3 4 5 6 7

TN (%)

0.0 0.1 0.2 0.3 0.4

TOCTN




DPA07a-1


-14000-12000-10000-8000 -6000 -4000 -2000 0 2000

Layer Depth (cm)

0-23

23-50

50-65

65-90


pH2 4 6 8 10

pH 0pH incpH KCl

DPA07a-2


-5000 -4000 -3000 -2000 -1000 0 1000

Layer Depth (cm)

0-30

30-45

45-50

50-70


pH2 4 6 8 10

pH 0pH incpH KCl

DPA08-1


-6000 -5000 -4000 -3000 -2000 -1000 0 1000

Layer Depth (cm)

0-60

60-70

70-80

80-100


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0 1 2 3 4 5

TN (%)

0.00 0.02 0.04 0.06

TOCTN

TOC (%)0.0 0.4 0.8 1.2 1.6

TN (%)

0.00 0.04 0.08 0.12

TOCTN

TOC (%)0.0 0.4 0.8 1.2 1.6 2.0 2.4

TN (%)

0.00 0.04 0.08 0.12 0.16

TOCTN


37


DPA08-2


-12000 -10000 -8000 -6000 -4000 -2000 0 2000

Layer Depth (cm)

0-45

45-50

50-60

60-90


pH2 4 6 8 10

pH 0pH incpH KCl

DPA09-1


-2500 -2000 -1500 -1000 -500 0 500

Layer Depth (cm)

0-20

20-40

40-45

45-80


pH2 4 6 8 10

pH 0pH incpH KCl

DPA09-2


-5000 -4000 -3000 -2000 -1000 0 1000

Layer Depth (cm)

0-40

40-55

55-65

65-80


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0 1 2 3 4 5 6

TN (%)

0.00 0.04 0.08 0.12 0.16 0.20

TOCTN

TOC (%)0.0 0.4

TN (%)

0.00 0.04 0.08

TOCTN

TOC (%)0.0 0.5 1.0 1.5 2.0 2.5

TN (%)

0.0 0.1 0.2 0.3

TOCTN




DPA10-1


-4000 -3000 -2000 -1000 0 1000

Layer Depth (cm)

0-40

40-63

63-80

80-95


pH2 4 6 8 10

pH 0pH incpH KCl

DPA10-2


-2500 -2000 -1500 -1000 -500 0 500

Layer Depth (cm)

0-50

50-60

60-80

80-100


pH2 4 6 8 10

pH 0pH incpH KCl

DPA11-1


-5000 -4000 -3000 -2000 -1000 0 1000

Layer Depth (cm)

0-50

50-63

63-75

75-100


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0.0 0.5 1.0 1.5 2.0 2.5 3.0

TN (%)

0.00 0.05 0.10 0.15 0.20 0.25

TOCTN

TOC (%)0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2

TN (%)

0.0 0.1 0.2 0.3 0.4

TOCTN

TOC (%)0.0 0.5 1.0 1.5 2.0 2.5

TN (%)

0.00 0.05 0.10 0.15 0.20

TOCTN


39


In summary, a higher proportion of soils along the western segments of all ponds sampled in March/April 2014 were subaqueous, which meant these soils were reclassified as subaqueous ASS subtypes (see Appendix 1). However, the pH before and after incubation for 16 weeks had not changed significantly indicating that the materials originally classified as either hyposulfidic (mostly) and hypersulfidic did not change Table 3-2.

Underlying the hypersulfidic and hyposulfidic materials, to the maximum depth of investigation (~1 m to 1.50 cm) are mottled heavy clay layers (i.e. black, olive grey, dark grey, brownish grey and reddish grey clay) with calcium carbonate accumulations. The vertical and horizontal distribution of these clay layers are displayed in the soil-regolith hydro-toposequence model in Figure 5-1 .

The high levels and distribution of iron monosulfides in the Dry Creek ponds have been promoted by:

(i) the highly depositional environment (closed evaporation ponds),

(ii) high organic matter concentrations (Figure 3-4),

(iii) low Fe and carbonate concentrations (precipitated early in salt production process),

(iv) low re-suspension (due to very slow seawater inflow/through-flow velocities and more sheltered nature of the bunded ponds).

Photographic comparisons between: Profile DAP7A-01 photographed and sampled 16th December, 2013 (Figure 3-5; Figure 3-7; Figure 3-9; Figure 3-11) following an extensive DRY PERIOD (showing a very hard, indurated and compact thin gypsum crust with relatively smooth wavy shallow surface topography) and Profile DAP7Ad-01 photographed and sampled 26th March, 2014 (Figure 3-6; Figure 3-8; Figure 3-10; Figure 3-10) – following an extreme high rainfall event in February 2014 (showing a relatively friable/soft thin gypsum crust with distinct evidence that the original gypsum crust/layers have been altered to produce a relatively cracked deeper wavy surface topography).

DPA12-1


-2000 -1500 -1000 -500 0 500 1000

Layer Depth (cm)

0-40

40-60

60-70

70-80


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0 2 4 6 8

TN (%)

0.0 0.1 0.2 0.3 0.4 0.5 0.6

TOCTN



Figure 3-5 Profile DAP7A-01 photographed and sampled 16th December, 2013 following an extensive DRY PERIOD

Figure 3-6 Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014


41

Figure 3-7 Profile DAP7A-01 photographed and sampled 16th December, 2013 following an extensive DRY PERIOD

Figure 3-8 Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014



Figure 3-9 Profile DAP7A-01 photographed and sampled 16th December, 2013 – following an extensive DRY PERIOD showing a hard continuous gypsum crust ranging from 3cm to 10cm thick

Figure 3-10 Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014 showing a fragile discontinuous gypsum layer ranging from 3cm to 10cm thick

Figure 3-11 Close-up views of sections of Profile DAP7A-01 photographed and sampled 16th December, 2013 – following an extensive DRY PERIOD showing a hard continuous gypsum crust ranging from 3cm to 10cm thick

Figure 3-12 Close-up views of sections of Profile DAP7Ad-01 photographed and sampled 26th March, 2014 – Following extreme high rainfall event in February 2014 showing a fragile discontinuous gypsum layer ranging from 3cm to 10cm thick


43

3.1.4 S oil Mineralogy

The semi-quantitative determination of minerals in the whole soil by X-ray diffraction (XRD) is presented in Table 3-1. Quartz is the major mineral in these soils together with gypsum and halite. Interestingly, halite is present in high amounts in the surface gypsum crusts, which suggests that with rainwater addition leaching will more readily dissolve the crusts than if the crust comprised mainly gypsum. Kaolinite and Illite-mica were of secondary importance (minor). At depth (30cm to 90 cm), in profiles DPA6-02 (layer DPA6-02.6) and DPA7a-01 (layers DPA7a-01.3 to DPA7a-01.6) high amounts of Mg-substituted calcite, aragonite and halite were identified in the friable subsoil layers. The sub-dominant or minor Mg-substituted calcite was likely derived from shells (previously aragonite), and dominant Illite-mica and minor kaolinite. A close examination of the X-ray diffraction (XRD) diagrams in appendix 3, indicates fine grained kaolinite and illite-mica.

Table 3-1 Mineralogical composition of selected soil samples from ponds PA6, PA7a and PA9 Client ID Qtz Hl Gp Cal Mg-Cal Arg Ab Or Kln Ill/Mca Am Ja

DPA6-02.1 T D T

DPA6-02.2 SD D

DPA6-02.3 M D

DPA6-02.4 T SD D

DPA6-02.6 M M M D SD

DPA6-02.8 M D T T T T

DPA7ad-01 T T D

DPA7a-01.2 T T D

DPA7a-01.3 D SD M M SD M M T T T

DPA7a-01.4 CD SD T M CD M M T T

DPA7a-01.6 D SD T T SD M M T T

DPA9-01.1 M D

DPA9-01.5 M D

DPA9-01.6 D SD M T M M T T T

DPA9-01.8 SD SD T T M T M D

Where: D – Dominant (>60%), CD – Co-dominant (sum of components >60%), SD – Sub-dominant (20-60%), M-Minor (5-20%), T-Trace (<5%). Qtz – quartz, Hl – halite, Gp – gypsum, Cal – calcite, Mg-Cal – magnesium substituted calcite, Arg – aragonite, Ab – albite, Or – orthoclase, Kln – kaolin, Ill/Mca – illite/mica, Am – amphibole

3.1.5 Organic c arbon and nitrogen

Details of trends in the amount of organic carbon and nitrogen in soil profiles are given in Figure 3-4 . Nitrogen data was used to calculate carbon to nitrogen ratios to assist in determining the organic carbon origins (Table 3-2).

Most surface and near surface layers had C:N ratios <10 indicating organic carbon derived from non-vascular aquatic plants e.g. algae or perhaps soil microbial biomass.



For those samples from shallow layers it is likely they contain organic matter of mixed origin.

Samples collected at depth in several profiles, namely DPA03d and DPA04d where the C:N ratios were low and mainly <7 indicating that the organic matter was not derived from terrestrial vascular plants and was likely formed under conditions that were relatively nutrient rich (Table 3-2).

Samples from several profiles, namely DPA03d-2.2 to 2.4 and DPA06d-02.2 to DPA06d-02.4 -have C:N>10 (and C:N > 100) at depth, which probably represents humic material consistent with organic bands observed in these profiles (Table 3-2).. However, for those in shallow layers it is likely they contain organic matter of mixed origin.

3.1.6 C las s ific ation and ac idific ation and deoxygenation/smell hazard as s es s ment

ASS material and profile classification was carried out for each soil sample collected, according to the definitions and methods presented in Section 2.2.

A summary of the ASS materials for each layer/horizon and subtype classification for each profile is presented in Table 3-2. Acid sulfate soil subtype classification was achieved using the key described in Appendix 1 (Fitzpatrick et al. 2008; 2010). The ASS subtype classification was carried out for each soil profile collected during both sampling campaigns and allocated an “Acidification and deoxygenation/smell hazard assessment” (see chapter 6). Acidification and deoxygenation/smell hazard assessment was based on: (i) landscape position (Figure 3-1), (ii) soil morphology (Appendix 2), (iii) acid base accounting (Figure 3-4; Appendix 5) and AVS data (see Appendix 5), (iv) pH data (Figure 3-4; Appendix 4), (v) ASS material and subtype classification and acidification potential Table 3-2 Table 3-2). Acidification and deoxygenation/malodour hazard categories used in this report are: high (Yellow), medium (Brown) and low (Blue).


45

Table 3-2 Samples from section 2 ponds: summary of ASS material classification, ASS subtype soil profile classification, other major soil morphology features used to determine acidification hazard ratings (where a sulfuric soil** has a high rating, hypersulfidic soil* has medium rating and hyposulfidic soil has a low rating)

Sample ID. Depth Material Profile

Other soil morphology features

Monosulfidic Material

C:N Ratios

DPA03d-1.1 0-20 Hyposulfidic Hyposulfidic Gyp gr, Black Monosulfidic (M) 7.38 DPA03d-1.2 20-45 Hyposulfidic

MC black Monosulfidic (M) 5.02

DPA03d-1.3 45-50 Hyposulfidic

HC black Monosulfidic (M) 4.87 DPA03d-1.4 50-100 Hyposulfidic

LC Grey/red m 1.20

DPA03d-2.1 0-15 Hyposulfidic Hyposulfidic Gyp gr, Black Monosulfidic (H) 6.59 DPA03d-2.2 15-25 Hyposulfidic

Shells (80%) Monosulfidic (H) 68.4


Shells (50%) Monosulfidic (H) 54.3 DPA03d-2.4 30-90 Hyposulfidic

Shells (90%) Monosulfidic (H) 200


Sapric (90%) 17.9


MC black Monosulfidic (H) 8.53


HC black Monosulfidic (M) 9.88 DPA04d-1.4 45-100 Hyposulfidic

Sh (40%), grey Monosulfidic (M) 41.1


Gel,n=>4 Monosulfidic (H) 7.43

DPA05d-1.1 0-10 Hyposulfidic Hyposulfidic Gyp crust Monosulfidic (H) 5.03 DPA05d-1.2 10-25 Hyposulfidic

Black Monosulfidic (H) 10.9


HC grey/olive Monosulfidic (H) 9.38 DPA05d-1.4 45-75 Hyposulfidic



HC dark grey 3.16


MC,Gyp gr, Bla Monosulfidic (H) 12.7


Shells (20%) Monosulfidic (H) 95.4 DPA06d-01.4 80-90 Hyposulfidic

HC dark grey 5.27

DPA06d-02.1 0-35 Hyposulfidic Hypersulfidic Gyp gr, Black Monosulfidic (H) 14.5 DPA06d-02.2 35-50 Hyposulfidic



Shells (60%) Monosulfidic (H) 222 DPA06d-02.4 80-85 Hyposulfidic

HC Grey/olive Monosulfidic (H) 11.5

DPA06d-02.5 85-100 Hypersulfidic

Sapric, Brown 19.7

DPA07ad-01.1 0-23 Hyposulfidic Hyposulfidic Gyp gr,/ crust Monosulfidic (M) 6.83 DPA07ad-01.2 23-50 Hyposulfidic

S, Brwn Gyp gr Monosulfidic (M) 84.0

DPA07ad-01.3 50-65 Hyposulfidic

S, Grey Gyp gr Monosulfidic (M) 162 DPA07ad-01.4 65-90 Hyposulfidic

LC, soft 197

DPA07ad-02.1 0-30 Hyposulfidic Hyposulfidic Gyp gr,/ crust Monosulfidic (H) 5.74 DPA07ad-02.2 30-45 Hyposulfidic S,Grey Gyp gr Monosulfidic (H) 5.70 DPA07ad-02.3 45-50 Hyposulfidic

MC, Black Monosulfidic (H) 18.9

DPA07ad-02.4 50-70 Hyposulfidic

HC, Olive Sh10 6.91


HC Grey/olive Monosulfidic (H) 8.86


HC Grey/olive Monosulfidic (H) 12.8 DPA07d-01.4 70-80 Hyposulfidic

Monosulfidic (H) 181


HC Grey/olive Monosulfidic (M) 15.9


HC Grey/olive 29.5 DPA07d-02.4 55-90 Hyposulfidic

Shells (60%) 41.3


Shells (10%) 15.8



Table 3-2 – continued Samples from section 2 ponds: summary of ASS material classification, ASS subtype soil profile classification, other major soil morphology features used to determine acidification hazard ratings (where a sulfuric soil** has a high rating, hypersulfidic soil* has medium rating and hyposulfidic soil has a low rating)



Monosulfidic C:N Ratios


MC Black Monosulfidic (H) 10.1


HC Olive Monosulfidic (M) 8.54 DPA08d-01.4 80-100 Hyposulfidic

Shells (60%) Monosulfidic (M) 132


Shells (60%) Monosulfidic (M) 50.5


HC Black Monosulfidic (L) 18.8 DPA08d-02.4 60-90 Hyposulfidic

Sa, grey m 38.8


Gyp gr, Black Monosulfidic (H 6.61


S Olive, Sh 30% Monosulfidic (H 5.80 DPA09d-01.4 45-80 Hyposulfidic

S Grey, Sh 60% 10.2


Gyp gr, Black Monosulfidic (H) 22.2


HC Black Monosulfidic (H) 8.47 DPA09d-02.4 65-80 Hyposulfidic

HC, grey, red m 8.97


HC Black Monosulfidic (H) 11.1


HC Dk grey Monosulfidic (H) 10.8 DPA10d-01.4 80-95 Hyposulfidic

HC Olive 7.76


HC Black Monosulfidic (H) 9.21


HC Black Monosulfidic (H) 9.95 DPA10d-02.4 80-100 Hyposulfidic

LC, gry, black m 5.15




HC Brown Monosulfidic (H) 10.6 DPA11d-01.4 75-100 Hyposulfidic

HC Olive, Yel m 11.6

DPA12d-01.1 0-40 Hyposulfidic Hypersulfidic Gyp gr, Black Monosulfidic (H) 6.62 DPA12d-01.2 40-60 Hyposulfidic

MC Olive, Yel m Monosulfidic (H) 7.72


HC Olive Monosulfidic (H) 13.4 DPA12d-01.4 70-80 Hypersulfidic

Brown, sapric 13.6

**Where the soil classification is a Sulfuric soil, sulfuric material (pH<4 at time zero

incubation) has been identified in a layer or horizon (at least 15cm thick) within 150 cm of the soil surface.

*Where the soil classification is a Hypersulfidic soil, hypersulfidic material (pH creased to <4 after incubation for at least 16 weeks) has been identified in a layer or horizon (at least 10cm thick) within 150 cm of the soil surface.

Monosulfidic material: High (H); Medium (M) and Low (all others)

Texture: S = Sand (i.e. Medium Sand), CS = Clayey Sand; LS = Loamy Sand; SL = Sandy Loam; L = Loam; SCL = Sandy Clay Loam; ; CL = Clay Loam; ZCL = Silty clay Loam; LC = Light Clay; LMC = Light Medium Clay; MC -= Medium Clay; MHC = Medium Heavy Clay; HC = Heavy Clay. S = Medium sandy; K = coarse sandy; F= fine sandy and Z = silty McDonald and Isbell (2009; page 164)

Other: Gyp = gypsum; gr = gravel; m = mottles, n = n-Value (see appendix


47

3.2 Drains

3.2.1 Background

A sequence of drains occur adjacent to ponds PA3 to PA12 and are situated below ponds PA3 and PA11 on the eastern side of The Ridley Dry Creek salt field. The drains adjacent to ponds PA3 to PA11 are bounded to the east by Bolivar wastewater treatment plant (Figure 3-1). In some locations, there are low-lying areas where water remained in the drains or the soils were mostly saturated. At the time of the walkover survey, in December 2013, the drains were generally dry with some wetter areas, mostly on the northern boundary due to seepage from pond PA3.

Only one drain was sampled in December 2013. During the second sampling phase (denoted with “d”: DPADd-01) in March/April 2014, four (4) soil profiles (comprising 16 samples) were sampled (see site map Figure 3-1; Table 3-5 for summary descriptions and Appendix 2 for profile descriptions/photographs). At each site, GPS co-ordinates and site descriptions were recorded. Grid coordinate locations (WGS84 datum).

3.2.2 Reconnaissance survey: soil acidity

As shown in Figure 3-13 for profile DPAD-01 the pH(T=zero) and pH incubation (16 weeks) data confirmed the identification of mostly hyposulfidic materials (mostly with pH ca. 8). This profile contains high amounts of monosulfidic material. Samplings in both December and March/April encountered thick (0-30 cm) black, organic-rich monosulfidic black ooze in all the wetter areas.

Figure 3-13 Initial pH and incubation pH (16 weeks) plotted against depth for drain DPAD-01 profile collected

In summary, the soil profile in the drains are composed dominantly of hyposulfidic materials and the ASS sub-type classification being hyposulfidic clayey soils with monosulfidic material.

DPAD-01

pH2 4 6 8 10

0-3

3-10

10-30

30-80

80-100 pH 0pH inc



3.2.3 Detailed s urvey: s oil ac idity and ac id-bas e ac c ounting

Acid-base accounting was carried out according to the methods described in Section 2.2 and comprised analyses for sulfide-S (SCR or Cr-reducible S), Retained Acidity (RA), Titratable Actual Acidity (TAA), Acid Neutralising Capacity (ANC) and Net Acidity (NA). Acid-base accounting and pH data (pHOX, pHINC & pHW), for each soil layer, are presented in Figure 3-14. These data were used to inform the acidification hazard assessment that is presented in and Table 3-5. The total amount of non-organic reduced-S (or reduced inorganic sulfur – RIS), contained mainly within sulfide minerals (SCR), is determined by the Cr-reducible S technique (Ahern et al. 2004). The total amount of acid generated, assuming complete oxidation, can be quantified, usually in mol H+ tonne-1, or taking into account the bulk density, as mol H+ m-3. However, shielding of sulfide minerals by Fe-(oxy)-hydroxide minerals, may limit sulfide oxidation, in effect decreasing the amount of potential acid available for reaction.

Figure 3-14 pH, acid base accounting, total organic carbon and total nitrogen data plotted against depth for each drain profile collected

DPAD-1


-8000 -6000 -4000 -2000 0

Layer Depth (cm)

0-15

15-25

25-45

45-90


pH2 4 6 8 10

pH 0pH incpH KCl

DPAD-2


-2000 -1000 0 1000 2000 3000

Layer Depth (cm)

0-0.5

0.5-3

3-10.0

10-13

30-50


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0 1 2 3 4

TN (%)

0.00 0.04 0.08 0.12

TOCTN

TOC (%)0.0 0.2 0.4 0.6 0.8

TN (%)

0.00 0.05 0.10 0.15

TOCTN


49

Figure 3-14 continued - pH, acid base accounting, total organic carbon and total nitrogen data plotted against depth for each drain profile collected

As well as potential acidity, the amount of acidity already present in the soil can be quantified as titratable actual acidity (TAA). In sulfuric materials, retained acidity may form a major component of stored acid (e.g. stored in mineral phases such as jarosite and schwertmannite). The sum of acidity generated by SCR, TAA and retained acidity represents the acid generating potential (AGP) of the sample. As well as taking into account the total acid potential of the sample, acid generated post-sampling and prior to analysis is included as part of total potential of the sample.

The soil profile in drain DPAD-1 that was re-sampled in March/April 2014 compared to that in December 2013 remained unaltered (i.e. classified the same, namely Hyposulfidic clays) (Table 3-5).

The net acidity values exceeded zero for only one (1) out of 4 sites sampled, namely in drain DPAD-2 (Figure 3-15), which was extremely high (maximum of 2,700 moles H+/tonne). Values were substantially higher towards the soil surface and decreased with depth (Figure 3-14). There was generally high ANC in all subsoil layers where calcite, Mg-calcite and aragonite (shell fragments) have been identified by X-ray diffraction (Table 3-4, Table 3-3; Appendix 3).

Generally there was no significant change noted between pH values in samplings in March/April 2014 compared to December 2013. Underlying the sulfuric, hypersulfidic

DPAD-3


-1400-1200-1000 -800 -600 -400 -200 0 200 400

Layer Depth (cm)

0-15

15-25

25-40

45-90


pH2 4 6 8 10

pH 0pH incpH KCl

DPAD-4


-1000 -800 -600 -400 -200 0 200 400 600

Layer Depth (cm)

0-20

20-40

40-90


pH2 4 6 8 10

pH 0pH incpH KCl

TOC (%)0.0 0.1 0.2 0.3 0.4 0.5

TN (%)

0.00 0.02 0.04 0.06 0.08

TOCTN

TOC (%)0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

TN (%)

0.00 0.04 0.08 0.12

TOCTN



and hyposulfidic materials, to the maximum depth of investigation (~1 m to 1.50 cm) are mottled heavy clay layers (i.e. black, olive grey, dark grey, brownish grey and reddish grey clay) with calcium carbonate accumulations. The vertical and horizontal distribution of these clay layers are displayed in soil-regolith hydro-toposequence model in Figure 5-1.

The high concentrations and distribution of iron monosulfides in drains DPAD-1; DPAD-3 and DPAD-4 Dry Creek ponds have been promoted by:

(i) the highly depositional environment (closed evaporation ponds),

(ii) high organic matter concentrations (Figure 3-4),

(iii) low Fe and carbonate concentrations (precipitated early in salt production process),

(iv) low re-suspension (due to very slow seawater inflow/through-flow velocities and more sheltered nature of the bunded ponds).

3.2.4 S oil Mineralogy

The semi-quantitative determination of minerals for the whole soil by X-ray diffraction (XRD) for profile DPADd-2.1 in the drain sampled in March/April 2014 is presented in Table 3-3. Quartz is the dominant mineral in the soil together with gypsum, halite and jarosite. Jarosite, which forms at pH 3.5 to 4 is a diagnostic mineral for the identification of sulfuric materials. Table 3-3 Mineralogical composition of soil sample from drain DPADd-02 sampled in April, 2013

Client ID Qtz Hl Gp Kln Ill/Mca Ja

DPADd-02.1 M SD D T T SD

Where: D – Dominant (>60%), CD – Co-dominant (sum of components >60%), SD – Sub-dominant (20-60%), M-Minor (5-20%), T-Trace (<5%). Qtz – quartz, Hl – halite, Gp – gypsum, Kln – kaolin, Ill/Mca – illite/mica, Ja – jarosite The semi-quantitative determination of minerals for the surface salt efflorescences in profile DPADd-2.1 (Figure 3-15 ) sampled in December, 2013 is presented in Table 3-3. Halite, hexahydrite, epsomite and gypsum were dominant in the white salt efflorescences. However in the yellow salt efflorescence sample, ammonium carnallite together with halite and gypsum was identified.

Table 3-4 Mineralogical composition of soil samples from drain PAD-02 sampled in December, 2013 CSIRO id. Sample id. Colour State Mineralogy

2914-39451 1 Yellowish white

As-received Halite, hexahydrite

DPAD-02.1 Air dried Halite, hexahydrite

2914-39452 4 White As-received Halite

DPAD-02.1 Air dried Halite

2914-39453 6 Yellow As-received Halite, hexahydrite, gypsum, ammonium carnallite

DPAD-02.1 Air dried Halite, hexahydrite, gypsum, (ammonium carnallite)

2914-39454 10 White As-received Halite, epsomite

DPAD-02.1 Air dried Halite, epsomite, hexahydrite, gypsum


51

Figure 3-15 Selected range of photographs in drain DPADd-2 showing profile of the sulfuric soil DPADd-2.1 (top two photo’s), white surface salt efflorescences (middle two photo’s illustrating field measurement of low acidity: pH <1.5) and iron precipitates (bottom left hand side photo) and a remnant of an aluminium drink can that has been dissolved by the extreme acidic conditions (bottom right hand side photo)



3.2.5 C las s ific ation and ac idific ation and deoxygenation/malodour hazard as s es s ment

ASS material and profile classification was carried out for each soil sample collected, according to the definitions and methods presented in Section 2.2.

A summary of the ASS materials for each layer/horizon and subtype classification for each profile is presented in Table 3-5. Acid sulfate soil subtype classification was achieved using the key described in Appendix 1 (Fitzpatrick et al. 2008; 2010). The ASS subtype classification was carried out for each soil profile collected during both sampling campaigns and allocated an “Acidification and deoxygenation/smell hazard assessment” (see chapter 6).

Acidification and deoxygenation/malodour hazard assessment was based on: (i) landscape position (Figure 3-1), (ii) soil morphology (Appendix 2), (iii) acid base accounting (Figure 3-14; Appendix 5), (iv) pH data (Figure 3-14 and Table 3-5; Appendix 4), (v) ASS material and subtype classification (Table 3-5). Acidification and deoxygenation/malodour hazard categories used in this report are: high (Yellow), medium (Brown) and low (Blue).

Table 3-5 Samples from section 2 drains: summary of ASS material classification, ASS subtype soil profile classification, other major soil morphology features used to determine acidification hazard ratings (where a sulfuric soil** has a high rating, hypersulfidic soil* has medium rating and hyposulfidic soil has a low rating)



Monosulfidic Material

C:N Ratios

DPADd-01.1 0-15 Hyposulfidic Hyposulfidic Gyp grit black Monosulfidic (H) 3.96 DPADd-01.2 15-25 Hyposulfidic


DPADd-01.3 25-45 Hyposulfidic

HC Brown Monosulfidic (H) 11.01 DPADd-01.4 45-90 Hyposulfidic

MC, Sh (30%) 103.82

DPADd-2.1 0-0.5 Sulfuric Sulfuric Yellow, crust 1.29 DPADd-2.2 0.5-3 Sulfuric

Yellow, soft 2.46


Orange, crust 9.56 DPADd-2.4 10-30 Hyposulfidic

Brown, HC 2.74


Red; HC mud 1.80




MC, Black Monosulfidic (H) 5.72 DPADd-3.4 45-90 Hyposulfidic

HC grey,red m Monosulfidic (H) 4.08


MC, Sh (20%) Monosulfidic (H) 7.53


HC grey,red m Monosulfidic (H) 2.46 **Where the soil classification is a Sulfuric soil, sulfuric material (pH<4 at time zero

incubation) has been identified in a layer or horizon (at least 15cm thick) within 150 cm of the soil surface.

*Where the soil classification is a Hypersulfidic soil, hypersulfidic material (pH creased to <4 after incubation for at least 16 weeks) has been identified in a layer or horizon (at least 10cm thick) within 150 cm of the soil surface.

Monosulfidic material: High (H); Medium (M) and Low (all others)


53

3.2.6 Organic c arbon and nitrogen

Details of trends in the amount of organic carbon and nitrogen in soil profiles are given in Figure 3-14. Nitrogen data was used to calculate carbon to nitrogen ratios to assist in determining the organic carbon origins (Table 3-5).

Most surface and near surface layers had C:N ratios <10 indicating organic carbon derived from non-vascular aquatic plants e.g. algae or perhaps soil microbial biomass. For those samples from shallow layers it is likely they contain organic matter of mixed origin.

Samples collected at depth in profile DPADd-01.4 have C:N > 100, which probably represents humic material consistent with organic bands observed in these profiles (Figure 3-14).. However, for those samples from the shallow layers it is likely they contain organic matter of mixed origin.

4BRAPID METAL RELEASE


4. R AP ID ME T AL R E L E AS E

Summary

The rapid metal release tests using a water extraction were undertaken on selected samples from sites at Dry Creek salt fields to determine the potential mobility and bioavailability of nutrients, metals and metalloids.

The samples were mainly sampled from the gypsum ponds in section 2, but included samples from 3 drains and a site next close to the eastern perimeter of the ponds where contamination from a former Trade dump has leaked into the site.

The soils showed little change between original and incubated soil in terms of pH, consistent with high buffering capacity in the soils, and there was a change to higher Eh during the incubation. In general, the shallow gypseous soil layers released high Ca and SO4. There was also a slight decrease in several trace elements in some samples, possibly due to sorption during the incubation process.

The range of concentrations for most solutes analysed in the extractions was high. Ammonium was present at moderately high concentrations in some samples, up to 2 mg l-1. A number of trace elements were also elevated including As (up to 8.4 µg l-1), Cr and Cu (up to 18 µg l-1), U (up 55 µg l-1), and especially Mo (up to 1406 µg l-1). The data show that several contaminants are potentially mobile at the ambient pH of these soils. The contaminated site contained very high concentrations of a number of metal contaminants.

4.1 Introduc tion

The pH and Eh of water are the most important master variables controlling the solubility and sorption characteristics of metals and metalloid contaminants. In acid sulfate soil areas, pH is often the dominant control on metal cations with high concentrations being common particularly at pH < ca. 4.5 (Shand et al. 2010; Simpson et al. 2010). Predicting the quantities of contaminant release is difficult, especially in oxidised soils as contaminants are often associated with a range of mineral fractions as well as organic matter (Shand et al. 2012).

A number of soil samples were selected to determine the potential availability of nutrients and metal/metalloid contaminants from the soils. This was undertaken as a dilute water extraction based on the methodology of Simpson et al. (2010), with samples selected from the ponds from a range of soil depths. The soils were subsequently allowed to incubate for a period of 8 weeks to determine if changes occurred during oxidation of the samples. The technique was designed to simulate the rewetting of dried soils, and in this case the drying followed by rewetting of the soils by freshwater. Higher salinity extractions were not undertaken, and it is likely that saline water would have a different effect on the mobilisation of elements in the soils than fresh water. A total of 37 soil samples from 11 pond’s (16 profiles), along with 4 samples from 2 drains were selected for these tests and analysis. One sample was selected from the site next close to the eastern perimeter of the ponds where contamination from a former Trade dump has leaked into the site and yellow and brown salt efflorescences were abundant (Figure 4-2). This sample was acidic (pH 4.06) and will be considered separately to the ponds for clarity of the plots.


55

Figure 4-1 Surface of soil at contaminated site showing bright yellow efflorescences of ammonium carnallite, halite, and epsomite (see section 3.2.4 for more details and soil characteristics).

4.2 Methodology and analytic al tec hniques

Soil samples were air dried at 40 0C, and 25 g of each sample was weighed into clean acid-washed 250 mL Nalgene extraction bottles and resuspended in 250 mL of deionised water for a period of 24 hours in an end over shaker. Water blanks were run with the batch extraction to monitor water quality throughout the experiment. After 1 hour, a 25 ml aliquot was sampled to measure water quality at the start of the extraction, with the measurements repeated at the end of extraction (24 hours). Water quality measurements included dissolved oxygen, pH, alkalinity/acidity, redox potential (Eh), and specific electrical conductance (SEC).

At the completion of the extraction phase, the samples were centrifuged to settle solids and allow the supernatant to be filtered for chemical analysis using Millex 0.45 micron PVDF syringe filters. Analyses for a suite of major and trace elements including metals, metalloids nutrients were run on the filtered water extracts to provide a detailed profile of each sample’s chemistry.

Nitrogen species, Cl and PO4 were analysed by colorimetric analysis using an Auto Analyser; Br, F and SO4 by ion chromatography; and NPOC by a TOC Analyser in the Adelaide Waite laboratories at CSIRO. For cation analyses, water samples were transported to the CSIRO laboratory at Lucas Heights, Sydney by courier and analysed for a range of major and trace elements.

A subsample of each water sample was taken for direct metals analysis using an inductively coupled plasma-atomic emission spectrometer (ICP-AES) (Varian730 ES or Agilent 700 series) fitted with an argon sheath torch using in-house method C-229 and operating instructions recommended by the manufacturer. High salinity samples were analysed using the method of standard additions for the determination of aluminium, iron, manganese and zinc. Calcium, sodium, potassium, magnesium, sulfur and



strontium were analysed by diluting the sample then analysing against matrix matched calibration standards prepared from certified stock solutions (Accustandard, USA). The remaining elements were analysed by inductively coupled plasma-mass spectrometry (ICP-MS) (Aglient 7500 CE) using in-house method C-209 and operating instructions recommended by the manufacturer. Samples were diluted and analysed against matrix matched standards which were prepared from a set of three multi-element stock solutions (High Purity Standards, USA).

4.3 S oil extrac tion data

A comparison of the pH change between the original extraction and the incubated sample extraction following the 8 week incubation period (Figure 4-2) shows that a decrease in pH occurred during oxidation. However, pH remained moderately high in most samples, consistent with hyposulfidic soils and acid-base accounting data indicating a high buffering capacity for the soils in these ponds and drains. Alkalinity showed little change during the incubation; however, the two highest alkalinity samples displayed a significant decrease but alkalinity remained moderately high (> 1 meq l-1). The specific electrical conductance (SEC) of a number of soils decreased during incubation. The reason for this is not clear but may be due to soil heterogeneity or a washing out of salts from the bulk soil during the drying process.

During incubation, there was an increase in redox potential (typically greater than 50 mV) for many soils indicating that significant oxidation is likely to occur upon drying, albeit at circumneutral pH.

Major cations and anions showed similar correlations between initial and incubated extractions. Of the minor elements, F increased significantly in some incubated samples, up to 2.9 mg l-1. Nitrogen species were dominated in general by high organic N (difference between total N and inorganic N-species) but with elevated NH4 in some samples (up to 2 mg l-1 NH4-N, and a wide range of concentrations (0.3 – 8 mg l-1 total N). Dissolved organic carbon also varied widely (2-47 mg l-1). Most trace elements were also similar between initial and incubated soils, the exceptions being decreases in Cu and Sc. The reasons for this are not clear, but may be due to sorption during incubation. Ammonium (NH4) increased in some of the incubated extractions suggesting potential for release of this reduced N-species.

A Piper plot of the data is shown in Figure 4-3, with seawater as a reference. The data show a significant spread away from seawater composition: there is a trend towards Ca-SO4 type waters for many samples, and also a trends towards Mg and Na dominance. It is likely that gypsum dissolution as well as exchange reactions have played a dominant role in these trends.

There are some clear trends with depth but these vary e.g. some profiles are more saline at depth whilst others are fresher. Only one complete profile PA6.2 was completed for metal release. This showed a general increase in SEC and Eh with depth, but with a distinct decrease in sample PA2.3 which coincided with a maxima in pH (Figure 4-4 as well as alkalinity Figure 4-5). Sample PA2.3 was a sulfidic shelly grit underlying gypseous material, above a heavy clay. The upper gypseous layers contained very high Ca and SO4 concentrations.

Trace elements concentrations were variable (Figure 4-6 ): several elements (Al, Cu, Fe) showed a minima in the middle of the profile at PA2.3, whilst others displayed a general increase (Li, Mn, Mo, U, V). Scandium, in contrast was the only metal to decrease with depth. Molybdenum is present at high concentrations, slightly higher than noted for ponds in section 4 (Fitzpatrick et al. 2014).


57

Figure 4-2 Plots of pH, SEC, Eh and alkalinity, comparing data from sampled soils with the same soils incubated for 8 weeks.

Selected trace elements have been plotted against pH on Figure 4-7, where the narrow range in pH can be contrasted with those in section 4 (pH 3.6 – 8.5; Fitzpatrick et al. 2014). Trace elements show a diversity of trends (Figure 4-7), and the data are shown along with ANZECC guideline values for 95% ecosystem protection (freshwater – dotted line; marine – dashed line). The dilutions used in the extraction provide only a guide to those contaminants released and soluble at this specific dilution. However, previous studies using this technique hove shown that the concentrations derived have proved useful as a guide to real impacts (Shand et al. 2010).

The differences in pH between the ponds are also reflected in higher Eh and low alkalinity at lower pH (Figure 4-2). Trace elements show a diversity of trends with pH (Figure 4-7).

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Figure 4-3 Piper plot showing the relative proportions of major elements in soil extractions

The pH control for many metals, particularly the transition metals, has been well established, with high concentrations at low pH, whilst it is known that metalloids (e.g. As, Mo, Sb) form negatively charged oxyanions which can be mobile at neutral to high pH due to limited sorption. The high Al noted for some samples is unlikely to be due to dissolved Al, as solubility is low at the circumneutral pH’s of most samples. It was noted that some samples remained cloudy even after filtering, therefore, the high Al is likely to be in the form of colloids that are smaller than the pore size of the industry standard filters used (0.45 µm). Most metal concentrations were low, as expected at these pH’s (e.g. Ni, Figure 4-7).

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59

Figure 4-4 Depth profile of PA 6.2 showing depth trends of pH, Eh and SEC

Molybdenum (Mo) is present at high concentrations in a number of samples (up to 1400 µg l-1). It is known to bind strongly to organic matter over a range of pH. Copper (Cu) is also known to bind strongly with organic matter, but both elements do not show a clear relationship with measured DOC. Uranium was present at pH>7 in many samples (Figure 4-7) and it is likely that complexing with carbonate ligands is the dominant control.

The variation in trends with pH for the trace elements overall shows that a number of chemical controls are important for mobilisation into the fluid phase. The changes in soil material from gypsum, through shelly grits overlying heavy clay and, in some cases with ancient deeper mangrove soils will play a significant role as highly variable sources of potential contaminants as well the pH-Eh matrix controlling solubility and speciation. Nevertheless, the study has highlighted that a number of contaminants are, or are likely to be, bioavailable and mobile in many of these salt ponds. The concentrations of most metals and metalloids in drains was typically lower, but fewer samples were studied.

The contaminated site, in contrast, contained very high concentrations of a number of contaminants and a summary is given in Table 4-1. The concentrations of NH4, F and the metals are very high in this acidic sample, whilst Mo was not present above detection limit.

The simple water extractions suggest that contaminant mobilisation in the soils may be an issue following rewetting of the ponds or during any disturbance. This summary indicates which contaminants are likely to be present and the conditions under which they may be mobile. The effect of sweater addition to the ponds has not been tested but may be significantly different in terms of what solutes and how much is released.

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Figure 4-5 Depth profile for major elements, Sr and TOC

Concentration (mg l-1)

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Figure 4-6 Depth profile for trace elements

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Figure 4-7 Plots of trace elements plotted against pH highlighting the different behaviour of these elements.

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Table 4-1 Concentrations of selected contaminants in sample DPAD-02.2 for t0 and t8 water extractions.

Element T0 T8

pH 4.06 4.06

F (mg l-1) 24 27

NH4-N (mg l-1) 8.6 10

Al (µg l-1) 45700 46000

Cu (µg l-1) 3740 3900

Mo (µg l-1) <1 <1

Ni (µg l-1) 2050 4200

Zn (µg l-1) 63100 70000

5BSOIL-REGOLITH HYDRO-TOPOSEQUENCE MODELS TO EXPLAIN AND PREDICT CHANGES IN SOILS OVER TIME AND SPACE


5. S OIL -R E G OL IT H HY DR O-T OP OS E QUE NC E MODE L S T O E XP L AIN AND P R E DIC T C HANG E S IN S OIL S OV E R T IME AND S P AC E

Summary One representative transect or soil-regolith hydro-toposequence model in the form of a cross-section was constructed to describe, explain and predict the spatial and temporal heterogeneity of: (i) acid sulfate soil properties comprising a range of ASS materials and Subtypes, (ii) near surface features such as salt efflorescences (gypsum & halite), shells and cracks and (iii) deep (>~50cm) underlying mottled heavy clay layers. The models help to visualise the soil morphology and soil chemical data; and illustrates the complexities and importance of understanding specific sites to assess:

• detailed behaviour and implications of the various ASS materials (i.e. hypersulfidic, hyposulfidic and monosulfidic),

• deep features in soil horizons & layers (i.e. peats; black, olive grey, dark grey, brownish grey and reddish grey heavy clays),

• shallow features (i.e. salt efflorescences & wet/dry monosulfidic material, shells) • surface water ponding • temporal changes in acid sulfate soil transformations from December 2013

(Summer) to March/April (Autumn) 2014 following a major reflooding event and part drying has not changed the nature and classification of the various ASS materials – because of the high amount of carbonates present (i.e. high neutralising capacity) in the surface layers (~0-50cm),

• degree of external and internal factors controlling pedogenic pathways and processes of soil evolution (i.e. extrinsic and intrinsic pedogenic thresholds, pedogenic rates and acid sulfate soil processes, such as the formation of monosulfidic, hypersulfidic and hyposulfidic materials)

5.1 S oil-regolith hydro-topos equenc e models

An understanding of the detailed behaviour of various ASS materials (e.g. sulfuric, hypersulfidic, hyposulfidic and monosulfidic) and features (e.g. surface salt efflorescences and underlying clays) in layers, horizons and deep regolith is fundamental to the successful local site characterisation of ASS in the salt ponds at Dry Creek. Soil-regolith hydro-toposequence models help to describe and predict the spatial heterogeneity of ASS properties and processes that occur as a consequence of fundamental shifts in the “environmental equilibrium” brought about by the impact of management practices such as the establishment of the salt ponds and subsequent drying/draining or re-flooding. ASS in such fluctuating water environments are not stable and therefore may undergo rapid change depending on whether water levels are dropping or rising. ASS materials change depending on the water status of the soil (saturated or unsaturated), which controls whether chemical processes are oxidising or reducing, and the acid status.

Conceptual soil-regolith hydro-toposequence models in the form of cross-sections enable workers to develop and present a mechanistic understanding of complex spatial and temporal soil-regolith environments (e.g. Fritsch and Fitzpatrick 1994). The regolith is the unconsolidated earth material present above bedrock and includes the upper soil layers. These soil-regolith models are cross-sectional representations of soil-regolith


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profiles that illustrate vertical and lateral changes that occur across the pond hydro-toposequences being studied. They also tell a story explaining the complex soil, hydrological and biogeochemical interactions that have led to the development of an ASS problem (e.g. Fitzpatrick and Merry 2002). These models may also incorporate various management options linked to different scenarios. This can be achieved by mapping the wide distribution of acid sulfate soil materials by classification of soil types and subtypes.

To highlight the spatial heterogeneity of acid sulfate soil properties and ground/surface water interactions in ponds PA3 to PA12 a soil landscape cross-section, in the form of soil-regolith toposequence model (Figure 5-1 ) has been constructed to help visualise the large quantity of results from the studies discussed in the previous chapters. In this soil-regolith model, the spatial variation of all ASS materials identified are displayed in detail using a standard set of graphic symbols such as for hypersulfidic, hyposulfidic and monosulfidic materials. They also display other related features formed as a consequence of the formation ASS such as soil cracks and salt efflorescences caused as a consequence of the reflooding of the ponds between February 2014 and March/April 2014 (i.e. formation of ASS with subaqueous features). In the model the spatial extent (distribution) of the various ASS sub-types (e.g. hyposulfidic clayey soils) are indicated, which is based on numerous observations in the field from the soil pits and auger samples collected.

Finally, this soil-regolith model can also be used as a framework or basis to explain some of the key intrinsic features and external drivers that render the various acid sulfate soils identified to be either relatively stable or susceptible to rapid change (Fitzpatrick et al. 2012a). For example, Fitzpatrick et al. (2012) define Extrinsic and Intrinsic pedogenic thresholds (Muhs 1984) rather loosely as a circumstance by which a “relatively modest change” in an environmental driver can cause a major change in soil subtype alteration (i.e. soil evolution from a Hypersulfidic/Hyposulfidic clay soil to a Sulfuric clay soil) and soil properties.

5.2 P onds PA3 to PA12

The conceptual cross-section diagram in Figure 5-1 illustrates a cross-section through the centre of pond PA6, which was relatively wet along the western segments of each pond in March/April 2014 showing the spatial heterogeneity of ASS materials, ASS subtypes and specific related features such as clay layers and abundant occurrence of “dry” white salt efflorescences. The substantial increase in rainfall from February 2014 to March/April 2014 resulted in water flooding and high water table levels mostly along the western segments of ponds PA3 to PA12 (Tonkin Consulting 2015).

A consequence of the rewetting/reflooding of the western segments is the formation of ponded saline water with shallow: (i) hyposulfidic subaqueous soils (shelly gritty/sandy) soils with thick monosulfidic material and (ii) hypersulfidic subaqueous shelly gritty/sandy soils with thick monosulfidic material.

In contrast, along the eastern segments of ponds PA3 to PA12 where little or no ponding occurred, the soils classified as: (i) hyposulfidic soils (mostly clayey) with thick monosulfidic material.

Ponds PA3 to PA12 showed no changes in ASS properties after being flooded. Consequently, they continued to display widespread presence/perseverance of hyposulfidic and hypersulfidic materials as shown in Figure 5-1



The cross section/hydro-toposequence model displayed in Figure 5-1 comprises three components: (1) an overall cross section, which links the detailed cross sections of the ponded western segments (2) and dryer eastern segments (3) near the bund walls with vertical scales exaggerated to show details of the major soil horizons and sediment layers.

This representative cross section for Section 2 displays in detail the spatial distribution the major horizons/layers (vertical scale exaggerated scale) and water levels from West to East (horizontal scale less exaggerated) to display and integrate the following features:

• Topography, including salt ponds, bund walls, tidal creek in mangrove swamp • Vegetation - Mangroves and samphire • Colour photographs (inset) showing landscape views and detailed soil profiles • Major soil horizons / sediment layers: soil colour, texture (including fragments

of gypsum), crusts (halite and gypsum) • Acid sulfate soil materials (monosulfidic, hypersulfidic and hyposulfidic

materails), integrates the incubation data (16 weeks) and Acid Base Accounting data

• Acid sulfate soil classification (e.g. Hypersulfidic subaqueous soil with monosulfidic material)

• Water levels / hydrological data from piezometer measurments (Tonkin Consulting 2015).

• AHD levels In summary, this model shows the spatial heterogeneity of ASS materials, ASS subtypes and related near surface features such as the abundant occurrence of “dry” white salt efflorescences. The models also clearly displays the deep underlying (>~1 m to 1.50 cm) mottled heavy clay layers (i.e. black, olive grey, dark grey, brownish grey and reddish grey clay) with calcium carbonate accumulations.


67

In summary,

Figure 5-1 Representative soil-regolith hydro-toposequence model for section 2 based largely on the soil features for pond PA6 in autumn (March/April, 2014) showing the spatial distribution of: (i) water levels from West to East (horizontal scale less exaggerated), (ii) topography, including salt ponds, bund walls, tidal creek in mangrove swamp and AHD levels, (iii) vegetation (mangroves and samphire), (iv) major acid sulfate soil materials: monosulfidic, hypersulfidic and hyposulfidic (vertical scale exaggerated) and (v) soil



horizons (gypsum crusts / fragments =- Gypsic horizons; halite crusts = salic horizons) and sediment layers based on (colour and texture (light brown clay / shell grit).

5.3 Degree of external and internal fac tors c ontrolling pedogenic proc es s es in s alt pond evolution and rehabilitation for wes tern and eas tern s egments

A combined soil-regolith model is presented for Ponds PA3 to PA 12 – Western segments (Figure 5-2) and Ponds PA3 to PA 12 – Eastern segments (Figure 5-3) to illustrate changes in Acid Sulfate soil formation processes during the following 5 major sequential periods:

A. Pre-salt pond construction period (> 50 yrs ) B. Salt pond construction activity (6 months ~ 50 yrs ago). C. Salt production period (~50 yrs). D. Draining/drying of salt pond activity (late 2013). E. Reflooding after heavy rainfall events (February to June 2014).

This combined model illustrates the key external drivers or thresholds that render the various ASS subtypes and features (e.g. cracks) relatively stable or susceptible to slow or rapid change (Fitzpatrick et al. 2012a). The dominant Acid Sulfate Soil pedogenic processes are assigned to each sequential model, which incorporates the hydro-toposequence model discussed in Section 5.2 above (Figure 5-1 using the following 3 pedogenic concepts:

(a) Extrinsic and intrinsic pedogenic thresholds (Muhs 1984). The pedogenic threshold is a value, unique to a particular soil system, beyond which the system adjusts or changes, not just in rate but also in soil type or subtype. In an extrinsic pedogenic threshold, an external factor changes progressively, which triggers abrupt, fast or slow pedogenic changes. This is usually caused by climatic, geomorphic or human-induced changes (e.g. salt pond drainage). In contrast, intrinsic pedogenic thresholds occur when a system changes without a change in external variable.

(b) Pedogenic rates [e.g. dynamic balance of thickness (Johnson and Watson-Stegner 1987)]. (c) Acid sulfate soil processes [sulfidization & sulfuricization (Fanning and Fanning 1989)]. Where sulfidization describes the processes leading to the formation of sulfides (or Hypersulfidic materials) and sulfuricization describes those processes responsible for the formation of sulfuric acid (sulfuric materials).

The predictive soil-regolith model (Figure 5-2) summarises the following key pedogenic changes in Acid Sulfate soil formation processes: A. Formation of: (i) Non-Acid sulfate soils (Red brown earths etc.) prior to pond construction – eastern segments and (ii) Coastal acid sulfate soils with hypersulfidic material in mangrove swamps– western segments B. Formation of: (i) Non-Acid sulfate subaqueous soils when salt pond was constructed - . eastern segments and (ii) Acid sulfate subaqueous soils with hypersulfidic material when salt pond was constructed - . western segments C. Slow build up of Fe-sulfides under long-term subaqueous ASS conditions from 1920’s to 2013 under salt water. D. Formation of Hyposulfidic soils with thick monosulfidic materials. E. Fast build up of Hyposulfidic clayey soils after dissolution of the gypsum crusts and salt efflorescences and the leaching down salts (halite) under oxidised conditions in


69

some areas due to fast drying during the draining of pond PA7a (reflooding after heavy rainfall events and fast rewetting/ reflooding between February and March/April 2014). The following terms and abbreviations are used in Figure 5-2 and Figure 5-3: Ex- Extrinsic pedogenic threshold; In - Intrinsic pedogenic threshold; Dy - Dynamic balance of thickness; Dp – deepening; Rv – removals; Up – upbuilding; Pr(s) - Progressive pedogenesis (slow: relative to previous window); Pr(f) - Progressive pedogenesis (fast relative to previous window); Ab - Abrupt pedogenesis (relative to previous window); Re - Regressive pedogenesis; St - Static pedogenesis; Sulfide – sulfidization; Sulfuric - sulfuricization (Fitzpatrick et al. 2012a) The combined soil-regolith models presented in Figure 5-2 for Ponds PA3 to PA 12 – Western segments and in Figure 5-3 for Ponds PA3 to PA 12 – Eastern segments illustrates via stages A to C the modification of water levels by bund installations and salt pond construction, which causes a slow build up [Pr(s)] of sulfides under long-term subaqueous ASS conditions from 1920’s to 2013. These processes are followed by fast drying stages (D) during the draining/drying of ponds in late 2013. This is followed by (E) post reflooding events after heavy rainfall events and fast rewetting/reflooding between December and March/April 2014 resulting in fast build up [Pr(f)] of soluble sulfate salts, Mg-calcite, halite and gypsum (Up). In general, soil profiles along the western segments in ponds PA3 to PA12 comprised hyposulfidic (dominant) and hypersulfidic subaqueous sandy/shell grit soils with medium to low acidification hazard ratings and medium malodour hazard ratings. In general, soil profiles along the eastern segments in ponds PA3 to PA12 comprised hyposulfidic (dominant) and hypersulfidic clayey soils with low acidification hazard ratings and medium malodour hazard ratings.



Western segments of ponds PA3 to PA12 Period or Activity: ASS subtypes

Soil-regolith hydro-toposequence models Dominant pedogenic processes

A: Pre-salt pond construction (> 50 yrs ) Acid sulfate soil in mangroves (Hypersulfidic subaqueous soils) - Tidal

St - Static pedogenesis; Dy - Dynamic balance of thickness

B: Salt pond construction: (6 months ~ 50 yrs ago) Subaqueous ASS formation with no tidal influence

Extrinsic pedogenic threshold (Ex) caused by human-made changes (bund wall and pond construction) with rapid flooding of saline water. Rapid formation of ASS Subaqueous soils with no tidal influence

C: Salt production in pond (~50 yrs) Hyposulfidic subaqueous soils (shell grits / clayey soil) with MBO and gypsum/halite crust formation Hypersulfidic subaqueous shell grits / clayey soil formation

Progressive slow pedogenesis [Pr(s)] in <50cm layers in upbuilding sulfides (Up) / (Sulfide) Sequential transformation from tidal Acid sulfate subaqueous clayey soil to Hyposulfidic to Hypersulfidic subaqueous clayey soils – with MBO

D: Draining of salt pond (late 2013) e.g. simulation of Pond PA7a

Extrinsic pedogenic threshold (Ex) caused by human-made changes (draining of ponds) Abrupt pedogenesis (Ab) in rapid formation of wide cracks to 3.5m and profile deepening (Dp) Progressive fast pedogenesis [Pr(f)] in removals of water & sulfides (Rv) and upbuilding of soluble sulfate salts, Mg-calcite, halite and gypsum (Up)

E: Reflooding after heavy rainfall events February to March/April 2014 Partial dissolution of gypsum/halite crusts

Extrinsic pedogenic threshold (Ex) caused by natural climatic event: heavy rainfall events (rapid reflooding) changes. Progressive fast pedogenesis [Pr(f)] in removals of water & sulfides (Rv) and upbuilding of soluble sulfate salts, Mg-calcite, halite and gypsum (Up)

Figure 5-2 Predictive soil-regolith model for Salt Ponds PA3 to PA 12 western segments illustrating the dominant pedogenic pathways and processes


71

Eastern segments of ponds PA3 to PA12 Period or Activity: Non-ASS and ASS subtypes

Soil-regolith hydro-toposequence models Dominant pedogenic processes

A: Pre-salt pond construction (> 50 yrs ) Non-Acid sulfate soils (Red brown earths etc.)

St - Static pedogenesis; Dy - Dynamic balance of thickness

B: Salt pond construction: (6 months ~ 50 yrs ago) Subaqueous soil formation Non-Acid sulfate subaqueous soil

Extrinsic pedogenic threshold (Ex) caused by human-made changes (bund wall and pond construction) with rapid flooding of saline water. Rapid formation of Non-ASS Subaqueous soil

C: Salt production in pond (~50 yrs) Hyposulfidic subaqueous clayey soil formation Hypersulfidic subaqueous clayey soil formation

Progressive slow pedogenesis [Pr(s)] in <50cm layers in upbuilding sulfides (Up) / (Sulfide) Sequential transformation from Non-Acid sulfate subaqueous clayey soil to Hyposulfidic to Hypersulfidic subaqueous clayey soils

D: Draining of salt pond (late 2013)

Extrinsic pedogenic threshold (Ex) caused by human-made changes (draining of ponds) Abrupt pedogenesis (Ab) in rapid formation of wide cracks to 3.5m and profile deepening (Dp) Progressive fast pedogenesis [Pr(f)] in removals of water & sulfides (Rv) and upbuilding of soluble sulfate salts, Mg-calcite, halite and gypsum (Up)

E: Reflooding after heavy rainfall events February to March/April 2014

Extrinsic pedogenic threshold (Ex) caused by natural climatic event: heavy rainfall events (rapid reflooding) changes. Progressive fast pedogenesis [Pr(f)] in removals of water & sulfides (Rv) and upbuilding of soluble sulfate salts, Mg-calcite, halite and gypsum (Up)

Figure 5-3 Predictive soil-regolith model for Salt Ponds PA3 to PA 12 eastern segments illustrating the dominant pedogenic pathways and processes

6BACID SULFATE SOIL CLASSIFICATION MAPS AND HAZARD RATING MAPS


6. AC ID S UL F AT E S OIL C L AS S IF IC AT ION MAP S AND HAZAR D R AT ING MAP S

6.1 C ons truc tion of ac id s ulfate s oil c las s ific ation maps

Each soil profile was allocated an acid sulfate soil subtype according to the Acid Sulfate Soil Identification Key (Appendix 1; Fitzpatrick et al., 2010). The key is designed for people who are not experts in soil classification systems, assisting them to identify five acid sulfate soil types (subaqueous, organic, cracking clay, sulfuric and hypersulfidic soils) and 18 sub-types based on the occurrence of sulfuric, hypersulfidic, hyposulfidic, or monosulfidic material, and clayey or sandy layers.

Acid sulfate soil subtypes were identified for soil profiles at all sites following surveys in December 2013 and March/April 2014 (Table 3-2, Table 3-5). Soils that did not satisfy the acid sulfate soil type classes were named as “other non-acid sulfate soil types”.

Acid Sulfate Soil classification maps were constructed that identify areas defined by “polygon boundaries” where an acid sulfate soil class is likely to occur. The ASS classification map classifies a number of soil properties throughout the depth of the soil profile and allocates it to a soil class. To construct acid sulfate soil classification maps, the following six (6) input steps were used:

Step1: Each profile (or sampling site) was classified in accordance with the following procedure, as applied to soil classification keys, which is based on the presence or absence of ASS materials with the highest hazard ASS material keying out first, as follows: (i) sulfuric material keys our first, (ii) hypersulfidic material keys out second, (iii) hyposulfidic material keys out third and (iv) lastly all other non-acid sulfate soil types. The classification of ASS materials (i.e. sulfuric, hypersulfidic, hyposulfidic or monosulfidic) is based mainly on the initial pH (pH at time zero) and after incubation for at least 16 weeks as shown in Table 3-2 and Table 3-5.

A soil profile that classifies as a “Sulfuric soil”, requires sulfuric material (i.e. pH <4 at time zero incubation) to be identified in a layer or horizon, which is at least 15 cm thick within 150 cm of the soil surface. A soil profile that classifies as a “Hypersulfidic soil”, requires hypersulfidic material (i.e. decrease in pH to pH 4 or less after incubation for at least 16 weeks) to be identified in a layer or horizon, which is at least 15 cm thick within 150 cm of the soil surface.

Step2: Visual identification of additional “key soil / water features” such as:

• Surface water levels, 2.5 m below the surface water level to estimate areas with “subaqueous soils” = W

• Surface water levels, 0.50 m above the surface water level to estimate areas with “hydrosols” = Hyd

• Drained soils with water level below 50 cm: Unsaturated = Uns • Salt efflorescences = Ef, • Gypsum / Halite crusts = Gyp • Monosulfidic material that is wet (Mow) or dry (Mod) • Organic = O • Clays = Cy • Sands = Sa • Loams = Lo • Shell grit gravel = Sh • Sulfuric material = Su


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• Hypersulfidic material = He • Hyposulfidic material = Ho • Non-acid clays = Non Examples of these features are displayed in “Map Key Legends” for ponds PA3 to PA 12 (see below Table 6-2 to Table 6-7 and Figure 6-1 to Figure 6-6).

Step 3: Each sampling site was classified (e.g. sulfuric clay or sulfuric sand as shown in Table 6-1) in accordance to the dominant acid sulfate soil material present (i.e. Soil subtype in accordance to the soil identification key outlined in Appendix 1) and texture (i.e. Soil Subtype in accordance to the soil identification key in Appendix 1). Table 6-1. Map Legend showing potential soil map units ordered by landscape (ponded water level) and then acid sulfate soil class and texture. Landscape Acid Sulfate

Soil Class Soil Texture Class Soil Map Unit Name

Subaqueous (0 to 2.5m water depth)

Hypersulfidic Clay Hypersulfidic subaqueous clays Hypersulfidic Loamy Hypersulfidic subaqueous loams Hypersulfidic Sandy Hypersulfidic subaqueous sands Hyposulfidic Fine Hyposulfidic subaqueous clays Hyposulfidic Medium Hyposulfidic subaqueous loams Hyposulfidic Coarse Hyposulfidic subaqueous sands Monosulfidic Ooze Monosulfidic subaqueous ooze Non-acid Fine, Medium or

Coarse Non-acid subaqueous soils

Hydrosols (saturated within 50cm below soil surface)

Sulfuric Fine Sulfuric hydrosols clays Sulfuric Coarse Sulfuric hydrosols sands Hypersulfidic Fine Hypersulfidic hydrosols clays Hypersulfidic Medium Hypersulfidic hydrosols loams Hypersulfidic Coarse Hypersulfidic hydrosols sands Hyposulfidic Fine Hyposulfidic hydrosols clays Hyposulfidic Medium Hyposulfidic hydrosols loams Hyposulfidic Coarse Hyposulfidic hydrosols sands Monosulfidic Ooze Monosulfidic hydrosols ooze Non-acid Fine, Medium or

Coarse Non-acid hydrosols soils

Unsaturated (unsaturated within 50cm below soil surface)

Sulfuric Fine Sulfuric clays Sulfuric Coarse Sulfuric sands Hypersulfidic Fine Hypersulfidic clays Hypersulfidic Medium Hypersulfidic loams Hypersulfidic Coarse Hypersulfidic sands Hyposulfidic Fine Hyposulfidic clays Hyposulfidic Medium Hyposulfidic loams Hyposulfidic Coarse Hyposulfidic sands Monosulfidic Ooze Monosulfidic ooze Non-acid Fine, Medium or

Coarse Non-acid

Gypsum crust Halite crust



Step 4: Based on information from steps 1 to 3 together with soil surveyor and local knowledge, allocate dominant Acid Sulfate Soil Subtypes [e.g. Hyposulfidic (~80 %) & hypersulfidic (~20 %) hydrosol clays] and related soil features to map polygons on the digital NearMap (http://www.nearmap.com/) aerial image taken in November, 2013 as shown for ponds PA3 to PA12 (Figure 6-1 and Figure 6-3) and Figure 6-3.), pond PA7a and drains (Figure 6-3; Figure 6-4).

Soils along the western segments in ponds PA3 to PA12 comprise hypersulfidic and hyposulfidic subaqueous sandy/shell grit soils with medium to low acidification hazard ratings (Table 6-2) and medium deoxygenation/malodour hazard ratings (Table 6-3).

Soils along the eastern segments in ponds PA3 to PA12 comprise hyposulfidic hydrosol loams over clays with low acidification hazard ratings (Table 6-2) and medium deoxygenation/malodour hazard ratings (Table 6-3). Table 6-2. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for ponds PA3 to PA12 with acidification hazard ratings

Map Symbol Map Unit Name

Western segments

He 1 WSaShMow Hypersulfidic (~40%) & hyposulfidic (~60%) subaqueous sandy/ shell grit soils with monosulfidic material (wet)

Eastern segments

Ho 1 HydCyMow Hyposulfidic (~90%) & hypersulfidic (~10%) hydrosol loams over clays with monosulfidic material (wet)

Acidification hazard categories used in maps and tables in this report are: high (Yellow), medium (Brown) and low (Blue).

Table 6-3. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for ponds PA3 to PA12 with Deoxygenation/malodour hazard ratings Map Symbol Map Unit Name

Western segments

He 1 WSaShMow Hypersulfidic (~40%) & hyposulfidic (~60%) subaqueous sandy/ shell grit soils with monosulfidic material (wet)

Eastern segments

Ho 1 HydCyMow Hyposulfidic (~90%) & hypersulfidic (~10%) hydrosol loams over clays with monosulfidic material (wet)

Deoxygenation/malodour hazard categories used in maps and tables in this report are: high (Yellow), medium (Brown) and low (Blue).



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Soils along the southern segments in pond PA7a comprise hyposulfidic subaqueous clayey soils with low acidification hazard ratings (Table 6-4) and medium deoxygenation/malodour hazard ratings (Table 6-5).

Soils along the northern segments in pond PA7a comprise hyposulfidic hydrosol loams over clays with low acidification hazard ratings (Table 6-4) and medium deoxygenation/malodour hazard ratings (Table 6-5).

Table 6-4. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for pond PA7a with acidification hazard ratings


Southern segments

Ho1 WCyMow Hyposulfidic subaqueous loams over clays with monosulfidic material (wet)

Northern segments

Ho2 HydCyMow Hyposulfidic (~100%) hydrosol loams over clays with monosulfidic material (wet)


Table 6-5. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for pond PA7a with Deoxygenation/malodour hazard ratings


Southern segments

Ho1 WCyMow Hyposulfidic subaqueous loams over clays with monosulfidic material (wet)

Northern segments

Ho2 HydCyMow Hyposulfidic (~100%) hydrosol loams over clays with monosulfidic material (wet)




Soils along the drains DPAD-01, 03 and 04 comprise hyposulfidic subaqueous hydrosol loams over clays with low acidification hazard ratings (Table 6-6) and medium to high deoxygenation/malodour hazard ratings (Table 6-7).

Soils along the drain DPAD-02 comprise Sulfuric hydrosol loams over clays with high acidification hazard ratings (Table 6-6) and low deoxygenation/malodour hazard ratings (Table 6-7).

Table 6-6. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for drains DPAD-01, 02, 03 and 04 with acidification hazard ratings


Drains DPAD-01, 03 and 04

Ho WCyMow Hyposulfidic subaqueous loams over clays with monosulfidic material (wet)

Drain DPAD-02

Su HydCyEf Sulfuric (~80%) & hyposulfidic (~20%) hydrosol loams over clays with salt efflorescences


Table 6-7. Dominant and subdominant soil subtypes and other features (e.g. texture) and map symbols for drains DPAD-01, 02, 03 and 04 with deoxygenation/malodour hazard ratings


Drains DPAD-01, 03 and 04

Ho WSaShMow Hyposulfidic subaqueous loams over clays with monosulfidic material (wet)

Drain DPAD-02

Su HydCyMow Sulfuric (~80%) & hyposulfidic (~20%) hydrosol loams over clays with salt efflorescences


Step 5: Based on steps 1 to 4, identify lists of “potential or preliminary” soil map units and symbols as shown in the map legends displayed for ponds and drains in Table 6-2 to Table 6-7.

Step 6: Allocate final Soil Map Symbols (e.g. Su1) and Soil Unit Names (e.g. SuHydCy) for each polygon after creating final map overlay boundaries on a digital NearMap (http://www.nearmap.com/) aerial image taken in November, 2013 (i.e. electronic/digital and hardcopy formats) as shown for ponds in Figure 6-1, Figure 6-2; Figure 6-3 and Figure 6-4; and drains in Figure 6-5 and Figure 6-6.

A back check is then conducted to identify how well the map units ‘honoured’ the sites that occurred in each map unit and agreed with the map unit description, and a further iteration of the map will be conducted to update and refine. The final Soil Classification Maps are presented in Figure 6-1, Figure 6-2; Figure 6-3 and Figure 6-4; and drains in Figure 6-5 and Figure 6-6.



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Confidence level of soil classification mapping It is often not possible to fully classify soils in specific areas because of lack of access to properties (e.g. deep water, areas with a low ability to support a load or with low bearing capacity i.e. has an n-Values (Appendix 2) > 1, no road or track access). For this reason, the following levels of confidence are used to classify soil-landscapes:

(i) high confidence when a high quantity of detailed soil profile observations are made of areas or map units via soil pit, auger or road cutting investigations,

(ii) moderate confidence when only reconnaissance observations are made of areas or map units through few detailed soil profile observations via pits, auger or road cutting investigations – but mostly via visual observations through either walking across landscapes (e.g. selected transects) or windows of a moving vehicle due to satisfactory road access and road cuttings;

(iii) fair to provisional confidence because soil-landscape classification is based on a knowledge of similar soils in similar environments (e.g. knowledge extrapolation based on soil or geological maps documented during the office assessment) especially where no road or property access was available during field investigations.

Acid sulfate soils and their classification are strongly dependant on water conditions as a change in water level will typically influence soil redox conditions and its acid status. Hence, it should be noted that the acid sulfate soil map is not an end in itself and to be a useful aid to any form of land management, it has to be interpreted, often with supplementary information for the user. Such a person or group may find it difficult to even read a soil map, despite the kind of guidance given in this report, and may not realise the potential value of soil maps to their land management interest. It may be necessary for a professional expert to produce “interpretative maps”, based on soil maps, but adding other information relevant to the specific application of the map (e.g. different water levels in parts of the ponds will likely alter or reverse the occurrences of certain soil Subtypes).

6.2 Ac id s ulfate s oil c las s ific ation maps for ponds PA3 to PA12

The Soil classification legend (Table 6-2; Table 6-3) and maps (Figure 6-1; Figure 6-2) for ponds PA3 to PA12, which essentially comprises a moderate confidence level of classification and shows that at the time of the “field survey” (i.e. March/April, 2014) the following spatial distribution of the wide range of acid sulfate soil subtypes comprising acid sulfate soil materials and associated features with:

• Hypersulfidic and hyposulfidic subaqueous sandy/shell grit soils with monosulfidic material

• Hyposulfidic and hypersulfidic hydrosol loams over clays with monosulfidic material

6.3 Ac id s ulfate s oil c las s ific ation maps for pond PA7a

The Soil classification legend (Table 6-4; Table 6-5) and maps (Figure 6-3; Figure 6-4) for ponds PA7a, which essentially comprises a moderate confidence level of classification and shows that at the time of the “field survey” (i.e. March/April, 2014) the following spatial distribution of the wide range of acid sulfate soil subtypes comprising acid sulfate soil materials and associated features with:



• Hyposulfidic subaqueous hydrosol loams over clays with monosulfidic material • Hyposulfidic hydrosol loams over clays with monosulfidic material (wet)

6.4 Ac id s ulfate s oil c las s ific ation maps for drains

The Soil classification legend (Table 6-6; Table 6-7) and maps (Figure 6-5; Figure 6-6) for drains DPAD-01, 02, 03 and 04, which essentially comprises a moderate confidence level of classification and shows that at the time of the “field survey” (i.e. March/April, 2014) the following spatial distribution of the wide range of acid sulfate soil subtypes comprising acid sulfate soil materials and associated features with:

• Hyposulfidic subaqueous hydrosol loams over clays with monosulfidic material • Sulfuric and hyposulfidic hydrosol loams over clays with salt efflorescences.

INSERT SOIL MAP with COLOUR CODE for ACIDIFICATION HAZARD – using high resolution base maps generated by other related projects such as LiDAR. Figure 6-1 Acid sulfate soil classification and acidification hazard rating map for ponds PA3 to PA12 (using legend in Table 6-2)

INSERT SOIL MAP with COLOUR CODE for DEOXYGENATION/MALODOUR HAZARD – using high resolution base maps generated by other related projects such as LiDAR. Figure 6-2 Acid sulfate soil classification and deoxygenation/malodour hazard rating maps for ponds PA3 to PA12 (using legend in Table 6-3 )

INSERT SOIL MAP with COLOUR CODE for ACIDIFICATION HAZARD – using high resolution base maps generated by other related projects such as LiDAR. Figure 6-3 Acid sulfate soil classification and acidification hazard rating maps for pond PA7a (using legend in Table 6-4)

INSERT SOIL MAP with COLOUR CODE for DEOXYGENATION/MALODOUR HAZARD – using high resolution base maps generated by other related projects such as LiDAR. Figure 6-4 Acid sulfate soil classification and deoxygenation/malodour hazard rating maps for pond PA7a (using legend in Table 6-5 )

INSERT SOIL MAP with COLOUR CODE for ACIDIFICATION HAZARD – using high resolution base maps generated by other related projects such as LiDAR. Figure 6-5 Acid sulfate soil classification and acidification hazard rating maps for drains DPAD-01, 02, 03 and 04 (using legend in Table 6-6)

INSERT SOIL MAP with COLOUR CODE for DEOXYGENATION/MALODOUR HAZARD – using high resolution base maps generated by other related projects such as LiDAR. Figure 6-6 Acid sulfate soil classification and deoxygenation/malodour hazard rating maps for drains DPAD-01, 02, 03 and 04 (using legend in Table 6-7)


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6.5 Ac id s ulfate s oil hazard ratings for ac idity and deoxygenation/smell

6.5.1 Hazard or ris k evaluation

This section comprises investigations and interpretations that are primarily focussed on determining the relative hazards associated with the presence of ASS materials and more importantly with the various ASS subtypes.

Defining and Assessing Hazards

Acid sulfate soil materials when disturbed can lead to the following hazards:

a. Acidification;

b. Deoxygenation/malodours (i.e. presence of monosulfidic material)

c. Contaminant mobilisation.

It is acknowledged that there are other hazards associated with acid sulfate soil materials such as the production of odours, noxious gases and dust. These hazards may be identified and acknowledged in reports dealing with the detailed assessment of acid sulfate soil materials.

The field and laboratory analyses carried out using current standard Acid Sulfate Soil protocols for sampling, field characterisation, laboratory analysis and data presentation (see Chapter 2) help determine whether ASS materials present a potential hazard to ponds and whether further investigation is required to elucidate risk. Information emanating from the data and interpretations in Chapters 1 to 5 will therefore:

a. Report on the presence, nature and extent of observed ASS materials;

b. Advise on potential hazards posed by ASS soil materials where possible;

c. Make recommendations on the requirement for further analyses including the number of samples to be analysed.

Defining and Assessing Risk

Risk is a measure of both the consequences of a hazard occurring, and the likelihood of its occurrence (MDBA 2010). Consequence is the impact of the acid sulfate soil materials being expressed, and primarily takes into account environmental and water quality impacts, both to the salt fields and adjacent tidal coastline (mangroves). Level of consequence will be determined in consultation with environmental and salt field managers for each identified hazard in a specific salt pond using a standardised Table 6-8.



Table 6-8: Standardised table used to determine the consequence of a hazard occurring.

Descriptor Definition

Extreme Irreversible damage to wetland values and/or adjacent waters; localised species extinction; permanent loss of water supplies

Major Long-term damage to wetland values and/or adjacent waters; significant impacts on listed species; significant impacts on water supplies

Moderate Short-term damage to wetland values and/or adjacent waters; short-term impacts on species

Minor Localised short-term damage to wetland values and/or adjacent waters; temporary loss of water supplies

Insignificant Negligible impact on wetland values and/or adjacent waters; no detectable impacts on species

Likelihood is the probability of disturbance of the acid sulfate soil material and requires understanding of both the nature and severity of the acid sulfate soil materials (e.g. extent, net acid generating potential, etc) as well as contributing factors influencing the risk (e.g. disturbance of acid sulfate soil materials, wetland management regime).

Level of likelihood will be determined separately for each hazard type. This is due to the variability of contributing factors for each hazard. Likelihood should be determined by assessing the probability of disturbance of the acid sulfate soil materials (Table 6-8). Examples of disturbance include:

• re-wetting of acid sulfate soil materials after they have oxidised;

• acid sulfate soil materials that are currently inundated and that may be oxidised; or

• acid sulfate soil materials that are currently inundated and that may be dispersed by flushing (e.g. scouring flows).

Table 6-9: Likelihood ratings for the disturbance scenario (from MDB 2010).

Descriptor Definition

Almost certain Disturbance is expected to occur in most circumstances

Likely Disturbance will probably occur in most circumstances

Possible Disturbance might occur at some time

Unlikely Disturbance could occur at some time

Rare Disturbance may occur only in exceptional circumstances


81

Risks are ranked using a standardised risk assessment matrix in Table 6-8. Table 6-9 is used as the product to estimate the likelihood of disturbance of the acid sulfate soil materials and the consequences to wetland values and/or adjacent waters. This must also take into account the scientific assessment of the nature and extent of the acid sulfate soil materials present at the site as confirmed through the field and laboratory analyses through detailed ASS analyses.

According to MDBA (2010) acid sulfate soil scientists conducting detailed assessments cannot alone determine the level of consequence or likelihood at a given wetland – input of relevant managers of the salt fields and adjacent tidal coastline (mangroves) areas will be critical. As such, assessment of risk must be made in consultation with the salt fields and adjacent tidal coastline managers. This is to ensure that acid sulfate soil scientists have an understanding of the wetland values and context of wetland management for the site.

Table 6-10: Risk assessment matrix (Standards Australia/Standards New Zealand, 2004).

Likelihood category Consequences category

Extreme Major Moderate Minor Insignificant

Almost Certain Very High Very High High High Medium

Likely Very High High High Medium Medium

Possible High High High Medium Low

Unlikely High Medium Medium Low Low

Rare High Medium Medium Low Low

Legend: It is suggested that, sites with Very High: Very High Risk - immediate action recommended;

High: High Risk - senior management attention needed;

Medium: Moderate Risk - management action may be recommended. Agency responsible must be specified;

Low: Low Risk - manage by routine procedures (should be monitored regularly to determine whether the hazard is increasing).

Reporting on Risk Reports of assessments will establish the level of risk associated with each identified hazard at a wetland using the framework outlined here and in consultation with relevant wetland managers. In order to assist wetland managers in decision-making, the level of risk outlined in final reports should be accompanied by an explanation of the major contributing factors to the risk level (e.g. water management regimes, water chemistry, wetland values etc).



6.6 Ac idific ation hazard

The pond acidification hazard ratings for ponds PA3 to PA12 (Table 6-2; Figure 6-1), pond PA7a (Table 6-4; Figure 6-3) and drains DPAD-01, 02, 03 and 04 (Table 6-6; Figure 6-5) were assigned based on the subtype of acid sulfate soil material, the depth of occurrence, proportion, and distribution in the polygon.

Acid sulfate soil hazard ratings were assigned, with polygons rated as high (yellow), medium (brown) and low (blue). This assessment was based on data obtained during the March/April, 2014 field survey for ponds. It is important to realise that the pond acidification and deoxygenation/malodour hazard ratings status could change with time, e.g. acid sulfate soil materials can change from hypersulfidic (or even hyposulfidic) to sulfuric as the soil dries and/or is re-flooded. These changes can occur relatively rapidly (Fitzpatrick et al., 2009), and if net acidities are high the change from sulfuric to sulfidic can be months to years (Shand et al., 2010; Baker et al., 2013).

Generally, acidification categories used in this report are:

• High acidification rating (yellow map unit colour) indicated that sulfuric (dominant) or hypersulfidic soil materials were present near the surface throughout the polygon.

• Medium acidification rating (brown map unit colour) indicated that hypersulfidic or hyposulfidic soil materials were present, usually in the subsoil and in about 50% of the polygon.

• Low rating (blue map unit colour) indicated that hyposulfidic materials (dominant) were present near the surface throughout the polygon.

Ponds with high (i.e. yellow) acidification rating should be monitored regularly, and have management plans in place to activate if triggers are reached, as they are more likely to increase in acidification hazard. Wetlands with lower ratings are less likely to be of concern and would require less monitoring.

6.7 S oil deoxygenation/malodour hazard

The pond deoxygenation/malodour hazard ratings for PA3 to PA12 (Table 6-3;Figure 6-2), pond PA7a (Table 6-5; Figure 6-4) and drains DPAD-01, 02, 03 and 04 (Table 6-7;Figure 6-6) were assigned based on the subtype of acid sulfate soil, the depth of monosulfidic material occurrence, proportion, and distribution in the polygon.

Generally, deoxygenation/malodour hazard categories used in this report are:

• High rating (yellow map unit colour) indicated that high amounts of monosulfidic materials (wet) were present at or near the surface (i.e. is exposed and not covered by a crust or topsoil) throughout the polygon.

• Medium rating (brown map unit colour) indicated that monosulfidic materials (wet) were present, usually in the subsoil or is covered by a thick (3 to 15 cm) continuous gypsum crust at the time of sampling and in about 50% of the polygon.

• Low rating (blue map unit colour) indicated that no monosulfidic materials (wet) materials (dominant) were present near the surface throughout the polygon.


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6.8 S odic ity hazard

Sodic soils are characterized by low permeability and thus restricted water flow because the clay and organic fractions of these soils are dispersed.

All the ASS soils mapped in section 2 classify as “Very saline to Highly saline soils” (Table 6-11) and comprise “flocculated clays” (i.e. fluffy or loosely aggregated clay particles). Consequently, these saline topsoils and surface layers with salt efflorescences are prone to wind erosion. However, if these saline soils with relatively freely draining topsoils are not treated with “calcium-based soil amendments” they will likely transform to “sodic soils” over time due to leaching with rain water (i.e. low levels of salinity). This will occur because of the leaching of the high levels of soluble salts and the formation of sodic soils with resultant low levels of total salt and high levels of exchangeable sodium (Na).

Sodic soils develop very poor structure and drainage over time because sodium ions on clay particles cause the soil particles to deflocculate, or disperse. Sodic soils are hard and cloddy when dry and tend to crust. Water intake is usually poor with sodic soils, especially those high in silt and clay. Poor plant growth and germination are also common. Table 6-11: Salinity hazard as defined by the electrical conductance of a saturation extract (ECse) and 1:5 soil:water extract (i.e. soil is extracted with distilled water)1

Salinity hazard

ECse dS/m

Effects on plant yield

1:5 Soil/Water Extract (dS/m)

Loamy sand

Loam Sandy clay loam

Light clay

Heavy clay

Non-saline <2 Negligible effect

<0.15 <0.17 <0.25 <0.30 <0.4

Slightly saline

2-4 Very sensitive plants effected

0.16-0.30

0.18-0.35

0.26-0.45

0.31-0.60

0.41-0.80

Moderately saline

4-8 Many plants effected

0.31-0.60

0.36-0.75

0.46-0.90

0.61-1.15

0.81-1.60

Very saline 8-16 Salt tolerant plants uneffected

0.61-1.20

0.76-1.45

0.91-1.75

1.16-2.30

1.60-3.20

Highly saline >16 Salt tolerant plants effected

>1.20 >1.45 >1.75 >2.30 >3.20

1EC 1:5 - the electrical conductance of a 1:5 soil:water extract (i.e. soil is extracted with distilled water), normally expressed in units of siemens (S) or decisiemens (dS) per meter at 25°C. While the EC1:5 method is quick and simple it does not take into account the effects of soil texture. It is therefore inappropriate to compare the EC1:5 readings from two soil types with different textures. It is possible to approximately relate the conductivity of a 1:5 soil-water extract (EC1:5) to that of the saturation extract (ECse) and predict likely effects on plant growth. The above criteria are used for assessing soil salinity hazard and yield reductions for plants of varying salt tolerance, ECse is saturated paste electrical conductivity (after Richards, 1954) and EC1:5 is the corresponding calculated electrical conductivity of a 1:5 soil:water extract for various soil textures.

7BSUMMARY


7. S UMMAR Y

1.1 B rief s ummary

Spatial and temporal changes in acid sulfate soil environments The following four independent standard methods were applied to assess ASS acidification deoxygenation/malodour in ponds PA3 to PA12 and adjacent drains: (i) soil morphology descriptions, (ii) incubation experiments (tests), (iii) acid-base accounting and (iii) peroxide pH testing on selected samples. These highlighted considerable variability among sites in ponds and drains with regard to acid generation, neutralisation capacity and deoxygenation/malodour development.

The results also highlighted little or no temporal changes in soil pH and acid neutralising capacity between December, 2013 and March/April 2014 (~4 months). However, in pond PA7a, the gypsum crust, which was generally very hard, indurated, compact and relatively smooth in December, 2013 had changed between the two monitoring periods and transformed to a friable/soft thin gypsum crust. This suggested that the original hard gypsum crust/layers had been altered to produce a relatively cracked deeper wavy surface topography following an extreme high rainfall event in February 2014.

Acidification and deoxygenation/malodour hazard assessment ratings were undertaken based on: (i) soil morphology features, (ii) ASS material and subtype classification, (iii) pH data, (iv) and (v) acid base accounting and AVS and (v) landscape position. Acidification and deoxygenation/smell hazard categories were classified as: (i) high, (ii) medium or (iii) low.

In summary, we have established that soil acidification and deoxygenation/smell hazards in the salt ponds and drains in section 2 were highly variable and ranged from low to high as shown in the Acidification and deoxygenation/malodour rating maps which overlay the Acid Sulfate Soil Subtype maps.

Soil-regolith models and Acid sulfate Soil Maps To aid in understanding the spatial heterogeneity of acid sulfate soil properties, a generalized representative soil landscape cross-section in the form of a conceptual soil-regolith toposequence model has been developed for: (i) western segments of ponds PA3 to PA12 and (ii) eastern segments of ponds PA3 to PA12. The soil map, in combination with the soil-regolith toposequence models, presents an understanding of ASS distribution in three dimensions.

The temporal soil-regolith models and maps have been included to describe the current understanding of ASS distribution and to demonstrate predictive scenarios for changes occurring over time (i.e. progression from pond draining (dry) to reflooding after thunder storm events and future possible rehabilitation conditions such as limestone application and revegetation). These soil regolith models have been constructed from field and laboratory data and surveyor knowledge. These conceptual soil-regolith process models clearly illustrate complex vertical and lateral changes that occur across pond hydro-toposequences. For example, they illustrate the complexities and importance of understanding specific sites to assess the detailed behaviour and implications of various ASS materials (e.g. sulfuric, hypersulfidic, hyposulfidic and monosulfidic), features in layers and horizons (e.g. gypsum crusts, salt efflorescences, shells), shallow regolith materials (e.g. layers of black, olive, brownish-grey and reddish-grey heavy clays) and different management options (e.g. revegetation and limestone application).

7BSUMMARY

85

More significantly, they also explain the complex soil, hydrological and biogeochemical interactions that have led to the following changes in properties of the gypsum crust for pond PA7a: (i) hard crust in December 2013 following a dry period and (ii) friable and soft in March/April 2014 following a wet period in February, 2014.

The soil maps (Acid Sulfate Soils and Other Soils) of the ponds PA3 to PA12 and adjacent drains provide a statement of the environment as it is expressed through the soil at the time it was investigated in March/April 2014 (i.e of the soil materials, soil profiles and soil subtypes surveyed in March/April 2014).

In summary, the acid sulfate soil maps in combination with the generalised conceptual toposequence models presents an understanding of acid sulfate soil distribution in three dimensions.

1.2 C ommunic ation Ac tivities

Eight PowerPoint talks have been presented to a wide range of audiences on the nature and properties of Acid Sulfate Soil in the Dry Creek salt fields.


8. R E F E R E NC E S

AECOM (2013) Preliminary Conceptual Site Model - Potential Acid Sulfate Soil – Cheetham (Dry Creek) Saltfields AECOM Australia Pty Ltd. Client: Ridley Corporation Limited ABN: 33006708765

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