Sediment sources and transport to the Logan-Albert River ...hlw.org.au/u/lib/mob/20141028162657_e69b02cd2239d6b2d/sediment... · Sediment sources and transport to the Logan-Albert

July 2010

Sediment sources and transport to the Logan-Albert River

estuary during the January 2008 flood event Gary Hancock and Gary Caitcheon

Water for a Healthy Country Flagship Report series ISSN: 1835-095X

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Citation:Hancock G and Caitcheon G 2010. Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood even. CSIRO: Water for a Healthy Country National Research Flagship.

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Cover Photograph:

Logan River estuary at the M1 crossing during the January 2008 flood event

Photographer: Phillip Ford © 2009 CSIRO

Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood event e iii

ACKNOWLEDGEMENTS We thank Tim Pietsch, Danny Hunt (CSIRO) and Jo Burton (SEQHWP) for their assistance with sample collection. Sample preparation and analysis was undertaken at CSIRO by Colin McLachlan and Chris Leslie (gamma spectrometry), Mark Raven (XRF,) and Claire Wright (ICP-MS).

We also thank Paul Rustomji and Jon Olley for their reviews of early drafts of the report.

This study was funded by the South-East Queensland Healthy Waterways Partnership and the CSIRO Water for a Healthy Country Flagship.

Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood event e iv

EXCECUTIVE SUMMARY This study was undertaken for the South East Queensland Healthy Waterways Partnership (SEQHWP) to determine the sources of sediment in the Logan River estuary, and investigate the sediment transport times and processes controlling sediment delivery to the estuary. The study focused on a major flow event in January 2008, estimated to have a recurrence interval of one in ten years. Sediment tracing techniques were applied using sediment and soil samples collected in mid-January about one week after the January flood event. Additional sampling of deposited and suspended sediment was undertaken in May 2008 to investigate the effect of the January 2008 event on estuarine turbidity.

The tracing methods used fell into two categories: 1) fallout radionuclides (Caesium-137, Lead-210 excess, Beryllium-7) used to determine the erosion processes producing the sediment, and 2) major and trace elements, used to determine the spatial source of sediment in the tributary catchments. The study focussed on the clay and very fine silt faction (<10 µm) of the sediment which is the main cause of turbidity in the estuary.

The following conclusions were made about the sources of sediment delivered to the Logan River Estuary and the main river channels (Logan River, Albert River and Teviot Brook) during the January 2008 flood event.

o Spatial tracing using major and trace element geochemistry indicates that the majority (approximately 70%) of the sediment delivered to the Logan estuary during the flood event originates from soils derived from the Lamington Group rocks. The Lamington Group geology covers the southern and eastern parts of the catchment, including the upper and mid-Albert River catchment, and the eastern part of the Logan catchment, including Running and Christmas Creeks (see Figure below).

o Channel bank erosion is the major sediment source. It contributes 50%-75% of the sediment along all reaches of the major rivers except the upper-most part of the Logan upstream of O’Brien’s Crossing. Channel bank proportions are greatest in the upper and mid-catchment region of the Albert River and the mid-catchment region of the Logan downstream of Rathdowney.

o The proportion of surface soil erosion to river sediment is mostly in the range 20-25% of total sediment input. Exceptions are the Upper Logan above O’Brien’s Crossing (approximately 80% surface soil), Canungra Creek (~40%), and the upper Teviot Brook and mid-Logan reaches below Josephville where the surface soil contribution is <15%. It is not clear whether grazing land or national park forest is the dominant surface soil source and further research is required to determine this.

o Beryllium-7 data indicate that another significant source of sediment is produced by shallow subsoil erosion not including channel bank soil. The likely subsoil sources include hillslope scalds/rills and/or cultivated soils. These erosion sources contribute 20-40% of sediment over much of the catchment. Exceptions are the upper Logan and the mid-Albert. Significant locations include upper Teviot Brook, and the mid Logan River from Laravale to South Maclean. Spatial tracing of sources using soil geochemistry indicates creeks draining Marburg-derived soils (Cannon, Knapps, Sandy and Allan Creeks) are significant sources of these subsoils to sediment delivered to the lower Logan River.

o Beryllium-7 and Lead-210 ratios indicate that re-suspension of deposited sediment stored within stream and river channels was not a significant sediment source. The implication of this observation is that transit times for the delivery of sediment from the catchment to the estuary are short, and are of the order of the average recurrence interval of the January event (10 years) or less.

Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood event e v

o Within the estuary, more than half the mobile (re-suspendable) sediment fraction sampled in May 2008 (4 months after the January event) was found to be associated with the January 2008 event. This result suggests that sediment delivered during floods contribute significantly to the ongoing turbidity seen in the estuary. Given the relatively short sediment transit times this information indicates that catchment works to reduce sediment fluxes may reduce estuarine turbidity within a time frame of years rather than decades.

This study has used sediment tracing methods to determine the timing of sediment delivery and processes generating high turbidity in the Logan River estuary. The outcomes provide a clear understanding of the principal sediment source areas and sediment generation (erosion) processes that took place during a recent major flood originating in the mid-upper Logan-Albert catchment.

Upper Albert

Lower Albert

Upper Logan

Lower Teviot

Lower Logan

Mid Logan

Upper Teviot

70%

0%Relative contributions

to Logan Estuary

Lam

ingt

on

Mar

burg

Wal

loon

{

ChannelBank

Sub-soil

SurfacSoil

Relative erosioprocess contribut

Executive Summary figure illustrating the principal outcomes of the Logan River study. Red boundary lines delineate major catchments.

Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood event e vi

CONTENTS 1. Introduction ......................................................................................................... 1

2. Sample collection and analysis ......................................................................... 1 2.1. Sediment samples .................................................................................................... 1

2.1.1. River sampling.......................................................................................................1 2.1.2. Estuary sampling ...................................................................................................3 2.1.3. Soil samples ..........................................................................................................6

2.2. Sediment Analysis .................................................................................................... 8 2.2.1. Sample pre-treatment............................................................................................8 2.2.2. Tracer measurement .............................................................................................9

3. Sediment tracing methods ............................................................................... 10 3.1. Tracer criteria and capabilities................................................................................ 10 3.2. Spatial tracing ......................................................................................................... 12 3.3. Erosion process identification using fallout tracers................................................. 13

3.3.1. Caesium-137 .......................................................................................................13 3.3.2. Excess Lead-210.................................................................................................13 3.3.3. Beryllium-7...........................................................................................................14

4. Results ............................................................................................................... 15 4.1. Spatial tracing of sediment sources........................................................................ 15

4.1.1. Selection of elements for discrimination ..............................................................15 4.1.2. Mixing model results............................................................................................17

4.2. Fallout Tracer results .............................................................................................. 21 4.2.1. 37Cs and 210Pbex...................................................................................................21 4.2.2. Sediment sourcing using 7Be...............................................................................23 4.2.3. Determining erosion sources along the river networks: combining fallout and spatial

tracing results ......................................................................................................27 4.2.4. Significance of in–channel sediment storage as a sediment source....................28

4.3. Estuary sediment dynamics.................................................................................... 29 4.3.1. Estuarine turbidity................................................................................................29 4.3.2. Tracing “new” sediment delivered to the estuary .................................................31

5. Conclusions....................................................................................................... 34

References .................................................................................................................. 35

Appendix ..................................................................................................................... 37

Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood event 1

1. INTRODUCTION In this report we present the results of a study to determine the sources of sediment in the Logan River estuary and investigate the erosion processes, transport processes and travel times controlling sediment delivery to the estuary. The study focuses on a major flood event in January 2008, estimated to have a recurrence interval of one in ten years (EHMP, 2009). The event occurred after intense rainfall across the Logan and Albert River catchments, particularly in the headwater catchments (Bureau of Meteorology, 2008). Studying this flood was aimed at improving sediment source information for the Logan and Albert Rivers determined by previous studies in 2001 (Caitcheon et al., 2001; Douglas et al., 2003; Wallbrink, 2004). This study used higher spatial resolution of sampling of sediment sources and deposition areas, and focussed on the type of event which delivers most of the sediment to the estuary; i.e. high rainfall resulting in highly energetic bank-full river flows. Analysing sediment sampled from this event also allows us to assess estuary sediment dynamics and make use of an additional tracer (beryllium-7) to provide additional erosion source information. Two distinct regions were studied; the catchments of the Logan and Albert Rivers upstream of the estuary, and the Logan estuary from approximately 5 km downstream of Waterford to the river mouth. The sampling and analytical approach of the study was: a) within the catchment determine the sources of sediment delivered to, and transported through the river system following a major flow event in January 2008; b) within the estuary investigate sediment sources contributing to the turbidity in the estuary. This report contains a description of the sample collection procedures, analytical methods, and the sediment tracing methods used to identify erosion sources (spatial sources and erosion processes) responsible for the delivery of sediment to the Logan and Albert Rivers. The importance of this event in the context of its contribution to turbidity in the Logan estuary is also reported.

2. SAMPLE COLLECTION AND ANALYSIS

2.1. Sediment samples

2.1.1. River sampling

Field trips for sample collection occurred during 21-25 January 2008, about one week after peak flood flow, and during 19-23 May 2008. A list of all the soil and sediment samples collected during these trips is given in the Appendix. The location and spatial distribution of sampling of hillslope soils was mainly influenced by road access, but factors such as geology, topography and land-use were also used to determine site selection such that an optimum spatial coverage and representation of the catchment was achieved (see for example, Pennock and Appleby, 2002). In general, hillslope and channel bank sampling was specific to sites of active erosion. This was usually associated with recent evidence of down-slope overland transport of mobile soil on hillslopes, or, in the case of channel banks, evidence of bank collapse.

Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood event e 2

All river sediment samples and some of the estuary samples were collected in the January field trip, with samples from Sandy Creek, Cannon Creek and upper Burnett Creek being the only sediment samples collected in May. Only deposits of fine sediment that were clearly associated with the January 2008 event were collected, in line with the main objectives of this study; i.e. to provide information on the sources and transport of fine sediment being delivered to the estuary during large flow events. Road crossings along the length of the catchment were used to access river sites on the three main tributaries; Teviot Brook, the Logan River and the Albert River. Some potentially important minor tributaries were also sampled (e.g. Canungra Creek). River network sediment sampling sites are shown in Figure 1.

Figure 1. Sites of in-stream sediment deposited collection. Note that sample numbers 408, 409 (Sandy Creek sediment) 411 (Cannon Creek) and 415 (Upper Burnett Creek - stream course not shown) were collected in May 2008. All other samples were collected in January 2008 (See Appendix for sample site descriptions).


At nearly all sites sediment deposits associated with the January event were clearly evident (Figures 2-6). It is likely this material was mostly deposited as the river receded from peak flow. Typical locations of deposited sediment included channel bank benches, low points in areas of overbank flow (Figures 2 and 4), perched deposits of sediment on horizontal sections of bridges, support beams and other natural or man-made surfaces (Figure 3). Even coarse organic debris (tree litter) caught in riparian vegetation was often found to contain fine sediment in sufficient quantities for analysis (Figure 5). Presumably this sediment was transported and trapped together with the litter during peak flow. Sediment was possibly even “filtered” from the water as the litter formed a dense mat of material in the bushes and trees.

2.1.2. Estuary sampling

Deposited estuarine sediment samples were collected in January 2008, and suspended sediment and mangrove surface mud samples were collected in May 2008. The sampling locations are shown in Figure 7. Overbank deposited sediments associated with the January flow event were collected from the Logan estuary, mainly upstream of the Albert River junction (samples 131-135). Bottom sediment samples representing longer-term sediment deposits were also collected in January using an Eckman grab sampler. These included bottom sediments from the channel in the estuarine reach of the river (137-141), and one sample from southern Moreton Bay (136). In May suspended sediments (samples 401-407) were collected using a continuous flow centrifuge (CFC). This apparatus enables the continuous pumping of water directly from the river through a centrifuge (Figures 8 and 9). Sediment particles greater than ~1 µm are retained in the centrifuge bowl. The CFC allows the collection of grams of sediment from many hundreds of litres of water. The samples were collected at various locations in the estuary on both the ebb and flood tide to investigate the sources of sediment in the estuary. Soft surface mud in estuary mangroves and on the exposed gently sloping estuary banks was also collected in May (Figure 10). This sediment represents the potentially ”mobile” surface sediment that is able to be suspended on the incoming tide and deposited on the retreating tide. These locations are the most likely source of resuspended sediment in the estuary.


Figures 2-6. Some river sampling sites showing sediment deposited during the January 2008 flood event.

5

6

32

4


Figure 7. Estuarine sampling sites. The CFC site “401” was collected ~10 km upstream of the estuary from fresh water but is considered part of the estuary study. See Appendix for sample descriptions.

Figures 8-10. CFC sampling and deposited “mobile” mud in the Logan estuary

401

406

134

405407

404133

141131,132 403402140

135139

138

137

136


2.1.3. Soil samples

Catchment soil samples were collected during both field trips and were complemented with data from soil samples collected by Wallbrink (2004) in 2000 and 2001. The sampling aimed to collect samples representing the various potential sources of sediment eroded from the catchment during the January flood event. Seventeen soil samples were collected in January, mainly from the Albert catchment, and 9 samples were collected in May. These included hillslope soils representing the different geological units and the two major land uses in the catchment, National Park forests and other forested conservation areas, and grazing land. Other erosion sources were sampled, including soils from actively eroding channel banks, and a small number of soils from cultivated fields, gullies and hillslope scalds. The latter two sources are collectively termed “subsoils” as they contain soil from below the surface soil A-horizon which had been exposed by erosion. Soil sample locations are shown in Figure 11. Samples were obtained by combining between 3 and 5 samples collected from sites with similar characteristics within a few kilometers of each other. For hillslope samples the sites had the same major land use with similar slope and vegetation cover, and were contained within the same geological unit. At each site many (30-40) individual “grab” samples were taken over an area of approximately 5-10 thousand square meters. These were combined into a single sample. Thus each representative hillslope sample contained 100-200 individual grab samples along 10-20 km transects. Only the “mobile” component of the surface soil was collected. Mobile surface soil is defined as surface soil that had clearly been transported down-slope after recent rain, including soil at the base of a hillslope, soil in culverts (Figure 12) and animal tracks, and loose soil in exposed (non-grassed) areas (Figures 13 and 14). Only the top 10-20 mm of the soil was sampled. Combined hillslope surface soil samples were further sub-divided according to the geological unit they originated from. Three geological units covering most of the area of the upper catchment were selected to be geochemically characterised; soils derived from the Marburg Formation, the Lamington Group and the Walloon Sub-group (Figure 19). Channel bank samples were collected from 3 sites along an approximately 5 km river reach and combined for analysis. Similar to hillslope sampling, multiple grab samples were collected at each site. Photos of typical collection sites are shown in Figures 15 and 16. Each eroding channel bank profile was sampled by scraping a thin layer (<10 mm) of soil from the exposed vertical bank face. Because the whole vertical face was sampled a small component of surface soil or overbank sediment deposits from the top of the bank was included in the sample. Similarly, runoff from cultivated soils (Figure 17) and mobile subsoil samples were collected from gully and scald sites that were clearly identifiable as being actively eroding (Figure 18).


Figure 11. Location of soil sample collection sites. Some of these site collections were combined to produce 27 samples for analysis. See Appendix for sample descriptions.


Figures 12-14. Examples of surface soil sampling sites.

2.2. Sediment Analysis

2.2.1. Sample pre-treatment

All soil and sediment samples were first fractionated to separate the fine (<10 µm) particle fraction. This clay and very fine silt fraction was used for analysis because it is the fraction which most efficiently carries pollutants (e.g. nutrients, pesticides) into rivers and estuaries, and is the major cause of turbidity. Particle size separation also enables a direct comparison to be made between sediment sources and sinks, an essential part of our sediment tracing method. Since the concentrations of many tracer parameters are dependent on the size of the sediment particles being analysed, limiting the particle size fraction to a small range virtually eliminates particle size effects. The particle sizing technique employed at CSIRO Land and Water involves settling procedures. Sediments are first soaked in water and then agitated to disaggregate the soil and sediment particles. The coarse fraction of the sediment (>50 µm) is first removed using a settling procedure, with the fine fraction being decanted. Water is added to the settled (coarse) fraction, the sediment resuspended and the procedure

12 13

14


Figures 15-18. Examples of channel bank sampling sites (15,16), a cultivated soil site (17) and mobile subsoil in an eroding scald (18). repeated. The decanted suspension containing particles <50 µm is then used to isolate <10 µm sediment using similar settling procedures, but using longer settling times. The <10 µm sediment suspension is then dried at 50° C in a dehydrator and the dry sediment ground in a ring mill. Sub-samples are taken for gamma spectrometry, x-ray fluorescence (XRF), inductively coupled plasma mass spectrometry analysis (ICP-MS) and loss-on-ignition (LOI).

2.2.2. Tracer measurement

A broad range of parameters were measured to geochemically characterise soils and sediments. The parameters included fallout tracers (210Pb, 137Cs, 7Be), major and minor elements and loss-on-ignition (LOI is measured after heating the <10 µm sample to 450° C). Gamma spectrometry was performed at CSIRO Land and Water laboratory in Canberra, following similar procedures to those outlined by Murray et al. (1987) and Leslie (2009). The method involves the compaction of the powdered <10 µm sample into perspex containers, which are then sealed using a screw-on lid with an o-ring seal. After a three

1615

1817


week period to allow for the ingrowth of 222Rn, the sample is counted using high resolution Ge detectors. Radionuclides measured include, 238U, 226Ra, 210Pb, 228Ra, 228Th, 137Cs and 40K. XRF and ICP-MS analyses provide a range of major and minor elements and is performed at the CSIRO Land Water laboratory in Adelaide. This method entails the fusion of the samples into a Li-borate disc and spectral analysis following the procedures of Norrish and Hutton (1969). A suite of 11 major elements and 19 trace elements are measured by this technique. ICP-MS measures additional elements to some of the XRF measurements, as well as providing superior sensitivity of analysis on some transition and many rare earth elements measured by XRF. ICP-MS analysis involves the leaching of the sample by microwave digestion with strong acids (1:3 HNO3:HCl). Diluted samples were introduced by nebuliser into a plasma for analysis. Hydrogen was introduced as a reaction gas and Helium as a collision gas to remove potential mass interferences. Approximately 55 elements were measured by this technique.

3. SEDIMENT TRACING METHODS

3.1. Tracer criteria and capabilities The tracing techniques used in this study are described in Hancock and Pietsch (2008). A brief summary follows. Sediment tracers used in this study make use of a physical or chemical characteristic of the sediment that behaves conservatively during erosion and sediment transport; i.e. it remains attached to sediment particles despite exposure to water and particle abrasion. Thus, selection of suitable tracers considers the environmental conditions of sediment sources, transport and sinks, especially factors such as changing water salinity. Elements that are involved in ion-exchange reactions between sediment and saline water (e.g. Ba, Na), or scavenging by sulphides in anoxic marine systems (As, U) are not suitable as tracers of sediment moving from a freshwater catchment into a saline estuary. Another essential criteria for tracer selection is source discrimination; the concentration of a tracer in the different erosion sources should be distinct such that it allows the sources to be distinguished. Since the suspended sediment load transported by a river usually represents a mix of sediment derived from different erosion processes and spatial sources, it is unlikely that a single tracer can provide unambiguous discrimination of potential sources. Most tracer applications require a suite of tracers to determine a characteristic signature or ‘fingerprint’ for each source. The source fingerprints are then compared with equivalent measurements of the transported end-member; these end-members being suspended sediment downstream of the source catchments, or sediment deposited in a “sink” (e.g. areas of overbank deposition or an estuary). The best estimate of the contributions of each of the sources is then determined. Major sediment sources identified using this approach include soils associated with major rock types, differentiation of surface and subsurface soils such as surface soil eroded from uncultivated land-uses (forest/pasture), and channel bank erosion.

6

5

8


It is emphasised that sediment tracing generally only gives the relative proportions (e.g. as a percentage) of the various sources. A complete sediment budget requires estimates of sediment loads using other techniques, such as in-stream monitoring, catchment modelling, or sediment core chronologies. In general, sediment tracing techniques can be divided into two categories – spatial sourcing and erosion process tracing. These are described separately below.


3.2. Spatial tracing Spatial sourcing of sediment uses a combination of tracers that distinguish parts of a catchment. The tracers commonly used at CSIRO Land and Water include major and trace element geochemistry, determined using techniques such X-ray fluorescence (XRF), ICP mass spectrometry (ICPMS), and gamma spectrometry. Measurements are made of both source (eroding soils) and sink (e.g. river sediment) material to determine the relative source contributions of material derived from areas of different rock types in samples taken downstream (e.g. Wallbrink et al., 2003; Hancock et al., 2007). The application of these tracers involves a 2-step process where tracers are first examined to determine those that clearly discriminate potential source materials. The selected tracers are then analysed in a multivariate mixing model to apportion a given sediment mixture between those sources. The best estimate of the relative contribution from each source is obtained by minimizing the difference between the measured tracer value in the sediment mixture, with that calculated using a range of different proportions of the various sources. For this study a “Monte-Carlo” type mixing model was used to randomly select different combinations of source samples and compare their calculated “mixed” concentration with the downstream sediment mixture. The process is repeated 3000 times and the results averaged. For a mixture of, for example, 3 sources, the concentration of each element i in the resulting mixture Cm is determined using the following equation:

CiCBiBAiAmi TRTRTRC (1)

where TAi, TBi and TCi are the randomly selected concentrations of tracer i in sources A, B and C, and RA, RB, RC are the relative proportions of the tracers in the two sources such that

1 CBA RRR

and 0,, CBA RRR .

Using n tracers the best estimate of the relative contribution from each source to the “target” (sink) sediment is obtained when

n

i si

simi

C

CCABS

1

(2)

is minimised.

miC is the average of the 3000 calculated mixtures and Csi is the average

of the mixed sediment sink, or “target” sediment.


3.3. Erosion process identification using fallout tracers Erosion process tracing identifies the process leading to sediment mobilization, such as sheet erosion of surface soil, gully erosion of subsoil, and channel bank collapse. This method uses fallout tracers 137Cs, 210Pb, and 7Be to distinguish surface soil. These tracers (described below) are deposited from the atmosphere mainly in association with rainfall and strongly bind to fine-grained particles in soil. In doing so they label a thin layer of surface soil over the earth’s surface. Due to their different half-lives and deposition histories each radionuclide provides unique information on the source of the sediment and the processes controlling its erosion. These are summarised for common erosion sources in Table 1. Fallout tracers 137Cs, 210Pb and 7Be are measured simultaneously by gamma spectrometry.

3.3.1. Caesium-137

Caesium-137 is an anthropogenic product of atmospheric nuclear weapons tests that commenced in the early 1950s. Fallout of 137Cs effectively ceased in the mid-1970s so its input to Australian soils represents a single “pulse” delivered mostly in the period 1955-1965. Once deposited, 137Cs becomes tightly bound to fine soil particles, particularly clays. Over the last 50 years there has been some downward migration of these particles, such that 137Cs is now concentrated mainly in the upper 10 cm of the soil profile (Wallbrink et al., 1999). Thus high activities of 137Cs are typically seen in undisturbed surface soils in forested regions and pastures with a history of low intensity grazing. High levels of 137Cs in river sediment indicate high surface soil contributions. Conversely sediment devoid of 137Cs is assumed to have a subsoil origin, although it is noted that channel bank erosion can produce low but finite values of 137Cs due to the small surface soil component associated with collapsing banks. Overbank deposition of sediment during floods provides an additional ongoing source of 137Cs deposited on top of a river bank, and can potentially be returned to the river after bank collapse during floods.

3.3.2. Excess Lead-210

Fallout 210Pb (half-life 22 yrs), measured as “excess” 210Pb (210Pbex) is a naturally-occurring radionuclide generated by the decay of 222Rn in the atmosphere. It is continually precipitated on the soil surface, mainly with rainfall, and is determined from the “excess” of 210Pb activity over its long-lived parent 226Ra. The three nuclides (226Ra, 222Rn and 210Pb) are all members of the uranium decay series. The maximum concentration of 210Pbex in soils is usually found at the surface, decreasing approximately exponentially with soil depth and reaching undetectable levels at depths of approximately10 cm (Wallbrink et al., 1999). Excess 210Pb measurement by gamma spectrometry is less sensitive to low concentrations than 137Cs and it is not usually detected in channel bank material due to its low concentrations. Thus its use is essentially confined to that of a hillslope surface soil tracer, although Wallbrink et al., (2002) have used it to estimate sediment residence times in the Brisbane River by sampling long-term overbank sediment deposits. Since this study focuses on just one flood event we did not apply the Wallbrink et al. (2002) technique in this work.


3.3.3. Beryllium-7

Be-7 (half-life 53 days) is also naturally-occurring and is created in the atmosphere by the reaction of cosmic rays with nitrogen and oxygen. As it has a short half-life it provides information on a different time-scale to 210Pb and 137Cs, 7Be being mainly applied to the tracing of sediment eroded during single flood events and deposition-resuspension cycles. Its short half-life means that it is usually only detected in the surface 2-3 mm of soil. However, because it is continually deposited (mainly with rainfall) and accumulates rapidly in exposed soils it can also be used to distinguish erosion of hillslope surface soils from erosion of recently exposed subsoils, either in gullies, recently cultivated (tilled) soils, or from hillslopes stripped of their topsoil layer. Excess 210Pb and 137Cs concentrations are usually low or absent in these sources. On a catchment scale, 7Be tracing can only be usefully applied where a discrete period of widespread heavy rain across a catchment has followed a relatively dry period. Such an occurrence allows the labelling of surface hillslope soils and other exposed soil surfaces (such as eroding subsoils) with a relatively uniform concentration of 7Be. The rainfall event in the Logan-Albert catchments in January 2008 fulfilled these requirements, allowing the use of 7Be to aid in the distinguishing of sediment sources. Estimation of the extent of resuspension of sediment stored within the river channel is another potential application of 7Be. Sediment deposited in the river channel during previous flow events and stored underwater will have little or no detectable 7Be, but will retain the signal of the longer-lived tracers. Thus a reduction of 7Be in transported sediment without an associated reduction in 137Cs and excess 210Pb indicates resuspension of in-channel deposited sediment, a result which has implications for the estimation of the transit time of sediment being delivered from the catchment to the estuary. Table 1. Summary of the presence or absence of a tracer in different erosion sources Tracer Surface soil Exposed and

eroding subsoils Channel bank In-channel

sediment 137Cs Present Absent Present in low levels Present Excess 210Pb

Present Low or absent on a short time scale

Not usually detected Present

7Be Present* Present * Not usually detected Absent * After recent significant rainfall


4. RESULTS

4.1. Spatial tracing of sediment sources

4.1.1. Selection of elements for discrimination

Prior to implementation of a mixing model for estimation of sediment source proportions, all gamma spectrometry, ICP-MS and XRF results were converted to “ashed” or mineral-based concentrations using the LOI measurements. This was done to eliminate concentration variations caused by varying amounts of organic matter. Although all of the coarse organic matter is removed by particle-size separation procedures, fine organic material can form aggregations with fine sediment particles and be carried through to the <10 µm fraction. Organic matter can also grow as coatings on the sediment particles during transport. Geochemical analysis is used to characterise soils from geologically-distinct regions and hence spatially identify areas of the catchment which are major sediment sources. This is done using a mixing model (see section 3.2). A total of 48 elements were measured by XRF, ICP-MS and gamma spectrometry on soils from source areas and river/estuary sediment, and each element was statistically assessed to determine how well it discriminated soil sources. Hillslope surface soil samples were used to characterise sources, and grouped according to their geological province (source rock type). To improve the statistical analysis, soil samples collected during the 2001 regional study were also measured and included in this analysis. Three major rock types were selected (Figure 18); the Marburg Formation (9 surface soils samples), Lamington Group (10 samples) and the Walloon Subgroup (6 samples). Although other geological groups are present, the area covered by them is relatively small and they occur mainly in the lower catchment where rainfall, river flow velocities and hillslope gradients are relatively low. Thus it is unlikely that these parts of the catchment are contributing a significant amount of sediment to the estuary, and they have not been included in the analysis. The initial phase of the analysis includes the grouping of measurements of soils from each major rock type, and the calculation of the mean and standard errors for each element in these groups. A mean’s standard error (M) is calculated by dividing the standard deviation of the mean by the square root of the number of sample measurements. The next step is to eliminate non-discriminating elements and increase the sensitivity of the mixing model predictions. Element selection was made by using the statistical t-test to determine how well two sources are discriminated. The term Tab is given by the difference between the mean concentrations in source a and b of an

element ( ba XX , ), divided by the standard error of that difference; i.e.

)( 22MbMa

ba

ab

XXT

(1)


Values of T can range from 0 (no discrimination) to >5 (excellent). For soil samples derived from the Marburg and Lamington rock types T values of 4 and above (equivalent to a t-test with P ~0.001) were selected as providing good discrimination between the two soils such that they significantly improved the sensitivity (i.e. reduced the uncertainty) of mixing model source estimation. Good Marburg-Lamington discrimination was found for 30 elements. Good discrimination was also seen for many elements between Lamington and Walloon regions although T values were generally lower, mainly due to the higher standard errors on the Walloon mean values. However, for Marburg and Walloon, discrimination less distinct for most elements. No T values greater than 4 were found, and most of the T values in the range 3-4 were associated with rare earth elements (REEs). Thus, while mixing model estimates of the proportion of Lamington-derived sediment are well defined, the estimation of discrete Marburg and Lamington proportions is less certain, and is sometimes not possible.

Figure 18. Major rock types and soil sample collection sites (including subsoils). Soils from the 2001 regional study were also used to characterise soil groups.

Ru

nn

ing

Ck

Christm

as Ck

Cannon Ck

Knapps Ck

Tamrookum Ck

Sandy Ck

Allan Ck

Ru

nn

ing

Ck

Christm

as Ck

Cannon Ck

Knapps Ck

Tamrookum Ck

Sandy Ck

Allan Ck


Based on their T values the following 19 elements were selected to provide optimum discrimination between the three geological provinces: Si, Ti, Fe, V, Mg, P, Cr, Ga, Zn, Zr, Sc, Y, Dy, Ho, Er, Tm, Yb, Pb, Th. The elements 226Ra, Ca and Na were added to this list when river sediment not exposed to saline water was being considered. The best discrimination between Lamington and Marburg soils is given by Ga (T = 12), Fe, Mg, Si (T = 9-10), Zn and Sc (T = 5-6). Although 10 of the REEs fall in the range T = 4 to 5, only 5 of these were used in order to reduce bias introduced by using many elements with similar chemical properties.

4.1.2. Mixing model results

As outlined in section 3.2, the mixing model incorporated Monte Carlo simulations. Table 2 gives the results of geological source area contributions to selected sediment sinks. These sinks are characterised by the mean of several measurements taken from representative sediment samples. Note that estuary sediment has been divided into 2 sample types; 1) overbank sediment collected in the estuary immediately after January ’08 event; 2) bottom sediment, mangrove mud and suspended sediment collected about 4 months after the event. The latter sediment represents sediment delivered to the estuary over the longer term (see estuary section). Albert River estuarine sediment was not well characterised as only one site could be accessed downstream of the Albert River confluence with the estuary, and this sediment probably contained a significant fraction of Logan sediment. It is therefore not considered as an estuarine sink term. Other sediment locations used as “target” sinks for the mixing model include the Lower Albert River, the Lower and Upper Logan River, and Lower and Upper Teviot Brook. The Lower Albert is defined as the region downstream of (and including) Mundoolun Bridge (sample 6, Figure 1); the Lower Logan is defined as being downstream of (and including) Laravale (sample 13); Lower Teviot Brook is defined as downstream of Coulson. Uncertainties on all sediment source predictions are estimated by considering the standard errors on mean values () of sources and sinks and running the mixing model using the extreme limits of this range (i.e. using the two limits generated by the sum of the mean ± ). Uncertainties estimated this way correspond to approximately one standard deviation. As noted above, Marburg and Walloon derived soils are not well distinguished and model results from these sources are sometimes not reliable. This was particularly the case for the estuary samples where consecutive model runs with different Marburg and Walloon proportions as starting points gave different results for the predicted Marburg and Walloon proportions, but not Lamington. Thus, the modelled Lamington contributions are considered accurate, as is the total non-Lamington proportion (i.e. Marburg + Walloon).


An example of the relative differences in tracer elements from the various sources and sinks is shown in Figure 19. This is a ternary plot of the oxides of Si, Fe and the rare earth element Ho. As shown in Table 2, mixing model results indicate that the Lamington Group dominates sediment input to the estuary (~70 ±10% of sediment input), both during the January 2008 event and longer term since these two values are not significantly different. The Marburg and Walloon sources collectively contribute c.30 ±10%, with most of this coming from Marburg derived soils. Previous spatial tracing work in the Logan catchment and South Moreton Bay region by Douglas et al. (2003) indicated that the Walloon subgroup was only a minor contributor (<5%) to south Moreton Bay sediment adjacent to the Logan estuary, consistent with our results. On the other hand the Marburg soils were predicted by Douglas et al. to have a higher component in estuary sediment than seen here; 40-50% compared to 20-30%. This may be partly due to the use of isotopes of Nd, Sr and Pb as tracers in Douglas et al.’s work, providing additional discrimination compared to this current study. On the other hand, excellent discrimination is seen between the Lamington and Marburg source areas using our tracers, and ICP-MS analysis has provided high quality REE data helping to discriminate Walloon and Marburg soils (Figure 19). We suggest the higher Lamington and lower Marburg contributions obtained in this study may reflect the rainfall distribution in this event, with the heaviest falls occurring in the Lamington Group (the south–east) region of the catchment (BOM, 2009).


Figure 19. Ternary diagram of Si, Fe and Ho proportional data, showing the relationship between rock-type based soil units and lower catchment sediment sinks. Sediment from the Lower Logan has similar geochemistry to estuarine sediment and the mixing model produces similar source proportions to those of the estuary (Table 2). Albert River sediment on the other hand is geochemically closer to the Lamington source term. For both the Lower and Upper Logan sediment the modelled Marburg and Walloon contributions are considered more reliable than for estuarine sediment due to the addition of Ca and Na as tracers. It is expected that Lower Logan sediment will match the “event” estuarine sediment, since the estuary samples were collected within the Logan estuary upstream of the confluence with the Albert River. The applicability of the model to distinguish Lamington derived sources from Marburg and Walloon sources is shown by the model results for the Upper and Lower Albert. The model predicts 100% Lamington for the Upper Albert, even with all three soil groups

SiO2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Fe2O3

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Ho

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Marburg FormationLamington GroupWalloon Estuary (all) Lower AlbertLower Logan


included in the mix. This result is expected, given that the Upper Albert catchment almost entirely contains Lamington Group derived soils. The Lower Albert result also has >90% Lamington source contribution, indicating that most of the sediment originates upstream of Mundoolun. This result is consistent with the high rainfall intensity in the upper catchment reported by the Bureau of Meteorology (2008). Upper Logan River sediment is dominated by Lamington sources (85%), with a minor Walloon component (15%). The Marburg component is <10%. These results indicate that for the January 2008 flood most of the mid-catchment sediment originates from Lamington soils in the Christmas Creek and Running Creek catchments. The Lower Logan contains significant Marburg-derived sediment (up to 25%). The likely sources here are the mid-western catchments of Knapps Creek, Cannon Creek, Sandy (Sheepstation) Creek and Allan Creek. Sediment from the upper catchment of Teviot Brook is dominated by Walloon-derived soils (90-100%), but an increasing proportion of Marburg soils (up to 35%) occurs in lower Teviot Brook below Coulson. Table 2. Proportions (as %) of sediment transported from the three major geological source areas in the Logan-Albert catchment to sediment deposition zones. Uncertainties are approximately one standard deviation. “Estuary (event)” refers to the sediment collected from the January 2008 flood event. “Estuary (long-term)” includes sediment collected from in-channel and bank deposition sites

Sediment deposition zone

Marburg Lamington Walloon

Estuary (event) 21 55

74 10

5 5 5

5

Estuary (long-term) 27 55

68 10

5 5 5

5

Lower Logan 16 105

75 11

5 9 5

5

Upper Logan 0 100

87 5

5 13 5

5

Lower Albert 0 100

100 0

10 n.a.*

Upper Albert 0 50

100 0

5 n.a.*

Upper Teviot Brook 0 100

n.a.* 100 0

10

Lower Teviot Brook 25 1010 n.a.* 75 10

10

n.a. These sources were not included in the mixing model since their spatial coverage in the catchment is very small or absent.


4.2. Fallout Tracer results

4.2.1. 37Cs and 210Pbex

The surface soil fallout tracers, 137Cs and excess 210Pb show an approximately linear relationship for hillslope surface soils. Figure 20 shows the National Park forest values are mostly higher than pasture, although there is considerable overlap. Overall the mean National Park (NP) concentrations of 137Cs and 210Pbex are about 50% higher than pasture (Figure 21, left). This trend has been seen in other catchments (e.g. Hancock et al., 2007) and is forest is probably related to rainfall, with most of the NP sites being in the more elevated regions of the catchment where rainfall is generally higher. Higher rainfall leads to greater fallout of the atmospherically-derived tracers. Channel bank and subsoil both have low fallout tracer concentrations and cluster near the origin in Figure 20. Some channel banks have detectable 137Cs (up to ~2 Bq kg-1) due to surface soil included in bank collapse. It is also likely that some channel banks include overbank sediment deposits, possibly deposited in the last 50 years. Thus the detection of low concentrations of 137Cs in these sediments is relatively common, and has been observed in other Australian studies with 137Cs values mostly lying in the range 0.5-1.5 Bq kg-1 (e.g. Wallbrink et al., 2003; 2004; Hancock et al., 2007). Cultivated soils also have detectable 137Cs and 210Pbex due to the mixing of surface and subsurface soils by ploughing. The surface tracer concentrations are generally slightly higher than channel banks.

Figure 20. A plot of surface soil tracer measurements for soil sources collected from pasture, National Park forest, channel banks and subsoils.

137Cs (Bq kg-1)

0 2 4 6 8 10 12 14 16

21

0P

b ex

(Bq

kg-1

)

0

50

100

NP hillslopesGrazed hillslopes Channel bankRiver sediment All surface soilsSubsoilsCultivated


Figure 21 (left) shows mean soil tracer values for soil sources along with mean sediment values from various river deposition areas. Error bars signify ±1 standard error. All of the radionuclide values for river sediment are much lower that the pasture and forest surface soil values. Using the mean 137Cs and 210Pbex values as the reference concentrations for all surface soils (Table 3), surface soil contributions of between 14% and 32% are calculated for river sediments. For the estuary the surface soil contribution is 25 ±3%. Figure 21 (right) shows the tracer values for river sediment at an expanded scale. Lowest surface soil contributions occur in Teviot Brook and the Lower Logan; the highest occur in Canungra creek, this catchment having a surface soil input 1.5 to 2 times higher than elsewhere. The remaining 65-80% of sediment inputs must come from soils eroded below the layer of 137Cs and 210Pbex penetration in the soil profile. As shown in Figure 20 this could include channel banks, gully/scald subsoils and cultivated soils. Previous work in the Moreton Bay catchment using tracers and SedNet sediment budget modelling concluded that the majority of the sediment comes from channel bank erosion (Caitcheon et al., 2001). The SedNet model indicates that the contribution from other subsoil sources such as gullies is small. Using radionuclide tracers, Wallbrink (2004) concluded that for the Brisbane River catchment about 75% of sampled sediment originated from subsoil erosion. Subsoil sources and their contributions at different points in the catchment are investigated in the following section using 7Be in conjunction with the other tracer data.

Figure 21. (Left) 137Cs and 210Pbex in river sediments. The soil sources are represented by mean values of data shown in Figure 20. (Right) An expansion of the plot on the left showing the distribution of results from deposition areas.

137Cs (Bq kg-1)

0 1 2 3 4 5

21

0P

b ex

(Bq

kg-1

)

0

10

20

30

40

50

60

Canungra Ck

Lower Logan

Teviot Bk

EstuaryUpper Albert

Lower Albert

Upper Logan

137Cs (Bq kg-1)

0 2 4 6 8 10 12 14 16

210P

b ex

(Bq

kg-1

)

0

50

100

NP hillslopesGrazed hillslopes Channel bankRiver sediment All surface soilsSubsoilsCultivated


Table 3. A summary of mean fallout tracer measurements (Bq kg-1 dry weight) in soil sources and river sediment sinks. n = number of 137Cs and 210Pbex measurements. Only January soil collection data is included for 7Be, with n being given in brackets.

n 137Cs 210Pbex 7Be

Soil sources Channel Bank 10a (4) 0.79 ±0.22 3.7 ±1.3 1.3 ±0.1 Pasture surface soil 14a (5) 8.09 ±0.75 74.2 ±9.9 78.6 ±10.9 NP forest surface soil 9 (6) 12.59 ±1.78 115 ±13 91.9 ±18.8 All surface soils 23 (11) 9.73 ±0.91 90.3 ±8.3 80.4 ±10.0 Subsoils 4 (4) 0.70 ±0.16 5.3 ±1.4 77.7 ±10.1 Sediment sinks Estuary (event) 4 (4) 2.28 ±0.16 28.3 ±2.0 52.2 ±9.9 Estuary (long-term) 11 (0) 2.48 ±0.15 28.8 ±2.1 n.a. b Upper Albert 8 (8) 2.25 ±0.11 24.8 ±2.3 31.8 ±5.3 Lower Albert 6 (6) 2.07 ±0.14 25.0 ±3.0 38.0 ±7.4 Upper Logan 5 (5) 2.30 ±0.48 33.8 ±10.8 36.9 ±6.0 Lower Logan 7 (7) 1.62 ±0.22 17.4 ±3.4 48.4 ±11.4 Canungra Ck 5 (5) 2.42 ±0.36 41.1 ±9.8 9.0 ±3.9 Teviot Ck 5 (5) 1.25 ±0.27 20.0 ±5.3 62.2 ±16.6

a Includes samples collected in 2001. b These samples were collected 4 months after the event and the 7Be measurements are therefore not applicable to the January 2008 event.

.

4.2.2. Sediment sourcing using 7Be

The application of a third surface soil tracer, short-lived 7Be (half-life 53 days) can provide better estimates of event-driven erosion processes and sediment sources along the length of the river network. As noted earlier, due to the widespread heavy rainfall occurring just prior to the January 2008 flood event and the dry period preceding it, all exposed soil in the catchment will have received a strong and relatively constant 7Be fallout signal. As noted above, these exposed soils include both hillslope surface soils, cultivated soils and exposed subsoils such as gullies and hillsope scalds, but not vertical channel banks. Because of the short time frame for the erosion and delivery of peak-flow sediment during the January 2008 event (~2-3 days) decay of sediment-bound 7Be activity is small. Thus the 7Be activity of samples collected in the three-day period immediately after the event can be used as a tracer of sediment sources with only minimal decay-correction required. Table 3 shows that while subsoils contain very little 137Cs and 210Pbex, subsoil concentrations of 7Be are similar to surface soils. This is explained by the fact that these subsoils were collected as “mobile” soil, i.e. subsoils which had clearly moved from their source (gully, cultivated field, etc.) during the January 2008 event, and so had been labelled by 7Be associated with recent rainfall. On the other hand there is little or no 7Be in (vertical) channel banks. The similarity in 7Be concentration in all exposed soils indicates that 7Be can be used to discriminate between near vertical channel banks and other subsoil sources.


Albert River Figure 22 is a plot of all three surface tracers in river sediment as a function of distance along the Albert River, from site 112, approximately 5 km downstream of the river’s headwaters, through to the estuary. The plot shows significant variations in 7Be activity (red symbols), with major peaks being seen in the upper catchment (0-30 km) and in the 80-100 km reach. A trough occurs in the 40-70 km reach. These variations appear to correspond somewhat with 210Pbex concentrations (black symbols), although the 7Be excursions are greater. Nevertheless, the co-variation of 7Be and 210Pbex must be at least partly due to varying proportions of surface soil in the river sediment. The main 7Be peaks appear in the upper 7 km of the right Albert Branch, and just downstream of the confluence of the Albert River with Stockyard Creek. The lowest 7Be and 210Pbex concentrations occur at site 116 (Newton bridge), and through a 30 km river reach from Kerry Bridge through to Mundoolin Bridge. Although 137Cs shows some of the trends exhibited by 7Be and 210Pbex, they are less marked with Albert River 137Cs sediment concentrations varying by less than ±25% of their mean value. This is consistent with a high channel bank input over most of the river length. Since there is little or no 210Pbex and 7Be in channel bank sediment their concentrations more directly reflect surface soil inputs, with channel bank soil acting as a diluent. For 137Cs a small but significant concentration is measured in <10 µm channel bank soil (0.79 ±0.22 Bq kg-1, Table 3). Thus sediment concentration fluctuations due to variable inputs of surface soil are buffered by high channel bank inputs. Although the relative trends in sediment-bound 7Be and 210Pbex show correlation along the Albert River, in some river reaches divergence in the concentrations of the two tracers occurs. This is best illustrated by the river sediment activity ratio of 7Be and 210Pbex, shown in Figure 23. Surface soil measurements made on hillslope samples collected from the Logan and Albert catchments in the week immediately after the January flood have a 7Be/210Pbex ratio of 0.89 ±0.08. Figure 23 shows that significant deviations from the hillslope ratio are seen in the river sediment, with all deviations being positive; i.e. at no point does the ratio fall below 0.9. The deviations occur in sediment from the upper 30 km and in the 68-80 km reach, with the 7Be/210Pbex ratio approaching values of 2.0 in these reaches. The elevated ratios are mostly due to increases in concentrations of 7Be; i.e. there seems to be an additional source of 7Be in some parts of the catchment that is not matched by 210Pbex. We propose that this sediment source is consistent with erosion of recently exposed subsoil, (i.e. exposed within the last few years). This soil is 7Be-rich relative to 210Pbex because of the high 7Be/210Pbex ratio in rainfall (Baskaran et al., 1997), and because the recent exposure of the soil has not allowed sufficient time for the concentration of longer-lived 210Pbex to accumulate. The subsoil erosion delivering 7Be to the streams channels could be associated with erosion from hillslopes where surface soil (>5-10 cm) has been previously stripped, either by sheet erosion or by rilling. Clearing of vegetation and urban development can expose subsoils leading to the erosion of soils containing relatively low excess 210Pb and relatively high 7Be. Other possible subsoil sources include eroding gully floors and cultivated fields, although neither of these seem likely as significant sediment sources. Gullies are relatively uncommon in the Albert catchment, and cultivated soils mostly occur on low gradient floodplains adjacent to the river. A previous South-East Queensland regional study


indicated that cultivated soils are a minor but significant source of sediment to the Brisbane and Logan Rivers (Caitcheon et al., 2001; Wallbrink, 2004), but this study does not indicate the same conclusion. Further discussion on the likelihood of cultivated soils as a source of sediment the Logan River is given in section 4.2.3.

Figure 22. Concentrations of surface soil tracers in the Albert River sediment (left) and Logan sediment (right), measured from the headwaters to the estuary.

Figure 23. 7Be/210Pbex ratios in the Logan and Albert Rivers, from the headwaters to the estuary. Logan River Plots from the Logan River are also shown in Figures 22 and 23. Apart from the relatively high surface soil tracer concentrations at the uppermost Logan sampling location (site 16 in Figure 1), 137Cs shows similar trends to the Albert River, with the concentration variation of 137Cs being lower than 7Be and, to a lesser extent, 210Pbex.

Again, this is probably due to relatively high channel bank inputs. Overall the relationship

Albert River

Distance from headwaters (km)

0 20 40 60 80 100

7B

e/2

10 P

b ex

0

1

2

3

4

Hillslope surface soil ratio

Logan River


0 20 40 60 80 100 120 140

7B

e/2

10P

b ex

0

1

2

3

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hillslope surface soil ratio

Logan River


0 20 40 60 80 100 120 140

7B

e, 2

10P

be

x (B

q kg

-1)

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7C

s (B

q k

g-1)

0

1

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5Be-7 210Pbex 137Cs

headwatersestuary

Albert River


0 20 40 60 80 100

13

7C

s (B

q kg

-1)

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3

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e, 2

10P

b ex

(Bq

kg-1

)

0

10

20

30

40

50

60137Cs210Pbex

7Be

headwaters estuary


between 7Be and 210Pbex is not as close as it is along the Albert. This is reflected by 7Be/210Pbex ratio (Figure 23) which shows greater positive deviations from the surface soil value than is shown in the Albert. The deviations indicate likely inputs of recently exposed subsoil, especially in the middle catchment from Laravale to South Maclean (60-110 km from the headwaters). Teviot Brook Overall, there is an increasing trend in 210Pbex and 137Cs concentrations in Teviot Brook sediment downstream from the headwaters to the Logan confluence (Figure 24). While this indicates an increasing surface soil contribution in the lower part of the catchment it should be noted that the tracer concentrations coming from the upper catchment are very low and indicate a surface soil contribution of <10%. Thus the increasing trend downstream probably indicates a trend towards surface soil contributions typically seen in the Logan and Albert catchments (15-25%). The 7Be/210Pbex ratio is erratic but indicates that in addition to channel banks significant contributions from exposed subsoils have occurred.

Figure 24. Concentrations of surface soil tracers and tracer ratios in Teviot Brook from its headwaters to the junction with the Logan River.


30 40 50 60 70 80 90 100

7B

e/2

10P

bex

0

1

2

3

4

5

6

Hillslope surface soil ratio

Teviot Brook


30 40 50 60 70 80 90 100

137 C

s (B

q kg

-1)

0.0

0.5

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e, 2

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b ex

(Bq

kg-1

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140137Cs210Pbex

7Be


4.2.3. Determining erosion sources along the river networks: combining fallout and spatial tracing results

Using the three fallout tracers in combination with spatial tracing allows estimates to be made of the contributions of the different erosion sources along the length of the river systems. In the first instance we have taken the simple budget approach of comparing the relative surface soil estimates given by 7Be and 210Pbex and using these to distinguish subsoil contributions from both shallow hillslope erosion and channel bank sources. 137Cs is not used here because of the potentially complicating effect of its small but positive concentration in channel banks. Later we check the 7Be and 210Pbex budget approach using all three fallout tracers in the mixing model. The contribution of surface soil to river sediment along a given reach is estimated from the ratio of the 210Pbex concentration of the sediment to that of the reference 210Pbex concentration of hillslope surface soil (mean hillslope 210Pbex concentration = 90 ±8 Bq kg-1, Table 3). Based on this value the fraction (F) of surface soil in the Albert River is found to be 20-25% along the length of the Albert River. Applying 7Be in a similar way (surface soil reference concentration = 80 ±10 Bq kg-1) produces values ranging from 30-60%. We attribute the additional 5-35% surface soil component, as estimated by 7Be, to shallow subsoil erosion (other than channel bank). The remaining proportion of eroded soil is attributed to channel bank erosion. This approach can be summarised by,

FSS = FPb (2)

FSB = FBe – FSS (3)

and FCB + FSB + FSS = 100 (4) where F is the fraction (as %) of the surface soil (subscript SS), subsoils (SB) and channel bank (CB) contributing to river sediment. FBe and FPb refer to the surface soil fractions as estimated by 7Be and 210Pbex.This approach has been used to determine erosion sources along the length of the Albert and Logan Rivers (Table 4). For the Albert River a peak in the proportion of sediment due to channel bank erosion (75 ±10%) is seen in the mid-catchment reaches. The proportion of shallow subsoil sources are around 20% in the upper 20 km and the lower 40 km. The proportion of these subsoil sources appears lowest in the mid-catchment region although this may be related to the high input from channel bank erosion. For the Logan River channel bank erosion appears relatively low in the 20 km reach upstream of Innisplain (<25%), but becomes the major sediment source downstream of this point. Apart from the headwater reach where the surface soil proportion is 60-80%, surface soil input along most of the River is similar to the Albert, at around 20%. However values of <10% occur in the 80-100 km reach (from just downstream of Beaudesert to the Teviot Brook junction). This appears to be due to a combination of high channel bank and subsoil inputs, with the decrease in 210Pb and 137Cs indicating that these sources in combination at least doubled their input along this reach. The 7Be data indicates that subsoils are significant (35 ±5%) in the 60-100 km reach. This reach corresponds to input from creeks draining Marburg soils on the western side of the Logan catchment, including Knapps Creek, Cannon Creek and Sandy Creek. A


significant increase in Marburg contribution to the Lower River is also consistent with input from these creeks. While cultivated fields adjoining the mid-Logan River are another possible source of sediment-bound 7Be, these soils do not have a strong Marburg signature, being mainly derived from Lamington sources. Thus we consider cultivated soils a less likely source of sediment to the mid-Logan than the western Creeks catchments. In Teviot Brook the relative behaviours of 7Be and 210Pbex indicate that as much 40% of the sediment eroded from the catchment upstream of Boondah is recently exposed subsoils, with most of the remainder being channel bank. Spatial tracing indicates most of the Teviot Brook sediment comes from soils developed on the Walloon rock type above Boonah, indicating that the upper catchment is the major sediment source, and that erosion processes in this area (subsoil and channel bank erosion) are the dominant erosion process. It is not clear, however, if these inputs are associated with hillslope scouring or cultivation. Contributions from surface soils in the lower catchment are likely, with tracers indicating that both surface soil and Marburg-derived contributions rise from <10% to 20-25%. The erosion source results determined above using 7Be and 210Pbex are supported by application of the Monte Carlo mixing model utilising all three fallout tracers, 7Be, 210Pbex and 137Cs. Soil and sediment activities shown in Table 3 are used to characterise sources and sinks, and the results for the lower Albert and Logan catchments are shown in Table 4. In general the uncertainties of the mixing model predictions are higher than the 7Be and 210Pbex budget approach. Nevertheless, the mixing model results confirm the 7Be and 210Pbex budget results, i.e. the dominance of channel bank erosion and the presence of recently exposed subsoils as a significant source, with subsoils predicted to be as high as 40 ±10% in the mid-Logan region. Surface soil contributions are also consistent with our 210Pbex estimates, being <25%.

4.2.4. Significance of in–channel sediment storage as a sediment source

The high values of the 7Be/210Pbex ratio along most of the major river channels appear to rule out in-channel re-suspension of fine sediment deposited in the channels during previous flow events as a significant sediment source. As is summarised in Table 1, 7Be is certain to be low or absent from in-channel sediment storages whereas 210Pb and 137Cs should be present with values similar to those measured in the river during this event. Hence, if re-suspension of sediment was significant, 7Be concentrations of transported sediment would decrease relative to 210Pbex leading to a decline in the 7Be/210Pbex ratio to values less that of the surface soil ratio. While the plots in Figure 23 show evidence that this process may be occurring in isolated reaches, with a decline in the ratio at 40-50 km in both the Albert and Logan Rivers, and around 60 km in Teviot Brook, the rapid rise in the 7Be/210Pbex ratio further downstream indicates that the process is not significant compared to other sediment sources. Interestingly, the 7Be/210Pbex ratios drop at the lower end of the catchment as the river approaches the estuary and river gradients lessen, perhaps indicating re-suspension is occurring here. Certainly, as is shown in section 4.3 below, re-suspension of sediment within the estuary is significant.


The discussion above does not relate to channel bank incision, which is a special case of sediment storage and remobilisation. As noted above, overbank deposition of sediment during flood events followed by channel bank incision during a later event will effectively lead to remobilisation of deposited sediment. However, for the purposes of this study this process is defined solely as channel bank erosion. Table 4. Proportion (as %) of various erosion sources delivered as sediment to rivers, calculated using an excess 210Pb and 7Be budget. The proportions are equivalent to FSS, FSB and FCB (see text for details). Also shown are the results of mixing model runs using mean values of all three tracers for the source and sink terms. Var. = variable within the range given. River reach Reach description Method Surface

soil (%) Recently exposed

subsoil (%) Channel Bank (%)

Albert River 0-30 km Headwaters to Ward Bridge 7Be, 210Pb budget 25 ±5 20 ±10 55 ±10 40-70 km Kerry to Mundoolun “ 20 ±5 5 ±5 75 ±10 70-110 km Mundoolun to estuary “ 25 ±5 20 ±5 55 ±10 Lower Albert Mundoolun to estuary Mixing model 15 ±3 30 ±10 55 ±10 Logan River 0-25 km Headwaters to O’Brien’s X 7Be, 210Pb budget 80 ±10 10 ±10 10 ±10 25-50 km Rathdowney to Laravale “ 25 ±5 0-40 20-60 60-100 km Josephville to South Maclean “ 15 ±5 35 ±5 50 ±10 100-140 km South Maclean to estuary “ 20 ±5 20 ±10 60 ±10 Lower Logan Josephville to estuary Mixing model 10 ±3 40 ±10 50 ±10 Teviot Brook 0-50 km Headwaters to Boondah 7Be, 210Pb budget 8 ±5 Var. 25-50 60 ±10 50-90 km Boondah to Logan confluence “ 20 ±5 Var. 0-60 Var. 20-75 Lower Teviot Boondah to Logan confluence Mixing model 10 ±3 45 ±10 45 ±10

4.3. Estuary sediment dynamics

4.3.1. Estuarine turbidity

Delivery of river-borne sediment to estuaries results in the mixing of the “new” sediment derived from recent erosion with “old” estuarine sediment already present in the estuary prior to the flood event. One of the important management questions relating to river catchment management and the minimisation of turbidity in estuaries concerns the residence time of river sediment in the estuary. This question can be re-stated as, “how much turbidity seen in tidal estuaries is due to sediment delivered recently by the river, and how much is due to the mobile, re-suspendable sediment that has accumulated in the estuary over longer periods?”. If the latter source dominates turbidity then a reduction in catchment loads may have little or no immediate effect on estuarine turbidity, with improvements to water quality only occurring after some decades or longer.

It is well known that a zone of high turbidity exists in the Logan-Albert estuary, from a reach near the M1 highway bridge (sample 406 in Figure 7, or EMP site 205) extending


approximately 12 km upstream to the region near EMP site 213, about 30 km upstream of the estuary mouth. The suspended sediment data for the sample collection undertaken in May 2008 illustrates this phenomenon (Figure 25). Suspended sediment concentrations rise from 44 mg L-1 about 42 km upstream of the estuary (sample 401) to concentrations approaching 300 mg L-1 at the M1 site (samples 405 and 407), approximately 19 km upstream of the estuary mouth. Concentrations are low <30 mg L-1 within 8 km of the estuary mouth.

This non-conservative increase indicates an “internal” source of suspended sediment generated within the upper and middle estuary. One obvious potential source is the re-suspension of deposited sediment from the river banks and mangrove flats (Figure 10). This soft unconsolidated sediment is potentially a large source of mobile, re-suspendable sediment, defined as sediment capable of being resuspended and deposited along the estuarine reach as a result of water flow induced by tidal action. While some of this sediment must inevitably be transported out of the estuary, but presumably its total mass is being continually topped up by “new” sediment carried by river water, especially during floods like the January 2008 event. If long-term sediment export from the estuary can be quantified, knowledge of the relative proportions of “new” and “old” sediment allows an estimate of the time required for catchment erosion mitigation works to have an effect on reducing the load of mobile sediment stored in the estuary to the point where turbidity is reduced.

Figure 25. Estuarine suspended sediment (SS) concentrations in May 2008. The shaded area represents the zone of high turbidity. Distances become more negative moving upstream from the estuary mouth.

Distance from estuary mouth (km)

-50 -40 -30 -20 -10 0 10

SS

(m

g L-1

)

0

100

200

300


4.3.2. Tracing “new” sediment delivered to the estuary

The disequilibrium seen in the concentrations of thorium series nuclides in estuarine sediments provides a signal that can distinguish “old” and “new” sediment. The technique is described in detail in Hancock (2000). This technique utilises the different chemical properties of radium and thorium, two elements naturally present in all soils and sediments, together with the fact that the thorium (232Th) series isotopes in fresh-water sediment usually exhibit “secular equilibrium”.

Figure 26 shows the decay scheme for the relevant thorium series nuclides. In fresh water these nuclides generally have approximately the same activity concentration (called “secular equilibrium“) due to the particle reactive nature of both radium and thorium in freshwater. But in salt water 228Ra desorbs leaving an activity deficiency relative to its parent 232Th, and its daughter, 228Th. Since 232Th is extremely long-lived (half-life 14 billion years) its activity does not change significantly on a time frame of years to decades. However, 228Th is relatively short-lived (half-life 1.9 years) and over a period of months to a few years it decays back towards the lower 228Ra activity. The outcome of this process is that “new” sediment recently delivered by fresh river water has an 228Th/232Th activity ratio close to one (i.e. secular equilibrium) and “old” estuarine sediment with an estuarine sediment age 3-4 years or more will have a 228Th/232Th ratio of <1, generally being in the range 0.6-0.8. By determining the pre-January 2008 estuarine end-member ratio (the “old” ratio), the relative contributions of old estuarine sediment and new inputs from river floods to the suspended load can be calculated.

Figure 26. Illustration of the 232Th decay scheme. 228Ra is lost by ion-exchange with dissolved cations in saline water leading to a reduction (over a period of a few years) in the 228Th/232Th activity from a value of 1.0 to a value of around 0.7.

(soluble in salt water)

“new” sediment: 228Th/232Th ~1.0

“aged” sediment: 228Th/232Th ~0.7

232Th(1.4 x 1010 y)

228Ra20-40% loss

sediment grain

228Th(1.9 y)

(soluble in salt water)





232Th(1.4 x 1010 y)

228Ra20-40% loss

sediment grain

228Th(1.9 y)

232Th(1.4 x 1010 y)

228Ra20-40% loss

sediment grain

228Th(1.9 y)


Figure 27 summarises the estuarine 228Th/232Th values for January 2008 flood sediment (red symbols, circled) and suspended (CFC) sediment collected 4 months later in May 2008 (black symbols). The 228Th/232Th values of mobile mud-bank samples (open circles) are similar to the CFC samples indicating mud-banks are a major source of the suspended material. Also shown are horizontal lines representing the “old” sediment ratio (0.746, solid line) and its uncertainty (±0.018, two dotted lines). This value is determined by the mean 228Ra/232Th of all deposited sediment samples from the mud-banks, and is the value that the sediment 228Th/232Th ratio will attain after a period of about 6-7 years (~3-4 228Th half-lives). Given the long period of time since the last significant influx of sediment into the estuary (in the year 2000, or about 8 years previously) it is reasonable to assume that prior to the January 2008 flood estuarine sediment would have been characterised by an “old” ratio.

New sediment is represented by the value 1.0, this being the ratio found in sediment in which the 232Th-series is in secular equilibrium. Measurements of 7 river sediment samples from the lower Logan and Albert rivers had a mean ratio of 1.001 ±0.019.

Sediment ratios from the January event straddle the horizontal line representing a value of 1.0. This result is expected because the samples represent “new” freshwater sediment just delivered to the estuary; i.e. the sediment was deposited at peak flow and had no chance to mix with older estuarine sediment. The May 2008 suspended (CFC) sediment samples all show lower ratios, lying mid-way between the “new” and “old” end-members. Thus the component of “new” sediment in May 2008 (Fnew) is calculated from

oldnew

oldmeasnew RR

RRF

(5)

where measR is the 228Th/232Th ratio measured in suspended (CFC) sediment in May 2008,

oldR and newR are the 228Th/232Th ratios of “old” and “new” sediment, estimated, as

described above, to be 1.0 and 0.746 ±0.018 respectively. Taking a mean measR for the

high turbidity region gives a value of 0.892 ±0.015, and substituting this value into Eq. (5) gives Fnew = 0.57 ±0.07; i.e. 57 ±7% of the mobile sediment in the estuary in May 2008 was delivered during the January 2008 event.

This result shows that, although the estuary has retained significant quantities of “old” mobile sediment delivered in previous few years (43 ±7% of the total mobile mass), large river flow events such as the January 2008 event contribute half to two thirds of estuarine turbidity in the 3-4 months following the event. The potentially high trap efficiency of the estuary for sediment delivered during floods is a likely contributing factor to this result. Depending on the rate of export of sediment from the estuary into southern Moreton Bay, this result suggests that reducing sediment inflows could reduce the amount of mobile estuarine mud as, over time, sediment is resuspended and exported from the estuary by tidal exchange.


Figure 27. Sediment 228Th/232Th activity ratios in the Logan-Albert estuary. Dashed lines represent estuary sediment ratios for “new” (1.0), “old” or “aged” (0.746 ±0.018). Dotted lines indicate error bars on the ratios. The red symbols indicate measured values for sediment deposited within the estuary by the January 2008 event, and the solid line represents the average of suspended sediment samples collected in the turbid zone in May 2008 (0.892 ±0.015).

Distance from estuary mouth (km)

-50 -40 -30 -20 -10 0 10

Sed

imen

t 22

8T

h/2

32T

h

0.7

0.8

0.9

1.0

1.1

Suspended sediment May '08"mobile" bank sediment May '08Deposited sed., Jan '08 event

"new" river sediment

"aged" estuarine sediment

average estuary


5. CONCLUSIONS

Conclusions relating to sources of sediment delivered to the Logan estuary and the main river channels (Logan River, Albert River and Teviot Brook) during the January 2008 flood event are:

Spatial tracing using major and minor element geochemistry indicates that the majority (~70%) of the sediment delivered to the Logan estuary during the flood event originates from soils derived from the Lamington Group geology. Analysis of other estuarine sediment samples from sites representing average or “mixed” estuarine sediment indicates this is also the case over the longer-term.

Channel bank erosion is the major sediment source, being 50-75% along all reaches of the major rivers except the upper-most part of the Logan upstream of O’Brien’s Crossing . Channel bank proportions are greatest in the upper and mid-catchment region of the Albert River and the mid-catchment region of the Logan below Rathdowney.

Surface soil inputs along the main river channels are mostly in the range 20-25% of sediment input. Exceptions are the Upper Logan above O’Brien’s Crossing (~80%), Canungra Creek (~40%), upper Teviot Brook (<10%) and the mid-Logan reaches below Josephville (<15%). It is not clear whether grazing land or national park forest is the dominant surface soil source. Future research using stable isotope tracers may provide the discrimination required to separate these sources.

7Be data indicate that subsoil erosion, not including channel bank erosion, from an undetermined erosion process contributes 20-40% of sediment over much of the catchment. Exceptions are the upper Logan and the mid-Albert. Significant locations include upper Teviot Brook, and the mid Logan River from Laravale to South Maclean. Spatial tracing of sources using soil geochemistry indicates creeks draining Marburg-derived soils (Cannon, Knapps, Sandy and Allan Creeks) are significant sources of these subsoils to sediment delivered to the lower Logan River. The erosion processes generating these subsoils are likely to include hillslope scalds and rills.

7Be and 210Pb ratios indicate that re-suspension of deposited sediment stored within stream and river channels was not a significant sediment source. The implication of this observation is that transit times for the delivery of sediment from the catchment to the estuary are short, and are of the order of the average recurrence interval of the January event (10 years) or less.

Within the estuary, at least half the mobile (re-suspendable) sediment fraction sampled in May 2008 (4 months after the January event) was found to be associated with that event. This result indicates that floods such as the January event contribute significantly to the ongoing turbidity seen in the estuary.


REFERENCES

Bureau of Meteorology (2008): South East Queensland Floods, January 2008. http://www.bom.gov.au/hydro/flood/qld/fld_reports/South_East_QLD_Floods_January_2008.pdf

Baskaran, M., Ravichandran, M. and Bianchi, T.S. (1997). Cycling of 7Be and 210Pb in a high DOC, shallow, turbid estuary of south-east Texas. Estuarine, Coastal and Shelf Science, 45, 165-176.

Caitcheon, G, Prosser, I., Wallbrink, P., Douglas G., Olley, J., Hughes, A., Hancock, G. and Scott, A. (2001). Sediment delivery from Moreton Bay’s main tributaries: a multifaceted approach to identifying sediment sources. Proceedings of the Third Australian Stream Management Conference, volume 1, pp.103-107, Brisbane Queensland, August 27-29, 2001.

Douglas, G., Palmer, M. and Caitcheon, G. (2003). The provenance of sediments in Moreton Bay, Australia: a synthesis of major, trace element and Sr-Nd-Pb isotopic geochemistry, modelling and landscape analysis. Hydrobiologia 494, 145–152.

Hancock, G.J. (2000). Identifying resuspended sediment in an estuary using the 228Th/232Th activity ratio: the fate of lagoon sediment in the Bega River estuary, Australia. Marine and Freshwater Research, 51, 659-67.

Hancock, G.J., Wilkinson, S.N. and Read A. (2007). Sources of sediment and nutrients to the Gippsland Lakes assessed using catchment modelling and sediment tracers. CSIRO Land and Water Science Report 70/07. http://www.clw.csiro.au/publications/science/2007/sr70-07.pdf

Hancock, G.J. and Pietsch, T. (2008). Tracing and dating techniques employed at CSIRO Land and Water. CSIRO Land and Water Science Report 64/08. http://www.clw.csiro.au/publications/science/2008/sr64-08.pdf

Leslie, C. (2009). Analysing environmental radioactivity in soils and sediments using high-purity germanium gamma detectors at CSIRO Land and Water: Procedures and Protocols. CSIRO Land and Water Science Report 12/09. http://www.clw.csiro.au/publications/science/2009/sr12-09.pdf

Murray A. S., Marten R., Johnston A., and Martin P. (1987). Analysis for naturally occurring radionuclides at environmental levels by gamma spectrometry. Journal of Radioactive and Nuclear Chemistry, 115, 263-288.

Norrish, K. and Hutton J.T. (1969). An accurate X-ray spectrographic method for the analysis of a wide range of geological samples. Geochimica et Cosmochimica Acta 33, 431-453.

Pennock, D.J. and Appleby, P.G. (2002). Site selection and sampling design, In: Handbook for the Assessment of Soil Erosion and Sedimentation Using Environmental Radionuclides; pp 15-40. Edited by F. Zapata, Kluwer Academic Publishers, Dordrecht, The Netherlands.


EHMP (2009). Summary Report of the flood event in the catchment of the Logan and Albert Rivers, January 2008. South East Queensland Healthy Waterways Partnership, Brisbane. http://www.healthywaterways.org/_uploads/ehmp/filelibrary/jan08_floodevent_synthreport_21oct08.pdf

Wallbrink, P.J. (2004). Quantifying the erosion processes and landuses which dominate fine sediment supply to Moreton Bay, Southeast Queensland, Australia. Journal of Environmental Radioactivity 76, 67–80.

Wallbrink, P.J., Murray, A.S. and Olley, J.M. (1999). Relating suspended sediment to its original soil depth using fallout radionuclides. Soil Science of America Journal, 63, 369-378.

Wallbrink, P.J., Olley, J.M. and Hancock, G.J. (2002). Estimating residence times of fine sediment in river channels using fallout 210Pb. The Structure, Function and Management Implications of Fluvial Sedimentary Systems (Proceedings of an international symposium held at Alice Springs, Australia, September 2002). IAHS Publ. no. 276, 2002. Wallbrink, P.J., Olley, J.M. and Hancock, G.J. (2003). Tracer assessment of catchment sediment contributions to Western Port, Victoria. CSIRO Land and Water Technical Report, 08/03.

http://www.clw.csiro.au/publications/technical2003/tr8-03.pdf

Sediment sources and transport to the Logan-Albert River estuary during the January 2008 flood event 37

APPENDIX (Note: SAMPLE ID NUMBERS CORRESPOND TO SAMPLE LOCATIONS SHOWN IN FIGURES 1, 7 AND 11). SEDIMENT SAMPLES

In-stream sediment

Sample No. ID Date Type Location LA08001 1 21/01/2008 Deposited sed Albert R @ Martens St; Beenleigh

LA08002 2 21/01/2008 Deposited sed Albert R; lower

LA08003 3 21/01/2008 Deposited sed Albert R @ Stanmore Rd

LA08004 4 21/01/2008 Deposited sed Albert R @ Chardon Br Rd LA08005 5 21/01/2008 Deposited sed Albert R @ Waterford-Tamborine Rd

LA08006+105 6 21/01/2008 Deposited sed Albert R @ Mundoolin Bridge; d/s Canungra

LA08007 7 21/01/2008 Deposited sed Canungra Ck @ Biddaddaba Rd

LA08008 8 21/01/2008 Deposited sed Albert R

LA08009 9 21/01/2008 Deposited sed Albert R @ Nindooinbah Br

LA08010 10 21/01/2008 Deposited sed Albert R @ Kerry Br

LA08011 11 21/01/2008 Deposited sed Albert R @ Ward Br

LA08012 12 22/01/2008 Deposited sed Logan R

LA08013 13 22/01/2008 Deposited sed Logan R @ Williams Br


LA08015 15 22/01/2008 Deposited sed Logan R @ Len Drynan Br

LA08016 16 22/01/2008 Deposited sed Logan R @ O'Briens Crossing

LA08017 17 22/01/2008 Deposited sed Teviot Brook



LA08020 20 22/01/2008 Deposited sed Teviot Brook @ Smith Rd LA08021 21 22/01/2008 Deposited sed Teviot Brook LA08022 22 22/01/2008 Deposited sed Teviot Brook LA08023 23 22/01/2008 Deposited sed Logan R



LA08026+123 26 23/01/2008 Deposited sed Logan R


LA08028 28 23/01/2008 Deposited sed 1-2 km d/s Canungra

LA08029 29 23/01/2008 Deposited sed U/S Canungra

LA08030 30 23/01/2008 Deposited sed Canungra Ck

LA08101 101 21/01/2008 Deposited sed Canungra Ck @ Canugra bridge

LA08104+028 104 21/01/2008 Deposited sed Canungra Ck @ Benoble Bridge - d/s Canungra LA08105+006 105 21/01/2008 Deposited sed Albert river at Mundoolin bridge

LA08109 109 22/01/2008 Deposited sed Albert River, U/S Duck Ck LA08112 112 22/01/2008 Deposited sed Albert river, Lamington NP near Lost world


LA08114 114 22/01/2008 Deposited sed Albert river, ~ 2km d/s Lost World LA08116 116 22/01/2008 Deposited sed Albert river, Newton Bridge LA08118 118 23/01/2008 Deposited sed Running Ck, uppermost site

LA08123+026 123 23/01/2008 Deposited sed Logan river, Waterford bridge Hwy 95 LA08 408 408 21/05/2008 Deposited sed Sandy Ck @ Sandy Ck Rd.; S. Todd Bridge LA08 409 409 21/05/2008 Deposited sed Sandy Ck @ The Hollow Bridge LA08 411 411 21/05/2008 Deposited sed Cannon Ck. @ Round Mountain Rd. X LA08 415 415 22/05/2008 Deposited sed Burnett Ck. in NP

Estuary sediment

Sample No. ID Date Type Location

LA08131+132 131,132 16/01/2008 Deposited sed Skinners Creek Pontoon + Boat ramp

LA08133 133 16/01/2008 Deposited sed Skinners creek Boat U/S near golf course LA08134 134 16/01/2008 Deposited sed site 206, Waterford LA08135 135 16/01/2008 Deposited sed site 212 - d/s Riedels Rd LA08136 136 23/01/2008 Deposited sed E00304; Moreton Bay North of L-A estuary LA08137 137 23/01/2008 Deposited sed E00200; 0 km U/S estuary mouth

LA08138+139 138,139 23/01/2008 Deposited sed E00201; 2 km + 4.8 km U/S estuary mouth LA08140 140 23/01/2008 Deposited sed E00211; 7.8 km U/S estuary mouth LA08141 141 23/01/2008 Deposited sed E00203; 13.3 km U/S estuary mouth LA08 401 401 19/05/2008 Suspended sed (CFC) S&A Smith park; ~6 km U/S Waterford LA08 402 402 20/05/2008 Suspended sed (CFC) Jim Lowe's jetty, Redland channel LA08 403 403 20/05/2008 Suspended sed (CFC) Caravan Pk @ Ferry Rd LA08 404 404 20/05/2008 Suspended sed (CFC) Skinner's Pk, pontoon

LA08 404-2 404 20/05/2008 Deposited sed Skinner's Pk, pontoon LA08 405 405 20/05/2008 Suspended sed (CFC) M1 overpass pontoon

LA08 405-2 405 20/05/2008 Deposited sed M1 overpass pontoon LA08 406 406 21/05/2008 Suspended sed (CFC) Small reserve ~2km U/S M1

LA08 406-2 406 21/05/2008 Deposited sed Small reserve ~2km U/S M1 LA08 407 407 21/05/2008 Suspended sed (CFC) M1 overpass pontoon


SOIL SAMPLES

Hillslope Soils

Sample No. ID Date Type Location

LA08031 31 24/01/2008 open forest pasture Beaudesert-Boonah Rd Br.

LA08032 32 24/01/2008 Rainforest, Nat Pk French N.P.

LA08102 102 21/01/2008 Rainforest Rainforest hillslope mobile soil 5 sites: Karamun lookout

LA08121 121 23/01/2008 open forest pasture Mt Barney NP, parking lot. LA08125 125 24/01/2008 open forest Nat Pk Mt Tambourine, near ridge top, Canungra end. LA08126 126 24/01/2008 open forest Nat Pk Tambourine NP, Beaudesert-Beenleigh Rd. LA08 410 410 21/05/2008 Pasture Pasture Sandy Creek catchment LA08 412 412 22/05/2008 Pasture Pasture Koonalbyn and Knapp Creek catchment LA08 414 414 22/05/2008 open forest Nat Pk Mt Barney NP along Burnett Ck Rd. LA08 416 416 22/05/2008 Pasture Grazed hillslope along Burnett Creek catchment LA08 417 417 22/05/2008 open forest Nat Pk Mt French N Pk. LA08 418 418 22/05/2008 Pasture Grazed hillslope along Boonah-Beaudert Rd. LA08 419 419 22/05/2008 Pasture Grazed hillslope along Toorakum Ck Rd. LA08 420 420 22/05/2008 open forest Nat Pk Forest hillslope along Toorakum Ck Rd. MB00042 242 12/11/2000 Pasture Croftby region MB00046 246 12/11/2000 Pasture Hillview region MB00047 247 13/11/2000 Pasture Glenora region MB00051 251 14/11/2000 Pasture Cedar ck region MB00055 255 13/11/2000 Pasture Josephville region

Channel Bank soils

Sample No. ID Date Type Location LA08108 108 22/01/2008 Channel bank Albert River, u/s Duck Ck LA08110 110 22/01/2008 Channel bank Widgee Ck-Logan confluence LA08115 115 22/01/2008 Channel bank Albert river, ~ 2km d/s Lost World LA08120 120 23/01/2008 Channel bank Running Ck @ Ralston bridge LA08 413 413 22/05/2008 Channel bank Bank from highly eroding region in Knapp's Ck MB00044 244 12/11/2000 Channel bank Innisplain region MB00049 249 13/11/2000 Channel bank Tamrookum region MB00052 252 13/11/2000 Channel bank Teviot Brook MB00053 253 14/11/2000 Channel bank Mt Joyce region MB00054 254 14/11/2000 Channel bank Tamborine region

Subsoils

Sample No. ID Date Type Location LA08122 122 23/01/2008 Shallow gully in forest Mt Barney NP, near parking lot LA08117 117 22/01/2008 Scald on eroding hillslope Along Christmas Ck Rd LA08128 128 23/01/2008 Scald on hillslope Knapp’s Ck catchment LA08129 129 23/01/2008 Scald on hillslope Sandy Ck catchment

Cultivated soils

LA08107 107 22/01/2008 Mobile soil in run-off from

cultivated field Dunn’s farm near upper Canungra Ck MB00045 245 12/11/2000 Mobile cultivated soil runoff Hillview region MB00048 248 13/11/2000 Mobile cultivated soil runoff Glenora region

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