Attachment E.2 (i) Characteristics of the Dumping Site ... · PDF filePOC Maintenance Dredging ... Admiralty Tide Tables ... the sidescan record was digitised manually from paper roll

POC Maintenance Dredging Application | January 2014

Attachment E.2 (i) Characteristics of the Dumping Site – Impact

Hypothesis Update prepared by Irish Hydrodata Ltd (Nov 2013) & Video & Benthic

Grab Survey & Impact Hypothesis prepared by Aquatic Services Unit (Nov 2004)

Doc. Ref. 1178_1/13

DRAFT

CORK DREDGE SPOIL DISPOSAL SITE

IMPACT HYPOTHESIS UPDATE 2013

Produced for:

Port of Cork Company, Custom House Street,

Cork.

Prepared by:

Irish Hydrodata Limited Rathmacullig West,

Ballygarvan, Co. Cork.

Ph. 021-4311255

e-mail: [email protected]

November 2013

mailto:[email protected]

Cork Dredge Spoil Disposal Site – Impact Hypothesis Update 2013

i

CONTENTS

1. INTRODUCTION …… 1

2. PREVIOUS STUDIES/SURVEYS …… 2

3. SURVEY of NOVEMBER 2013 …… 3

4. SHALLOW GEOLOGY …… 7

5. DISCUSSION …… 11

6. CONCLUSIONS …… 21


Irish Hydrodata Ltd 1

1. INTRODUCTION

Port of Cork Company (PoC) is allowed to dispose of dredge spoil material extracted

from Cork Harbour within a specified area south of Power Head (Figure 1) under

license from the Environmental Protection Agency (EPA).

The Cork dredge spoil disposal site co-ordinates are presented below in Table 1.

The site was reduced in size in December 1996 and all dumping since then has

occurred in the smaller site.

ORIGINAL DUMPSITE (pre 1996) DUMPSITE (post 1996)

51° 43.00’ N 8° 11.55’ W 51° 43.00’ N 8° 10.18’ W 51° 43.00’ N 8° 09.00’ W 51° 43.00’ N 8° 09.00’ W 51° 44.50’ N 8° 11.55’ W 51° 44.50’ N 8° 09.00’ W 51° 44.50’ N 8° 09.00’ W 51° 44.50’ N 8° 10.18’ W

Table 1 Dump Site Location

Figure 1 Dump Site Location

PoC is currently (November 2013) in the process of applying for a new license and

as such was required to provide updated information to EPA regarding the current

state of the dumpsite. In early November 2013, Irish Hydrodata Ltd (IHD) was

commissioned by PoC to provide this updated information. This was to take the form

of a multibeam echosounding survey which would identify the expanse of areas

within the disposal site which consist of exposed bedrock and surface sediments.

The information could then be compared with that from earlier surveys to see if

dumped material was accumulating within the dumpsite.



2. PREVIOUS STUDIES/SURVEYS

Impact Hypothesis 1999

In January 1999, IHD carried out an impact hypothesis on the fate of material

dumped at the site [1]. The following information is extracted from that report and

shows that 6.73*106m3 of material was dumped at the site between 1978 and 1999.

Note that dumping in the years prior to 1996 was allowed in the large site (Figure 1)

and was limited to the smaller site after that time.

Regular dumping of spoil has been carried out at the disposal site since 1978. The main

navigation channel and berths in Cork Harbour including Ringaskiddy basin and deepwater

quay are routinely maintained to an advertised dredge depth by PoC. PoC is also responsible

for occasional capital dredging as part of the normal management of harbour resources.

Material was furthermore, dumped at the site from dredging as part of the Lee Tunnel Project.

From 1988 to 1994 maintenance dredging volume was approximately 95,000m3 per annum.

From 1995 to 1998 the maintenance dredging volume amounted to approximately 260,000m3

(source: PoC) leading to a total of 930,000m3 since 1988. The material from this dredging is

mostly composed of silt/clay as inferred from granulometric analysis of samples carried out by

Eolas (now Enterprise Ireland) over the years. The breakdown is approximately: gravel 0.5%,

sand 25.8%, silt/clay 73.7%.

Capital dredging projects from 1978 to 1994 accounted for almost 5*106m

3 of material in total

[5]. Approximately 3.4*106m

3 was removed from the Ringaskiddy Basin during this period

(3*106m

3 in 1980/81 and 0.4*10

6m

3 in 1990) and 1*10

6m

3 from the Lough Mahon/Tivoli area.

…. the material from Ringaskiddy was of the order of 88% silt/clay, 12% sand and <1%

gravel. Also, the Lough Mahon/Tivoli material was approximately 81% silt/clay, 19% sand

and <1% gravel.

From 1995 to 1998, disposal of surplus dredged material as part of the Lee Tunnel project

amounted to almost 1.2*106 tonnes (or 800,000m

3) [source: Cork Corporation]. The

volumetric composition of this material, based on borehole data from the Lee Tunnel location

[5] was: gravel 2%, sand 37% and silt/clay 61%.

Thus, approximately 6.73*106m

3 of material has been dumped at the site since 1978, 80.4%

of which was silt/clay, 19% sand and 0.6% gravel.

Archaeo-Geophysical Survey 1999

In June 1999, a marine geophysical survey [2] was conducted by IHD on the dredge

spoil disposal site. The survey consisted of sidescan sonar and magnetometry and

its purpose was to establish if artefacts of archaeological significance were present in



the area. As part of the reporting for that survey, the sidescan sonar data was

interpreted and a map constructed showing the expanse of exposed bedrock and

areas with sediment cover (Figure 2). The sidescan data was recorded on paper roll

with position fixes marked automatically. The position data (on Irish National Grid

(ING)) was logged digitally to computer. The finished map was achieved by manual

digitisation of the sidescan records from the paper rolls.

Multibeam Survey (INFOMAR) Sept-Oct 2008

The INFOMAR (INtegrated Mapping FOr the Sustainable Development of Ireland’s

MARine Resource) programme is a joint venture between the Geological Survey of

Ireland (GSI) and MI and is the successor to the Irish National Seabed Survey

(INSS). As part of this programme, MI carried out a multibeam bathymetry and sub-

bottom profiling survey off the south coast which incorporated the Cork dredge spoil

disposal site. The survey was carried out between September 23rd and October 8th

2008. The data is available from MI in various formats. For this report the

bathymetric data was acquired in XYZ format and a shaded relief map produced

showing the expanse of exposed bedrock and areas with sediment cover (Figure 3).

The acquired datasets contained positions in LAT/LONG on WGS-84 datum with the

Z-values reduced to Lowest Astronomical Tide (LAT) on the Vertical Offshore

Reference Frame model (VORF). For comparison with the other surveys, the

position data was converted to ING. Sub-bottom profiler data was obtained in raw

digital Coda format and relevant parts within the disposal area were extracted and

converted into images (Section 4).

3. SURVEY OF NOVEMBER 2013

This took the form of a multibeam echosounding survey which identified the expanse

of areas within the disposal site which consist of exposed bedrock and surface

sediments. The Marine Institute survey vessel ‘Celtic Voyager’ was chartered and

the survey carried out on November 9th 2013 under the supervision of IHD. The data

was processed by IHD and a shaded relief map produced on ING (Figure 4). The

depth data was reduced initially to OD Malin using tide gauge data from Ballycotton.

Admiralty Tide Tables (ATT) indicates that there is a 2.58m difference between OD

Malin and Chart Datum (CD) at Cobh. It further indicates that LAT Cobh is 0.1m

below CD Cobh leading to a 2.68m difference between ODM and LAT at Cobh. This

offset was used to shift the 2013 survey levels to LAT for comparison with the survey

of 2008.



Figure 2 Survey of 1999 – Ground Type from Sidescan Sonar Interpretation



Figure 3 Survey of 2008 – Shaded Relief Map



Figure 4 Survey of 2013 – Shaded Relief Map



4. SHALLOW GEOLOGY

The INFOMAR 2008 sub-bottom profiler (pinger) survey trackplot covering the dump

area is presented in Figure 5. Survey lines were run in a SW-NE direction at

approximately 100m line spacing. A series of sub-bottom profile images from the

pinger records are presented in Figures 6 to 11. These have been chosen to pass

through various sediment covered areas and from survey lines run towards the north-

east from which data are better quality due to weather conditions.

The shaded relief plots, Figure 3 & 4, show exposed rock to be widespread. The

profiler data, Figures 6-11, show that the sediment infill layer is relatively thin.

Sediment thickness varies throughout the area typically being 1m and occasionally

up to 2m in localised areas.

Figure 5 INFOMAR Survey of 2008 – Sub-bottom profiler tracklines.



Figure 6 Sub-bottom profiler image - Fix 26832-26834

Figure 7 Sub-bottom profiler image - Fix 26397 -26398



Figure 8 Sub-bottom profiler image - Fix 22979 – 22980

Figure 9 Sub-bottom profiler image - Fix 20751-20753



Figure 10 Sub-bottom profiler image – Fix 22543-22544

Figure 11 Sub-bottom profiler image – Fix 23834-23836



5. DISCUSSION

Table 2 lists the quantities of dredged material dumped at the site since 1978

(source: Port of Cork company). A combined total of 6.73*106m3 of dredged material

was dumped there between 1978 and 1999. This originated from a combination of

capital and maintenance dredging programmes.

Year Quantity (m3)

1978 – 1999* 6,730,000

2000 149,854

2003 441,931

2005 133,979

2008** 253,848

2011 272,075 Table 2 Quantities dumped at site

* Dumping in the years prior to 1996 was allowed in the large site (Figure 1) and was limited to the smaller site after that time. ** Dumping in 2008 took place in Aug/Sept, before the survey period of Sept. 23rd to Oct 8th.

Between 1995 and 1998, dumping rates were approximately 65,000m3 per annum

[1]. Thus, if we consider the years up to 1996, a total of 6,535,000m3 (6,730,000 – (3

x 65,000)) was dumped over the large site. Assuming a uniform distribution pattern

of dumping, this amounts to approximately 3,031,000m3 being dumped in the

reduced dump site during those years. So prior to 1999, approximately 3,226,000m3

of dredged material was dumped in the reduced site. A total of 979,612m3 was

dumped during the years 2000 to 2008 (before the survey of Sept./Oct. of that year)

and a total of 272,075m3 was dumped in the period after the survey of 2008.

The outline of the rock/sediment areas as interpreted in 1999 from the sidescan

sonar survey (Figure 2) shows that a substantial area consisted of bedrock. This

survey can be considered as a baseline for comparison with later surveys. It should

be noted though, that interpretation of the sidescan data is not as precise as that

from the later multibeam surveys. This is due to sidescan towfish layback and offset

from the survey line not being precisely known. Also, the sidescan record was

digitised manually from paper roll which by its nature is less accurate than the later

processing methods associated with multibeam data.

Between 1999 and the survey of 2008, some 979,612m3 of material was dumped at

the site. The outline of the rock/sediment areas as interpreted from the sidescan

sonar survey of 1999 is shown superimposed on the shaded relief map from the



multibeam survey of 2008 in Figure 12. Given the difference in accuracies and

precision of the survey methods there is good agreement between them. The main

apparent area of difference is a roughly triangular area located between 53500mN

and 53700mN and from the western boundary to about 188600mE. This appears as

an area of sediment in 2008 but was not mapped as such in 1999. No firm

conclusions regarding accumulated material should be drawn from this in view of the

inherent lack of comparative precision and the subjective nature of the sidescan

interpretation process.

Between the multibeam surveys of 2008 and 2013, some 272,075m3 of material was

dumped at the site. A visual comparison of the shaded relief maps from the surveys

of 2008 (Figure 3) and 2013 (Figure 4) shows little or no change in the expanse of

sediment on the seabed surface within the dump site between those years. For

completeness, Figure 13 shows the outline of the rock/sediment areas as interpreted

from the sidescan sonar survey of 1999 superimposed on the shaded relief map from

the multibeam survey of 2013.

A more rigorous comparison of the surveys of 2008 and 2013 was undertaken by

comparing depth profiles. Digital Terrain Models (DTM) were created for each

survey and profiles extracted along the lines shown in Figure 14. The profiles are

presented in Figures 15 to 19 and show no appreciable difference between the

surveys of 2008 and 2013.



Figure 12 Survey of 2008 – Shaded Relief Map, with 1999 data overlain



Figure 13 Survey of 2013 – Shaded Relief Map, with 1999 data overlain



Figure 14 Profile Line Locations



Figure 15 Profile Lines 1 to 3 (2013 in Red – 2008 in blue)















6. CONCLUSIONS

In the years 1978 to 1999, approximately 3,226,000m3 of dredged material was

dumped in the reduced dump site area. A total of 979,612m3 was dumped during

the years 2000 to 2008 (before the survey of Sept./Oct. of that year) and a total of

272,075m3 was dumped in the period after the survey of 2008.

A comparison of the interpretation of the sidescan survey of 1999 with the shaded

relief map from the multibeam survey of 2008 (almost 1 million m3 of material

dumped during this period) would not indicate any major accumulation of dumped

material to have occurred during that nine year period.

A comparison of the shaded relief maps from the surveys of 2008 and 2013 (over

272,000m3 of material dumped during this period) shows little or no change to

bathymetry to have taken place during that five year period. This is borne out by

comparison of depth profiles from these surveys.

The dump site consists mainly of exposed bedrock with patches of sediment.

Geophysical survey data from the INFOMAR survey of 2008 shows the sediment

thickness to be typically about 1m, occasionally reaching 2m.



REFERENCES

1. Cork Dredge Spoil Disposal Site Impact Hypothesis

Irish Hydrodata Ltd

1999

2. Cork Dredge Spoil Disposal Site Archaeo-Geophysical Survey

Irish Hydrodata Ltd

1999

Cork Dredge Spoil Disposal Site – Video And Benthic Grab Survey And

Impact Hypothesis

(September 2004)

Commissioned by: RPS – Kirk McClure Morton Carried out by: Aquatic Services Unit and Seabed Surveys International Ltd. (November 2004)

Introduction & Brief The Aquatic Services Unit (ASU) was commissioned by RPS-Kirk Mc Clure Morton, to undertake an assessment of the impact of the disposal of Cork Harbour dredge spoil (from the proposed Cobh Liner Turning Circle). In undertaking this ASU agreed to take benthic grab samples inside and adjacent to the proposed dumpsite and invited Seabed Surveys to undertake a video survey and interpretation of the general area of the bottom, the first to have been undertaken at the site. Fieldwork was undertaken on September 24th 2004. ASU were also requested to report on the commercial fisheries activities in the dumpsite and potential impacts. The Port of Cork Dump Site - Background The current dumpsite is a reduced version of the original dumpsite which has been in operation on a more or less continuous basis since 1978, having received by 2000 almost 7 million cubic metres of spoil from a combination of capital dredging and maintenance dredging operations. The most recent use of the dumpsite was for the disposal of ~300,000 m3 of soil from maintenance of the various shipping channels and wharf areas from Cork City to the Ringaskiddy and Cobh area. The original dumpsite was 3.0km x 2.8m, whereas the current site is reduced to about 47% of that (i.e. 1.4km x 2.8km). The current dumpsite was adopted in 1998 and is effectively the eastern ‘half’ of the original site. Table 1 presents the co-ordinates of this site.

Original Dumpsite Current Dumpsite 51° 43.00’ N 8 11.55’W 51° 43.00’ N 8 10.18’W 51° 43.00’ N 8 09.00’W 51° 43.00’ N 8 09.00’W 51° 44.50’ N 8 11.55’W 51° 44.50’ N 8 09.00’W 51° 44.50’ N 8 09.00’W 51° 44.50’ N 8 10.18’W

Table 1 Coordinates of the original Port of Cork Dumpsite and the Current Site Current disposal policy is to dispose of the spoil in the northern and southern sectors of the dumpsite. Thus a dredger would dispose of its load in the northern and southern halves of the dumpsite on alternate dumping runs. This is designed to maximise the spread of spoil within the site. The Quality of the Disposed Spoil – Past and Present The spoil which has been disposed at the site has varied significantly both in quantity and quality over the years and one can take it that, in general, capital dredging has resulted in the disposal of materials with higher coarse fractions (sand and gravel) and lower contaminant loads than spoil arising from maintenance dredging. The latter tends to have a significantly proportion of the finer silt/clay fraction (i.e. 70-80%), higher organic carbon and higher levels of heavy metal and organic contaminants. However, even

Aquatic Services Unit – Cork Dredge Spoil Disposal Site Benthic & Video Survey (2004) Version 1.0

2

within the latter there is a spread of composition with the material taken from the vicinity of the Cork City wharves having more elevated levels of contaminants than material dredged from elsewhere in Lough Mahon and the lower harbour areas. In the past these have included metals such as chromium, copper, lead, zinc and mercury as well as PAH’s. The current dredge-spoil is being excavated where there hasn’t been a record of elevated contaminant levels in the past and apart from a few outliers in the data, the trace metal and organic contaminant loads tend to be on the lower end of the contaminant ranges reported in the literature as causing adverse biological impacts (Long et al. 1995). Materials and Methods. General The video and grab surveys were carried out on the same day (24th September 2004) from the same, chartered vessel. Video Survey An NVD-FS Underwater Video Camera System was used to record footage of the seabed sediments, flora and fauna. The number of the site being surveyed was written on a clipboard and recorded on video before recording any seabed footage in order to ensure that each site was clearly identified on the video. The camera was lowered to the seabed on a rope using a derrick and the vessels position was recorded using a Trimble DGPS as soon as the camera hit the bottom. The water depth at each site was obtained using the Furuno echo sounder on board the vessel. Approximately 10 to 20 minutes of seabed footage was recorded at each site. When sufficient footage was collected the vessel’s position was recorded when the camera was hauled off the seabed. Both the “in” and “out” positions for the camera were recorded on an electronic charting and plotting sotware package, Microplot™, and also on the data sheets (Figures 1-3). The recorded footage was then transferred from mini-DV tapes to videocassettes for further biological analysis. The nature of the substrate, flora and fauna, interesting habitats or commercial species present are presented in the results. Grab Survey Benthic grab samples were taken by means of a 0.1m2 Stainless Steel Day Grab. At each of the sampling stations within the dumpsite box (S1-S5), three replicate samples were taken. At each of the stations outside of the dumpsite box, single grabs were taken. At each of the sampling stations a single sample (~ 40g) for grain size and organic matter was sub-sampled from one grab-sample. All samples were sieved through a 1.0mm mesh-sieve on board, fixed in saline formalin (10%) and stained with Rose Bengal. All samples were sorted by eye and preserved in 70% ethanol. The position, depth and time of each grab position were recorded and are presented in Table 2 and Figure 4 shows their positions relative to the dumpsite box. No grab samples were taken along the western and northern approaches to the dumpsite box because of the


3

hard nature of the substrate at all locations sampled. Video footage was taken at all these locations.

Time (UST) Latitude Longitude Depth (m) P1a 09:50:03 51° 43.7651’ N 8° 09.6255’ W 39 P1b 10:16:18 51° 43.7433’ N 8° 09.6001’ W 39 P1c 10:48:21 51° 43.7373’ N 8° 09.6074’ W 39 P2a 11:12:48 51° 44.2844’ N 8° 09.5774’ W 35 P2b 12:21:14 51° 44.2190’ N 8° 09.5370’ W 35 P2c 12:38:57 51° 44.2406’ N 8° 09.5387’ W 35 P3a 13:09:54 51° 43.7379’ N 8° 08.9921’ W 30 P3b 13:36:16 51° 43.7222’ N 8° 08.9746’ W 45 P3c 13:53:14 51° 43.6940’ N 8° 08.9671’ W 36 P4a 14:27:57 51° 43.1949’ N 8° 09.5152’ W 49 P4b 14:40:24 51° 43.1908’ N 8° 09.5764’ W 46 P4c 14:48:44 51° 43.1887’ N 8° 09.5650’ W 47 P5a 15:29:50 51° 43.7468’ N 8° 10.1199’ W 35 P5b 15:35:15 51° 43.7641’ N 8° 10.0877’ W 34 P5c 15:41:06 51° 43.7750’ N 8° 10.0635’ W 32 P6 17:19:01 51° 43.6416’ N 8° 08.4346’ W 46 P7 17:31:07 51° 43.8203’ N 8° 07.5167’ W 45 P8 18:17:11 51° 43.9194’ N 8° 08.0781’ W 45

1 Table 2: Positions and depths of successful grab sampling stations


4

Figure 1 Camera positions used in the Cork Dumpsite Survey (September 2004)

Figure 2 Camera positions around the Cork Dumpsite Survey (September 2004)


5

Figure 3 Camera positions around the Cork Dumpsite Survey (September 2004)

N

1km

P1

P2

P3

P4

P5

P6

P7P8

Figure 4 Grab positions around the Cork Dumpsite Survey (September 2004)


6

Results – Video Survey General Comment The following section describes the twelve video camera sites in terms of habitat present and fauna visible. It is not possible to describe the biological communities present on the video footage in great detail, as no infaunal grab data was available at the time of analysis for the sedimentary sites and where the rocky habitat is concerned a dive survey would be required to positively identify species present. However, where possible, species names have been listed in brackets where they were clearly identifiable from the video footage. Text in square brackets and italics was added by G. Morgan (ASU) having viewed the video footage. Frame grabs from the video survey are presented in Appendix 1 of this report. Camera 1 (Plate 1.1-1.4 Appendix 1) Depth: 39m. Habitat: Three different habitats were visible at this site. Initially the habitat is muddy mixed sediment of muddy sand/mud with shell debris and pebbles which then changes to silted bedrock and boulders on a muddy plain. Species: Crabs are the only fauna visible on the sedimentary habitats. The muddy plain has many large and small burrows and feeding holes. The rocky habitat supports a sparse faunal community of cup corals (Caryophyllia smithii), starfish (Asterias rubens), hydroids and bryozoans. [Many small crabs were visible in places in areas of soft sediment with burrows] Camera 2 (Plate 2.1-2.2 Appendix 1) Depth: 35m. Habitat: Muddy mixed sediment of mud/muddy sand with some shell, cobble and pebbles, which then grades into an area of rippled muddy sand. Species: No fauna were visible at this site, however many faunal burrows and feeding holes are evident. [Occasional small crabs were visible, apparently using burrows] Camera 3 (Plate 3.1-3.4 Appendix 1) Depth: 30m. Habitat: Silted bedrock with small areas of muddy sand. Species: The rocky habitat supports a faunal community of urchins (Echinus esculentus), encrusting sponges and cup corals (C. smithii). No fauna are visible on the sedimentary habitat.


7

[The bedrock was formed in places into step-wise ledges. The encrusting faunal elements were scattered to frequent over the hard substrate as were Echinus urchins; including those mentioned above hydroids were also in evidence. There were several small shoals of fish evident in the area. These were wrasse-like species, which closely resembling Goldsinny Wrasse and Cuckoo Wrasse (females) Camera 4 (Plate 4.1-4.4 Appendix 1) Depth: 45m. Habitat: Heavily silted bedrock this gives way to muddy gravel with boulders and finally muddy gravel dunes. Species: Fauna visible on the rocky habitat includes urchins (E. esculentus), starfish (A. rubens) and cup corals (C. smithii). Hermit crabs, burrowing polychaetes and one burrowing sea cucumber (similar to Neopentadactyla mixta) are visible in the sedimentary habitat. [Several fish are visible in this area including gadoid-like species (possibly Pollack) as well as wrasse-like species (Goldsinny). Also visible, on the bottom, were goby-like or cottid-like species (2 individuals)] Camera 5 (Plate 5.1-5.2 Appendix 1) Depth: 49m. Habitat: Mud plain with a heavily silted area of bedrock. Species: Numerous faunal burrows and feeding holes are visible on the muddy habitat, while a sparse fauna of cup corals (C. smithii) and starfish (Luidia sp.) occur on the rocky habitat. [A small lobster is visible retreating into a hole in the bedrock] Camera 6 (Plate 6.1 Appendix 1) Depth: 35m. Habitat: Muddy mixed sediment of muddy sand/mud with shell and pebbles, which then grades into a plain of muddy sand. Species: No fauna visible on these sedimentary habitats only burrows and feeding holes.


8

Camera 7 (Plate 7.1-7.2 Appendix 1) Depth: 34m. Habitat: Silted cobbles and pebbles with scattered large boulders and rocky outcrops. Species: The rocky habitat of boulders and bedrock support a sparse fauna of urchins (E. esculentus), starfish (A. rubens), brittlestars, hydroids and bryozoans. Brittlestars and spider crabs are visible on the cobble and pebbles. [A wrasse-like species is visible also in this transect (?Goldsinny)] Camera 8 (Plate 8.1-8.2 Appendix 1) Depth: 32m. Habitat: Silted bedrock, boulders, cobbles and pebbles. Species: The rocky habitat supports a faunal community of urchins (E. esculentus), brittlestars, sponges, hydroids/bryozoans, starfish (A. rubens) and faunal crusts. Camera 9 (Plate 9.1 Appendix 1) Depth: 46m. Habitat: Silted bedrock. Species: The only fauna visible from this poor footage are starfish (A. rubens) and urchins (E. esculentus). Camera 10 (Plate 10.1 Appendix 1) Depth: 47m. Habitat: Heavily silted bedrock and boulders with small areas of muddy gravel. Species: Fauna present include starfish (A. rubens), urchins (E. esculentus), brittlestars and cup corals (C. smithii). [A prawn (Nephrops) is visible in this shot retreating into a burrow and unidentified macro-crustacean (bigger than a prawn and smaller than a lobster) retreating under a small rock ledge. Occasional large protruding tubes are visible in the sedimentary areas and one wrasse-like fish] Camera 11 (Plate 11.1 Appendix 1) Depth: 45m. Habitat: Muddy gravel dunes. Species: No fauna visible.


9

Camera 12 (Plate 12.1-12.2 Appendix 1) Depth: 30m. Habitat: Silted cobbles, pebbles and boulders on muddy gravel. Species: Sparse fauna visible includes starfish (A. rubens), urchins (E. esculentus), crevice dwelling sea cucumbers, hydroids and bryozoans. Some encrusting algae and fauna also present. Video Survey – Conclusion The epifaunal communities recorded from the video are: 1 Typical of rocky habitats, species recorded are common and often widespread on

rocky habitats 2 The faunal community visible at the video sites was low in terms of diversity and

abundance, however this is no indication of pollution or otherwise in the area. Would have to know what type of community was there before the dumping commenced in order to comment on the significance of the community now present.

3 The species recorded cannot be used to give any indication as to the presence or absence of dump site nearby

The muddy and sandy habitats did not support an extensive faunal community on the surface. However, there was substantial evidence on the surface that an extensive infaunal habitat was present i.e. burrows and mounds. The grab samples taken would give a more detailed picture of what is present at these sites. [It was clear from the camera shots in every part of this study area that the seabed comprises a mosaic of many different habitats including jagged, step-like ledged bedrock, low moulded bedrock, gravel, cobbles, boulders and silted coarse sandy gravel and muddy sand or mud over sand. The key point however, it that no one habitat predominates within the whole area and most camera drops revealed a range of habitats. Some of the hard substrate areas had a fair dusting of silt, which was thick in places and some areas had extensive mud patches but there wasn’t any obvious indication that soft sediment had built up anywhere ] Results – Grab Survey Across the 8 stations sampled (P1-P5 inside the site and P6-P8 outside and to the east), a total of 60 taxa were identified. A full listing of these is presented in Appendix 2. The majority of these were taken to family level, although Nematoda and Nemertea were left as higher taxa.


10

Several burrowing anemones were encountered at several stations; these were identified as Peachia cylindrica. This identification must remain tentative, however, as it was based on a single extended individual and it remains possible this taxon belongs to the Edwardsiidae. Most families (and their constituent species) are of widespread occurrence in Irish waters. A notable exception is Chaetoderma nitidulum (family Chaetodermatidae), a rarely recorded burrowing mollusc, whose distribution in Irish waters is uncertain. Although only family level data are presented and analysed, in several cases more than one species per family was present. This does not unduly influence the results, however, as on the whole species within a family have similar, if not equal, responses to impact levels. Benthic Infauna - Discussion Figure 5 presents an ordination of the family matrix, using mean values for the stations at which three replicates were obtained. Stations P1 and P8 clearly separate from the remaining stations, which form a relative loose grouping, with a smaller separation of stations P4 and P5. Further analysis excluding stations P1 and P8 did not reveal any more detailed groupings (not presented). The underlying reason for the separation of station P1 relates to the numerical dominance of Capitellidae (exclusively composed of Capitella capitata, a known indicator of disturbance), which reach high numbers in two of the three replicas. This is further exemplified by the low familial diversity at this station, with a mean Shannon-Wiener index of 0.71, contrasting to values of 2.50-3.00 at the other stations. Nevertheless a cursory examination of Appendix 2, reveals that a healthy community is still present, as a significant proportion of families present in the other stations still occurs at Station P1. Furthermore, overall family levels are not depleted, as 25 families were present, compared to an average of 24 families at the other stations. It should also be pointed out that one of the replicates (P1A) harboured far lower densities of Capitella, and in all likelihood, the high densities are a remnant of a past disturbance event (i.e. dredge spoil dumping), which is known to induce patchiness in benthic communities. It is less clear why Station P8 separates out from the other stations, but this is more than likely linked to the high densities of the polychaet families Onuphidae and Phyllodocidae, that only occur in low densities at the other stations. An additional factor contributing to this separation may be linked to the granulometry at station P8, which contained higher levels of coarser material. Stations P4 and P5 harbour a slightly different mix of taxa and a different numerical combination of constituent taxa, which causes a small separation of these stations, away from the remainder of stations. These differences are best interpreted as patchiness in the community, rather than a separate community. Overall, it can be concluded that the benthic community present at the dumpsite belongs to a single distinct community, on top of which is overlain a mosaic of small-scale spatial differences, resulting in differential taxon presence and numerical abundance.


11

Table 3 Granulometry figures for Cork Dump Site Grab Samples (Sept 24th 2004)

Grab Sites Fraction Grain Size (%) P1 P2 P3 P4 P5 P6 P8 % GRAVEL* <2 mm 69.9 28.7 53.1 3.9 1.5 2.8 29.9 % SAND 2 mm-0.63 mm 29.7 28.2 28.6 69.0 87.2 95.3 69.9 % MUD <0.063 mm 0.4 43.1 18.3 27.1 11.3 1.8 0.2 * All fine gravel Although the Dump Site has been in use for several years, and undergoes a disturbance event nearly every year, (the most recent being July of 2003) due to dumping of dredge spoil, it seems that the site is acting as a dispersive site, with little evidence of organic enrichment and prolonged disturbance. Although, high densities of potential organic enrichment indicators (Capitella capitata) were encountered at two replicate grabs from station P1, and although smaller abundances of this species and other taxa which indicate disturbance (esp. Lumbrineridae) were present, it seems plausible that these isolated patches are remnants of past dumping effects, rather than indicative of a more prolonged degradation in community health. This may be supported by the fact that (i) the two replicates in question (P1B and P1C) were only separated by 10m, with the third replica (P1A) harbouring far lower densities (of Capitella) was separated by 50m and (ii) that although disturbance taxa are present at other stations, their numbers tend to be low and highly variable, again indicative of spatial patchiness.


12

P1

P2P3

P4

P5

P6

P7

P8

Axis 1

Axi

s 2

Figure 5 Detrended Correspondence Analysis of family level data


13

Impact Hypothesis Dumping of dredge spoil has several effects on benthic communities, both short and longer term, which at dispersive sites results in a mosaic of effects and ensuing communities. The immediate effect of dumping will be that the resident community will be smothered with finer sedimentary material, which will not necessarily result in all species becoming obliterated, as the majority of taxa in the community exhibit good mobility (based on family level identifications) and they may be able to burrow upwards, perhaps with the proviso that the thickness of the deposited material is not too great in any single deposition. This will be aided by the high dispersion of the deposited material, as indicated by the dispersion model. Due to the prevailing currents at the site, this initial impact phase will be more concentrated along an E-W axis. Longer-term impacts can go in several directions, although the residual drift at the site is reported to be to the North and North East (Anon 1999). Based on the biology of the key species in this habitat (e.g. burrowing amphipods, polychaetes, molluscs) some brief hypothesis can be put forward. The biotope as a whole will have low sensitivity to smothering by sediment because most species are shallow burrowing and live within the upper layers of the sediment matrix. Numerous animals will be able to move up through the deposited sediment within hours or days so recovery can be quite immediate. Equally, most resident species are adapted to mobile sedimentary conditions and as such will be able quickly recolonise the surficial layers of the sediment matrix. However, small patches of locally enriched and/or disturbed fauna will remain for longer time scales, akin to the community observed at Station P1. Gradually over time, these faunal adjustments will diminish and the fauna will return to pre-impact status. Again, this process will be aided by the apparent dispersive nature of the site, as indicated by the dispersal model and the current fauna over much of the dumpsite Most sampled species in the biotope are burrowing infauna so will not be affected by an increase in suspended sediment, a frequent by-product of dumping. Some species may even benefit from increased food supply if the suspended sediment has a higher organic content. Overall species composition and richness is not expected to be affected. While, it is difficult to accept that the deposition of very significant amounts of spoil at the site can occur fairly frequently without some impact on the benthos, those impacts, based on the evidence of the current survey and a similar one previously undertaken by Neiland in 1993 (Neiland 1994?), appear not to be very significant. Neiland, in her survey (which incorporated the full area of the old dump site) also noted a wide range families (40) and good Shannon-Weiner Diversity index values (1.75-2.78) at all but one of the sites she sampled. She concluded:

‘The faunal composition of the sites sampled at the dredge spoil dumpsite compared favourably with sites outside the dumpsite. There was no indication of any build-up of deposited material. In conclusion, it can be


14

said that the present dumping operations at the site are not having a deleterious effect on the benthos’

RPS-KMM’s model indicates that the depositional rate across the dumps site will range from about 2cm to 6cm (assuming a bulk density of about 1 for the spoil). Neiland (1994?) quotes Essink et al (1992) as indicating that the survival of macrobenthic species (presumably infauna only) as being dependent both on the thickness and nature of the deposited material (e.g. mud or sand). They concluded that the fatal deposition depth for most macrobenthic was in excess of 10cm. This might suggest that the Cork Dumpsite is sufficiently dispersive to result in a thinner spread of spoil to allow for many macrobenthos to survive these deposits, which may account for the apparently rapid recovery rate at the site (i.e. within about 12months). Nevertheless, it would seem unlikely that some localised depletion in the fauna wouldn’t take place due to initially patchiness in the depth of the deposited soil. However, what may be happening is that these affects become evened out as the soil becomes more dispersed and the more impacted patches are re-colonised from the edges or from the plankton etc. Epifauna While, the infauna may be adapted at least on the community scale to cope with a degree of smothering, the epilithic fauna of sponges, bryozoans, cup-corals and hydroids may be more susceptible due to their sedentary or near-sedentary habit, especially in areas where locally heavy deposits of spoil occur on bedrock and other coarse materials and remain for extended periods. Indeed, the attached fauna on cobbles, boulders and bedrock was considered to have been rather sparse, despite the fact that species identifications were not possible in many cases. Nevertheless, most of the areas where bedrock or boulders were visible exhibited an epilithic community, indicating that despite the deposition, a distinctive range of taxa is supported in areas with suitable substrate. What we don’t know is whether the diversity and density in this community is being affected by the near annual dumping events in the area. Finally, the presence of a range of fish species and macrocrustaceans feeding in the area is probably also suggestive of a relatively diverse community in overall terms. Fisheries In terms of impact on the fish living in the dump, it is unlikely that the dumping has a significant impact on adult or even larval fish as fish can, by and large, avoid sediment plumes. There direct or indirect mortality (through gill disease or other aggravated condition) is likely to be relatively low as a result of the dumping. Some impact on demersal (bottom) laid fish eggs (e.g. of Cuckoo Wrasse) cannot be rule out, however, if these are present during the disposal period. At the population level however, such impacts are unlikely to be very significant as vacant fish niches are likely to be filled from adjacent areas and the patchiness of the dumping activities is likely to mean that and


15

mortalities of eggs would in any case also be patchy. It is suspected that herring spawn it that general area (as part of a much wider spawning area) during November and February. If spoil were dumped at either of these times then some localised egg mortality might occur. The eggs begin to float away after about two weeks so that after such a delay dumping would be unlikely to result in any damage to eggs. In terms of commercial the area of the dumpsite is clearly unsuitable for trawling because of it’s extensive exposed rock substrate, which would damage trawling gear and indeed this may have been one of the considerations for choosing the site originally. While it is possible that some shellfish potting (lobster & crab) could take lace at the site, traditionally the area is avoided because of it’s status as a dumping ground (pers. comm.. DCMNR, Cork). The DCMNR has not traditionally received any complaints about the dredge spoil dumping at the site over the years. Concluding Remarks The evidence of the current survey is consistent with several undertaken previously at the site which report that the dredge spoil disposal site comprises a mosaic of coarse substrate habitats including much bedrock and that deposited dredge spoil appears to disperse widely away from the site rather than build up within it. Also, while there is some evidence of disturbance and organic enrichment at some sites within the infaunal benthic community, diversity levels were not consistent with significant degradation at any of the sites sampled. The epifauna of the hard substrates although apparently sparse, is nevertheless distinctive. However, there is insufficient known about this community in the area generally to say with confidence whether it is being impacted by the disposal activities at the site currently. While this survey identifies no obvious adverse impacts from the disposal activities, it cannot rule a wider and more subtle ecological affect e.g. increased productivity due to the introduction of large amounts of organic carbon, or subtle shifts in species compositions and in diversity in certain areas due the addition of large amounts of organic matter-rich fines into the local environment. Recommendations Dumping should if feasible avoid herring spawning times in November and February


16

References Anon (1999) Cork dredge spoil disposal site – Impact hypothesis. A report for Port of

Cork Company and Cork Corporation by Irish Hydrodata Ltd. (March 1999)

Essink, K., Steyaert, F.H.I.M., Mulder, H.P.J., De Joneg, V.N., Van Heuval, T. & J. Van

Den Bergs. (1992) Effects of dredging activities in the Ems Estuary and the Dutch Wadden Sea. Netherlands Institute for Sea Research. Publcations Series No. 20.

Long, E. R., Macdonald, D. D., Smith, S. L., Calder, F. D. (1995). Incidence of Adverse

Biological Effects Within Ranges of Chemical Concentrations in Marine and Estuarine Sediments. Environment Management. 19 (1), 81-97.

Neiland, S (1994?) Cork Harbour: Monitoring the Benthic Environment. (Department of

Marine, Fisheries Research Centre, Abbotstown, Dublin 15.


17

Appendix 1 Video Survey Frame-Grabs


18

Plate 1.1 Habitat of muddy sand/mud with shell and debris taken from Camera 1

Plate 1.2 Habitat of pebbles and silt taken from Camera 1


19

Plate 1.3 Habitat of silted bedrock with cup corals visible taken from Camera 1

Plate 1.4 Habitat of muddy plain with large burrows taken from Camera 1.


20

Plate 2.1 Muddy mixed sediment taken from Camera 2

Plate 2.2 Rippled muddy sand with burrows taken from Camera 2


21

Plate 3.1 Silted bedrock with cup corals and encrusting sponges taken from Camera 3

Plate 3.2 Urchin on silted bedrock taken from Camera 3


22

Plate 3.3 Bedrock with a patch of muddy sand, cobbles and pebbles taken from Camera 3

Plate 3.4 Muddy sand with pebbles and burrows taken from Camera 3


23

Plate 4.1 Heavily silted bedrock taken from Camera 4

Plate 4.2 Muddy gravel with cobbles and boulders taken from Camera 4


24

Plate 4.3 Starfish and cupped corals on silted boulders taken from Camera 4

Plate 4.4 Muddy gravel taken from Camera 4


25

Plate 5.1 Mud plain with faunal burrows taken from Camera 5

Plate 5.2 Heavily silted bedrock with cup corals taken from Camera 5


26

Plate 6.1 Mud/muddy sand with burrows taken from Camera 6

Plate 7.1 Urchin on silted boulders and cobbles taken from Camera 7


27

Plate 7.2 Brittlestars on bedrock taken from Camera 7

Plate 8.1 Urchins and faunal crust on bedrock taken from camera 8


28

Plate 8.2 Brittlestars on bedrock and cobbles taken from camera 8

Plate 9.1 Urchin on silted bedrock taken from Camera 9


29

Plate 10.1 Heavily silted muddy gravel taken from Camera 10

Plate 11.1 Muddy gravel taken by Camera 11


30

Plate 12.1 Encrusting algae and fauna on a boulder taken from Camera 12

Plate 12.2 Silted cobbles, pebbles and boulders taken from Camera 12


31

Appendix 2 Benthic Infaunal Families P1A P1B P1C P1 P2A P2B P2C P2 P3A P3B P3C P3 Acteonidae Ampeliscidae 6 3 5 4.67 1 5 1 2.33 7 6 1 4.67Ampharetidae 2 0.67 0.00Amphiuridae 1 3 1.33 1 0.33 4 2 2.00Aoridae 2 4 1 2.33 2 0.67 1 0.33Atylidae 2 0.67 0.00 0.00Bathyporeidae Calianassidae Capitellidae 75 500 600 391.67 10 2 4.00 62 20.67Cardiidae 6 2.00 2 0.67 5 6 3.67Chaetodermatidae Cirolanidae 1 0.33Corbulidae 4 1 1.67 0.00 8 2 3.33Crangonidae 1 0.33 0.00Diastylidae 1 1 3 1.67 1 1 0.67Fibulariidae Glyceridae 7 7 5 6.33 3 5 1 3.00 1 2 1 1.33Goneplacidae Goniadidae 1 0.33Haloclavidae 1 0.33 5 16 2 7.67 1 0.33Haustoriidae Hiatellidae 1 0.33 3 1 1.33 0.00Leptonidae 1 0.33 0.00 0.00Leuconidae Lumbrineridae 35 45 26.67 8 10 1 6.33 33 11.00Magelonidae 1 1 0.67 0.00Maldanidae Montacutidae 1 0.33 0.00Naticidae 1 0.33 0.00Nematoda Nemertea 1 0.33 1 0.33 2 1 1.00Nepthyidae 3 5 2.67 2 14 5.33 1 1 0.67Nereididae Nuculidae 3 2 1.67 0.00 1 3 1.33Oedicerotidae Onuphidae Oweniidae 4 1.33

Appendix 2 contd: Benthic Infaunal Families P1A P1B P1C P1 P2A P2B P2C P2 P3A P3B P3C P3 Pectinariidae 1 1 0.67 2 0.67 1 0.33Pholoidae 4 1 2 2.33 1 0.33 1 0.33Phoxocephalidae 2 0.67 1 0.33Phyllodocidae 3 1 2 2.00 2 3 1.67 0.00Poecilochaetidae 1 0.33Polynoidae 1 0.33 0.00Portunidae 2 1 1.00 0.00 1 0.33Priapulidae 1 0.33 0.00 0.00Processidae Pyramellidae 1 0.33 0.00 0.00Sabellidae Scalibregmatidae 1 2 1.00 37 12.33 4 26 1 10.33Scaphandridae 1 0.33 1 2 1.00Scrobicularidae 1 0.33 3 1.00Sigalionidae 1 1 0.67 4 1.33 1 0.33Solenidae Spatangidae Spionidae 7 2.33 2 0.67 5 4 3.00Syllidae 2 0.67Terebellidae 2 0.67 8 2.67 2 0.67Thyasiridae 4 1.33Upogebiidae 1 0.33 0.00Veneridae 1 1 0.67 1 0.33


33

Appendix 2 contd: Benthic Infaunal Families P4A P4B P4C P4 P5A P5B P5C P5 P6 P7 P8 Acteonidae 2 0.67 0.00 Ampeliscidae 0.00 3 2 7 4.00 8 2 2Ampharetidae 1 1 2 1.33 2 1 1.00 2 1 Amphiuridae 2 0.67 0.00 1 Aoridae 0.00 0.00 Atylidae 0.00 0.00 Bathyporeidae 1 0.33 Calianassidae 1 2 1.00 0.00 Capitellidae 2 0.67 0.00 9 3 4Cardiidae 3 4 2 3.00 1 0.33 1 1Chaetodermatidae 1 0.33 0.00 Cirolanidae 0.00 0.00 Corbulidae 1 10 1 4.00 1 1 0.67 Crangonidae 0.00 0.00 Diastylidae 2 2 1.33 0.00 Fibulariidae 2 1 Glyceridae 4 2 2.00 3 1 1.33 1 3 5Goneplacidae 1 0.33 0.00 Goniadidae 0.00 0.00 Haloclavidae 0.00 1 3 1.33 1 Haustoriidae 2 Hiatellidae 1 0.33 0.00 Leptonidae 2 0.67 0.00 Leuconidae 1 1 0.67 0.00 Lumbrineridae 1 1 2 1.33 3 1 1.33 2 Magelonidae 1 2 1.00 1 1 0.67 Maldanidae 1 0.33 0.00 Montacutidae 1 0.33 0.00 1 Naticidae 0.00 0.00 1 1 1Nematoda 2 12Nemertea 3 1.00 2 0.67 1 Nepthyidae 6 4 1 3.67 12 14 6 10.67 2 2 Nereididae 1Nuculidae 1 3 8 4.00 1 1 1 1.00 1 1Oedicerotidae 1 0.33 2 1 1.00 Onuphidae 2 3Oweniidae 0.00 0.00


34

Appendix 2 contd: Benthic Infaunal Families P4A P4B P4C P4 P5A P5B P5C P5 P6 P7 P8 Pectinariidae 1 0.33 1 1 0.67 Pholoidae 0.00 0.00 1 1Phoxocephalidae 3 1.00 0.00 Phyllodocidae 1 0.33 1 0.33 3 15Poecilochaetidae 2 0.67 3 1.00 1 Polynoidae 0.00 0.00 Portunidae 0.00 0.00 1 1Priapulidae 0.00 0.00 Processidae 1 0.33 0.00 Pyramellidae 0.00 0.00 Sabellidae 3 Scalibregmatidae 5 1 2.00 0.00 9 1 Scaphandridae 5 1.67 0.00 1 Scrobicularidae 7 9 5 7.00 2 1 1.00 1 Sigalionidae 0.00 1 0.33 Solenidae 1 2 1.00 0.00 Spatangidae 1 0.33 Spionidae 1 3 1.33 1 2 1.00 1Syllidae 0.00 0.00 3Terebellidae 0.00 1 1 0.67 2 2Thyasiridae 10 5 4 6.33 1 0.33 Upogebiidae 0.00 0.00 Veneridae 5 4 1 3.33 3 2 1.67 2


35

Documents

Attachment E.2 (i) Characteristics of the Dumping Site ... · PDF filePOC Maintenance Dredging ... Admiralty Tide Tables ... the sidescan record was digitised manually from paper roll