Cefas contract report: ME5403 Module 7

Project ME5403

Applied science to support the licensing of dredging,

disposal, renewables and general construction and

associated monitoring under FEPA, CPA and the future

Marine Act

Module 7 – Application and development of Sediment

Profile Imagery (SPI)

Authors: Silvana Birchenough, Ruth Parker, Thi Bolam, Claire

Mason, Jon Barry and Silke Kröger.

Issue date: 7th June 2013

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Cefas Document Control

Application and development of Sediment Profile Imagery

Submitted to: The Marine Management Organisation (MMO) and The Department of

Environment, Food and Rural Affairs (Defra)

Date submitted: 07/06/13

Project Manager: Sonia Kirby & Clare Powell

Report compiled by: Silvana Birchenough, Ruth Parker, Thi Bolam, Claire Mason, Jon Barry and

Silke Kröger

Quality control by: Chris Vivian

Approved by & date: Jan Brant

Version: 5

Version Control History

Author Date Comment Version

Silvana Birchenough 17/05/13 Draft 1

Chris Vivian 22/05/13 QA comments 2

Thi Bolam & Ruth Parker 22/05/13 Comments 3

Silvana Birchenough 23/05/13 Editorial changes & text 3a

Jan Brant 31/05/13 Comments 3b

Silvana Birchenough 04/06/13 Edits 4

Jan Brant 04/06/13 Final QA 5

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Application and development of Sediment Profile Imagery

Silvana Birchenough, Ruth Parker, Thi Bolam, Claire Mason, Jon Barry and Silke Kr

Head office

Centre for Environment, Fisheries & Aquaculture Science

Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK

Tel +44 (0) 1502 56 2244 Fax +44 (0) 1502 51 3865

www.cefas.defra.gov.uk

Cefas is an executive agency of Defra

Application and development of Sediment Profile Imagery

Authors:

a Birchenough, Ruth Parker, Thi Bolam, Claire Mason, Jon Barry and Silke Kr

Issue date: 07 June 2013

Centre for Environment, Fisheries & Aquaculture Science

Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK

44 Fax +44 (0) 1502 51 3865

Cefas is an executive agency of Defra

5

Application and development of Sediment Profile Imagery

a Birchenough, Ruth Parker, Thi Bolam, Claire Mason, Jon Barry and Silke Kröger

0

Executive Summary

The aim of this module was to collect parallel information with SPI technology and DGT gels (passive

samples) to enable a further vertical characterisation of sediments in a dredged material disposal

site. This is the first time that the two techniques have been used at Cefas to monitor an area

subjected to dredged material disposal, which in this case was Souter point disposal site. The specific

aims were to assess: i) the utility of these techniques, ii) the logistics of testing and employing the

combination of techniques (SPI and DGT gels), iii) the speed of data return from these two

techniques and iv) the value of SPI and DGT gels as complementary techniques to provide additional

capability into a existing monitoring context and v) if the data generated from these two techniques

could support a cost-effective survey.

The collection of good quality SPI images made possible a rapid assessment of the status of an area

based on the calculation of the following biological and physical parameters:

1) surface sediment type (measured from the upper 5 cm sediment layer);

2) prism penetration depth (gives an indication of relative sediment compaction;

3) sediment boundary roughness (indicates the degree of physical disturbance or biotic activity

at the sediment water boundary) and sediment apparent redox potential discontinuity

depth (aRPD) (is the gradient of colour change between paler oxidized surficial sediments

and darker reduced sediment at depth).

Additionally, the use of the DGT gels allowed mapping depth profiles of various metals within the

sediments in the disposal site. The higher resolution provided by the DGT gels provides insight into

metal specific resupply and behaviour within disposal site sediments. It highlighted the comparative

availability of metals in sediment pore-waters and provides new information on whether sediments

are acting as a source/sink for metals. A modelling approach provides more robust assessment of

specific metal behaviour between and within sites. Combined, these techniques illustrate the

disconnect between total metal concentrations and availability to pore-waters and for which metals

release is related to a disposal activity or not. It highlights that the total metal concentration is rarely

a good descriptor of release to the pore-waters in this case and link between total metal reservoir,

associated environmental drivers (TOC, PSA) and pore-water chemistry (DOC, AVS) will determine

the risk posed from metals associated with disposal activity.

The overall information generated from the SPI and other sediment information (PSA, TOC, bulk

metals) resulting from this work evidenced that the fauna and sediments in the vicinity of the

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disposal areas showed a distinct presence of added dredged material and a reduction in faunal

numbers when compared with the reference areas. The ability to sample with SPI allowed rapid

coverage of large areas and provided a good reliable set of information, which enabled

characterisation of the sediments, fauna and the aRPD across different areas. The use of SPI also has

been applied for disposal site monitoring at Souter Point since 2005 and has also allowed

characterisation of the presence of dredged material in the centre of the disposal area.

The combined approaches of SPI (rapid spatial technique to identify comparative site redox and

disposal material) and DGT sampling (and associated environmental variables) at selected sites can

provide an improved assessment of the risk posed from disposal sites sediments in terms of direct

metal release to the sediment pore-water (potential bioavailability), across the sediment –water

interface (source/sink) and also under disturbance events (storms). The combined techniques can be

readily linked within monitoring programmes in a cost-effective manner and targeted to site or

contaminant specific issues.

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Table of contents

Contents

Cefas contract report: ME5403 Module 7 ........................................................................................... 1

Introduction ........................................................................................................................................... 3

Disposal site regulation and monitoring ............................................................................................ 4

Background of the DGT method .......................................................................................................... 6

Aims of this module .............................................................................................................................. 8

Methods: Souter Point case study (Aims 1 & 2) ................................................................................ 8

Background of Souter Point disposal site ........................................................................................... 9

Sampling approach ............................................................................................................................. 9

DGT probe deployment and retrieval and analysis .......................................................................... 11

Total Metals ...................................................................................................................................... 12

Statistical approaches and analysis................................................................................................... 13

Results (Aims 1 and 3) ........................................................................................................................ 13

DGT fluxes and profiles ..................................................................................................................... 16

Macrofaunal communities ................................................................................................................ 22

Discussion ........................................................................................................................................... 25

Application of gel technology and SPI in monitoring and assessment studies (Aim 3) ............. 25

Capabilities .......................................................................................................................................... 27

Limitations of SPI and DGT technologies (Aim 4) ........................................................................... 29

Recommendations for future routine application (Aim 5) .............................................................. 31

Conclusions and way forward ........................................................................................................... 32

8. Dissemination .................................................................................................................................. 34

8.1 Presentations meetings/Study groups or conferences ............................................................... 34

8.2 Papers (in preparation) ............................................................................................................... 35

9. References ....................................................................................................................................... 36

Appendix 1: Images ............................................................................................................................ 42

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Introduction

The use of the Sediment Profile Imagery (SPI) technology and their images have been demonstrated

to be an effective tool to disseminate scientific results to regulators, non-specialists, industry and

wider stakeholders including the general public. Initial efforts were supported by the contract

ME1401 to develop SPI capability as a routine tool for monitoring marine environments. The SPI

technology has proven to be an effective manner to collect, communicate and disseminate

information to a wide range of stakeholders.

During this module (project ME5403) the aim was to develop the SPI capability in relation to passive

samplers, as it was recognised that information obtained by undertaking work in parallel with these

two techniques could help to answer regulatory needs. This work was designed to combine the SPI

and DGT gels to place them into a full operation as a tool for monitoring in support of the regulatory

needs. The idea of implementing the DGT passive samplers technique in Cefas was to explore their

performance as a cost-effective tool with a rapid return of information to assist the existing work

conducted under monitoring to support marine licenses. The use of DGT gels alongside the SPI

technology is a developed method, which has been applied to sediment systems, showing a robust

return of information and successful results (Teal et al., 2009, 2013). However, this is the first time

that Cefas applied these two techniques during the same survey (e.g. the SPI and DGT gels in

parallel) to provide additional information into an existing monitoring context in relation to dredged

material.

One key focus of this module was to use a combination of the existing SPI technology with existing

Diffusive Gradient in Thin-films (DGT) gels. This work enabled the matching of SPI sediment images

with metal profiles measured by the DGT gels as well as quantitative sediment chemistry

measurements of nutrients, metals, organics etc. These novel gel based responsive materials are a

simple method allowing more informative surveys of offshore related chemical distribution to be

carried out to complement existing monitoring practices.

The work undertaken under this module was at Souter Point dredged material disposal site, which

provided a suitable scenario for testing a combination of new techniques. The site is annually

monitored by Cefas on behalf of the MMO and Defra. A multi-disciplinary team of sedimentologists,

biogeochemist and chemists based at the Cefas Lowestoft laboratory, worked on all aspects of this

work. Some of the initial work was to prepare and deploy the gel probes as well as to understand the

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logistics of deployment, laboratory analysis and to also conduct a testing trial of gels with freshly

collected sediment cores collected at Souter Point disposal site to assess the performance of the gel

as sediment analytical tools.

During the development of this work, Cefas scientists have interacted during meetings and

workshops with other academic partners (namely Dr. Andrew Mayes at UEA and Dr. Gary Fones at

Portsmouth University) to gain additional understanding of the DGT gel technology as well as

deployment and cost-effective testing. The results obtained under this module have been further

disseminated to Cefas colleagues and others (i.e. academic colleagues) also working on this topic.

The techniques developed under this module could potentially be adopted for future disposal site

monitoring. For example the use of SPI is a technique that is routinely employed. At present the use

of grabs to collect bulk sediment samples only have limited penetration when compared to sediment

corers, which can penetrate deeper into the sediment and can also provide a profile of sediment

layering, which can help to provide a more detailed sampling sediment chemistry as well as the

faunal response in these areas. The combination of SPI with in situ samplers for selected chemical

components significantly enhances the usefulness of this tool for environmental impact assessment,

providing a rapid tool for monitoring the current status of dredged material disposal sites.

Disposal site regulation and monitoring

There are approximately 150 sites licensed for dredged material disposal around the UK, however by

no means all the sites are used in any one year. The majority of these sites are located off the coast

of the mainland, mostly within a few miles of a major port or estuary entrance, within estuaries (e.g.,

Humber), (Bolam et al., 2006). Annually, some 25 - 50 million wet tonnes of dredged material are

disposed of at these sites. Individual quantities can range from a few hundred to several million

tonnes. Equally, the nature of the material may also vary from soft silts to boulders and crushed

rock, although the majority is finer material (Bolam et al., 2006).

At some disposal sites, the material disposed of is a combination of capital and/or maintenance

dredged material. The quantities of dredged material are often referred to as quantities of returns

(in tonnage) for specific sites. Some of the disposal sites have been used for decades (up to 100

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years) and so in some cases, disposal of these materials started well before statutory controls for the

protection of the marine environment were enforced (Eagle et al., 1979; Birchenough et al., 2006).

The disposal of dredged material was licensed under FEPA 1985 Part 2 until 6th April 2011 when it

was superseded by the Marine Licensing section of the Marine and Coastal Access Act 2009 (MCAA)

following guidelines laid down by the OSPAR Convention 1992 and the London Protocol 1996. The

licensing authority for England under the MCAA has been the Marine Management Organisation

(MMO) since 1st April 2010 when they took over the role from the Marine and Fisheries Agency.

Prior to issuing a disposal licence, alternative disposal options, including beneficial uses of dredged

material (Murray, 1994) must be explored by the applicant, for example, beach recharge, coastal

defence and habitat enhancement (Waldock et al., 2002). However, open water disposal in licensed

sites is in many cases the best practicable environmental option and also the only economically

realistic one for the dredged material (Birchenough et al., 2006).

In licensing the disposal of dredged material at sea, several national and international agreements

(e.g., the London Protocol of 1996 (LP96), the OSPAR Convention, the Habitats and Species Directive

(92/43/EEC), the Wild Birds Directive (79/409/EEC), the Water Framework Directive ( 2000/60/EC)

and the Waste Framework Directive (2008/98/EC)), must be taken into account, to determine

whether likely impacts arising from the dredging and disposal are acceptable (MEMG, 2003). Criteria

considered under the various conventions and directives include the presence and levels of

contaminants in the materials to be disposed of, along with perceived impacts on any sites of

conservation value in the vicinity of disposal.

Cefas’ role is to provide scientific advice to the MMO on the suitability of the material for sea

disposal at the application stage and, once a licence is granted, to check through disposal site

monitoring that licence conditions are met and that no unexpected effects occur. Advice on the

licensing of dredged material disposal at sea is provided by Cefas’ Regulatory Assessment Team who

collates advice as appropriate from relevant Cefas experts. Work conducted under the FEPA

monitoring contract SLAB5 helps underpin the scientific rationale in support of this advice. The work

conducted under this ME5403 module also aims to complement the work conducted under that

contract.

Cefas has a tiered approach to assessing which disposal sites should be recommended to the MMO

for sampling in any one year. This tier-based approach considers a number of possible issues or

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environmental concerns that may be associated with dredged material disposal within a risk-based

framework (Bolam et al., 2009). Cefas’ duty is then to design an appropriate monitoring plan as part

of our ‘check monitoring’ process on behalf of the regulator. These monitoring activities result in the

acquisition of physical and biological datasets that, in addition to their primary function, can be

utilised to gain further understanding of the marine ecosystems in and around the disposal sites and,

ultimately, enable better management of the activities.

The aim of this module is to provide applied science to support the licensing and monitoring of

dredged material disposal sites under FEPA and the Marine Act. The aim of applying the SPI

alongside the DGT gels at disposal site areas could help to support the current monitoring conducted

under the contract SLAB5. The idea using the SPI camera to characterise areas that have been

subject to historic and current dredged material disposal has helped to: i) visualise the status of the

seafloor and associated benthic communities, ii) provide a rapid return of information, which is easy

to communicate, iii) enabled the study of vertical additions of dredged material and also assess the

presence/absence of fauna as well as delimitation of the aRPD. The use of DGT gels in sediments

collected from an active disposal site has provided the opportunity to assess metal speciation and

the remobilisation of metals at a detailed vertical distribution within the sediment profile in

sediments. This assessment provided a rapid return of information and also enhancing the spatial

coverage of a disposal site. The application of methods such as the ones tested in this module could

provide a cost-effective monitoring design at disposal sites.

Background of the DGT method

The Diffuse Gradients in Thin films (DGT) is a method that has been in use for determining metal

concentrations in natural waters for more than 15 years and was patented in 1993 (Davison and

Zhang 1994). Passive sampling devices based on the DGT principle are sold commercially through

DGT-Research (http://www.dgtresearch.com/DGTResearch/Info.html). DGT consist of a Chelex resin

embedded within a hydrogel, overlaid with a diffusive layer of hydrogel and a filter. These devices

have been successfully employed in sampling and analysis of metal concentrations in soils, water

column and sediment pore-water (Davison et al. 1997,Tankere-Muller et al. 2007; Teal et al., 2009;

Teal et al., 2013) and can also be used for other ionic species, for example phosphate and sulfide.

DGT technologies can determine the flux of the ‘labile’ fraction of chemical species within sediment

pore-waters, to the gel sampler and therefore provide a better description of the concentrations and

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supply of metal and other contaminant exposure to sediment pore-water and hence fauna. The

Figure 1 below illustrates the dynamics and steps involved in controlling metal partitioning between

the particulate phase (as described by total metal sediment concentrations), dissolved pore-water

and sampling by a DGT passive sampler.

Figure 1. Reactions of metal phases between DGT, dissolved pore-water and particulate phases

(From Ciffroy et al., 2011)

Figure 2 below shows the schematics with the concentration profiles of a DGT probe composition

whilst being deployed. The advantage of DGT probes is that they are reasonably priced (sediment

probes are ~£80-100 each) and concentrate the analyte into the gel, hence improving the amount of

metal available for analysis in relation to any given analytical detection limit. Their performance in

various sediment types is also increasingly well defined and studies have already linked biological

response using DGT labile metal, bioavailability and toxicity studies (King et al., 2005; Belzunce-

Segarra et al., 2009; Jolley et al., 2009; Rigaud et al., 2009; Roberts et al., 2013). Limited studies have

also applied these samplers to sediment in the context of contamination studies at capping sites

(Knox et al., 2012) or disposal sites (Fredette and French, 2004) and also linked metal cycles (Teal et

al., 2013).

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Figure 2. Schematic of DGT probes and flux profile in sediments.

Aims of this module

This work has investigated the combining of SPI image with in situ sensors for metals components. Specific objectives were:

1. To develop and test the DGT gel capability in connection to SPI technology.

2. To identify a ‘testing’ disposal site for a trial use of the gel technology in support of FEPA

monitoring,

3. To quantify the detection capability of the DGT gel technology alongside the SPI technology

during monitoring and assessment studies.

4. To identify the limitations to its safe/effective use.

5. To produce recommendations for future routine applications within Cefas and in

combination with SPI experts.

Methods: Souter Point case study (Aims 1

& 2)

The work developed under this module was undertaken alongside the current monitoring effort

conducted under the SLAB5 contract. A suite of sediment corers were collected alongside the SPI

Sediment

Conce

ntr

atio

n

∆g Distance into sediment

Ca

Cpw

Resin layer

diffusion gel

filter}diffusion layer

(c)

(b)

(a)

Sediment

Conce

ntr

atio

n

∆g Distance into sediment

Ca

Cpw

Resin layer

diffusion gel

filter}diffusion layer

(c)

(b)

(a)

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survey, mainly to test new the DGT gels in sediments to inform the vertical presence of metals

present in these areas alongside the SPI images (informing the sediments type, aRPD and faunal

presence). This overall approach is a cost-effective manner to survey sediment subject to dredged

material disposal. The results from this work are aimed to complement the current level of large

scale monitoring of the Souter point disposal site.

Background of Souter Point disposal site

The work conducted under this module has concentrated at the Souter Point (SP) disposal site. The

SP disposal site is located at a depth of approximately 40 m, but this shallows by up to 5 m at the

inshore end, due to historical accumulations of minestone and fly-ash material. Between December

2004 and April 2005, a trial level bottom-capping project was undertaken in the centre of the site.

The Port of Tyne disposed of 60,000 m3 of contaminated dredged material (CDM), which was then

capped with clean material (Blake, 2009; Birchenough et al., 2007). Cefas has continued to monitor

Souter Point disposal site prior to, during and post the capping trial. The monitoring program at

Souter point is based on impact hypotheses, which are set up for addressing important questions

such as: what is the fate of contaminants (including metals) imported to the site with the disposed

material and what effect does this have on ecological components? At present little is known

regarding metal speciation or detailed vertical distribution and partitioning of metal contaminants

within the sediments. The aim of this work was to apply diffusive gradient in thin films (DGT)

technology as a complementary tool to the routine monitoring conducted at the SP disposal site to

provide an improved understanding of metal behaviour and fate. While the established practise of

analysing trace metals in bulk sediment samples gives important information about absolute

concentrations and such associated potential hazards, the idea of looking at depth resolved profiles

of metal fluxes as measured by DGT might improve our understanding of how mobile and thus

available these metals are, or in other words what actual risk they might pose. This is the first time

that this type of detailed vertical work is undertaken at this disposal site, this work enabled a robust

level of information across all biological and physico-chemical variables.

Sampling approach

A total of four replicate samples with a 0.1 m2 NIOZ box-corer were collected at 3 stations: i)

Reference station 4 corers, located south of the disposal site and ii) station C and station S, 3 corer

replicates were taken from stations both located within the disposal site (Figure 3). Sub-coring for

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DGT deployment was carried out before incubation of the sub-cores, the details of the DGT sampling

are provided in the sections below.

In parallel five replicate Sediment Profile Imagery (SPI, Rhoads and Germano, 1982, Germano et al.,

2011) images were taken at each of the stations where the DGT passive sampler was deployed.

Sediment Profile Imagery (SPI) is a rapid, in-situ technique, which takes vertical profile pictures of

the upper 20cm of the sediment system. The SPI camera works “like an inverted periscope”, the

camera possesses a wedge-shaped prism with a plexiglass faceplate and an internal light provided by

a flash strobe. The back of the prism has a mirror mounted at a 45° angle which reflects the image of

the sediment-water interface at the faceplate up to the camera. The imaging system (a Nikon D-100

camera) provides in situ information of sediment characteristics (i.e., physical description) and the

presence and location of large fauna and biological activity (e.g., burrows, tubes, oxic voids etc.) (as

indicated in Birchenough et al., 2006; Birchenough et al., 2012, Birchenough et al., 2013). Visual

assessment of sediment colour can be used to contrast sediment redox state, in particular iron

reduction (loss of brown) and pyrite formation (black) (Teal et al., 2009; 2012).

Figure 3. Souter Point disposal site displaying all of the stations sampled and stations on the

disposal sites (S, C) and reference (R)(station).

Supporting sediment characterisation:

Supporting measurements to complement the DGT probes and characterise the sediment at each of

the stations were also collected. They are described below.

R

SC

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Oxygenation of the upper sediment layer was measured with oxygen pore water profiles obtained

with oxygen microelectrodes (Unisense) using a method adapted from Rabouille et al., (2001).

Sediment characteristics were derived from vertical slices of sub-cores from a NIOZ box-corer at

resolutions 0-0.5, 0.5 to 1 cm and then at 1 cm intervals, stored at -20 °C or analysed immediately.

These sample slices were analysed for particle size, porosity, chlorophyll and total organic carbon.

Particle size analysis (PSA) was derived using a method developed by Mason et al. (2011). In short, a

sub-sample of each sediment was screened at 1 mm and laser sized using a Malvern Mastersizer

2000. The remaining sample was wet split at 1 mm, and the > 1 mm sediment was oven dried and

then dry sieved over a range of test sieves down to 1 mm. Sediment < 1 mm was oven dried and

weighed. The results from these analyses were combined to provide a full distribution. Summary

statistics, including % gravel, % sand and % mud were derived from the full distribution dataset.

Total Organic Carbon (TOC) was analysed using broadly similar methodology described by Verado et

al., 1990. In short samples were freeze-dried. They were then ground to homogenise the sample.

Inorganic carbonate was removed from a 1.3 g sub-sample using sulphurous acid to excess. Sub-

samples (~0.5 g) were then weighed into tin cups and analysed using a Carlo Erba EA1108 Elemental

analyser.

Chlorophyll a and pigments were extracted in 90 % buffered acetone (Fisher Scientific) and

refrigerated before analysis. A Turner Designs Model 10AU filter fluorometer (Sunnyvale) was used

to measure extracted chlorophyll a fluorescence before and after acidification as described in Sapp

et al. 2010. The fluorometer was calibrated using a solution of pure chlorophyll a (Sigma-Aldrich, St.

Louis) with the concentration being determined spectrophotometrically. The percentage error of

chlorophyll a analyses was <2 % relative to Turner-certified reference material. Porosity was

calculated using the dry weights and wet weights of known volumes of sediment slices assuming a

sediment particle density of 2.7 g cm-3 and a seawater density of 1.035 g cm-3 (Sapp et al. 2010).

DGT probe deployment and retrieval and analysis

The DGT probes and procedural blanks were de-oxygenated in a 0.01 M NaCl solution overnight

using oxygen free-nitrogen. The cores were placed in the incubating tank filled with oxygenated

seawater and were stabilised for 2 hours before deployment of the probes. For each core, two

probes were used: the Chelex gel probe (for metals determination) and the AgI gel probe (for

sulphide determination). The probes were inserted into the sediment core, leaving 1-2 cm between

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the top of the probe window and the sediment/water interface (as described in Roberts et al., 2013).

Furthermore, Chelex and AgI gel discs were deployed in the incubating tank in parallel with the

probes. The probes and discs were deployed for 24-28 h. The time and temperature were recorded

at the deployment and retrieval points. On removal, nano-pure water was used to rinse off any

sediment traces that remained on the surface of the probes/discs. They were stored in a labelled bag

and kept in the refrigerator prior to transfer to the laboratory for analysis.

Chelex gel: The gel was removed as per the practical guide provided by DGT Research Ltd. For the

probe, the gel was sliced at 0.5 cm resolution and eluted in 1 ml of 1 % HNO3 for 24 h before analysis

of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and

Inductively Coupled Plasma –Atomic Emission Spectroscopy (ICP-AES). The results of each slice are

then combined to constitute the sediment profiles down the core.

AgI gel: The AgI gels were removed from the probes as per the practical guide provided by DGT

Research Ltd and covered with a hydrated plastic film. The gels were then scanned while wet in a

flat-bed scanner. The greyscale intensity of the scanned images will be analysed with the software

Image J. Using the calibration curve derived by Teasdale et al., 1999, total dissolved sulphides were

quantitatively measured in the gels.

Total Metals

A sub-core from each station was taken and sliced according to its visual description. Each slice was

subsequently analysed for total metals on the <63 µm sediment fraction. Typically, 0.2 g of the

sieved and freeze-dried sediment sample was digested in a mixture of hydrofluoric, hydrochloric and

nitric acids using enclosed vessel microwave. The hydrofluoric acid was then neutralised by the

addition of boric acid and the digest is made up in 1 % nitric acid and further diluted prior to analysis

by ICP-MS and ICP-AES. Quantification of Al, As, Cd, Cr, Cu, Fe, Li, Mn, Ni, Pb, Rb and Zn was done

using external calibration with Indium as internal standard. A certified reference material was run

within each sample batch for quality control. Results are reported in mg kg-1 (ppm).

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Statistical approaches and analysis

Statistical analysis was undertaken on the metal plots for each station to examine any difference in

metal behaviour within or between the three stations. Initially, profile plots of all eight metals were

completed at all sites. For metals exhibiting the biggest differences between sites (Pb, Ni, Mn and

Fe), further modelling was done to tease out the statistical evidence for these differences. We

describe this modelling below.

The depth profiles for each of the metals at the three stations was smoothed by a Generalised

Additive Model (GAM) (Wood, 2006) using the R package mgcv (R Development Core Team, 2010).

We used thin plate regression splines to smooth the data and the degree of smoothing was set to

the minimum needed to explain the main fluctuations in the profile. Two different kinds of models -

one assuming independence and one assuming one-lag correlation were required to model the

depth profiles of the metals. Both models were used to fit a GAM model to the metal profile and

examine the variance (mid 95 % envelope) of points around the smoothed line. Using this model

within and between site differences could be examined. Full details of the modelling can be found in

Parker et al. (in prep).

Results (Aims 1 and 3)

The monitoring at Souter Point has been undertaking by Cefas (formerly MAFF) since the 1970’s. The

sediments in the disposal site, which is the immediate area where the contaminated dredged

material was disposed of in 2005, have been described as an admixture of sand and muddy sands in

the centre of the capped area (Cap1, Cap2 and Cap5) and sandy mud (at stations Cap 9 and Cap 7)

(see Figure 1). The reference station located to the north (TC2) was also observed to be a

combination of gravelly muddy sands, while those to the south of the disposal site (stations TC3 and

TC4) consisted of sandy muds (Birchenough et al. 2007). As part of the ‘check monitoring’

programme, zinc and mercury showed higher concentrations during 2005 at the stations located in

the centre of the disposal site. During earlier surveys conducted in the area zinc concentrations also

have been noted to be higher mainly to the west of the disposal site. Earlier surveys (e.g. in 2006)

showed an increased in copper concentrations, which was also observed at station Cap 7 (west of

the centre of the disposal site) (Birchenough et al. 2007). Previous work conducted under the large

monitoring effort in this area (e.g. work conducted under SLAB5) helped to inform and target a suite

of stations to test the DGT work alongside the SPI images.

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A summary of sediment characteristics for the three stations is shown in Table 1 a and b and Figure

4. Bulk sediment and metal flux profiles are in Figure A1, Appendix 1. All stations were composed of

muddy sands. Porosity in the upper layers of the sediment at reference station was lowest (0.48

mg/m2) and elevated in the deeper sediment layers at the disposal stations. Total organic carbon

was lowest at the reference station with higher carbons at the two disposal stations. Porosity and

total organic carbon vertical profiles (Figure 4b-c) illustrate the difference between the reference

station which showed a background decrease in porosity with depth and decreasing carbon. In

contrast, the disposal stations exhibited complex silt/clay, porosity and carbon signatures down-core

related to disposal events. The heterogenous structure in vertical profiles illustrated the disposal

events at the impacted stations. The pigment profiles were similar across the stations and illustrate

the water column source with similar degradation profiles with depth (Figure 4 d-e). The oxygen

penetration and profiles were similar for all the stations, with diffusion-type profiles and with

oxygen consumed within the upper 1 cm of the sediment. The deeper redox conditions

demonstrated by the SPI images using Fe3+ colour (Figure 5) were deepest at the reference station,

and shallowest at the disposal stations. The SPI images also showed the occurrence of sulphide

formation (black colouration) to be shallower in the disposal station sediments and more intense

when compared to the reference station.

Table 1a. Average sediment characteristics from sliced sediment cores (0 to ~10 cm). Number in

brackets is one standard deviation.

Station Silt/clay (%) Porosity

(mg/m2)

Chlorophyll

(mg/m2)

Phaeo-

pigment

TOC

(% m/m)

Oxygen

penetration

(OPD) - cms

Reference 17.0 (3.7) 0.45 (0.04) 3.0 (2.3) 14.0 (7.0) 1.3 (0.3) 0.5 (0.2)

Disposal S 49.2 (20.7) 0.62 (0.05) 3.4 (2.4) 14.2 (6.9) 5.6 (1.6) 0.4 (0.2)

Disposal C 22.4 (16.9) 0.53 (0.05) 4.7 (3.9) 14.7 (7.4) 5.4 (0.9) 0.4 (0.1)

Table 1 b. Averaged total metal concentrationFigure 1, Appendix 1). *Cd at layer 8

Figure 4. Vertical profiles of sediment properties at the three stations (reference, station C and

station S) - a) Silt/clay (%) b) Porosity c) Total Orga

e)phaeopigment

a)

d) e)

Average Concentrations

Reference (n=4)

Disposal C (n=7)

Disposal S (n=6)

Table 1 b. Averaged total metal concentration from bulk samples from core layers (full plots are in *Cd at layer 8-9cm <0.2mg/kg

4. Vertical profiles of sediment properties at the three stations (reference, station C and

a) Silt/clay (%) b) Porosity c) Total Organic carbon (%m/m) d) Chlorophyll and

b) c)

d) e)

Ni (mg/kg) Cd (mg/kg) Pb (mg/kg) Mn (mg/kg)

50.0 <0.18 136 445

49.6 0.50 172 510

50.6 0.46* 164 475

15

from bulk samples from core layers (full plots are in

4. Vertical profiles of sediment properties at the three stations (reference, station C and

nic carbon (%m/m) d) Chlorophyll and

Mn (mg/kg) Fe (g/kg)

445 38.9

510 39.6

475 39.1

16

Figure 5: Example Sediment Profile Images (SPI) along a transect through the disposal site marked

on Figure 3. Images from the three stations are marked (S, C and R)

DGT fluxes and profiles

The DGT metal fluxes for all stations and 5 heavy metals of main concern were plotted in Figure 6.

DGT metal fluxes were calculated for each deployed DGT probes at each station and the average flux

profiles (±sd) were plotted for each metal at each of the 3 stations alongside the total metal

concentration (Figure 6). The limits of quantification (LOQ) for each metal DGT analysis (for a typical

24 h deployment) were (ng ml-1): Cd; 0.073, Pb: 0.044, Ni: 0.086, Fe: 12.6, Mn: 0.214.

Iron and Manganese: The DGT flux profiles showed high resolution information in iron (Fe) and

manganese (Mn) remobilisation behaviours. Both metals were redox sensitive and used as

successive Terminal Electron Acceptors (TEAs) during the remineralisation of organic matter, Mn

before Fe. Their supply to the gel increased as they become reduced (move from particulate to

dissolved phases) in the sediments (Fe3+ to Fe2+, Mn4+ to Mn2+). Consistent with this, Fe and Mn DGT

flux profiles (Figure 6) showed the start of sub-surface remobilisation at about 1-2 cm and <1 cm

respectively. Mn release occurs as oxygen was depleted within the upper centimetre of the

sediment. Fe showed a rapid increase of supply close to the surface, but deeper than the oxic zone,

at all stations and continued supply to depth. The rate of increase of Fe resupply with depth at the

disposal stations was greater than at the reference station. Fe showed continued supply to depth

whilst Mn showed a subsurface peak. This is consistent with the higher organic matter loads at the

disposal sites and the increased reducing conditions found there. This is also corroborated by the SPI

images at the disposal site which show more reducing conditions higher up in disposal images. The

Fe fluxes were one order of magnitude higher than Mn fluxes. The profile shapes indicate a supply of

dissolved Mn across the Sediment – Water interface (SWI) into the water column but this was not

observed for Fe which is probably oxidised within the upper cm of the sediment where oxygen is

17

present. The DGT flux profiles indicate that the resupply to the gel is higher at the disposal sites

despite similar bulk Fe and Mn levels across the sites.

Cadmium: All 3 stations showed a peak of DGT available Cd at the SWI. Below the SWI, levels of Cd

supply were low at all stations apart from distinct peaks of higher Cd supply at distinct depths (0.1 to

0.2 fmolcm-2 s-1). There was no trend of Cd release down core in any of the stations. The lack of

difference in Cd supply between the reference and disposal stations would imply that Souter Point

stations were not a significant source of Cd release into the pore-water, associated with material

disposal.

18

Figure 6. Vertical profiles of metal flux to the DGT probes at the three stations (reference, station C and station S) - a) Fe b) Mn c) Ni d) Pb e) Cd

19

Lead: Lead profiles showed increasing flux to the DGT gel down the station cores, with flux rate

increasing in all stations in the deeper sediment layers. The fluxes at the reference station and at the

disposal station S were similar, whilst disposal station C showed the highest fluxes (Figure 6). The

variance in Pb flux with depth was lower at the reference stations and highest at the disposal

stations. This variance was similar to other metals, illustrating the complexity in metal cycles

introduced by disposal operations. The total levels of particulate Pb were highest at the disposal

station C, but only slightly elevated in comparison to the highest supply rate observed. This

discrepancy showed that controls of metal release could be complex and therefore cannot be

determined from total sediment metal content alone. Both disposal stations could be acting as

sources of pore-water Pb to the water column in contrast to the reference station.

Nickel: All 3 stations showed an increase in Ni supply to the gel in the upper few centimetres of the

sediment, compared with consistent (and lower) supply rates with depths greater than 5cm. The

overall supply of Ni to the sediment pore-water throughout the profile at Disposal station C was

higher than the other two stations. Similar to Pb behaviour, both disposal stations could be acting as

sources of pore-water Ni to the water column in contrast to the reference station. For Ni this could

be driven by local release to pore-waters in the upper layers of the sediment (0 to 5 cm).

AgI gels – sulphide: Metal availability and mobility can be closely linked to the amount of free

sulphide ions in sediments. Deployment of AgI gel probes into the sediments cores revealed that

free sulphide was at or below the limit of detection for the DGT based method evaluated through

colour scanning. This correlated well with the high concentrations of free Fe and Mn ions observed

in the metal profiles, as any free sulphide would have reacted with the Fe and Mn to form insoluble

iron/manganese- sulphide complexes, which would have become unavailable to the gel.

A summary of the metal behaviour obtained at the 3 disposal stations as derived by DGT profiles and

comparison to total bulk metal reservoir is presented in Table 2.

Metal flux profile modelling:

Figure 7 shows natural log depth profile plots for all eight metals. For Cd, Cr, Zn and Cu it is difficult

to distinguish the profiles between the references and disposal sites. For the remaining four metals

(Pb, Ni, Mn and Fe), the 95 % envelope plots in Figure 7 below illustrate the differences between the

stations.

20

For Fe, the envelopes overlap throughout the profile and it is impossible to statistically distinguish

the stations from each other. In contrast, for Ni, the reference and station C profiles are consistently

different, and the station S profile diverges from the other two with increasing depth. The two

disposal stations S and C have similar profiles for Mn, but the reference station profile separates off

slightly from the other two at depths below about 8 cm. The reference and station C profiles were

visually very different for Pb. However, the large amount of variation for site S made it difficult to

distinguish this station from the other two.

Figure 7. 95 % envelopes for the profiles of Ln metal fluxes to the passive sampler at each station

a) Pb b) Ni c) Mn d) Fe.

-1.5 -1.0 -0.5 0.0

-15

-10

-50

Ln Pb

ReferenceStation C

Station S

-4 -3 -2 -1 0 1

-15

-10

-50

Ln Ni

2 3 4 5 6

-15

-10

-50

Ln Mn

-6 -4 -2 0 2

-15

-10

-50

Ln Fe

21

Table 2. Summary metal behaviour at the 3 disposal stations as derived by DGT profiles and

comparison to total bulk metal reservoir (SWI = sediment-water interface)

Metal Enriched

in

disposal

sediments

Depth profile and flux to

DGT

Flux across SWI Insight given by DGT

profiles

Ni No Shallow sub-surface peak of Ni release at disposal sites only. Supply to gel consistent with depth across all sites. Flux to gel higher at station C.

Flux to water column at disposal sites, associated with a shallow sub-surface peak.

Supply of Ni to water column at disposal sites. Pore-water chemistry controls supply to gel at station C.

Cd Yes Shallow subsurface peak at all sites. Distinct peaks of remobilisation and flux to gel. Some LOQ issues. Not coupled to total sediment metal (bulk or profile)

Flux out of sediment at all stations, associated with shallow sub-surface peak

Release not linked to disposal source. Likely phytodetritus source but controls related to redox (Fe/Mn)

Pb Yes Increased supply to gel with depth Flux to gel significantly higher at station C.

Flux to water column at disposal sites, associated with a shallow sub-surface peak (Pb release from Mn reduction?)

Higher disposal total metal only released at station C. Other factors controlling DGT uptake (S, DOC etc). Link to Mn particulate reduction ~ high Pb Partitioning coefficient

Fe No Increased Fe supply to gel below oxic layer (>1cm) Rate of increase and flux greater at disposal sites. Flux is maintained or increases with depth.

None – oxic layer prevents release

Higher iron release at disposal sites – linked to increased anoxia at depth & elevated TOC No SWI exchange limited by oxic layer

Mn Yes Increased resupply as oxygen saturation decreases. Peak resupply in upper 4 cms and then decline to depth Flux to the gel and depth/rate of increase with depth is higher at the disposal sites

Out of sediment at all sites but higher at disposal sites.

Release governed by increased anoxic conditions at disposal sites (~ fines and TOC).

22

Macrofaunal communities

Macrofaunal analysis collected from grab samples collected under the larger monitoring programme

SLAB5, identified a total of 2489 individuals and 61 taxa at Souter Point from the samples collected

during 2011 (Figure 8 a-b). The main taxonomic groups were represented by Annelida (56 %),

Mollusca (11 %), Miscellanea (5 %), Echinodermata (23 %), and Crustaceans (5 %) (Figure 8-c),

showing that the disposal site station are populated by a reduced number of benthic species when

these were compared to the stations located outside the disposal site (shown as reference stations

in Figure 1).

The total abundance of individuals ranged from 101 to 324 per 0.1 m2 across the study area in 2011.

Although some stations (e.g. CAP9, TC3, TC4) showed significantly higher total abundances than

others, many stations from within and outside the disposal site exhibited comparable numbers of

individuals, between 275 and 324 per 0.1 m2 (Figure 8a). The total number of species was doubled at

TC3 when compared to Cap 1, which was expected (Figure 8b).

Figure 8. Univariate measures collected for benthic communities at Souter Point disposal site in

2011, these are: a) total number of individuals, b) number of species and c) main taxonomic

groups.

0

50

100

150

200

250

300

350

CAP 1 CAP 2 CAP 5 CAP 9 TC 3 TC 4

No

of in

divi

dual

sN

o of

spe

cies

a)

Stations

0

10

20

30

40

50

60

70

80

90

CAP 1 CAP 2 CAP 5 CAP 9 TC 3 TC 4

b)

0 10 20 30 40 50 60

Echinodermata

Annelida

Mollusca

Crustacea

Miscelania

% contribution

Mai

n ta

xono

mic

grou

ps

c)

23

Sediment Profile imagery interpretation

The SPI images obtained during the May 2011 survey confirmed the presence of dredged material

layers, showed as dark or black sediment presence and thin layers of silts and sand in the centre of

the disposal site (Figure 9b-c). There was a limited SPI penetration at station Cap1, mainly due to the

compacted nature of the sediment layers. Images indicated the presence of some coal fragments

observed on the surface of the sediment (Figure 9a). In contrast, at Cap7 (located immediate outside

the disposal site) showed also indication of muddy sediments with presence of surface fauna

(*tentative identification corresponds to the bryozoan Alcyonidium diaphanum). Some images also

showed indication of the burrowing echinoderm Ophiura sp. (Figure 9d).

The station POT6, located north of the disposal site showed clear evidence of the presence of

benthic burrowing infauna polychaetes and also attached Serpulids polychaetes (*tentative

identification corresponds to Pomatoceros sp.) (Figure 9e). At station SPI12 (which is one of the

southern reference stations) there was also indication infauna and burrowing activity in the top

surface of the image (Figure 9f). Data collected at northern stations further away from the centre

(TC3) showed the presence of fine sediments, surface fauna (e.g. sea pen *tentative identification

corresponds to Virgularia mirabilis) and feeding voids observed at 3-4 cm (Figure 9g).

The overall aRPD calculation ranged from 2.0 to 6.0 cm across the stations (Figure 9a-g), which

demonstrated shallow aRPD layers in the disposal site area, since there is some fauna observed in

the newly added material. There are clear deep aRPD layers at the stations located north and south

of the disposal area. The aRPD measured at the reference station was over 5 cm, which

corresponded to the biological activity (Figure 9 f-g). The aRPD depth values are the most routinely

measurable and defensible parameter in SPI images. The aRPD depth is base don the colour change

of the sediment profile from the brow colour tonnes at the surface (oxidative state; Lyle 1983) to the

grey-black colour tones at depth. The aRPD values provide a good estimate of the depth of oxidised

sediment and have important weighting on determining the condition of benthic community

(Germano et al., 2011).

24

Figure 9 (a-f). Sediment profile images (SPI) collected at Souter point disposal site in 2011,

displaying stations: a) Cap1, b) Cap2, c) Cap5 (also described as C in this study), d) Cap7, e) POT04,

f) SPI12 and g) TC3 (also described as R in this study). SWI=sediment water interface, DM= dredged

material, SE=surface fauna, I=infaunal polychaete, v=void and B= burrow, C=coal fragments. Scales

on left-hand side are 2 cm intervals.

In an ecological context the ability to collect benthic grabs alongside the SPI information has

provided valuable complementary information. The SPI showed the presence of infauna, their

distributions and vertical sediment layering, as well as the presence of dredged material presence in

the area. The SPI images have also showed the presence of biogenic structures (e.g. voids, burrows)

and indicated signs of early colonisation in the areas in the vicinity of the disposal site. This

information is valuable for the understanding of organism-sediment interactions as well as study of

benthic systems in this area (Birchenough et al., 2006; Birchenough et al., 2012; Birchenough et al.,

2013). The ability to observe benthic systems in situ has helped to characterise the status of this area

and the numerical information provided by the grab has also provided a quantitative assessment.

Clearly the use of SPI for benthic assessments provided a clear improvement from the traditional

ecological sampling methods with grab samples in this area (Birchenough & Frid, 2009).

a) b) c) d)

e) f) g)

SWI

SWISWI

SWI

SWISWI

SWI

DM DM

SE

SP

VV

C

I

I

B

IB

SE

25

Discussion

An effective monitoring plan needs to be fit for purpose and provide robust scientific evidence to

inform the regulators. The collective approaches of using the SPI (to provide a rapid spatial

technique to identify comparative site redox and disposal material) combined with DGT gel sampling

(and associated environmental variables) at Souter Point provided an improved assessment of the

sediments, mainly in relation to the direct metal release to the sediment pore-water (potential

bioavailability), across the sediment –water interface (source/sink). The combined techniques can be

readily linked within monitoring programmes in a cost-effective manner and targeted to site or

contaminant specific issues. The sections below also outline specific recommendations and lessons

learnt from this work.

Application of gel technology and SPI in

monitoring and assessment studies (Aim

3)

Current marine strategies are targeting our efforts to assess the status of marine systems. In UK

waters, the combination of complementary science (R&D, monitoring and current practices)

provides evidence-based advice to regulators (Bolam et al, 2006). The parallel approach undertaken

under this module will complement the current advice and, ultimately, provide further details during

a license application at dredged material disposal sites. Cefas’ work is aimed to obtain maximum

benefit from this work, providing cost-effective assessments in support of monitoring practices for

seafloor systems. The work undertaken in relation to the SPI technology and DGT has highlighted the

following topics:

• Application of high resolution DGT passive samplers to the three stations in this study has

revealed several new insights into the behaviour and controls of various metals within the

sediments associated with disposal as provided by the high resolution flux profiles. These

profiles showed comparative resupply of metal to pore-waters between different stations

(disposal and non-disposal), trends in fluxes with depth (notably Pb), fluxes across the

sediment-water interface (Mn, Cd) and changes in resupply for a metal between stations

(notably Ni, despite a consistent total Ni reservoir). The higher resolution understanding

provided by the gels and hence fuller understanding of metal resupply and availability within

26

sediment pore-waters provides new information on whether sediments are acting as

source/sink for metals and links to disposal activity.

• For some metals there doesn’t seem to be a strong disposal signature related to the total

metal reservoir (either profile or bulk levels). This is seen for Cd, where the release pattern is

unrelated to depth profiles of the total metal and also the total sediment levels which are

elevated in the disposal stations. This has also been identified for both Pb and Ni where

metal flux at station C is elevated despite contrasting total metal levels at this station in

comparison to the other two stations. It appears that this comparison between the total

metal reservoir and availability to the passive sampler also illustrates the complexity of

metal cycling within sediments once released to the pore-water. The availability or lack of

other pore-water chemical species (DOC, sulphur species) will also control metal availability.

The lack of detectable sulphide species in these sediments is likely to be the reason for high

comparative availability of metal ions to the passive sampler.

• The use of SPI has proven to be an effective and rapid tool for monitoring dredged material

disposal sites. The use of the SPI has helped under this work to monitor the presence of

dredged material, fauna, sediment type and aRPD. A full analysis of the monitoring effort

conducted at Souter Point under SALB5 auspices and this module is currently being

produced (Birchenough et al. in prep.)

Associated sediment modelling of DGT metal profiles:

Comparison of metal profiles between stations has usually occurred by visual comparisons.

However, this is not statistically robust and with higher variances induced by disturbance is is

essential to have a method which can detect metal differences within and between sites or changes

over time. The modelling of the DGT metal profiles has demonstrated;

• A new methodology which allows statistical analysis and investigation of high resolution

metal profiles.

• Provides increased confidence in an assessment of the differences between sites, processes

driving them and how disposal is affecting them.

• It provides increased power to statistically determine status and variances of conditions and

detect changes over time or space.

27

Capabilities

This study has been able to highlight various aspects of the SPI and DGT performance, capability and

limitations which are listed and discussed below and provide guidance on their future application

Capability of the DGT and SPI technology:

• Deployment of the gels can provide high resolution flux profiles of a suite of metals

• They can provide insight into areas of release of metal to sediment pore-waters (with depth

and between stations)

• The can provide estimates of fluxes into and from the sediments, and whether the sediment

could be acting as a source or sink post disposal or other management actions.

• When combined with other supporting information (organic matter, sediment type, redox,

metal loading, SPI) the metal profiles can highlight the changes in processes likely to be

driving metal behaviour and contrast between stations, in particular the heterogeneity

created through disposal events.

• The links between total sediment metal reservoir and release to the pore-water can be

investigated. As shown here metal resupply to pore-water often does not reflect the total

metal reservoir and disposal effects of total metal loading on biology may be more complex.

DGT fluxes can provide some insight into the potential bioavailable fraction and areas of

release/exposure within the sediment and with space.

• The gel metals (potentially bioavailable fraction) can improve links to biological effects &

toxicity monitoring.

• The SPI capability has proven their utility at Souter Point disposal site as it has helped to

monitor the presence of dredged material disposal layers, faunal presence ( in the disposal

and at reference stations), sediment types and the aRPD layers, which have helped to relate

to the status of the stations and overall area ( Birchenough et al., 2009)

• The overall combination of the SPI and DGT information has enabled us to obtain a more

detailed level of information from the disposal site. The ability to provide profiles of metals

and understand the depth of the metals alongside other measurements (e.g. chlorophyll a,

% silt/clay, porosity, phaeopigments, TOC and OPD) as well as the faunal presence,

sediments at stations were there was dredged material dispose of when compared to

reference stations has advantages, specially when trying to characterise the station

subjected to disposal activity. This level of information could help to identify future disposal

28

areas as well as improving current knowledge of exiting sites with higher contractions of

metals.

Methodology & application of DGT technology and SPI within monitoring programmes:

• Relatively easy technique to use and to build into the monitoring programme alongside

other measurements of total metals given coring equipment is available.

• Standard laboratory cleaning procedures are required – these are relatively inexpensive /

routine to set-up and easy to check with appropriate handling and DGT deployment method

blanks.

• Higher resolution measurements (i.e. a slicing resolution of 1cm or above, compared to

0.5cm resolution applied within this module) for sediment types and other key variables are

needed but this level of sampling depends on the question asked of this technique so costs

can be adapted accordingly.

• Incubation times for the gels range from 24 to 36 h to allow sufficient accumulation of

metal. Samples must be kept in appropriate conditions for this time (cool, dark, aerated) but

the ship-time required to collect such cores is comparatively short (~ 1-2 h). In-situ

deployments (i.e. having the gels on the face of the SPI camera) would require considerable

time for the vessel to be on station.

• In this study deployment of the gel samplers was standardised to 24-36 h and gave good

metal LoQs for most elements. Generally there are no standard or recommended

deployment times reported in the literature but future standardisation and determination of

optimum probe deployment time would be appropriate for varying sediment types and

matrices (DOC etc) to check flux calculation assumptions (see Chiffroy et al., 2011).

• Overall, DGT costs can be higher than analysis of a total metal. However, this can be cost-

effective when aimed at specific questions of metal release into pore-waters, depth

information and flux to water column that total metal information cannot supply.

• The use of SPI technology has proven it to be an effective and cost-effective tool for disposal

site monitoring, helping to target specific areas where there is presence of dredged and non-

dredged material areas. Some of these types of approaches could be ‘tailor’ to answer

specific monitoring questions for example, in areas were there is historic legacy of metals

and/or contaminants or to support future areas where there is a need to place localised

sediments with high presence of metals and /or contaminants ( e.g. capping areas)

29

• The rapid return of information from the SPI survey, helped to identify the

presence/absence of fauna as well as biogenic structures (e.g. burrowing activity, polychaete

tubes, etc.), provided a rapid assessment of the sediment types and redox layers in the

stations analysed.

• The SPI technique has been effectively applied in dredged material monitoring in the US

(Germano et al., 2011). The SPI technology has been also employed in the UK to monitor

dredged material disposal site, particularly at and specifically at Souter Point ( Birchenough

et al 2009)

• Overall the use of the SPI technology with DGT samplers could provide a rapid and cost-

effective monitoring design, helping to spatially cover large areas with the SPI technology

and then ground-truthing with a dedicated effort (e.g. sediment cores). A fit-for purpose

design could then enable the monitoring of metals, sediment and fauna to provide a rapid

baseline information where there is suspected high metal concentration, which could help

to keep localised disposal areas with an accurate knowledge of high concentrations of

metals.

Limitations of SPI and DGT technologies

(Aim 4)

The combination of techniques employed in this module has proven to be effective in providing a

rapid assessment for this area. The SPI survey provided additional details on the vertical layering of

the sediment and the fauna (e.g. showing early signs of colonisation in the disposal areas as well as

showing evidence of biogenic structures in the reference areas), this technique is widely accepted

for monitoring areas where dredged material disposal has taken place (Germano et al., 2011) and in

the UK the SPI technique has also become a routine sampling tool to assess sediment status. The

opportunity to complement the SPI work with the DGT gels has helped to advance our current

understanding on how the SPI technology could be deployed with additional DGT gels for disposal

site monitoring. The DGT trial has also highlighted some limitations of the technique which are

detailed below:

• To successfully deploy DGT gels, there is a need to undertake a sediment corer survey on

board (although a routine piece of equipment) as well as incubation equipment for gel

incubations (on-board or in the lab). Previous research conducted by Teal et al. (2009)

deployed the SPI camera and attached the DGT gels to the face plate of the camera. In this

30

study there were initial discussions to undertake a similar approach as conducted by Teal et

al. (2009). However, due to the logistic constraints (e.g. time, deployment and calibration ),

the option to collect SPI images and incubate sediment corers to aid DGT deployment was

deemed to be the best option under this module.

• Calculations of the metal fluxes (and approximate metal concentrations) rely on a number of

assumptions of performance of the sediment/pore-water matrix (Davison et al., 2007).

However, these are increasingly supported by a broad literature base and DGT user

community.

• Heterogeneity and complexity of sediment processes can make profiles and status

associated with area/stations difficult to interpret. However, this can be overcome by

focused sampling on appropriate spatial scales and resolution. Links to gels and more rapid

spatial techniques can provide a broader and more integrated application of DGT findings

(Teal et al., 2009; Teal et al., 2013).

• The Chelex DGT is only designed for a selected number of metals (Fe, Mn, Cu, Zn, Ni, Pb, Cr).

Future work would require several probes with different gel type to cover most of the

metals suite analysed for the conventional method (Al, As, Li, Hg, Rb). Samplers and resin

types for other metals and organic compounds (TBT) are under development.

• DGT profiles describe the amount of metal available to a gel from the pore-water but not

necessarily the dynamic between a total particulate metal level in sediment and the gel.

These complex dynamics (see Figure 1) can be controlled by other pore-water species (DOC,

AVS) and would be a topic for future work to aid determination of risk of metal

bioavailability from total metal levels in sediments.

• In relation to SPI, one aspect that will have to be considered is the colour changes in the

image, in relation to the aRPD measurement. At Souter Point, there has been some

additional sediment added to these areas (e.g. re-topping the capping material), hence in

some cases the additional material could not be a real aRPD, hence a good understanding of

the area and long-time series of SPI images could help to understand and characterise

accurately the aRPD measures at some of the stations in the disposal site.

• In relation to the SPI technology per se, image analysis requires training and QA. Cefas has a

good knowledge of SPI image analysis, and can rapidly help to identify areas subjected to

human activity.

31

Recommendations for future routine

application (Aim 5)

The monitoring of disposal sites in UK waters is a priority for the regulators, this work has

highlighted clear messages that are useful to consider when designing a monitoring survey. Firstly,

the use of SPI as a routine sampling tool to monitor dredged material disposal sites, has shown the

ability to provide a sound characterisation of the fauna, sediment types, presence and absence of

dredged material and allowed the delineation of the aRPD. Cefas has been monitoring the Souter

Point disposal site since 2005 with SPI and therefore the level of information that SPI can provide a

rapid provision of scientific evidence to characterise the status of the areas subject to dredged

material disposal as well as for assisting the design of a fit-for purpose monitoring. We have

highlighted some specific recommendation below:

• The use of SPI also helped to inform the collection of sediment corers, which were used in

this study (e.g. presence of dredged material and clean sediments) to target the area subject

to disposal of dredged material during the capping exercise. The continuous use of this

technique could help to design fit-for purpose benthic surveys, with detailed information on

the profile of sediments.

• The use of DGT gels helped to provide an informed profile of metals with depth in sediments

also provides a valuable method to consider alongside the SPI technique for rapid and

effective monitoring of areas subject to dredged material disposal. This method could be

adopted as complementary way to assess site legacy of metals or status of the areas

subjected to disposal activity.

• The use of the DGT gel technology has also proven it utility in helping to distil site specific

questions regarding metal source and sinks, which will help inform the management and

prevention of risks from dredged material disposal in these areas.

• Overall the combination of SPI and DGT can provide a detailed level of information to

support monitoring of these areas with a rapid spatial coverage and also alongside other

environmental characteristics for understanding the additional factors influencing these

marine environments (e.g. AVS/DOC).

32

• This work highlights the benefits of a dedicated SPI survey, enabling the rapid coverage of

seabed areas, and then a follow up DGT work could provide supplementary information for

further characterisation of a dredged material context or material which is suspected to

possess high metal concentrations.

• The techniques employed under this module could also be used to collect baseline

information to characterise new or existing disposal areas

The monitoring effort invested in the UK has concentrated on the quality and status of the marine

environment (Defra, 2010). However Charting Progress 2 also highlighted the lack of knowledge,

tools for assessment and data for characterising the state of shallow subtidal habitats (Foden et al.,

2011). At present, the UK has concentrated scientific monitoring efforts in support of the EU MSFD

which aims to protect and/or restore the European seas, ensuring that human activities are

conducted in a sustainable manner (Borja, 2006; Borja et al., 2010; Borja et al., 2011; Fleischer and

Zettler, 2009), targeting good environmental status (GES) by 2020. GES is defined as the

environmental status of marine waters where these provide ecologically diverse and dynamic oceans

and seas which are clean, healthy and productive within their intrinsic conditions and through its

sustainable use for current and future generations (Van Hoey et al., 2010). The assessment of GES is

based upon a series of 11 ecosystem descriptors covering aspects of biodiversity to energy/noise

parameters (Borja et al., 2011). Some of the information generated under this study can help to

support work on Descriptor 6 (seabed integrity) and Descriptor 8 (contaminants).

Conclusions and way forward

The work undertaken under this module has completed the parallel sampling and testing of SPI

technology with DGT gel techniques. This initial application of DGT passive sampler technology

alongside sediment bulk metal has highlighted the complex relationship found between contaminant

disposal load from particulates and metal availability to the pore-water. Furthermore it has

underlined the heterogeneity found in the sediments at disposals stations, both between stations

and with depth, which is clearly illustrated across the suite of measurements taken, from the visually

patchy nature of SPI images to the high variability observed in DGT depth profiles and flux rates.

Improved statistical modelling and detection technique, such as those presented here, will be

needed to determine disposal specific metal signatures, their controls and future changes.

33

While bulk sediment analysis for metals gives important information about the total quantity of

metals present, i.e. the size of the potentially available sediment metal reservoir and is indicative of

the potential hazard, it does not give information about the actual availability of these metals to the

various components of the ecosystem and thus the actual risk posed – either to the benthic

community or by flux into the overlying water column to the pelagic system. This is why

complementary methodologies such as DGT enable additional insights to understand some of these

questions. The clear differences in metal flux profiles recorded at different stations, which do not

strictly correlate with total metal concentrations in the corresponding slices, illustrate that

environmental parameters are influential in regulating flux and, by implication, availability/

bioavailability. This study evaluated a number of likely parameters, such as organic carbon content,

sediment particle size distribution, free sulphide concentration and chlorophyll a content and

highlighted some interesting relationships. An important example of this is found in the behaviour of

cadmium across all three stations – which while present at very different levels in the bulk sediments

showed similar release behaviour across stations, indicating that in this case its remobilisation is not

driven by input from disposal activities but rather down to biotic inputs (such as sedimented

phytoplankton blooms) that affected disposal and reference sites in equal measure and resulted in

more easily released metal reservoirs at corresponding depth. In contrast, one of the disposal

stations (C) did show increased release of lead and nickel into the water column likely linked to

metals brought to site with the disposed material.

In summary, the use of depth resolving passive samplers such as DGT is complementary to

conventional monitoring of disposal sites and can provide valuable additional information. Further

work to improve understanding of the controlling factors of metal release to pore-waters, and likely

exposure routes of biota within the receiving ecosystem as well as corresponding toxicological

implications would be beneficial in informing management decisions. Such studies could link spatial

surveys of total metal reservoir, pore-water flux (DGTs/gels) and controlling factors such as

DOC/sulphides (see Bull and Williamson; 2001; Knox et al. 2012). Better regional understanding of

the metal release pathways and controls may also help explain stations where total reservoir metals

do and do not tie up with observed biological effects and allow increased efficacy of management

measures through improved risk assessment. This regional approach and application of DGT passive

samplers (potentially combined with SPI) would be adaptable to a regional understanding of

contaminant behaviour and in particular MSFD descriptors (namely 6 and 8) which have linked

controlling processes (faunal presence, sediment type, organic carbon, redox)

34

Such increased understanding would not only enable more robust assessments of risks posed by

disposal of sediments with high contaminant loads or diffuse sediment contaminant issues and but

could also be used when assessing likely impact arising from sediment disturbance events, either

natural events such as storms or human activities such as fishing, dredging and construction.

8. Dissemination

The research developed under this module has been disseminated during a series of conferences

and working groups, these are indicated below:

8.1 Presentations meetings/Study groups or conferences

• R. Parker, T. Bolam, J. Barry, S. Kröger, C. Mason, S. Birchenough, B. Silburn, D. Sivyer, A. G. Mayes and G. R. Fones (2012) The application of passive sampler (DGT) technology for improved understanding of metal behaviour at a marine disposal site. 16th International conference on Heavy metals in the environment (ICHMET 16) Conference, 23-27th September at Rome, Italy.

• Thi Bolam, Ruth Parker, Claire Mason, Jon Barry, Silke Kröger, Briony Silburn, Dave Sivyer, Silvana Birchenough, Andrew Mayes and Gary Fones. The Application of Passive Sampler (DGT) Technology for Improved Understanding of Metal Behaviour at Marine Disposal Sites in the UK ICES Working Group on Marine Sediments 18-22nd March, Lowestoft.

• R. Parker, Thi Bolam, Claire Mason, Jon Barry, Stefan Bolam, Silke Kröger, Silvana Birchenough, Andrew Mayes and Gary Fones. The Application of Passive Sampler (DGT) Technology for Improved Understanding of Metal Behaviour at Marine Disposal Sites in the UK ICOBTE International Conference On Biogeochemistry of Trace Elements (Athens, Georgia, June 2013). Invited keynote.

• Thi Bolam, Ruth Parker, Claire Mason, Jon Barry, Silke Kröger, Briony Silburn, Dave Sivyer, Silvana Birchenough, Andrew Mayes and Gary Fones. The Application of Passive Sampler (DGT) Technology for Improved Understanding of Metal Behavior at Marine Disposal Sites. Conference on DGT and the environment (Lancaster, July 2013).

• Silvana Birchenough and Claire Mason. Fit for purpose monitoring: cost effective sampling to characterise a dredged material disposal site. Hyder consultancy LTD. Cefas, (Lowestoft, 18th September, 2012).

• Silvana Birchenough and Claire Mason. Monitoring and Assessment: An example of fit for purpose monitoring at Souter Point Dredged material disposal site. Environment Protection Agency Kuwait meeting Cefas, (Lowestoft, 1st May 2011).

35

• Silvana Birchenough. Application of the SPI Technology for application and development (Module 7, contract ME5403) MMO, (Date TBC)

8.2 Papers (in preparation)

1. R. Parker, T. Bolam, S. Kröger, C. Mason, S. Birchenough, B. Silburn, D. Sivyer, A. G. Mayes and G. R. Fones (in prep) The application of passive sampler (DGT) technology for improved understanding of metal behaviour at a marine disposal site. Environmental International.

2. S. Birchenough C. Mason. R. Parker, T. Bolam, S. Kröger, B. Silburn (in prep) Complimentary science to inform dredge disposal site monitoring – a holistic view of how to integrate different monitoring techniques. Marine Policy.

36

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Appendix 1: Images

Figure A1. DGT average flux profiles with total metal plots from discrete samples (Cadmium=Cd,

Lead=Pb, Nickel=Ni and Ion=Fe and Manganese=Mn). Note that for Cd at the Reference station,

total Cd concentration is actually the LOD value as there were all <LOD.

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

0 0.1 0.2 0.3 0.4 0.5

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(cm

)

Flux (fmol/cm2/s)

Cd Flux

Average Reference Station Total metal

-23

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-8

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0 0.5 1 1.5 2

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Cd Flux

Average Station C Total metal

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0

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

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Average Station S Total metal

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0

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)

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Average Reference Station Total metal

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-8

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2

0 0.5 1 1.5 2 2.5

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th (

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)

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Average Station C Total metal

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Average Station S Total metal

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43

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