LNG and Pollution

7/30/2019 LNG and Pollution

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Compiled by Arthur MacKayBocabec, NB, Canada

September, 2012

LNG Related Pollution

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Resource les are created from the contents of the working reference and publication les of ArtMacKay and are made available for reference purposes. They contain documents, drawings, pho -tographs and other resources accumulated over a 50 year period, including public domain materi -als as well as materials with copyrights held by Arthur MacKay and others.

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VallejoCPR Graphic

Home Risks & Dangers

Emissions Facts

The Bechtel-Shell plants will bring a number of sources of pollution into Vallejo:

The power plantThe LNG shipsThe diesel-fueled dredgers, tugs and Coast Guard security vesselsHelicopters

The Power Plant

According to Shell, the 900-megawatt power plant alone will release over 1,692 tons per year (that's 4.9tons per day!) of smog-producing, asthma-aggravating greenhouse gasses and cancer-causing toxic

pollutants into Vallejo's air. The following represent some of the emissions from the proposed power plant:

201.9 tons of Nitrogen Oxides (403,800 pounds)876.3 tons of Carbon Monoxide (1,752,600 pounds)41.7 tons of Volatile Organic Compounds such as Benzene (a known human carcinogen),Hydrocarbons (many known to cause cancer), and Reactive/Precursor Compounds (83,400

pounds)129.6 tons of PM-10 (very detrimental to health, as these particulates readily lodge in the lungs

and cause toxic effects; 259,200 pounds)18.3 tons of Sulfur Dioxide (a criteria pollutant that causes acid rain; 36,600 pounds).

These levels of contamination consider only the proposed power plant, and do not consider the transportships, LNG offloading, regasification facility, dredging, pipelines, trucking, and/or accidents at the facility.

Marine Vessel Emissions

LNG tanker emissions and the emissions of other so-called "secondary sources" are a major healthconcer n. These marine vessels are not subject to Bay Area or EPA emissions regulations, though they

may be subject to CEQA review. So far, Bechtel-Shell have avoided any public discussion of thesignificant emissions from secondary sources, other than to say that they should not be regulated becausethey are not attached to the land, according to Shell's David Thomson.

Unfortunately, unlike attempts to mitigate power plant emissions with 160-foot stacks, there is no way toredirect emissions from the vessels away from our town or our neighbors downwind.

LNG Tanker Emissions

The LNG tankers are powered by huge steam turbines, which are fueled by LNG, diesel and bunker fuel.
http://c/Users/Art/Desktop/LNG/index.htmlhttp://c/Users/Art/Desktop/LNG/LNG%20POLLUTION/index.htmlhttp://c/Users/Art/Desktop/LNG/LNG%20POLLUTION/index.htmlhttp://c/Users/Art/Desktop/LNG/index.html


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Shells David Thomson, a former LNG ship captain, stated that these tankers will burn 100 tons per dayof fuel, three times per week during their 24-hour turnaround and offloading time at the south end of MareIsland. Diesel and bunker fuel make up 20 percent of that amount -- 3,120 tons. The total fuel burnedfrom the LNG tankers alone would be:

100 tons per day, three days per week 156 days per year 15,600 tons per year

Emissions from Dredgers, Tugs and Coast Guard Security Vessels

Extensive and constant use of diesel-powered vessels will contribute significantly to the toxic emissions.Along with the LNG Tankers, these vessels contribute so-called "secondary emissions", which are notsubject to EPA regulations, and use diesel, one of the dirtiest and most harmful of the commercial fossilfuels.

Dredgers will contribute significantly to toxic emissions. Dredging to maintain the turning basin andoffloading terminal for the LNG ships will be virtually constant because the Napa River produces a highamount of silt. In addition, massive dredging will be required to deepen ten miles of the Pinole Shoal.

Multiple tugboats and Coast Guard security vessels will operate alongside the LNG tankers three days aweek.

UPDATE! Bechtel-Shell Admit Marine Vessel Emissions Will Exceed Power Plant Emissions!

On November 13, 2002, David Stein from the Bay Area Air Quality Management District addressed theCity's Health and Safety Subcommittee. Mr. Stein revealed that he had been given emissions data byBechtel-Shell for one tanker and one tugboat, and that those emissions alone would exceed thepower plant emissions!

Curiously, this is an underestimate of the actual emissions for the marine vessels because Bechtel-Shell leftout the multiple tugboats, the coast guard escort vessels, and the constant use of diesel-fueled dredgers.

Diesel Risks and Lack of Regulation of Marine Vessel Emissions

There are no standards for foreign-flag vessels entering U.S. ports -- all LNG ships are foreign flag. TheUnited States Environmental Protection Agency (EPA) is considering extending certain regulations toforeign-built vessels, but is receiving heavy opposition from the shipping industry. The EPA recognizesthat marine vessel emissions are a major concern and is currently proposing regulations that would requireall future marine vessels built in the U.S. to comply with emissions standards.

Diesel particulate matter is a huge modern health problem, accounting for 70 percent of the total toxicrisk to Californians from air pollution," according to the Bay Area Air Quality Management District.Diesel has recently been added to Californias Proposition 65 hazardous substance list, and garneredattention after the release of studies in early 2002 confirming that diesels toxic particulates cause lungcancer and other respiratory diseases. More on diesel pollution

Emissions Mitigation
http://www.baaqmd.gov/planning/plntrns/retrofit.htm


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One of Bechtel-Shell's recent ad campaigns was designed to lessen concerns about emissions from their proposed project. They offer the solution of emissions offsets that will allegedly Clear the Air inVallejo."

The problem with this ad campaign is that it omits a critical fact that most Vallejo and Solano Countyresidents would need to know -- that the impact of emissions trading on air pollution will be regional, notlocal. While the air may become cleaner elsewhere, it will become dirtier in Vallejo.

To begin operating their power plant in Vallejo, Bechtel-Shell would be required to trade "emissionscredits" with other polluting businesses. These businesses could be located anywhere in the huge 600-square mile, nine-county Bay Area Air Quality Management District . This would include counties as far away as Santa Clara and San Mateo.

Unfortunately, because there are no "point sources" of pollution in our area that can be scaled back enough to compensate for the massive increase in pollutants from the power plant alone, Bechtel-Shellwill have to go elsewhere to look for a business that will stop polluting so they can start polluting here.Bechtel-Shell would pay these businesses to pollute less to compensate for increasing Vallejo's

air pollution. No Mitigation of the Massive Marine Vessel Emissions

Even more egregious is Bechtel-Shell's concealment of the fact that they would not be required to mitigatethe massive amounts of pollution from the marine vessels. This is because of the regulatory structure - aslong as the power plant emissions falls below a certain level, they local regulators will not consider emissions from the marine vessels - despite the fact that they will exceed the power plant's.

So while emissions will be lowered in that other community, the Bay Area will suffer a net increase inemissions - because only the power plant emissions would be mitigated - the ships and boats will causeour overall Bay Area pollution to increase. And here, in Vallejo and Solano County, we will suffer from amajor local increase in pollution.

Related Links:Emissions Banking InformationDetailed discussion of Vallejo's Air Quality and impact of the project emissions Environmental ScientistGayle Edmisten Watkin

2002 maggdog communicationsPhotos courtesy of Michael Halberstadt, Joyce Scharf and Friends of VallejoCPR Page Last Updated Jan 8, 2003Email: [email protected]
mailto:[email protected]://c/Users/Art/Desktop/LNG/LNG%20POLLUTION/edmisten-watkin.htmlhttp://www.baaqmd.gov/permit/banking.htmhttp://www.baaqmd.gov/pie/basin.htm


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Speciation and bioavailability of mercury inwell-mixed estuarine sediments

Elsie M. Sunderland a,b, *,1 , Frank A.P.C. Gobas a , Andrew Heyes c , Brian A. Branfireun d ,Angelika K. Bayer d , Raymond E. Cranston e, Michael B. Parsons e

a School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 b

Office of Science Policy (8104S), Office of Research and Development, United States Environmental Protection Agency,1200 Pennsylvania Ave. N.W., Washington, DC 20007, USA

c Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, University System of Maryland, P.O. Box 38, Solomons, MD 20688-0038, USA

d Department of Geography, University of Toronto at Mississauga, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6 e Natural Resources Canada, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography,

P.O. Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2

Received 12 June 2003; received in revised form 19 November 2003; accepted 16 February 2004Available online 7 June 2004

Abstract

Despite regulations controlling anthropogenic mercury sources in North America, high levels of mercury in coastal fish andshellfish are an ongoing problem in Maritime Canada and the Northeastern United States. This study presents sediment coredata from a macrotidal estuary located at the mouth of the Bay of Fundy showing stratigraphic profiles of total andmethylmercury concentrations and potential methylation rates measured using stable mercury isotopes. The results show that incontrast to the expected methylmercury profile typically observed in unmixed sediments, methylmercury production occursthroughout the estimated 15-cm-thick active surface layer of these well-mixed sediments. The resulting large reservoir of methylmercury in these sediments helps to explain why mercury concentrations in organisms in this system remain high despiteemissions reductions. Current management policies should take into account the expected delay in the response time of well-mixed estuarine systems to declines in mercury loading, considering the greater reservoir of historic mercury available in thesesediments that can potentially be converted to methylmercury and biomagnify in coastal food chains.D 2004 Elsevier B.V. All rights reserved.

Keywords: Methylmercury; Estuaries; Enrichment factor; Sediment burial; Bay of Fundy

1. Introduction

Mercury emissions from anthropogenic sources inMaritime Canada and the Northeastern United Stateshave declined by more than 50% from peak levels inthe 1970s as a result of pollution control measures(Sunderland and Chmura, 2000) . However, there is no

0304-4203/$ - see front matter D 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.marchem.2004.02.021

* Corresponding author. Office of Science Policy (8104R),Office of Research and Development, United States EnvironmentalProtection Agency, 1200 Pennsylvania Ave. N.W., Washington, DC20007, USA. Tel.: +1-202-564-6754; fax: +1-202-565-2925.

E-mail address: [email protected] (E.M. Sunderland).1 This research was conducted while Dr. Sunderland was a

graduate student at Simon Fraser University and reflects the authors personal views. This study is not intended to portray policies or views of the U.S. EPA.

www.elsevier.com/locate/marchemMarine Chemistry 90 (2004) 91105


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evidence of similar declines in the concentrations of mercury in marine birds, fish and shellfish from theBay of Fundy region of Canada, which is a catchment

for atmospheric mercury contamination from indus-trialize d regions of Central Canada and the UnitedStates (Chase et al., 2001; Evers et al., 1998; NES-CAUM et al., 1998) . Methylmercury (MeHg) levels infish and invertebrates surpass Environment Canadastissue residue guideline of 0.033 ppm ( 0.16 nmol g

1)for the protection of all aquatic life (CCME, 2000;Chase et al., 2001) , and at the highest trophic levels,total mercury concentrations exceed the Health Can-ada guideline of 0.5 ppm (2.5 nmol g

1) for safeconsumption by humans (Gaskin et al., 1973, 1979; NESCAUM et al., 1998) . A better understanding of the relationship between concentrations in organismsand emissions reductions is needed to develop effec-tive strategies for reducing potential human healthimpacts of mercury in the Bay of Fundy.

The conversion of inorganic mercury to methyl-mercury is a critical process affecting the relation-ship between mercury inputs and concentrations in biota. The majority of mercury released as a byprod-uct of human activities and present in the environ-ment is inorganic mercury, but only the most toxic-organic form, MeHg, bioaccumulates in organisms

(Bloom, 1992) . There is considerable evidence that production of MeHg is principally a biologicallymediated reaction carried out by sulfate-reducing bacteria in marine sediments (Benoit et al., 1999;King et al., 1999) . Because these microbes areanaerobes, benthic sediments in coastal systemsoften provide the most suitable environment for MeHg production (Choi and Bartha, 1994) . Coastalsediments also act as a reservoir for past and present mercury inputs due to the affinity of inorganicmercury species for particulates and organic matter

(Gagnon et al., 1996; Mason and Lawrence, 1999) .Two of the main factors determining the exposure of coastal organisms to mercury are therefore: (i) theamount of inorganic mercury in the sediments that isconverted to MeHg; and (ii) the geochemical con-ditions that affect the activity of methylating bacteriaand the availability of inorganic mercury for meth-ylation. To gain insight into the temporal responseof mercury concentrations to changes in mercuryinputs, it is important to understand both of thesefactors.

The Bay of Fundy has the worlds larg est tides,reaching up to 16 m at the mout h of the bay (Gregoryet al., 1993) . Tseng et al. (2001) observed that mixing

of sediments in the fluid mud profile of a turbidmacrotidal estuary in France creates a distinct geo-chemical environment that facilitates the activity of microbial populations converting inorganic mercury toMeHg. Based on these data, we hypothesized that physical mixing in the Bay of Fundy will change thegeochemical characteristics of the surface sedimentsand increase the depth of the active sediment layer where methylation takes place. The active sediment layer is operationally defined in this study as sedimentsthat can potentially exchange mercury with the water column and buried sediments through resuspension,diffusion and burial. Thus, the thickness of the activelayer is a function of the depth of biological mixingand the depth of p hysical mixing/continual reworking(Boudreau, 2000) . The relatively thick active sediment layer in the Bay of Fundy may effectively increase theamount of total and methylmercury in the sediment compartment that is available to organisms, as compared to other more static estuarine systems.

In this paper, the effects of sediment mixing areexplored by investigating ambient profiles of totalmercury and MeHg and potential MeHg production

rates measured in sediment cores from contrastingsites at the mouth of a freshwater tributary and inwell-mixed regions of a coastal embayment located at the mouth of the Bay of Fundy. Evidence is presentedthat demonstrates the effects of mixing on the depthand geochemistry of the active sediment layer in thissystem. The implications for mercury uptake at the base of the food chain and the temporal response of this system to reductions in anthropogenic mercuryemissions are discussed.

2. Methods

2.1. Study site

Sediment cores were collected in PassamaquoddyBay and the St. Croix River Estuary between May andAugust 2001 (Fig. 1) . Passamaquoddy Bay is a semi-enclosed macrotidal estuary located at the mouth of the Bay of Fundy. The mean tidal range in Passama-quoddy Bay is 6 8 m, making it a turbid, tidally

E.M. Sunderland et al. / Marine Chemistry 90 (2004) 9110592


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dominated system (Gregory et al., 1993) . The St.Croix River is the main freshwater inflow to Passa-maquoddy Bay and runs along the border betweenCanada and the United States. Related investigations(Sunderland, 2003) show that total mercury concen-trations in surface sediments in Passamaquoddy Bayand the St. Croix River Estuary range between 50 and

750 pmol g 1

dry weight, with the highest concen-trations found at the head of the St. Croix River Estuary.

2.2. Field sampling

2.2.1. Push coresEight 15-cm-long surface sediment push cores

were obtained from a large volume, modified VanVeen grab sampler at selected locations in May andAugust 2001 using acid-washed PVC/Plexiglas core

tubes (Fig. 1) . Duplicate cores were collected at sitesSC-1, PB-3 and PB-7 and analyzed for total mercuryand MeHg. Push cores collected at sites PB-7 and PB-8 were only analyzed for total mercury. All cores wereextruded at 2-cm intervals in the laboratory on shore,and all samples were frozen until analysis. Sulfideconcentrations in the wet sediments of push core

subsamples were analyzed using an ion-specific elec-trode after addition of sulfide antioxidant buffer according to the method outlined by Wildish et al.(1999) . Redox potential (Eh) was measured at thesediment surface of gravity core and push core sampling locations using an Orion platinum redox elec-trode and a calomel reference electrode.

2.2.2. Gravity coresMultiple gravity cores ( n = 20) were collected to

characterize the geochemical profile of sediments in

Fig. 1. Map of the study area showing sampling locations for gravity cores, push cores and isotope cores.

E.M. Sunderland et al. / Marine Chemistry 90 (2004) 91105 93


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Passamaquoddy Bay and the St. Cr oix Rive r Estuaryusing a 1.5-m-long gravity corer (Fig. 1). Gravitycores were sectioned into 5-cm vertical intervals to a

depth of 20 cm, after which they were divided into 10-cm increments. Sediments were placed in polyethyl-ene sample containers and cooled at temperatures < 4j C to minimize chemical transformations followingextrusion. Vertical gradients of dissolved ammoniumand sulfate were measured in sediment porewaterswithin 24 h of sampling to estimate present-daysediment accu mulation rates followin g the methoddeveloped by Cranston (1991, 1997) . This methodestimates sediment burial rates with in a factor of 2 of radiometric dating (Cranston, 1991) and is particularlyuseful in erosion and transport regions of the estuarine basin where sediments cannot be dated using tradi-tional methods. All cores were freeze-dried and ar-chived for further analysis. In addition to totalmercury, gravity cores were analyzed for a spectrumof metals including Fe, Li, Mn and Pb. Subsamplesfor metal analysis were prepared by digesting 1.0 g of freeze-dried sediment in 5.0 ml of concentrated nitricacid for approximately 24 h at 60 j C. Flame atomicabsorption analyses were carried out using a Varian220FS spectrometer for Fe, Li and Mn. Electrothermalatomic absorption analysis of Pb was carried out using

a Varian 220FS spectrometer fitted with a VarianGTA110 graphite furnace. Relative precision andaccuracy limits, estimated from replicate analyses of CANMET-certified reference materials (STSDs 14)and an internal GSC standard (EMG-017), weredetermined to be F 3% for Fe, Li and Mn andF 5% for Pb. Total and organic carbon was deter-mined in 0.5 g of freeze-dried sediment using a LecoWR-112 carbon analyzer. Inorganic carbon was re-moved using 1 M hydrochloric acid prior to organiccarbon measurements. Precision and accuracy were

estimated to beF

0.03 wt.% based on replicateanalyses of calibration standards.

2.2.3. Sediment porewatersSediment porewater samples were separated from

selected push cores ( n = 2) and surface sediment samples ( n = 23) collected at the push core and gravitycore sampling locations. Porewaters were extractedunder a nitrogen atmosphere by transferring the bulk sample into 50-ml acid-washed polycarbonate centri-fuge tubes. Tubes were purged with N 2 prior to

transfer, centrifuged at 3000 rpm for 30 min, followed by vacuum filtration with disposable 0.2- Am cellulosenitrate filter units. All filters were rinsed with 1% HCl

and distilled deionized (18 V Millipore filtrationsystem) water immediately prior to use. Porewater samples for total mercury analysis were preserved in0.5% ultrapure HCl, while MeHg samples were im-mediately frozen until analysis.

2.2.4. Isotope coresAt two stations (SC-1 and PB-3), duplicate intact

sediment cores were spiked at 1-cm intervals withinorganic mercury isotope [91.95% 199 Hg(II) fromOak Ridge Batch #168490] that was pre-equilibratedwith seawater. Cores were incubated at ambient sea-water temperature for 4 h, extruded and frozen untilanalysis for conversion of 199 Hg(II) into methylatedmercury. The purpose of this work was to determine amethylation potential for these sediments rather than using the isotope as a tracer because the added199 Hg(II) may be more available for methylation thanthe in situ Hg(II).

2.2.5. PolychaetesPolychaete worms ( Nephtys sp.) were collected

from benthic sediments at the same sampling loca-

tions as push cores, gravity cores and isotope cores.Samples were obtained by immediately sieving thewet sediments collected using a modified Van Veengrab sampler on board the sampling vessel. Poly-chaetes were identified in the laboratory, flushed withdeionized water for 24 h and frozen until analysis for mercury. Biological samples were analyzed for totalmercury using the same methodology as sediment samples.

2.3. Mercury analyses

Samples for total and MeHg analyses were placed in 125-ml acid-washed polypropylene speci-men jars and were immediately cooled to < 4 j C.Upon returning to the laboratory, all samples werefrozen until analysis. Wet sediment samples wereanalyzed for total mercury by digestion in 5:2concentrated nitricsulfuric acid solution and oxida-tion with bromine monochloride (BrCl) under Class100 clean room conditions. Aqueous samples weredigested with BrCl for at least 12 h before analyses.



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Immediately prior to analysis, the excess bromine inall samples was neutralized with an equivalent volume of 10% hydroxylamine hydrochloride. All

samples were then reduced with stannous chloride, purged with nitrogen gas and trapped on gold packed columns. Quantification was by dual-stagegold amalgamation and cold-vapor atomic fluores-cence spectroscopy (CVAFS). T his procedure was based on EPA Method 1 631, Gill and Fitzgerald(1987) and Bloom (1989) . Methylmercury was de-termined by steam distillation, aqueous phase ethyl-ation using sodium tetraethylborate, purging ontoTenax k packed columns, gas chromatography sep-arat ion and CVAFS detection foll owing a technique by Bloom and Fitzgerald (1988) and Horvat et al.(1993) , modified by Branfireun et al. (1999) . Thesame methods were used for samples spiked with199 Hg(II) isotope except that detection was madeusing an HP4500 Inducti vely Coupled Plasma-MassSpectrometer (ICP-MS) (Gill and Fitzgerald, 1987;Hintelmann and Evans, 1997) .

The method detection limit (MDL) for total mer-cury in sediment solids was 0.95 pmol g

1 (n = 19),determined as three times the standard deviation of themean of the sample blanks. For aqueous samples, theMDL based on a 150-ml sample volume was 0.20 pM

(n = 18). Precision, measured as the relative percent difference (RPD) between digest duplicates (sediment solids) and analytical duplicates (aqueous phase),were 9.6% ( n = 24 pairs) and 5.7% ( n = 2 pairs),respectively. Calibration curves of at least r 2 = 0.99were achieved daily or samples were rerun. Accuracywas measured both by spike recoveries and using theMESS-3 marine sediment certified reference material(454 F 45 pmol g

1 ) from the National ResearchCouncil of Canada. Recoveries averaged 103 F 10%(n =12) and 459 F 80 pmol g

1 for all MESS-3

samples ( n = 9). Samples from runs with poor recov-eries ( < 80%) were reanalyzed. For MeHg, the MDLwas 0.032 pM ( n = 6) in the aqueous phase and 0.035 pmol g

1 (n = 16) for sediment solids. For ICP-MS,the detection limit was 0.075 pmol g

1 and samplereproducibility was 10% for ambient MeHg and 23%for the CH 3

199 Hg isotope concentration. Isotope de-tection was further constrained to 0.5% of the ambient concentration. The RPD for distillation duplicates was18.1% (n = 21), while the average recovery of spikes between 0.5 and 2.5 pmol g

1 of wet sediment was

106 F 26% (n = 12). Some of this variability can beattributed to uncertainty as to the true concentration of the sediment sample being spiked, as reflected in the

RPD of distillation duplicates. A wet to dry weight conversion was determined for each sample analyzed by oven-drying subsamples of wet sediments for at least 24 h at 60 j C.

2.4. Statistical analysis

Nonparamet ric bivariate corre lation matrices(Spearman rank correlation coefficients, r s) weredeveloped for gravity core and push core data toinvestigate covariation between total mercury (Hg-T), MeHg, %MeHg and potential methylation rates.For gravity core data, Hg-T profiles were analyzedas a function of other metals with known anthropogenic origins such as Pb and other geochemicaldata including porewater sulfate and ammoniumconcentrations.

3. Results

3.1. Speciation in the active sediment layer

Fig. 2 shows mercury speciation in sediment coresfrom contrasting physical regions. The St. Croix River station (SC-1) is located at the head of the St. CroixRiver Estuary where the sediment accumulation ratewas estimated to be between 1 and 2 mm year

1

based on the gradients in dissolved ammonium foundin the gravity cores using the method developed byCranston (1991, 1997) . In contrast, stations PB-3 andPB-4 are located on opposite sides of the main basinof Passamaquoddy Bay (Fig. 1) , near the center of twotidally dominated circulation gyres (Greenberg et al.,

1997) that are expected to result in significant mixingof these sediments.

3.1.1. Total mercury (Hg-T)At station SC-1 (Fig. 2a) , there is a pronounced

subsurface peak in total mercury (Hg-T) that may bethe result of historic mercury discharges from a chlor-alkali facility that operated along the river in the1970s. Concentrations of Hg-T in the sedimentsdecrease from the head of the river estuary into thecenter of Passamaquoddy Bay. The uniform Hg-T



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Fig. 2. Speciation of mercury measured in push cores from contrasting depositional (SC-1) and well-mixed sediments (PB-3 and PB-4). Datainclude ambient total mercury (Hg-T), methylmercury (MeHg) and the fraction of total mercury in the sediments present as MeHg (%MeHg).Mercury isotope experiments were used to estimate the potential methylation rates at the head of the St. Croix River Estuary (SC-1) and thecenter of Passamaquoddy Bay (PB-3).



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profiles at stations PB -3 and PB-4 o n both sides of Passamaquoddy Bay (Fig. 2b and c) provide further evidence that these sediments are also well mixed.

3.1.2. Methylmercury (MeHg)The effects of differing physical dynamics on

MeHg product ion are illustrated by the contrastingMeHg profiles (Fig. 2) at the head of the river estuary(SC-1) relative to the well-mixed areas in the center of Passamaquoddy Bay (PB-3 and PB-4). The fraction of total mercury present as methylmercury (%MeHg) inthese sediments is strongly correlated with potentialmethylation rates measured in cores spiked withmercury isotopes ( r s = 0.88, p < 0.01), supporting the premise that %MeHg is a reasonable approximation of the relative rates of Hg methylation in these sedi-ments. This relation ship has also been s een in other estuarine sediments (Benoit et al., 2003) .

At station SC-1, MeHg production is taking placein a narrowly constrained subsurface zone. There is asubsurface peak between 2 and 4 cm in ambient MeHg concentrations, %MeHg and potential methyl-ation rates measured in isotope cores. Ambient MeHgconcentrations decline rapidly in the oxic surface layer and beyond depths of several centimeters, whilemethylation rates indicated by both the %MeHg and

the isotope core data are low to nondetectable, re-spectively, in these depth intervals. For example, the%MeHg ranges between 0.54% and 0.76% in the 24cm subsurface peak in MeHg production at stationSC-1, compared to 0.28% in the surface layer, and between 0.11% and 0.34% at depths greater than 6cm. This profile is typical of those observed in other studies of relatively unmixed lake and estuarine sedi-ments, which show that the %MeHg in estuarinesediments is generally less than 0.5%, particularly inthe oxic surface sediments and at depth, and that

MeHg production occurs in a relatively narrow sub-surface zone within the sediments (e.g., Benoit et al.,1998a; Bloom et al., 1999; Gagnon et al., 1996 ).

In the mixed sediments at stations PB-3 and PB-4,the ambient MeHg profiles and %MeHg suggest that MeHg conversion is taking place at all depths in thesurface sediment layer. Methylmercury concentrationsand %MeHg are both relatively uniform at all depths(Fig. 2b and c) and potential methylation rates mea-sured at station PB-3 are detectable throughout theentire profile studied. At station PB-4, the %MeHg

ranges between 0.62% and 0.92%, which is in thesame range as the 24 cm subsurface peak in %MeHgat site SC-1 that corresponds to maximum methylation

rates. Additionally, the mean %MeHg in integratedsurface samples (0 10 cm depth) from multiplelocations throughout Passamaquoddy Bay ( n =45)was 0.88%, again, characteristic of sediments whereMeHg is being actively produced in situ in thesediment column. These data support the premise that in the well-mixed sediments of Passamaquoddy Bay,MeHg production is taking place both at the sedi-mentwater interface and throughout the 15-cm-thick active surface layer.

3.2. Porewatersolids partitioning

Porewater samples in this study represent opera-tionally defined dissolved concentrations of totalmercury and methylmercury since colloid al matter binds mercury in the < 0.2- Am size fraction (Guentzelet al., 1996) . Porewater co ncentrati ons of Hg-T ranged between 50 and 150 pM (Table 1) and are significant-ly elevated above the levels expected on the basis of solid-phase concentrations, as they are in the samerange as sites heavily impac ted by historical pollu tion,such as Lavaca Bay, TX (Bloom et al., 1999) . Ac-

cordingly, the range in partition coefficients (log K d)for Hg-T between 3.12 and 3.76 (l kg

1) in Passa-maquodd y Bay is lower than those observed in other systems (Bloom et al., 1999; Leermakers et al., 1995;Turner et al., 2001) . Elevated levels of Hg-T in pore-waters of Passamaquoddy Bay sediments are consis-tent with the effects of mixing in this system, which iscausing substantial recycling of Hg in the surfacesediments and an increased fraction of colloidally bound Hg-T in the porewaters.

Table 1Porewater Hg-T and MeHg data from surface sediment grabsamples at stations SC-1 and PB-1 through PB-5

Station Hg-T (pM) MeHg (pM)

SC-1 135 2.3PB-1 150 a 4.7 a

PB-2 55 N/APB-3 80 a 2.7 a

PB-4 50 3.4 b

PB-5 80 b 7.2 a

a Means of triplicate samples. b Means of duplicate samples.



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Porewater MeHg concentrations are also elevatedrelative to systems with similar Hg-T concen trationsin sediments such as the Patuxent River, MD (Benoit

et al., 1998a) , but partition coefficients (log K d )ranging between 2.20 and 3.00 (l kg 1) are in the

same range as values found in other studies (Benoit et al., 1998a; Bloom et al., 1999) . These results suggest that MeHg concentrations are enriched in both thesolid and dissolved phases and support the hypothe-sized increase in MeHg production in well-mixedsediments.

3.3. Geochemical characteristics of the sediment column

Fig. 3 shows porewater ammonium (NH 4+ ) andsulfate levels measured in gravity cores collected inPassamaquoddy Bay. Porewater NH 4

+ concentrationsthat are consistently >0. 5 mM occur below a depth of 30 cm at stat ion PB-3 (Fig. 3) and below 15 cm at station PB-4 (Table 2) .

Porewater NH 4+ concentrations >0.5 mM indicate

anoxic sediments that are below the active sediment layer due to lack of oxidation of amm onium produced

by decomposition of organic matter (Buckley, 1991;Buckley and Cranston, 1988) and allow an upper boundary to be placed on the depth of the activesediment layer. These sediments may be consideredtruly buried and effectively removed from further interaction with the sedimentwater interface. Datafrom other cores collected throughout PassamaquoddyBay further confirm that the depth of the activesediment layer based on porewater a mmonium datais generally between 15 and 30 cm (Table 2) . Thisrelatively large volume of sediments in the activesediment layer results in a large pool of historic Hg-T that can potentially be converted to MeHg.

Data on porewater sulfate levels in gravity coresfrom Passamaquoddy Bay indicate that sulfate reduc-tion is taking place at all depths within these sedi-ments, including at the sediment surface ( Fig. 3, Table2). Anoxic reduction of sulfate based on a geochem-ical threshold established in the literature is ind icated by porewater sulfate concentrations < 24 mM (Buck-ley, 1991; Buckley and Cranston, 1988) . In all Passa-maquoddy Bay sediments, porewater sulfate levels arevery close to this level, supporting the idea that these

sediments are in the oxic-transitory range that is most conducive for the activity of SRB.

Although porewater sulfate data (Fig. 3) indicateanaerobic reduction of sulfate, which typically corre-spond s to a redox potential of approximately 200mV (Wildish et al., 1999) , redox potentials (Eh)measured in surface sediments varied between 213 and 512 mV (Sunderland, 2003) . The largevariability in redox measurements and length of time(>5 min) needed in the field for the redox probe toachieve equilibrium may both signify the presence of

Eh microniches in the surface layer (Wildish et al.,1999) ; however, these data should be interpreted withcaution as variability may also reflect measurement errors associated with these types of Eh measure-ments. Sulfide concentrations measured in the surfacesediments using an ion-specific electrode were alsohighly variable, ranging between 10 and 4000 AM inreplicate samples taken at a single sampling station(Table 3) . The large variability in sulfide concentra-tions and the presence of Eh microniches show rapidtransitions in the sediment geochemistry in the surface

Fig. 3. Porewater sulfate and ammonium concentrations measuredin gravity cores from Passamaquoddy Bay and the St. Croix River Estuary. Sulfate concentrations < 24 mM indicate the anoxicreduction of sulfate and ammonium concentrations >0.5 mMindicate the presence of fully reduced buried sediments.



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layer that provide conditions most favorable to meth-ylating microbes and are indicative of the effects of organic-rich mottles or pockets in the surfacesediments.

Visual inspection of sediment cores from Passa-maquoddy Bay in the field revealed the presence of black, organic-rich mottles interspersed with thedominant light brown oxic clay muds. There wasalso detectible H 2S odour in the presence of thesemottles, indicating anoxia. Based on these data, wehypothesize that the anoxic organic-rich pockets

in Passamaquoddy Bay sediments effectively in-crease the volume of sediments suitable for forma-tion of MeHg by SRB by increasing the transitionzone between oxic and anoxic sediments. The result-ing geochemical environment would be comparableto that observed by Tseng et al. (2001) in a turbidmacrotidal estuary in France where methylation of mercury was measured in analogous anoxic pock-ets occurring within a fluid mud profile. Theseorganic carbon pockets facilitate MeHg produc-tion throughout the relatively deep active sediment

Table 2Geochemical characteristics of gravity cores from Passamaquoddy Bay

Station ID Length(cm)

Organic carbon(%)

NH4+ > 0.5 mM depth

interval(s) (cm) a SO4

2 < 24 mM depthinterval(s) (cm)

Range in SO 42

mM b

SC-1 105 1.11 4.21 50 105 50 105 20 26SC-2 55 0.41 1.05 NI 5 10 22 27PB-1 50 0.24 1.37 NI 0 5; 10 15 22 24PB-2 130 0.92 1.74 5 10; 15 130 50 60; 80 130 19 29PB-3 100 1.01 1.77 30 100 0 5; 50 60; 70 80; 90 100 22 26PB-4 130 1.05 1.65 15 130 0 5; 10 50 23 28PB-5 130 0.76 1.48 NI 0 10; 50 60; 120 130 23 26PB-6 130 1.11 2.17 5 130 0 5; 40 50; 120 130 23 26PB-7 140 0.81 1.57 100 140 15 20; 60 80 23 26PB-8 130 1.00 1.36 15 130 0 5; 40 50; 120 130 23 26PB-9 127 0.28 1.15 60 127 0 5; 10 15; 90 100; 110 127 20 26PB-10 105 0.94 1.39 40 105 60 70 23 28PB-11 130 1.15 1.34 40 130 NI 24 27

PB-12 130 1.46 1.60 60 130 NI 24 27PB-13 130 1.15 1.63 60 130 NI 24 27PB-14 130 1.03 1.68 NI NI 24 27PB-15 130 0.79 1.69 70 100 NI 24 27PB-16 130 0.87 1.04 50 130 NI 24 27PB-17 c 130 1.08 1.65 30 130 NI 24 27PB 18 75 0.44 1.43 NI NI 24 27

NI = no indication of reduction. There is an evidence of reduction in all cores except PB-14 and PB-18, and even in these cores, the sulfate levelsare very close to the geochemical cutoff characterizing reducing conditions.

a Concentrations of NH 4+ > 0.5 mM measured in porewaters indicates lack of oxidation of ammonium produced by decomposition of organic

matter. In a number of cores, the presence of consistently >0.5 mM NH 4+ at depth suggests anoxic buried sediments.

b Minimum to maximum SO 42 concentrations measured in porewaters throughout each core are reported. Note that the range in SO 4

2

concentrations are all very close to the geochemical cutoff (24 mM) indicating anoxic reduction of sulfate. This supports the supposition that

most of these sediments are in the oxic transitory range where there is a large gradient in redox potential, ideal for the activity of sulfate-reducing bacteria.c Top 30 cm of core PB-17 missing.

Table 3Variability in sulfide concentrations measured in surface sediment grab samples from Passamaquoddy Bay

Sulfide concentrations (uM)

Station Mean N Min Max

PB-1 213 9 23 1500PB-2 659 7 190 1300PB-3 554 12 32 1100PB-4 667 6 480 800PB-5 1471 9 10 4000PB-6 363 6 33 1000PB-8 167 3 42 370PB-9 393 4 30 1200PB-10 92 3 36 150



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layer in Passamaquoddy Bay, thereby accounting for the observed enrichment in MeHg in the sediment porewaters and the high %MeHg in the solid-phasesediments.

3.4. Anthropogenic mercury in Passamaquoddy Bay

Anthropogenic sediment enrichment factors(ASEFs) were calculated from Hg-T concentrations

measured in sediment cores at stations SC-1 and PB-3. Mixing of these sediments means it is not possibleto obtain detailed information on historical Hg-Tloading from these cores and that traditional datingmethods using 210 Pb and 137 Cs could not be applied(Smith, 2001) . However, ASEFs calculated from thedifference between mercury concentrations in thesediments that accumulated prior to human influenceand those at the surface provide a simple method for

Table 4Concentrations of metals measured in gravity cores

Station Sediment depth (cm)

Hg(pmol g

1)Fe(nmol g

1)Li(Amol g

1)Mn(Amol g

1)Pb(nmol g

1)

PB-7 0 2 204 48.0 5.48 6.46 67.62 4 219 45.3 4.90 6.37 67.64 6 219 44.8 5.48 6.70 72.46 8 219 37.8 5.48 5.35 67.68 10 214 39.2 5.33 5.44 72.410 + 219 41.0 5.48 5.72 72.4

PB 8 0 2 214 47.6 6.20 6.63 77.22 4 219 49.2 6.34 7.15 67.64 6 224 50.3 6.34 6.75 62.76 8 209 50.9 6.20 7.41 67.68 10 214 49.8 6.48 7.12 62.710 + 209 41.0 6.05 5.88 57.9

SC 1 0 284 44.2 4.76 5.37 38.6

5 219 41.9 3.89 5.61 43.410 244 46.9 5.62 6.13 48.315 214 52.1 6.20 6.81 29.020 125 54.1 4.47 6.55 38.630 70 50.1 6.05 6.92 24.140 55 53.7 6.20 7.15 24.150 90 54.6 6.20 7.48 24.160 184 54.4 6.48 6.83 24.170 65 56.0 6.63 7.44 29.080 65 63.6 6.92 8.17 24.1

PB-3 0 229 44.9 5.91 7.04 91.75 249 41.9 5.91 6.84 91.710 319 40.8 5.76 6.73 115.815 379 44.4 6.05 7.19 91.720 274 43.9 6.05 6.61 106.230 189 41.5 6.48 7.06 62.740 80 38.3 6.48 6.72 43.450 80 39.2 5.76 6.12 33.860 50 35.6 5.91 5.66 29.070 40 35.8 7.06 5.39 33.880 45 34.4 6.05 5.37 29.090 40 36.2 5.76 5.97 33.8100 40 34.9 5.91 5.66 33.8

0.359 0.758Correlation with Hg ( r s) 1 N/S p < 0.05 N/S p < 0.001

Pearson correlation coefficients ( r ) for metals as a function of Hg are shown below concentration data for each core. N/S = correlation is not significant.



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estimating the overall enrichment in this systemresulting from anthropogenic pollution.

Present-day burial rates of approximately 12 mm

year 1

measured in this study suggest that sediments below 40-cm depth in gravity cores should represent Hg-T concentrations in the sediments prior to signif-icant human sources of mercury, while allowing awide margin for integration of the sediment columndue to mixing. Diagenetic remobilization of mercuryin sediment cores can cause peaks in mercury con-centrations in the surface sediments that are not indicative of anthropogenic pollution (Benoit et al.,1998b; Walton-Day et al., 1990) . However, the lack of significant correlations between Hg-T concentr ationsand redox-sensitive metals such as Fe and Mn (Table4) suggests that redistribution of mercury throughdiffusion and co-precipitation is not a significant factor in gravity cores from Passamaquoddy Bay. To

isolate the natural and anthropogenic components of metal enrichment, iron (Fe) and lithium (Li) can both be used as normalizing factors to correct for the

mineralogi cal and granul ometric variability in thesediments (Loring, 1991) . However, there were nosignificant correlations between Hg-T and Fe or Li inthese sediments; thus, it can be assumed that theobserved Hg-T profiles are not caused by changes ingrain size and/or mineralogy. The range of back-ground concentrations (i.e., those that are naturallyoccurring) of Hg-T in Passamaquoddy Bay cores wasestimated from 95% confidence limits around Hg-Tconcentrations below 40 cm in the gravity cores.Anthropo genic sediment enrichment factors shownin Fig. 4 include the surface of gravity cores and pushcores collected at stations SC-1 and PB-3. For surfacesediments obtained from push cores at the samesampling stations (0 15 cm), Hg-T concentrations

Fig. 4. Anthropogenic sediment enrichment factors (ASEFs) for Hg-T at the head of the St. Croix River and the center of Passamaquoddy Bay.ASEFs are used to estimate modern/background Hg-T levels in Passamaquoddy Bay sediments. The lower graphs in the figure depict gravitycore Hg-T data, while ASEF profiles shown for the surface sediments are from push cores taken from the same sampling stations.



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measured in the upper horizon of the sediments weredivided by the upper 95% confidence limit value for background merc ury levels to produce the plots of

ASEFs shown in Fig. 4.The results presented in Fig. 4 show that ASEFs inPassamaquoddy Bay range between 3 and 6 and up to26.3 at the head of the St. Croix River where localizedhistorical discharges are likely the most important source of contamination. The enrichment factors for Passamaquoddy Bay are in the same range as other studies that show a global scale increase in atmosphericmercury deposit ion of two to four times the pre-industrial levels (Swain et al., 1992; Engstrom et al.,1994) , suggesting that the majority of Hg-T in thesesediments is derived from atmospheric sources. Thehigh degree of correlation between lead, which isknown to exhibit a strong anthropogenic sig nal, andHg-T concentrations ( r s = 0.76, p < 0.001; Table 4 ) provides further evidence of anthropogenic enrichment in these cores. The results of this analysis indicate that the majority of the mercury in the active sediment layer of Passamaquoddy Bay is from historic inputs of mercury from anthropogenic sources.

4. Discussion

This study presents evidence showing that mixingof the active sediment layer in Passamaquoddy Bay

results in geochemical changes in the sediment column that enhance the activity of methylatingmicrobes. In marine sediments, net methylation rates

are highest in the transition zone between oxic andanoxic conditions because these c onditions are most conducive to the activity of SRB (Hintelmann et al.,2000; King et al., 2001) . In addition, these microbesrequire o rganic matter as a substrate for microbialactivity (Mason and Lawrence, 1999) . Physicalmixing in the Bay of Fundy may enhance thetransfer of sulfate and carbon and introduces more bioavailable inorganic mercury into the deeper sed-iment, potentially stimulating the methylating activ-ity of SRB. Regular disturbances through mixingalso appear to create a unique geochemical environ-ment more likely to exhibit microzonal redox gra-dients, compared to the classic down profilegradients of sediments in which less physicallydynamic conditions may limit the activity of microbial populations that methylate mercury. Fig. 5 is aconceptual diagram that contrasts the features of mercury speciation and sediment geochemistry ob-served in well-mixed sediments in this study withthe characteristic profile of mercury speciation typ-ical of depositional s edime nts.

As illustrated in Fig. 5, production of MeHg in

sediments from unmixed depositional systems must be modeled as a two-compartment system, taking intoaccount that MeHg production occurs in a narrow

Fig. 5. Conceptual model of mercury speciation in contrasting depositional and well-mixed sediments.



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zone in the redoxcline below the oxic surface layer of these sediments. In well-mixed systems, such asPassamaquoddy Bay, the sedi ment compartment is

better described by System 2 (Fig. 5) where MeHg production occurs throughout a relatively deep activesediment layer and is facilitated by the presence of organic-rich anoxic pockets or mottles. Addition-ally, MeHg production occurs at the sedimentwater interface in the well-mixed sediments, potentially providing a vector for MeHg entry into the water column and resulting in the exposure of organismsfeeding at the sediment surface.

The dynamic physical mixing occurring in Passa-maquoddy Bay results in the creation of an approxi-mately 15-cm-thick active sediment layer. Burial provides the main removal mechanism for historicmercury that has accumulated over time. In Passama-quoddy Bay, the sediment burial rate estimated fromthis study is approximately 12 mm year

1 . Thismeans that the active sediment layer is comprised of arelatively large reser voir of Hg-T consisting of mainlyhistorical pollution (Fig. 4) that has accumulated inthe sediments over many decades. In contrast, in adepositional system, the active layer is typically muchshallower (e.g., 35 cm) resulting in a much smaller reservoir of Hg-T that can be potentially converted to

MeHg by methylating microbes.As an illustrative example, the reservoirs of MeHg

in mixed and unmixed systems with comparable Hg-Tconcentrations were estimated usin g the Hg-T datafrom gravity cores SC-1 and PB-3 (Fig. 4) and pushcore data for %MeHg in the 14-cm surface horizon(Fig. 2) . Using an average sediment density of 2.7 gcm

3 and an average concentration of solids in thesediments of 0.67 g cm

3 for both sites, the reservoir of MeHg on an areal (1 m 2) basis are approximately3.5 and 2.4 Amol in the mixed and unmixed sedi-

ments, respectively. According to these calculations,the reservoir of MeHg is almost 50% higher in thewell-mixed sediments when compared to depositionalsediments with similar Hg-T concentrations.

The physical mechanism of mixing may also provide a vector for MeHg entry into the water column and food web through organisms feeding at the sedimentwater interface. In the well-mixed sedi-ments, MeHg production occurs throughout the activesediment layer, including at the sedimentwater in-terface as illustrated in the push core profiles for

Passamaquoddy Bay (Fig. 2b and c) . In contrast, theoxic sediment layer in unmixed, depositional systemscan act as a geochemical barrier to diffusing MeHg

through the precipitation of MeHg with Fe and Mnhydroxides (Gagnon et al., 1996) . In depositionalareas, this oxic layer can inhibit the entry of MeHgto the water column and limit exposure of all but burrowing benthic organisms.

In the well-mixed sediments of PassamaquoddyBay, the enhanced levels of Hg-T and MeHg in the porewaters of surface sediments are consistent withrapid cycling of mercury in this system at the sedi-mentwater interface that is facilitated by the physicaldynamics of the area. Preliminary evidence for in-creased availability of mercury to organisms in well-mixed sediments is provided by the observed differ-ences in the mean concentrations of total mercurymeasured in polychaetes collected from sediment grabs at the head of the St. Croix River Estuary(n = 3) compared to well-mixed sediments in Passa-maquoddy Bay ( n = 10). These data show that con-centrations of mercury in polychaetes are significantlyhigher ( p < 0.01) in the well-mixed sites (55 F 14 pmol g

1 wet wt.) than at the head of the river estuary (38 F 5 pmol g

1), despite significantly lower spatially averaged concentrations of Hg-T in surface

sediments from Passamaquoddy Bay ( f 150 pmolg

1) relative to the head of the river estuary ( f 550 pmol g

1) (Sunderland, 2003) .The results of this study help to elucidate why

concentrations of mercury in organisms from thiscoastal system are still high despite large emissionsreductions. In Passamaquoddy Bay, there is a linear relationship between Hg-T and MeHg in the sedi-ments (Sunderland, 2003) , which means that increases or decreases in Hg-T emissions shouldeventually translate into corresponding changes in

MeHg concentrations in sediments and ultimatelyorganisms. However, the results of this study sug-gest that there is a large lag time between reducedmercury inputs and changes in ambient concentra-tions because historic mercury inputs are slowly being converted to MeHg over the 15-cm-thick active sediment layer and removal of mercurythrough sediment burial is relatively slow. Thishypothesis is currently being further tested throughthe application of a mercury cycling model for theregion.



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Acknowledgements

This work was supported by a strategic grant

from the Natural Sciences and Engineering ResearchCouncil of Canada (NSERC), the Gulf of MaineCouncil on the Marine Environment and the NSERC Postgraduate Scholarship Program (ES).We acknowledge the assistance of Janice Weight-man from Simon Fraser University who collectedand identified biological samples. We thank the staff at Huntsman Marine Science Centre, Fisheries andOceans Canada and the Geological Survey of Canada for supplementary data and technicalsupport during field data collection including HughAgaki, John Dalziel, Gareth Harding, Doug Loring,Bob Murphy, Peter Vass and Dave Wildish. Wewould also like to thank Phil Yeats and JohnDalziel at the Bedford Institute of Oceanographyand two anonymous reviewers for their helpfulcomments during preparation of this manuscript.This is Geological Survey of Canada Contribution No. 2003056.

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