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G10 Mercury in marine ecosystems

Tuesday, 26 July, 2011

TG10-P2 — 11:00-12:00 and 17:30-18:30
CHANGES IN MERCURY PARTITIONING AND SPECIATION IN THREE ADJACENT COASTAL SYSTEMS (PORTUGAL) DUE TO A HEAVY RAIN SEASON
Author: CANÁRIO, João1
(1) IPIMAR/INRB IP, jcanario@ipimar.pt

Resolution of the biogeochemical cycle of Hg within estuaries is complicated by their physical, chemical and hydrological heterogeneity, variation on productivity, biodiversity, mercury inputs, and propensity for mercury to bioaccumulate in food webs. Several physical-chemical factors have been studied in order to access Hg partitioning and speciation within estuaries. Nevertheless, the effect of the increase in freshwater and river runoff during heavy rain periods is poorly documented.

In summer 2009 and in the heavy rain winter of 2009/2010 water and sediments were collected in the Tagus and Sado estuaries as well as in the Óbidos Lagoon. Tagus is known to have a high Hg contamination while Sado and Obidos are much less contaminated. Water samples were analysed for dissolved and particulate mercury and methylmercury and sediments were also analysed for the two Hg species.

While in Sado no differences in Hg concentrations (HgT<19 ng L-1) were found in water in the two periods, in Tagus a considerable decrease in those concentrations was determined (summer: HgT 13-97 ng L-1; winter: HgT <DL-30 ng L-1). In contrast, it was observed a considerable increase of Hg in Obidos lagoon (summer: HgT < 1.3 ng L-1; winter: HgT 35-90 ng L-1). These changes were followed by a substantial decrease in salinity in the Tagus while in the other sites no considerable differences were detected in this parameter. Methylmercury concentrations followed a similar pattern for the three systems in spite the MeHg proportion (in %) in Sado and Obidos decreased substantially. In the Tagus its proportion did not varied albeit presenting 10 times less MeHg.

Our results suggest that for Tagus and Sado Hg partitioning and speciation are ruled by a salinity effect. Freshwater input into the estuaries may reduce the complexation effect on Hg reducing therefore its concentrations in solution. On the other hand, the increase of Hg in the water column in the Obidos lagoon suggests an increase of Hg runoff from agriculture soils and possibly an increase of atmospheric Hg deposition.

Our study points to the importance of considering several variables for a chemical quality characterization of a water system.

TG10-P3 — 11:00-12:00 and 17:30-18:30
RELEASE OF MERCURY FROM SEA WATER TO THE ATMOSPHERE IN JIAOZHOU BAY IN WINTER
Authors: LIU, Ruhai1, LING, Min1, XU, Liaoqi1, WANG, Yan1
(1) Ocean University of China, ruhai@ouc.edu.cn

The species of mercury, emission flux using flux chamber and their diurnal variances were studied continuously at a station in the Jiaozhou Bay, a semi-close bay near city.

The average ratio of the reactive mercury to dissolved mercury was about 0.50 in the seawater. The variation range of methylmercury concentration on November 19th was smaller than that in December 22nd. The methylmercury concentration changes little within 2.5m depth and higher at the bottom. The DGM concentration correlated with the reactive mercury/dissolved mercury significantly (P<0.01), and DGM had negative correlation with DOC, but not significant. The significant positive correlation (P<0.05) with UV radiation indicated that photoreduction played an important role on the formation of DGM. The profile distributions of DGM changed obviously and the concentration was higher at the bottom.

The flux of mercury from the seawater to the atmosphere was -0.78?1.72ng/(m2·h) measured at field and the average was 0.26ng/(m2·h) on November 19th, which showed obvious bimodal diurnal variations. The small peak occurred after sunrise and the second appeared at 11:10. There was evasion of mercury from the water to the atmosphere before 14:00 and after 14:00 the emission was small or negative. The estimated emission flux of mercury on the same day using a gas exchange model was 0.14?1.52ng/(m2·h), which had similar diurnal variation characteristics and has highly significant correlation (P<0.01) with the field result. The average flux modeled was 0.63ng/(m2·h). On December 22nd, the modeled sea-air flux was 0.23?2.26ng/(m2·h), and the average was 0.85ng/(m2·h), which increased at first and then decreased. The UV radiation affected the emission flux by influencing the concentration gradient of sea-air.

TG10-P4 — 11:00-12:00 and 17:30-18:30
INFLUENCE OF BIOTURBATION ON MICROBIAL PRODUCTION OF METHYLMERCURY IN CONTINENTAL SHELF SEDIMENTS
Authors: NOGARO, Geraldine1, HAMMERSCHMIDT, Chad R.1
(1) Wright State University, geraldine.nogaro@wright.edu

Microbial methylation processes in sediments are an important source of toxic monomethylmercury (MMHg) to aquatic ecosystems. Although bioturbation activities (feeding, digging of galleries, excavations, bioirrigation) by benthic fauna are known to influence many biogeochemical processes, the role of bioturbation on benthic MMHg production is poorly understood. We investigated the effects of bioturbating fauna on microbial production of MMHg in sediments sampled from the continental shelf of the northwest Atlantic Ocean in September 2009. Control (sieved) and macrofauna cores were incubated in a dark experimental chamber. The influence of benthic macrofauna was measured on gross rates and net MMHg production, sediment reworking, oxygen and dissolved organic carbon concentrations, and microbial metabolic activities. The presence of macrofauna stimulated microbial respiration and net MMHg production but had no observed effect on short term gross rates of Hg methylation. This research advances knowledge and understanding concerning the interactions between benthic fauna, microorganisms, and Hg/MMHg dynamics in aquatic systems. Such information will be especially useful in assessing the impact associated with pollutant-derived Hg and its potential influence on the production, distribution, and bioaccumulation of MMHg.

TG10-P5 — 11:00-12:00 and 17:30-18:30
DECOMPOSITION OF METHYLMERCURY IN SURFACE WATER OF THE NORTHWEST ATLANTIC OCEAN
Authors: BOWMAN, Katlin L.1, HAMMERSCHMIDT, Chad R.1
(1) Wright State University, bowman.49@wright.edu

Biological and photochemical processes can decompose toxic monomethylmercury (MMHg) and render mercury less available for biological uptake. However, and in contrast to freshwater systems, little is known about MMHg decomposition in the marine environment. We are investigating the kinetics and mechanisms of MMHg decomposition in seawater from multiple locations on the continental margin of the northwest Atlantic Ocean. Ship-deck incubation tests were performed during oceanographic cruises in 2009 and 2010. Preliminary results suggest that 1) both biotic and photochemical pathways are important, 2) rate constants of decomposition are similar among locations and comparable to those determined in freshwater lakes, and 3) the mechanism of photochemical destruction in seawater is different from that in lakes. Experiments in 2010 sought to identify alternative photochemical pathways. Quantitative knowledge of the kinetics and mechanisms of MMHg decomposition in seawater will help constrain oceanic budgets and cycling models.

TG10-P6 — 11:00-12:00 and 17:30-18:30
FUNCTIONAL IDENTIFICATION OF MICROORGANISMS THAT TRANSFORM MERCURY IN MARINE AND ARCTIC LAKE SEDIMENTS
Authors: KLAUS, Jaclyn E.1, ROMAS, Lisa M.1, BURGIN, Amy J.1, HAMMERSCHMIDT, Chad R.1
(1) Wright State University, klaus.12@wright.edu

Monomethylmercury (MMHg) is the toxic form of mercury that bioaccumulates and biomagnifies in aquatic food webs. The current paradigm is that bacteria in sediments, namely sulfate reducers, produce a significant portion of MMHg in aquatic systems. However, recent laboratory studies have suggested that iron–reducing bacteria also may be important. We are investigating the functional identity of microorganisms that produce and demethylate MMHg in aquatic sediments of two biogeochemically disparate systems—the remote continental shelf of the northwest Atlantic Ocean and oligotrophic arctic lakes on the North Slope of Alaska. Surface sediments were slurried with overlying water and amended with different metabolic inhibitors and substrates as well as enriched stable isotopes of Hg (200Hg2+ and CH3199Hg+). Preliminary results indicate that iron-reducing bacteria may be important methylators of Hg under certain biogeochemical conditions. This suggests that the potential to methylate Hg in the environment may be more pervasive among bacterial functional groups than understood previously.

TG10-P7 — 11:00-12:00 and 17:30-18:30
MERCURY SURVEYS IN OIL-AND-GAS BEARING SHELF OF THE KARA SEA
Authors: SHCHERBAKOV, Victor1, PITIRIMOV, Pavel2, MASHYANOV, Nikolay R.2
(1) VNII Okeangeologia, vnii-comp@yandex.ru; (2) St. Petersburg State University;

In 2006 -2007, a comprehensive geochemical and geophysical surveys of oil-and-gas bearing shelf were fulfilled in the southern part of the Kara Sea within the Ob and Baydaratskaya Bays. Geochemical exploration included mercury determination in ambient air, water, suspended materials, and bottom sediments. An analytical set based on Lumex RA-915+ Zeeman atomic absorption analyzer was used for air monitoring and rapid analysis of solid and liquid samples. The low detection limit and high selectivity of the Zeeman AAS enables rapid analysis using direct pyrolysis of sediments and lavsan filters (0.45 um), which were used for the suspended matter sampling. The cold vapour technique was used for sea water analysis.

The most interesting data showing the relationship between the geological structures of the gas-productive areas and mercury were obtained from the mercury distribution in the suspended solids collected in the near-bottom water horizon. Thus, in the Northern part of the Ob Bay, the mercury concentration in the suspended particles varies in a range of 0.1 – 3.6 ppm, and the elevated values exceeding 0.5 ppm are located within the known gas-condensate pools and prospect geological structures. The highest particulate mercury concentration, up to 3.6 ppm, was found in the vicinity of “Geophyzicheskoye” gas-condensate deposit. Gas (methane) plumes in water were detected by acoustic profiling in the same area. It is noteworthy that the elevated mercury concentration in the suspended particles in the gas-bearing areas is not attended with corresponding anomalies of mercury and other metals (such as Fe, Mn, Zn, Cu, etc.,) in bottom sediments. The mercury concentration in bottom sediments strongly depends on their granulometric composition, which is typical for non-polluted areas.

TG10-P8 — 11:00-12:00 and 17:30-18:30
MERCURY SPECIATION IN COASTAL CALIFORNIA BARRIER BEACH LAGOONS
Authors: GANGULI, Priya M.1, CONAWAY, Christopher H.2, SWARZENSKI, Peter W.2, KEHRLEIN, Nicholas C.1, FLEGAL, A. Russell1
(1) University of California, Santa Cruz, pganguli@ucsc.edu; (2) US Geological Survey;

Coastal lagoons associated with ephemeral barrier beaches along the California coastline are biogeochemically active ecosystems that also provide important habitat for fish and birds. These lagoons are often nutrient rich due to inputs from urban and agricultural sources and restricted in terms of circulation. Sometimes these systems become eutrophic and can be suboxic or anoxic during the dry season when they are physically isolated from the ocean. Because the conversion of inorganic mercury to bioaccumulative monomethylmercury (MMHg) is primarily mediated by anaerobic bacteria, coastal lagoon systems may be important areas of mercury methylation. To evaluate this, we measured MMHg and total mercury (HgT) in water samples from Malibu Lagoon, a 31 acre (0.12 km2) urban-impacted lagoon in Southern California. During dry season conditions (July), we sampled three water types over a 10-hour period: (1) surface water grab samples from Malibu Lagoon; (2) submarine ground water from a shallow (~3 meter) piezometer installed down gradient from the lagoon; and (3) coastal ocean water grab samples from the adjacent surf zone. The average MMHg concentration in unfiltered Malibu Lagoon surface water (2.3 pM) was ~5 times higher than the average MMHg concentration in unfiltered submarine ground water (0.43 pM) and ~18 times higher than the average MMHg concentration in unfiltered coastal ocean water (0.13 pM). MMHg concentrations did not change in response to tidal fluctuations. The average HgT concentration in unfiltered Malibu Lagoon surface water (8.7 pM) was also elevated relative to average unfiltered HgT concentrations in surf zone water (4.4 pM) and ground water (3.2 pM); however the HgT concentration differences were not as notable as those reported for MMHg. We also collected dry season (July) surface water grab samples from Younger Lagoon, an approximately 14 acre (0.06 km2) agriculturally-impacted coastal lagoon in Central California. Initial results suggest that unfiltered MMHg concentrations in that lagoon (2.3 to 4.9 pM) are elevated relative to typical MMHg values for coastal ocean water. In summary, these data suggest that mercury methylation is enhanced in some barrier beach lagoon systems and may thus play an important role in nearshore Hg speciation and budgets.

TG10-P9 — 11:00-12:00 and 17:30-18:30
A PRELIMINARY TOTAL MERCURY AND METHYLMERCURY BUDGET IN A COASTAL ESTUARY: OYSTER POND, CAPE COD, MASSACHUSETTS
Authors: BOTHNER, Michael H.1, LAMBORG, Carl H.2, CASSO, Michael A.3, DREVNCK, Paul E. 4, HAMMERSCHMIDT, Chad R.5, TABERSKY, Daniel6
(1) U.S. Geological Survey, mbothner@usgs.gov; (2) Woods Hole Oceanographic Institution; (3) US Geological Survey; (4) Universite du Quebec; (5) Wright State University; (6) Department of Chemistry and Applied Biosciences at ETH Zürich.

The Oyster Pond watershed and estuary in Falmouth, MA, has been a recent focus of research that estimates the magnitude of sources, sinks, and transport pathways of total mercury (Hg) and monomethylmercury (MMHg) in this ecosystem.

Estimated sources of total Hg and MMHg to this system include wet and dry deposition from the atmosphere, surface runoff, pore water diffusion, and groundwater advection. Processes by which Hg leaves the system are net deposition with accumulating sediments, river outflow, evasion, photodecomposition, and by outward migration of diadromous fish (river herring, American eels, and white perch) that have accumulated Hg while living in the pond. The two major findings from the budget analysis are: 1. emigrating fish could account for 40% of the MMHg exiting with river flow into coastal waters, and 2. septage introduced to groundwater from developed neighborhoods could cause conditions that enhance the transport of Hg to water bodies fed by groundwater.

The present net deposition rate of total Hg buried in sediments of Oyster Pond as determined in dated sediment cores is 37 µg/m2/year, about 3 times higher than the pre-industrial deposition rate (12.9 µg/m2/year in the 1860s). The highest Hg deposition rate occurred in the 1950s (118 µg/m2/year), possibly reflecting greater regional and local sources following World War II, which have subsequently diminished.

In oxic areas of the pond we measured the highest concentrations of MMHg in pond sediments (4.4 µg/kg), in pore waters (18 ng/L), and the highest diffusion fluxes of MMHg from pore water to overlying water (22 µg/m2/year). In contrast, the anoxic areas of the pond had significantly lower MMHg, yet had the highest total Hg in sediments (440 µg/kg), pore waters (90 ng/L), and fluxes to the overlying water (31 µg/m2/year). One consequence of man-made or natural processes (such as sea level rise) that increase the tidal and/or storm-induced flushing in Oyster Pond is that re-oxygenation of bottom waters would likely follow, resulting in increased MMHg fluxes from the sediment to the water column and subsequently to the food web.

TG10-P10 — 11:00-12:00 and 17:30-18:30
METHYLMERCURY IN SEDIMENT CORES FROM THE TAGUS ESTUARY (PORTUGAL): PARTITION, METHYLATION AND FLUXES
Authors: MONTEIRO, Carlos1, CESÁRIO, Rute1, CANÁRIO, João 1, CAETANO, Miguel1, HINTELMANN, Holger2, NOGUEIRA, Marta1, VÁLEGA, Mónica3, VALE, Carlos1
(1) IPIMAR/INRB IP, cemonteiro@ipimar.pt; (2) Trent University; (3) CESAM - Chemistry Department;

Mercury is currently considered one of the most hazardous metals to the environment. Among mercury compounds, methylmercury (MeHg) presents a serious risk to wildlife due to their known toxicity. Biogeochemistry and fate of MeHg in sediments is still not completely understood due to the complexity of factors influencing methylation, partitioning, and transport.

In order to contribute to better knowledge of MeHg biogeochemistry and fate in sediments four sites in the Tagus estuary were selected. Two highly contaminated (CN and BRR: HgT up to 125 µg g-1) and two with moderate contamination (ALCX and PE: HgT<1 µg g-1).

Sediment cores were collected (2010) and pore waters were separated by centrifugation. Concentrations of total mercury (Hg) and methylmercury (MeHg) in solid sediments and dissolved Hg (HgR and HgT) and MeHg were quantified in pore waters and overlying water. Other interpretative parameters such as total Al, Si, Fe, Mn, Corg, DOC, Cl-, SO42- and HS- concentrations were also determined.

Higher levels of MeHg were found in deeper layers of CN, BRR and ALCX cores (max: 201 ng g-1) while at PE the highest MeHg concentrations where determined in the topmost ones (max: 0.55 ng g-1). In general, pore water MeHg was higher in layers where a substantial decrease of HgR was observed, suggesting that this form of dissolved Hg was used for methylation. Enhancement of both dissolved and particulate MeHg were observed below the decrease of SO42- levels and increase of HS- concentrations suggesting that sulphate reducing bacteria were the main methylators. Noteworthy an enhance of pore water MeHg in CN and ALCX sediments matches with sulphide increase suggesting that MeHg formation is not inhibit by HS- and/or dissolved MeHg is complexed with sulphide.

Diffusive fluxes of Hg and MeHg were estimated. Upward Hg fluxes were found variable from site to site (JPE>JCN>>JBRR>>JALCX). Downwards MeHg flux was only found in BRR (J=-47.6 ng m-2d-1) while a similar upwards fluxes were found for the other sites (1.89 ng m-2d-1<JMeHg<1.28 ng m-2d-1). Thus, we estimate that molecular diffusion contributes to an increase of 320 mg of MeHg in water column per day.

TG10-P11 — 11:00-12:00 and 17:30-18:30
DOES DEPOSITION OF ATMOSPHERIC MERCURY IN ARCTIC REGIONS LEAD TO ELEVATED UPTAKE OF MERCURY TO MARINE PHYTOPLANKTON?
Author: HEGGØY, Anette1
(1)Norwegian University of Science and Technology, aheggoy@gmail.com

The phenomenon of AMDE, Atmospheric mercury depletion events, might represent a significant enhancement factor of the mercury deposition rate to Arctic environments. These events tend to occur during the period of early spring, leading to the concern of the effect of these events on Arctic ecosystems, as they might occur just before, or coincide, with the period of rapid growth of marine biota.

The variation of mercury concentration in phytoplankton and seawater collected from an Arctic fjord during a summer season was examined. A possible correlation between snow melting, plankton blooming and higher Hg concentrations was investigated.

Phytoplankton and seawater samples were collected from Kongsfjorden outside Ny-Ålesund, Svalbard, in three distinct periods during the summer months of 2010. Phytoplankton samples were collected using both plankton net and Niskin Go-flow water sampling bottles with Teflon coating. Plankton was obtained from the water by filtration, using glass fiber (GFC) filters and polyethersulfone (PES) filters.

The concentration of total mercury in the plankton samples was measured using High Resolution Inductively Coupled Plasma Mass Spectrometry (HR- ICP-MS). Corresponding phytoplankton biomass was indicated by chlorophyll levels measured in the water masses at the sampling point using CTD (conductivity, temperature and depth), and by fluorescence measurements of chlorophyll a, in collected samples. Water samples were analysed both on HR-ICP-MS and Cold Vapour Atomic Fluorescence Spectroscopy (CVAFS).

The levels of total mercury were compared with measured levels of metals such as aluminium to investigate the impact of particles and the erosion from a nearby river. Furthermore, the results were compared with data of snow melting, thawing, riverine outflow, and Hg concentrations in air and snow.

TG10-P12 — 11:00-12:00 and 17:30-18:30
MERCURY AND SEDIMENT TRANSPORT TO NORTH SAN FRANCISCO BAY
Authors: DAVID, Nicole1, MCKEE, Lester J.1, LEATHERBARROW, Jon E.1
(1) San Francisco Estuary Institute, nicoled@sfei.org

San Francisco Bay is currently listed as impaired on the Clean Water Act 303(d) list for mercury due primarily to elevated concentrations in sport fish and associated fish consumption advisories. Historic gold and mercury mining in the Sierra Nevada and Coast Range Mountains (California, USA), long range atmospheric deposition, agriculture, as well as expanding urbanization in the Central Valley are ongoing sources of mercury to San Francisco Bay. Delta outflow from the Central Valley currently provides about 92% of the freshwater and 44% of the sediment load and as such an important transport pathway for mercury and other particle-associated contaminants. Between January 2002 and June 2010, water sampling for analysis of suspended sediment (SSC) and mercury concentrations and continuous monitoring of turbidity were performed at the boundary between the Delta and the Bay to quantify mercury concentrations and loads associated with first flush and large storm events. Turbidity data were converted to SSC by the USGS using a robust correlation. During water years (WYs) 2002-2010, total mercury concentrations in water ranged from 0.23 to 75 ng/L and showed a strong correlation (r2 = 0.8) to suspended sediment concentrations. Continuous turbidity measurements and SSC data at the study location allowed for extrapolation of the water quality record to estimate daily average total mercury loads. Daily mercury loads ranged from 1.6 g to 32 kg, while annual mercury loads varied from a minimum of 38 ± 14 kg in WY 2007 to a maximum of 470 ± 170 kg in WY 2006. This dataset includes samples collected during a series of large storms in 2006 that resulted in peak flows with a return frequency of 7 years. Given the magnitude of the loads relative to other pathways to the Bay and the potential impact to water quality, in 2010 samples were also analyzed for dissolved, methyl, and acid labile mercury. Percent dissolved, total methyl, and acid labile mercury averaged 27% (n = 39), 1.6% (n = 16), and 6.1% (n = 16), respectively. These percentages were within the expected range based on previous work conducted in large, mixed land use watersheds. Combined with information on other transport pathways, this six-year mercury dataset along with the 16-year SSC record and the 56-year Delta outflow record is helping managers find ways to accelerate the long-term recovery of the Bay from mercury contamination.

TG10-P13 — 11:00-12:00 and 17:30-18:30
CYCLING OF DISSOLVED ELEMENTAL MERCURY IN THE EASTERN MEDITERRANEAN BASIN
Authors: FANTOZZI, Laura1, SPROVIERI, Francesca1, GRATZ, Lynne1, AMMOSCATO, Ivano1, COFONE, Franco1, PIRRONE, Nicola1
(1) CNR-IIA Institute of Atmospheric Pollution Research, l.fantozzi@iia.cnr.it

The formation and volatilization of elemental mercury (Hg0) in aquatic systems are important features of the environmental mercury cycle because, from a global perspective, ocean evasion of Hg0 to the atmosphere may account for up to 50% of total annual atmospheric emissions of mercury. Mercury levels and cycling were broadly examined in the eastern Mediterranean Sea during an approximately 3000 km campaign on board the R/V URANIA (National Research Council of Italy) from 26 August 2010 to 13 September 2010. Surface Dissolved Gaseous Mercury (DGM, dominated by Hg0), Total Mercury (TM) and Dissolved Total Mercury (DTM) concentrations ranged from 15.6 to 113.7 pg L-1, 298.7 to 18763.8 pg L-1, and 230.9 to 10987.7 pg L-1, respectively. Elevated concentrations of these species occurred near the coastal sites while lower concentrations were observed offshore, suggesting that organic matter is significant in controlling DGM formation in waters. The highest concentrations of DGM, TM and DTM were observed near Augusta (Sicily), one of the most industrialized and contaminated coastal environments in the Mediterranean region. In addition to the reduced presence of organic matter, limited Hg2+ availability may also be responsible for the low DGM values observed in offshore waters. A significant linear correlation between DGM and DTM was detected in the sea surface (r2 = 0.80; p ≤ 0.04), suggesting that the complexes of mercury (mostly organic Hg association) in the dissolved phase are photoreducible and contribute to DGM production. Furthermore, DGM profiles followed in part the vertical distribution of light, indicating photoreduction of Hg(II) complexes as a source of Hg0. In some cases, however, an increase in DGM concentrations was observed at the bottom in some stations, suggesting a biological involvement in the process of Hg0 production. Two daily trends of DGM concentration in surface water of coastal stations were also measured, demonstrating the temporal variation of DGM levels over short time intervals and the effect of solar radiation on DGM production. In sunny calm conditions DGM concentrations followed the trend of solar radiation intensity, reaching a peak value of 34 pg L-1 simultaneously with the maximum net atmospheric radiation (816 W m-2). Conversely, under variable meteorological conditions, a marked diurnal pattern in DGM was not detected. Finally, estimations of mercury evasion using a gas exchange model, which includes salinity, wind speed and water temperature as independent values, are reported (mean value 4.9 ng m-2 h).

TG10-P14 — 11:00-12:00 and 17:30-18:30
UNRAVELING THE MERCURY BIOGEOCHEMISTRY AT THE SEDIMENT – WATER INTERFACE IN AN INTERTIDAL ENVIRONMENT FROM COMBINED FIELD AND LABORATORY EXPERIMENTAL STRATEGIES
Authors: BOUCHET, Sylvain1, BRIDOU, Romain1, RODRIGUEZ-GONZALEZ, Pablo1, TESSIER, Emmanuel 1, MONPERRUS, Mathilde1, ABRIL, Gwenael2, ANSCHUTZ, Pierre2, THOUZEAU, Gerard 3, CLAVIER, Jacques3, AMOUROUX, David1
(1) IPREM-ECABIE, s_bouchet@hotmail.com; (2) EPOC Universite Bordeaux 1; (3) LEMAR-IUEM;

The Hg cycling in biologically productive coastal areas is of special importance because of the potential for bioaccumulation of monomethylmercury (MMHg) into aquatic organisms. In shallow coastal waters, the extended intertidal zone support most of the biogeochemical transformations of the ecosystem and represents a dynamic environment promoting the transformations of Hg species and their subsequent redistribution. To better understand the factors affecting Hg mobility and transformations in this environment, complementary field and lab incubation experiments using isotopically enriched tracers were performed in the Arcachon Bay, a tidal lagoon (SW France). Field experiments were performed at different seasons to assess the variability of the water column concentrations, the sediment – water flux densities (with benthic chambers) and the potential formation and degradation of MMHg and inorganic Hg (IHg) in both water and sediments. On the other hand, a laboratory experiment was specifically designed to assess with high resolution the fate of Hg in surficial sediments under redox oscillations, characteristic of coastal ecosystems.

Benthic fluxes of dissolved IHg and MMHg were found to be highly variable and differed between seasons by two orders of magnitude with the maxima occurring in late winter conditions. The organic matter mineralization appeared as a major process for the Hg species remobilization with its intensity regulated by the occurrence of sulfur reduced solid/dissolved species at the sediment – water interface during the warmer periods. The methylation and demethylation potentials were in opposition lower by a factor 2 during winter compared to spring or fall conditions. Benthic exchanges in the intertidal zones may represent a significant source of Hg species for the water column as demonstrated by dissolved concentrations that could doubled during low tide.

In the laboratory experiment, redox transition events were found to significantly enhance the aqueous Hg species concentrations (up to a factor 7), while the MMHg burden was not greatly affected (maximum 2-fold increase recorded). The remobilization of Hg species was mostly associated with the reactivity of Fe/S species while the variations of MMHg production were related to shift in IHg speciation.

Overall, the extents of methylation and demethylation potentials found in situ and in the laboratory experiment were comparable while the factors influencing the Hg mobility diverged, demonstrating how those two approaches complement each other.

TG10-P15 — 11:00-12:00 and 17:30-18:30
MERCURY AND ITS SPECIES IN THE ADRIATIC SEA
Authors: KOTNIK, Joze1, HORVAT, Milena1, OGRINC, Nives1, FAJON, Vesna1, SPROVIERI, Francesca2, PIRRONE, Nicola2
(1) Jozef Stefan Institute, joze.kotnik@ijs.si; (2) CNR-IIA Institute of Atmospheric pollution;

Mercury and its speciation were studied in surface and deep waters of the Ariatic Sea during two oceanographic cruises on board the Italian research vessel Urania in fall 2004 and summer 2005. Oceanographic cruises were part of the MedOceaneor and MERCYMS projects. Several mercury species (i.e. DGM - dissolved gaseous Hg, RHg - reactive Hg, THg - total Hg, MeHg - monomethyl Hg and DMeHg - dimethylmercury) together with some other water quality parameters were measured in coastal and open sea deep water profiles. Spatial and seasonal variations of measured Hg species concentrations in different indentified water masses were observed. THg concentrations in water column, as well as in sediments and pore waters were the highest in the northern, most polluted part of the sea as the consequence of Hg mining in Idrija and heavy industry of northern Italy. Further, Hg mass balance for the Adriatic Sea was calculated based on measurements and literature data. Main point sources, inflow of mercury by main rivers, exchange with the rest of the Mediterranean Sea, exchange with bottom sediment, main geotectonic active areas, and evasion to and deposition from the atmosphere were taken into account.

TG10-P16 — 11:00-12:00 and 17:30-18:30
INPUT PATHWAYS OF MERCURY IN THE COASTAL ZONE OF THE GULF OF GDANSK, THE SOUTHERN BALTIC SEA
Authors: SANIEWSKA, Dominika1, BELDOWSKA, Madgalena1, BELDOWSKI, Jacek2, SANIEWSKI, Micha?3, SZUBSKA, Marta1, ROMANOWSKI, Andrzej1, FILA, Grzegorz1, FALKOWSKA, Lucyna1
(1) University of Gdansk, Poland, d.murawiec@gmail.com; (2) Institute of Oceanology, PAS, Poland; (3) Institute of Meteorology and Water Management, Maritime Branch in Gdynia, Poland;

The Baltic Sea is an inland sea surrounded by economically-developed and industrialized countries. For this reason, it is particularly vulnerable to anthropogenic pollution originating from urbanized and densely populated Eastern and Central Europe. The depth of the Baltic Sea (average 52 m) and low rate of water exchange with the North Sea favor the accumulation of pollutants.
The aim of this research was to assess the extent of mercury pollution of the coastal zone of the Southern Baltic Sea and to evaluate the relative importance of the input pathways. For this purpose total mercury concentrations were measured in the atmospheric precipitation, in aerosols and in the water and SPM from rivers in different parts of the Southern Baltic coast in the years 2008-2010.

Hg concentrations observed in the Southern Baltic varied greatly, showing the highest average values near the Vistula mouth (median: 4.5ng·dm-3). Also near an industrial city (Gdynia) elevated concentrations of mercury in water and particulate matter were measured, compared to the open waters the Southern Baltic Sea. Among the studied rivers draining into the Gulf of Gdansk, the largest flux of mercury was introduced by Vistula (0.15 Mg·year-1). Kacza River and Oliwski Stream transported to the coastal zone of the Gulf of Gdansk similar loads of mercury (about 15 g·year-1), representing approximately 0.01% of the load brought by Vistula. Mercury which entered the Baltic Sea from rivers occurred mainly in the suspended form.

Hg concentrations in precipitation in Gdynia varied between 0.4 ng·dm-3 and 12.0 ng·dm-3, while mean concentration equaled 5.0 ng·dm-3. These values were close to mercury concentration found in different stations at the coast of the Southern Baltic Sea. Atmospheric deposition of mercury in Gdynia amounted to 2.9 g·km-2·year-1 and mainly depended on the concentration in precipitation and the intensity and duration of rainfall.

TPM concentration varied between 2 pg·m-3 and 142 pg·m-3 and was comparable to other coastal areas of the Baltic. Deposition flux of Hg in coarse particles during heating season reached 2 µg·m-2·season-1 and during non-heating season: 1 µg·m-2·season-1.

According to international HELCOM reports, Poland is indicated as a main mercury source among the Baltic Sea countries. Experiments performed in the coastal zone of the Southern Baltic Sea, indicate that values from these reports are significantly overestimated.

TG10-P17 — 11:00-12:00 and 17:30-18:30
DISTRIBUTION OF DISSOLVED TOTAL MERCURY AND METHYLMERCURY IN THE WESTERN EQUATORIAL PACIFIC AND BISMARCK SEA
Authors: YIGITERHAN, Oguz1, BALCOM, Prentiss H.1, FITZGERALD, William F.1, MASON, Robert P.1, MURRAY, James W.2
(1) University of Connecticut - Department of Marine Sciences, oguz.yigiterhan@uconn.edu; (2) University of Washington - School of Oceanography.

The equatorial Pacific is critically important in the global cycling of mercury (Hg). Most of the biological production in the open ocean is derived from recycled nutrients, while riverine inflows and re-suspended sediments enhance the production in coastal waters.

Seawater samples were collected during R/V Kilo Moana EUCFe 2006 research cruise at offshore and inshore stations, from 140 W to 145 E longitude at the equator, 2N, and 2S latitudes. The goal was to measure the distribution of dissolved total mercury (HgT) and monomethylmercury (MMHg) species in the Equatorial Pacific Ocean, and to relate these changes with the lateral transport of re-suspended particulate matter along the Equatorial Undercurrent (EUC). Although the sampling was focused on the depth of EUC, whole water column profiles were collected down to1000 m (6 depths). Additional samples were collected at possible Hg sources regions in the Bismarck Sea, close to Sepik River mouth and Vitiaz strait on the New Guinea Coastal Undercurrent (NGCU), and also at the coast of the New Ireland Island on the New Ireland Coastal Undercurrent (NICU).

MMHg showed an increasing trend from inshore to offshore stations at the depth of EUC. The highest MMHg value (462 fM) was observed at offshore station 140W, with a decreasing gradient (105 fM) from east to the west at the core depth of EUC. At the coastal stations, MMHg concentrations appear to be lower than our detection limits except near the coast of New Ireland (256 fM). In contrast to MMHg, there is not much concentration gradient for dissolved HgT between the inshore and off-shore stations. Some of the coastal stations have higher HgT concentrations, but concentrations typically ranged from 2-3 pM. Subsurface maxima observed for stations 170W, 180W and 145E may be related to particulate load carried with the EUC. Stations 140W, 170W and 149.5E appear to have higher surface HgT concentrations (4-5 pM), and stations 180W, 165E and 149.5E showed increasing concentrations down to 1000m. A subsurface maxima at 140W seems to correlate with the regional of rapid oxygen decrease at that station.

Tuesday, 26 July, 2011