B11B-0389
Total Mercury and Methylmercury in the Great Egg Harbor River Watershed, New Jersey, USA
Hydrologic and biogeochemical conditions are important factors in the transport and distribution of mercury (Hg) in New Jersey Coastal Plain watersheds that contain extensive freshwater wetlands and where Hg bioaccumulation is of concern. U.S. Geological Survey studies found Hg concentrations in top predator fish from the Great Egg Harbor River mainstem that ranged from 2.9 to 4.5 mg/kg (dry wt.) and exceeded 10 ng/L in the watershed's acidic streams. An ongoing study with the N.J. Department of Environmental Protection indicates that atmospheric deposition of Hg to the wetlands and streams may be augmented by substantial contributions of Hg from ground water. Although background levels of Hg in water from the underlying aquifer typically are less than 10 ng/L, concentrations in water from more than 600 domestic wells in southern New Jersey have been shown to exceed the drinking-water maximum contaminant level of 2,000 ng/L. Therefore, to determine ground-water inputs to the streams, samples of ground water discharging to the tributaries and mainstem as well as streamwater samples collected during various flow conditions were analyzed for total Hg and methylmercury (MeHg). Total Hg concentrations in ground water discharging to the tributaries and mainstem were low to moderate (0.29-22 ng/L) in relatively undeveloped areas (including wetlands), but higher (36 and 177 ng/L) in two urban/suburban areas where much of the Hg was in particulate form. In recent and ongoing studies, total Hg concentrations in unfiltered samples of surface water, except those for one suburban tributary, have ranged from 2.13 to 37.7 ng/L. Concentrations in the suburban tributary have ranged from 50 ng/L during a dry period to 250 ng/L during a wet period. Hg concentrations in samples from a wetlands-embedded reach of the mainstem varied markedly with flow. In addition to increases in concentrations of total Hg, UV absorbance and concentrations of dissolved organic carbon also increased with flow after rain events, whereas pH and concentrations of dissolved oxygen and nitrate decreased. These flow-related changes apparently result from inputs of water that has percolated through acidic, reducing wetlands soils. The biogeochemical environment of these soils, on the basis of hydrogen sulfide odors detected during piezometer placement, supports sulfate reduction and likely promotes methylation of Hg. MeHg concentrations were 0.48 ng/L after a rainfall in discharge from 0.8 m below the streambed at a mainstem wetlands site. Downstream, where the channel briefly emerges from wetlands, MeHg was detectable during a dry period only in the hyporheic-zone water from 0.15 m below the streambed and in ground water from a depth of 0.3 m (0.15 ng/L and 0.05 ng/L, respectively). MeHg was not detected in the ground-water samples from deeper points below the streambeds, but concentrations in surface water ranged from 0.17 to 2.88 ng/L. The concentration from a tributary surrounded by urban/suburban development was highest. MeHg concentrations in mainstem water did not always increase with streamflow; variations in antecedent hydrologic conditions in the wetlands may explain the unpredictable relation of concentration to flow. Overall, total Hg appears to be contributed to the streams by both ground water and atmospheric deposition, with methylation taking place at shallow levels in wetlands soils and stream sediments.
B11B-0390
Changes in Total and Methyl Mercury Concentrations and Fluxes Resulting From Clearcut Logging and Drought in Boreal Forest Wetlands and Hillslope Groundwaters
Two zero order boreal forest catchments in NW Ontario have been hydrochemically monitored since spring 2003. One of the cathcments, E1 was clearcut logged during mid summer 2004. Ground and surface water samples have been analyzed for Total and Methyl Hg THg, MeHg), DOC, major ion and nutrient concentrations over the duration of the project. Contrary to results from northern European forestry studies no significant changes in MeHg or THg concentrations in ground or surface waters were measured in the first two years after logging. However, there was approximately a two-fold increase in Hg transport from the logged watershed as a result of the increased runoff flux. Internal mass balance estimates suggest that proportion of MeHg contributed from a valley bottom has doubled in relation to MeHg contributions from logged hillslopes during the initial post harvest period. Conversely, the proportion of THg contributed from hillslope soils has increased by 80% during the post logging period in comparison to the valley bottom wetland. During 2006 the study site experience a severe drought with precipitation levels approximately 50% of normal. THg surface and groundwater concentrations in both the logged and reference watershed have increased on average two to six fold upon the resumption of more normal precipitation levels during the first half of 2007.
B11B-0391
Salmon and Wetland Influences on Streamwater Mercury Fluxes in Southeastern Alaska
Limited data indicate that mercury contamination in southeast Alaska is of growing concern due to the combination of rising Hg atmospheric imports from Asia, contributions of marine-derived mercury from spawning salmon, and the abundance of wetlands covering the region. Wetlands are prevalent (comprising 29% of the land area of the Tongass National Forest) and DOC concentrations are high (10-30 mg/L) in many southeast Alaskan brownwater streams. We investigated the Hg distribution in three watersheds with the goals of 1) obtaining original data on the concentrations of total and methyl Hg in regional catchments; 2) examining the extent to which the extensive areas of coastal wetlands may be facilitating the methylation of Hg, and 3) evaluating the influence of spawning salmon on Hg and nutrient export in streamwater. We measured Hg, nutrients, and ancillary water quality parameters and characterized dissolved organic carbon using chromatographic and spectroscopic techniques in streams draining three watersheds with varying wetland coverage. We also sampled tributary streams within the watersheds that drained individual landscape units across a gradient of vegetation types including upland, bog, and forested wetland to evaluate their contributions to streamwater Hg loads. Each stream was sampled before (June), during (August), and after (October) salmon spawning. Our initial results indicate that concentrations of total Hg in both mainstem and tributary streams were highly correlated with concentrations of bulk DOC and the percentage of DOC composed of hydrophobic acids, both of which were elevated in wetland-dominated sites. These results suggest that wetland landscapes are contributing disproportionately to riverine mercury export in southeastern Alaska.
B11B-0392
Mercury Biogeochemistry in Wetlands of the Western Adirondack Region, New York, USA
Wetlands are important controls of inorganic mercury and methyl mercury flux to surface waters. Research suggests that greater area of wetlands within a watershed is often correlated with greater amounts of dissolved mercury and methyl mercury in associated surface waters and fish; however, the importance of wetland type is seldom considered. This study quantifies differences in mercury biogeochemistry in individual wetlands of varying hydrologic setting in the western Adirondack region of New York, USA. Herein, we compare the pool size, flux, and residence time of mercury and methyl mercury in headwater wetlands perched at the top of their watersheds, with riparian wetlands lower in the landscape. The pool size of mercury was greater in the top 50 cm of peat in riparian wetlands as compared with headwater wetlands, and the molar ratio of Hg:C shows that 2-4x more Hg per unit C was retained in these riparian wetlands. Mercury concentrations in peat porewater were consistently greater in headwater wetlands than in riparian wetlands during the non-growing season when water table levels were high. MeHg concentrations peaked at the end of the growing season, when water table levels were low. Riparian wetlands were spatial and temporal hotspots of dissolved mercury and methyl mercury production, whereas headwater wetlands were less dynamic. Riparian wetlands provided the greatest flux of mercury and methyl mercury from wetlands to surface waters when compared to other wetlands within the same watershed. The residence time of mercury in riparian wetlands was ~200 years, whereas the residence time of mercury in headwater wetlands exceeded 500 years. Differences in the flux of mercury from wetlands was primarily determined by the hydrology of the different wetland types, rather than by the concentration of mercury in porewaters. Based on the residence time, the magnitude of the flux of mercury from wetlands should not rapidly change with changes in atmospheric deposition of mercury.
B11B-0393
Mercury Transport Following Storm Events from a Northern Forest Landscape
Concentrations and fluxes of mercury (Hg) species in surface waters of forested watersheds are affected by hydrological events. The mechanisms of Hg transport during events are poorly understood and yet may influence Hg bioavailability and exposure to aquatic biota. Three storm events were investigated (June, September, and November 2005) at a forested watershed in the Adirondack region of New York State, USA, with varying magnitude and intensity. Concentrations of Hg species increased during events both above and below wetlands in the watershed. While Hg flux was higher from wetland drainage, the Hg flux from the upland site exhibited a greater relative response to elevated watershed saturation. Hg species concentrations were not correlated with discharge, DOC, or TSS, with particulate Hg flux during events <20%. A counter-clockwise hysteretic response of DOC with increasing runoff contrasted with the clockwise response for Hg suggests different contributions from potential source areas for these solutes. Correspondence with elevated potassium and nitrate (p<0.05) suggests a contribution of Hg during the rising limb of the hydrograph associated with rapid delivery of throughfall Hg, potentially enhanced by hillslope hollows, to the stream channel. Wetland areas demonstrated a higher throughfall response, likely due to increased connectivity relative to the upland portion of the watershed. As the watershed saturates, Hg in discharge appears to shift to the flushing of the Hg soil pool. Our results emphasize how watershed attributes and storm characteristics affect Hg transport and bioavailability.
B11B-0394
Mercury Cycling in Agricultural and Non-agricultural Wetlands in the Yolo Bypass Wildlife Area, California: Water Column Processes
Organic matter (OM) plays a significant role in mercury (Hg) cycling. For instance, aromatic dissolved OM can enhance Hg solubility leading to greater cycling in the water column whereas bioavailable forms of OM may enhance Hg methylation by increasing the microbial activity of Hg-methylating bacteria. Differences in wetland management (e.g. fertilization, plant residue, water depth and movement) can influence the character of OM within the wetland, thus affecting Hg cycling as well. This study is investigating the role of OM in Hg cycling over a wide range of time scales and wetland management practices within the Yolo Bypass Wildlife Area, near Sacramento, California. We are comparing Hg and methylmercury (MeHg) concentrations in the water columns of three agricultural field types (wild rice, white rice, and shallow-flooded fallow) with those in two non-agricultural field types (seasonal and permanent wetlands). The time scales over which variations in Hg and MeHg concentrations are being investigated range from diurnal variations caused by fluctuations in photolytic reactions and microbial activity to seasonal variations caused by plant growth, land management, climate, and fertilization. We relate those concentration fluctuations to the dominant processes affecting OM cycling in the fields. We further evaluate the possible influence of S-bearing fertilizers, such as ammonium sulfate and zinc sulfate, on Hg methylation because of the role that sulfur plays in Hg cycling and Hg-OM interactions. Preliminary results indicate that dissolved OM (DOM) concentrations (operationally defined using a filter with 0.45 ìm pore diameter) increased from 9 milligrams of carbon per liter (mg-C/L) at inflow stations to as high as 30 mg-C/L within the water column of the wetlands. Based on measured optical properties, OM in these wetlands appears to be derived from a mixture of algal activity, plant exudates, and diffusion from the flooded soils, with the proportion of each source dependent on land use. Concurrent rise in both the Hg concentration (from 14 ng/L to 50 ng/L) and the fraction of Hg in the dissolved fraction (from 15 to 50 percent, based on filtration with 0.45 ìm pore diameter filters) mirrors the increase in DOM concentration, suggesting the importance of Hg-DOM complexation. Measurements of optical properties and field parameters taken at 15-minute intervals over a diurnal cycle indicate that conditions in the rice fields fluctuate greatly through the day, with dissolved oxygen dropping from 14 mg/L in the afternoon to 2 mg/L at dawn. Extreme and systematic fluctuations also were observed for other water properties, including spectrometric indicators of OM character. Further analysis of water quality constituents and their relation to Hg and MeHg cycling in these wetlands will be presented.
B11B-0395
Diminished Mercury Emission From Water Surfaces by Duckweed (Lemna minor)
Aquatic plants of the family Lemnaceae (generally referred to as duckweeds) are a widely distributed type of floating vegetation in freshwater systems. Under suitable conditions, duckweeds form a dense vegetative mat on the water surface, which reduces light penetration into the water column and decreases the amount of exposed water surface. These two factors would be expected to reduce mercury emission by limiting a) direct photoreduction of Hg(II), b) indirect reduction via coupled DOC photooxidation-Hg(II) reduction, and c) gas diffusion across the water-air interface. Conversely, previous studies have demonstrated transpiration of Hg(0) by plants, so it is therefore possible that the floating vegetative mat would enhance emission via transpiration of mercury vapor. The purpose of this experiment was to determine whether duckweed limits mercury flux to the atmosphere by shading and the formation of a physical barrier to diffusion, or whether it enhances emission from aquatic systems via transpiration of Hg(0). Deionized water was amended with mercury to achieve a final concentration of approximately 35 ng/L and allowed to equilibrate prior to the experiment. Experiments were conducted in rectangular polystyrene flux chambers with measured UV-B transmittance greater than 60% (spectral cutoff approximately 290 nm). Light was able to penetrate the flux chamber from the sides as well as the top throughout the experiment, limiting the effect of shading by duckweed on the water surface. Flux chambers contained 8L of water with varying percent duckweed cover, and perforated plastic sheeting was used as an abiotic control. Exposures were conducted outside on days with little to no cloud cover. Real time mercury flux was measured using atomic absorption (Mercury Instruments UT-3000). Total solar and ultraviolet radiation, as well as a suite of meteorological parameters, were also measured. Results indicate that duckweed diminishes mercury emission from the water surface as compared to open water controls. Decreases in emission rate varied linearly with percent duckweed cover, with lower fluxes occurring at higher percent cover. Mercury flux in the duckweed treatments as compared to open water treatments decreased from 17% in the lowest percent cover treatment to 67% in the highest percent cover treatment. The observed decrease in mercury emission suggests that duckweed limits emission via the formation of a physical barrier to diffusion.
B11B-0396
In Situ Micrometeorological Mercury Fluxes From Tidally-Exposed Wetland Sediments
Major research efforts have examined the influx of mercury to estuaries from point and non-point sources. However, little is known about the efflux of gaseous elemental mercury (Hgº) from tidally-exposed estuarine sediments back to the atmosphere, a potentially important re-distribution pathway of mercury on watershed to global scales. In the New Jersey Meadowlands in northeastern New Jersey, U.S.A., this route may be particularly important due to the high degree (sediment mercury concentrations up to 51 ug g-1 dry weight) and large areal extent of mercury contamination, coupled with the vast sediment surface area exposed to the atmosphere at low tide. Sediment-air vertical fluxes of mercury were studied at a tidal salt marsh within the New Jersey Meadowlands, Hudson County, NJ) in August 2005, May 2006, and June 2007. Vertical fluxes were estimated from in situ measurements of vertical concentration gradients of total gaseous Hg (>95% elemental Hg) coupled with vertical wind speed profiles and atmospheric stability correction factors for momentum and water vapor. Sediment-air mercury fluxes ranged from -461 to +253 ng m-2 h-1 and were highest during periods of peak solar radiation. Laboratory flux chamber studies with sediments from the New Jersey Meadowlands, and from the nearby Raritan and Passaic River estuaries demonstrate the importance of UV light and sulfide as controlling factors in mercury volatilization from tidally exposed sediments.
B11B-0397
Mercury Methylation, Demethylation, and Bioavailability in the Hyporheic Sediments of a Northern Wisconsin Wetland
It is generally accepted that wetland sediments have a high potential to produce methylmercury, yet the factors controlling the relevant chemical transformations are poorly understood. Previous studies suggest that sulfate- reducing bacteria play an important role in methylation, but iron-reducing bacteria may also participate in this process. Methylation rates are influenced by both the concentration of Hg(II) and its speciation, which affects its bioavailability. Net accumulation depends also on demethylation rates, rates which may be significant in these systems. The objective of this study is to gain a better understanding of the main factors controlling the bioavailability of inorganic mercury for the production of methylmercury in wetland hyporheic zones. Stable isotopes of mercury are being used to investigate potential methylation and demethylation rates in the hyporheic sediments of Allequash Creek, near Boulder Junction, WI. Other techniques that are being applied to examine the chemical and biological drivers of mercury methylation and bioavailability include tin-reducible mercury "titrations" to measure the concentration of strong mercury-binding ligands in porewater, 14C-acetate uptake assays to determine the activity of the native microbial consortia , ion exchange resin experiments to explore the role of dissolved organic carbon in mercury binding, and inhibition studies (e.g. molybdenum amendments) of sulfate-reducing bacteria to assess their role in producing methylmercury. Manipulations of environmental conditions in laboratory microcosms are used to determine the relative importance of physical factors, such as temperature, and biogeochemical factors, such as sulfate, sulfide, dissolved organic carbon (DOC), and iron levels, on the fate of mercury in hyporheic systems. Preliminary results show that while significant levels of inorganic mercury are present in the hyporheic groundwater, strong mercury-binding ligands in the wetland porewaters at a high carbon site may limit the bioavailability of mercury. Measurements of chemical parameters such as DOC, iron, sulfate, and sulfide concentrations in field samples will further clarify whether conditions exist that promote the microbial methylation of mercury.
B11B-0398
Importance of Sulfate-Reducing Bacterial Activity in Controlling Mercury Methylation in Anoxic Estuarine Sediment Slurries
Solution speciation of dissolved Hg has been considered an important factor controlling Hg methylation in anoxic sediments. Our previous research with sediments from the Venice Lagoon, Italy, however, has shown that the Hg methylation rate is affected by the activity of sulfate-reducing bacteria, which varies widely within the lagoon. To understand the role of sulfate-reducing bacterial activity in monomethylmercury (MMHg) production, we amended anoxic sediment slurries collected from Venice Lagoon with inorganic Hg and potential electron acceptors (sulfate or hydrous Fe(III) oxide) or metabolic byproducts of sulfate and Fe(III) reduction processes (sulfide or Fe(II)) and after 48h measured sulfate reduction rates, MMHg concentrations, and concentrations of dissolved Hg, Fe, sulfate, and sulfide. Addition of sulfide (final concentration: 0.2-6.3 mM) but not sulfate (final concentration: 29-54 mM) resulted in an exponential decrease in sulfate reduction rates and MMHg production with increasing concentrations of sulfide. These findings suggest that the negative relationship between dissolved sulfide and MMHg concentrations often found in freshwater and estuarine sediments can be caused by the decreased activity of sulfate-reducing bacteria. Addition of either Fe(II) (0-6.1 mM) or Fe(III) (0-3.5 mM) resulted in similar trends in MMHg production, an initial increase and subsequent decrease, as a function of added Fe, with a noticeable reduction in MMHg production in Fe(III)-amended slurries. Reduced Hg methylation in Fe(III)-amended slurries associated with the decrease in the sulfate reduction rate may be due to the enhanced activity of Fe(III)-reducing bacteria. Dissolved Hg concentrations in sulfide-, Fe(II)-, and Fe(III)-amended slurries were controlled mainly by FeS precipitation, which limits the availability of Hg for methylation in active sulfate-reducing slurries. Monomethylmercury production, however, was not correlated to the modeled concentrations of HgS0 and Hg(HS)20. Overall, our results suggest that the activity of sulfate-reducing bacteria and the availability of dissolved Hg are critical factors controlling MMHg production in anoxic estuarine sediments.
B11B-0399
Explorating coupled production of dissolved organic material and methyl mercury in a tidal wetland using the intrinsic chemical composition of the organic material
Elevated methyl mercury (MeHg) levels found in biota of the San Francisco Estuary have been attributed to methylation processes in the peat-rich tidal wetlands of the Estuary, where the concentration of dissolved organic matter (DOM) is tightly coupled to that of MeHg (r2=0.95). We sought to understand the geochemical processes that contribute to MeHg production by examining the composition of the co-occurring DOM. We measured spectral absorbance and fluorescence properties of DOM, as well as intrinsic chemical properties such as isotopic composition, lignin content, carbohydrate content, and bulk chemical functionality (by CPMAS-NMR). Carbon quality parameters independent of concentration such as specific UV absorbance, lignin abundance, aromatic content, biodegradability, and others were closely coupled to MeHg concentrations. This coupling, combined with the hydrologic forcing within the wetland, suggest that the zones of MeHg production are biogeochemically related to the zones of DOM release, thus providing a means to examine the underlying processes. The observed relationships were robust through the winter, spring, and fall seasons, despite a three- fold variation in MeHg and DOM concentration. The pattern of variation suggests sources of DOM and MeHg within peat pore waters rather than within the litter layer or water column. The various relationships with individual parameters will be discussed.
B11B-0400
Methyl and Total Mercury Budget of a Mid-Atlantic Estuarine Salt Marsh
Coastal and estuarine salt marshes are both efficient accumulators of particulate-bound inorganic mercury (Hg) and transformers of inorganic Hg to methylmercury (MeHg). As part of continuing studies on the biogeochemical controls, sources, and fate of Hg and MeHg in the Chesapeake Bay region, we have recently expanded our research to examine Hg and MeHg cycling in Chesapeake tidal marshes. Our main study site is the Kirkpatrick Marsh, a salt marsh at the Smithsonian Environmental Research Center (SERC) on the shores of a Chesapeake Bay sub-estuary, the Rhode River. Kirkpatrick Marsh is dominated by Spartina patens, Scirpus olneyi, Phragmites australis, and several other species and is influenced by a mean tidal range of approximately 30 cm. The marsh is currently and has previously been the subject of various biogeochemical studies, thus basic biogeochemistry, carbon, and nutrient cycling for this system is well understood. Research goals for our study include an estimation of the contribution of salt marshes to MeHg budgets in the Chesapeake specifically and in coastal zones more generally; a first look at the sources of Hg for methylmercury production in tidal marshes; and an improved understanding of the biogeochemical controls on net MeHg production and flux in these wetlands. The research study has two major components. One is a spatially-distributed investigation of the geochemical and microbial controls on MeHg production in this high sulfate/high sulfide wetland system. Detailed biogeochemical measurements were made across three marsh zones distinguished by vegetation/elevation characteristics. Microbial activity in the three zones peaks at depths approximately equal to the mean water table depth, but always in the upper 5-10 cm of soil. Pore water sulfide concentrations increase substantially with depth in marsh soil cores, with highest sulfide concentrations (up to 1.5 M) found deeper in the least frequently flooded site. Initial data show that MeHg concentrations are maximal in the top 5-10 cm of soil, right above the transition into high sulfide zones. In contrast to some other marine systems, our initial data reveals high MeHg concentrations (up to 2.5 ng/L) in marsh pore water across a wider range of sulfide concentrations between 5 and 400 uM. The other component of this research is the construction of comprehensive and temporally-intensive water, total mercury, and methylmercury budgets for the salt marsh. This includes local Hg deposition, continuous flow- weighted Hg/MeHg flux measurements through the main tidal channel, monthly Hg/MeHg measurements along a salinity gradient in the adjacent Rhode River, and various other hydrologic and climatologic measurements. Initial results indicate, as expected, that the marsh is a major sink for particulate bound Hg. Linking process scale measurements with larger-scale hydrology is a key step in attributing the source/sink characteristics of the marsh to spatial and temporal variability of processes within it.
B11B-0401
Measurement of Mercury Concentrations in Marsh Drainages Over a Tidal Cycle
This study was undertaken to characterize short-term temporal patterns in total mercury and methylmercury concentrations that would indicate transport patterns and to determine if drainages (marsh sediment and channels) in a mercury-contaminated marsh were sources or sinks for total mercury and methylmercury. Measurements of total mercury, methylmercury, and total suspended solids were made over a tidal cycle on two separate sampling events (January and June) at three locations in the contaminated marsh and two reference locations. During the first event, samples were collected by hand from a small boat every 30 minutes from approximately two hours before to two hours after high tide, using ultra-clean techniques. During the second event, water samples were obtained with automated ISCO sampling devices programmed to collect samples every 45 minutes during a one-half (12-hour) tidal cycle. Unfiltered total mercury and methylmercury concentrations were significantly higher at the location closest to the former chlor-alkali facility (up to 4,000 ng/l and 20 ng/L, respectively) compared to the location in a separate drainage (up to 180 ng/l and 5 ng/L, respectively) but in the same marsh. Concentrations at the reference stations (up to 28 ng/L and 0.7 ng/L, respectively) were considerably lower. Total mercury and methylmercury concentrations were generally lowest at high tide while concentrations during flood and ebb were comparable. Unfiltered total mercury and methylmercury concentrations tended to correlate with suspended solids concentrations. The percent of total mercury and methylmercury in the dissolved form decreased as unfiltered concentrations increased. There was no clear evidence that the mass of total mercury or methylmercury was higher during ebb than flood, suggesting that these locations are not a definitive source of either to downstream locations. If mercury is methylated in marsh sediment during the tidal cycle, the additional mass was small compared to the mass carried by the flood and ebb.
B11B-0402
Mercury Release from Soils and Sediments in the Sacramento River Watershed
Mercury released into water from soils and sediments contaminated by cinnabar (HgS) and gold mining is a major environmental concern in the Sacramento-San Joaquin Delta, California. To better understand the conditions resulting in Hg solubilization from these contaminated materials, six soil and sediment samples from the Coastal Range and the Sierra Nevada were subject to batch leaching experiments under varying conditions. Sequential extraction analyses of the soils and sediments indicated that most of the mercury was present as (1) Hg as HgS in samples affected by HgS mining, which occurred in the Coastal Range, (2) Hg bound to metal oxides in a background serpentine soil from the Coastal Range, (3) Hg bound to sediment organic matter in lake sediments from Camp Far West Reservoir, and (4) elemental Hg in a sluice sediment from Starr Tunnel. The effects of pH, ionic strength, inorganic ions (chloride, calcium), simple organic ligands (mercaptoacetic acid, salicylic acid, EDTA), and dissolved organic matter (DOM) on the release of Hg were investigated. Leaching experiments confirmed that the water-soluble fraction was small (9 to 350 ng/L) compared to the amounts of Hg associated with the solid samples (1 to 36 μg/g total mercury); however, these concentrations would be sufficient to result in increased methylation by sulfate-reducing bacteria in wetland systems. An increase in mercury release was observed with (1) increasing pH due to solubilization of soil organic matter, (2) decreasing ionic strength due to colloid stabilization, and (3) increasing chloride concentration due to the formation of complexes with mercury. The presence of calcium strongly inhibited mercury release. Among the organic ligands, mercaptoacetic acid, which binds Hg very strongly, was the most effective at solubilizing Hg. DOM, in the form of organic matter isolates, was also very effective at solubilizing Hg for all samples except the lake sediment sample, with the most aromatic organic matter isolates being the most reactive. The results of this study indicate that DOM is very important in the mobilization of Hg from soils and sediments and will influence the dissolution, mobilization, and bioavailability of mercury in wetlands associated with the Sacramento-San Joaquin Delta area.
B11B-0403
Beaver Ponds Increase Methylmercury and Nutrients Concentrations in Canadian Shield Streams
Beaver populations and the number of beaver dams are currently increasing in many Canadian regions. Since natural and anthropogenic impoundments have historically been identified as sources of the potent neurotoxin methylmercury (MeHg), beaver dams could also increase MeHg levels in streams. During summer 2006, we collected water samples upstream and downstream from twenty beaver dams of the Laurentians, located on the Canadian Shield. Samples were analysed for total Hg, MeHg and other chemical variables including DOC, TP, TDP, TN, and major ions. Significant increases of nutrients (DOC, TP, TDP, TN) and ammonium concentrations and depletions of oxygen, nitrate and sulphate concentrations between inlet and outlet show that beaver ponds provide environmental conditions that can favour methylation of inorganic mercury. Heterogeneity of the ratio MeHg/THg at the outlet among our sites was well explained by the estimated age of the impoundment, with methylation capacity of beaver ponds decreasing with age. Further, the geographic location of beaver ponds influenced water chemistry at the outlet, as we observed a dichotomy between northern and southern sites; these differences were based mainly on forest composition. On average, beaver impoundments increased MeHg concentrations by 5.7 fold, total Hg concentrations by 1.6 fold and nutrients concentrations by 2-3 fold. Overall, our results suggest that beaver dams may considerably increase MeHg and nutrients levels in downstream ecosystems. The impact of beavers on the cycling of contaminants and nutrients in boreal watersheds should therefore be considered in the management of their populations.
B11B-0404 [WITHDRAWN]
Methyl Mercury Production In Tropical Hydromorphic Soils: Impact Of Gold Mining.
Artisanal alluvial gold mining is important in many tropical developing countries and several million people are involved worldwide. The dominant use of mercury for gold amalgamation in this activity leads to mercury accumulation in soils, to sediment contamination and to methyl mercury (MMHg) bioaccumulation along the food chain. In this presentation we will present recent data on methyl mercury production in hydromorphic soils and tailing ponds from a former gold mining area located in French Guiana (South America). Comparison of specific fluxes between a pristine sub watershed and the contaminated watershed shows that former mining activities lead to a large enhancement of dissolved and particulate MMHg emissions at least by a factor of 4 and 6, respectively. MMHg production was identified in sediments from tailing ponds and in surrounding hydromorphic soils. Moreover, interstitial soil water and tailing pond water profiles sampled in an experimental tailing pond demonstrate the presence of a large MMHg production in the suboxic areas. Both tailing ponds and hydromorphic soils present geochemical conditions that are favorable to bacterial mercury methylation (high soil Hg content, high aqueous ferric iron and dissolved organic carbon concentrations). Although sulfate-reducing bacteria have been described as being the principal mercury methylating bacteria, the positive correlation between dissolved MMHg and ferrous iron concentrations argue for a significant role of iron-reducing bacteria. Identifications by sequencing fragments of 16S rRNA from total soil DNA support these interpretations. This study demonstrates that current and past artisanal gold mining in the tropics lead to methyl mercury production in contaminated areas. As artisanal activities are increasing with increasing gold prices, the bio- magnification of methyl mercury in fish presents an increasing threat to local populations whose diet relies on fish consumption.
B11B-0405
Size Distribution and First Flush Effects of Mercury Containing Particles in Highway Runoff Water
Human and environmental health concerns have recently prompted many California water quality control boards to lower the Total Maximum Daily Loads (TMDL) of Mercury into their water systems. A size distribution study of mercury containing particles was conducted in order to begin to understand the possible sources of the contamination in highway storm water runoff. Four storms were studied from a monitoring site in the Los Angeles area near the crossing of highways 605 and 91. Storm water ran through an extended detention basin made of earthen material with a maximum water depth of 1.17m. Grab samples were collected manually starting at the beginning of the runoff, continuing at every fifteen minutes for the first hour, followed by a collection every hour after that for the duration of the storm. The particle sizes were separated into five size ranges (larger than 100um, 20-100um, 8-20um, 0.45-8um, and 0-0.45um) by sequential filtration. The samples were then acid digested for further analysis. Five standard Mercury solutions ranging from 5 to 100 parts per trillion were prepared in nitric acid immediately before analysis. Samples were analyzed for both the Hg-199 and the Hg-202 isotopes using an Agilent 7500i Inductively Coupled Plasma Mass Spectrometer. Substantial sub-micron concentrations of mercury were detected from all four storms, and in all five particle size ranges studied. The total amount of Mercury detected from each of the storms ranged from 8.5 to 35.5 pptr. Bursts of rain correlate well with increases of influent Hg concentration. Although a First Flush effect can be seen in the first storm, it is not as strong and/or not shown at all in the remaining three. The detention basin used at the site was shown to be an efficient BMP, reducing the amount of Hg in the effluent runoff as much as 30 pptr and down to as little as 2 pptr. The majority of Hg was found in either the 8-20um or the 0-0.45um particle size ranges. Mitigation of either portion will be challenging, but necessary to meet proposed 50 percent reductions.
B11B-0406
Formation of Methyl Mercury During Restoration of Forested Wetlands in Relation to Hg, S and Fe Geochemistry
In 1999 the Swedish Parliament adopted fifteen National Environmental Quality Objectives (NEQO), one of these is the objective of "Thriving wetlands" with thee goal to restore 12 000 ha of wetlands until 2010. Given the current knowledge about methyl mercury (MeHg) production in wetlands, and subsequent bioaccumulation, the objective of thriving wetlands may be in conflict with other NEQO. In this project wetland restoration objects in different environmental settings (differing in primary productivity, climate and sulfur and iron geochemistry) are selected. After a pre-treatment period of 1-2 years, wetlands will be restored by increasing the ground water table. Methylation and demethylation rates, determined in incubation experiments using stable isotopes, will be linked to the chemical speciation of Hg, S and Fe in soil and soil solution using techniques like sulfur and iron X-ray absorption near edge spectroscopy (XANES) and Hg extended x-ray absorption fine structure (EXAFS) spectroscopy. This is done both prior to and during the restoration. Because of the strong link between Fe(II) and S(-II) geochemistry we hypothesize that net MeHg production is limited by the availability of dissolved, neutral Hg-sulfides in iron-rich environments. Preliminary data prior to restoration indeed indicate that besides primary productivity, the availability of neutral Hg-sulfides in the pore water of soils is important for the net production of MeHg.
B11B-0407
Enzymatic catalysis of mercury methylation by planktonic and biofilm cultures of sulfate- reducing bacteria
While biofilms are now known to be the predominant form of microbial growth in nature, little is known about their role in environmental mercury (Hg) methylation. Due to its long-range atmospheric transport, Hg contamination of food chains is a worldwide problem, impacting even pristine areas. Among different forms of mercury species, methylmercury (MeHg) is an extremely neurotoxic and biomagnification-prone compound that can lead to severely adverse health effects on wildlife and humans. Considerable studies have shown that in the aquatic environment the external supply of MeHg is not sufficient to account for MeHg accumulation in biota and in situ biological MeHg formation plays a critical role in determining the amount of MeHg in food webs; moreover, sulfate-reducing bacteria (SRB) has been identified as the principal Hg-methylating organisms in nature. In a wide range of aquatic systems wetlands are considered important sites for Hg methylation mostly because of the environmental factors that promote microbial activity within, and biofilms are especially important in wetland ecosystems due to large amount of submerged surfaces. Although recent work has focused on the environmental factors that control MeHg production and the conditions that affect the availability of inorganic Hg to SRB, much remains to be understood about the biochemical mechanism of the Hg methylation process in SRB, especially in the biofilm-growth of these microbes. Data from our previous study with SRB strains isolated from a coastal wetland suggested that the specific Hg methylation rate found was approximately an order of magnitude higher in biofilm cells than in planktonic cells. In order to investigate possible reasons for this observed difference, and to test if this phenomenon is observed in other strains, we conducted chloroform, fluroacetate and molybdate inhibition assays in both complete and incomplete-oxidizing SRB species (Desulfovibrio desulfuricans M8, Desulfococcus sp. Desulfobactor sp. BG8) grown in planktonic and biofilm form, as the acetyl- coenzyme A pathway involved with cobalamin has been hypothesized to be the pathway for Hg methylation. The purpose of this study was to probe whether differences in the enzymatically catalyzed process caused differential methylation rates between the species and also between the different forms of culture growth. Any attempts to control the environmentally undesirable Hg methylation process would benefit from a better understanding of the biochemical mechanism involved.
B11B-0408
Importance of Dissolved Neutral Hg-Sulfides, Energy Rich Organic Matter and total Hg Concentrations for Methyl Mercury Production in Sediments
Methyl mercury (MeHg) is the mercury form that biomagnifies to the greatest extent in aquatic food webs. Therefore information about factors determining MeHg concentrations is critical for accurate risk assessment of contaminated environments. The concentration of MeHg in wetlands and sediments is the net result of: 1) methylation rates, 2) demethylation rates, and 3) input/output processes. In this study, the main controls on Hg methylation rates and total concentrations of MeHg, were investigated at eight sites in Sweden with sediments that had been subjected to local Hg contamination either as Hg(0), or as phenyl-Hg. Sediments were selected to represent a gradient in total Hg concentration, temperature climate, salinity, primary productivity, and organic C content and quality. Most sediments were high in organic matter content due to wood fibre efflux from pulp and paper industry. The pore water was analysed for total Hg, MeHg, DOC, H2S(aq), pH, DOC, Cl and Br. The chemical speciation of Hg(II) and MeHg in pore water was calculated using equilibrium models. Potential methylation and demethylation rates in sediments were determined in incubation experiments at 23° C under N2(g) for 48 h, after addition of isotopically enriched 201Hg(II) and Me204Hg. In all surface (0-20 cm) sediments there was a significant (p<0.001) positive relationship between the experimentally determined specific potential methylation rate constant (Km, day-1) and % MeHg (concentrations of MeHg normalized to total Hg) in the sediment. This indicates that MeHg production overruled degradation and input/output processes of MeHg in surface sediments, and that % MeHg in surface sediments may be used as a proxy for net production of MeHg. To our knowledge, these are the first data showing significant positive relationships between short term (48 h) MeHg production and longer term accumulation of MeHg, across a range of sites with different properties (1). If MeHg was not normalized to total Hg, the relationship was not significant. For sub-sets of brackish waters (p<0.001, n=23), southern, high-productivity freshwaters (p<0.001, n=20) as well as northern, low-productivity freshwater (p=0.048, n=6), the sum of neutral Hg-sulfides [Hg(SH)20 (aq)] and [HgS0 (aq)] in the sediment pore water was significantly, positively correlated with both the potential methylation rate constant (Km) and total MeHg concentrations (2). This indicates that methylating sulphate reducing bacteria passively take up neutral Hg-sulfides, which are transformed to MeHg. Differences in slopes of the relationships were explained by differences in primary productivity and availability of energy-rich organic matter to methylating bacteria. High primary productivity at southern freshwater sites, reflected by a low C/N ratio (large contribution from free living algae and bacteria) in the sediment and a high annual temperature sum, resulted in high methylation rates. In conclusion, concentrations of neutral Hg-sulfides and availability of energy rich organic matter, but also total Hg concentrations in sediments are important factors behind net production and accumulation of MeHg . References: (1) Drott et. al. submitted, (2) Drott, A.; Lambertsson, L.; Björn, E.; Skyllberg, U. Importance of dissolved neutral mercury sulfides for methyl mercury production in contaminated sediments. Environmental Science & Technology 2007, 41, 2270-2276.
B11B-0409
Complexation of Inorganic Mercury by Cysteine Promotes Bacterial Methylation of Mercury
One critical factor controlling methylmercury (MeHg) accumulation in the environment is the chemical form of Hg(II) available for methylation by bacteria. Current models suggest that passive diffusion of neutral sulfide complexes may determine the bioavailability and methylation of mercury; however, these hypotheses have never been thoroughly tested. We have investigated how the chemical speciation of Hg(II) affects mercury methylation in washed cell suspensions of the Hg(II)-methylating bacterium, Geobacter sulfurreducens. In assays where the dominant Hg-binding ligand is either chloride or sulfide, MeHg is produced at a rate of about 10-21 mol MeHg/h/cell, with 1-5% of the total Hg(II) (HgT = 5 nM) being eventually methylated. The binding of Hg to cysteine greatly accelerates MeHg formation with near complete methylation of the added Hg(II). MeHg formation is directly proportional to the concentration of Hg-cysteine complex and can be reduced by increasing the proportion of Hg- chloride or Hg-sulfide species. The addition of Cu(II) results in a large reduction in the methylation of Hg(II) presumably as the result of the chemical oxidation of cysteine. Exudates released by G. sulfurreducens during growth appear to enhance mercury methylation in washed cell suspensions relative to control assays. This response is likely due to the release of cysteine or other thiols into the bulk medium during growth. The results of this study suggest a need to reevaluate our models for mercury uptake and methylation in anaerobic bacteria to include the importance of small molecular weight thiols in controlling methylmercury formation.
B11B-0410
Coupled Hydrological and Biogeochemical Controls on Methylmercury Production and Export from a Boreal Wetland
Through long-term addition of a mercury (Hg) stable isotope to a wetland, we have begun to unravel the complexity of Hg and methylmercury (MeHg) cycling in a Boreal wetland. As part of the METAALICUS project being conducted at the Experimental Lakes Area, the lake 658 wetland was annually amended from 2001-2006 with a mercury isotope at a level approximately 5 times the annual anthropogenic deposition. However, wetlands not only receive Hg directly from atmospheric deposition, but also from upland runoff and from adjacent water bodies during periods of inundation. As METAALICUS is a whole watershed experiment, both the adjacent lake and uplands were each amended with a different mercury isotope. This has allowed us to study the cycling of Hg within the wetland in a watershed context. What is clear from this integrated approach is Hg cycling is dependent on the complex interplay of hydrodynamic and biogeochemical factors which will form the focus of this presentation. The Lake 658 wetland is classified as a basin oligotrophic swamp, and is surrounded on three sides by steeply sloping uplands and on the fourth by a lake. The morphology of the wetland causes large portions of the wetland to be hydrologically disconnected for long periods during dry periods in the summer and by ice in winter. When flow occurs, it is along defined channels rather than by sheet flow, which is partially an artifact of the basin morphology. Thus, wetland form influences the wetland volume that contributes to Hg and MeHg export. The majority of the Hg isotope added to the wetland has been retained in the vegetation and upper few centimeters of peat, with less than 1% exported despite the substantial export of both inorganic ambient Hg and MeHg. As little newly deposited Hg, represented by the amended isotope has been exported, we hypothesize that Hg export from wetlands is strongly coupled to decomposition and the fate of dissolved organic carbon which binds both Hg and MeHg. While MeHg is found throughout the wetland, MeHg concentrations and potentials (measured by short-term assays) were greatest in areas that are hydrologically connected to the lake or upland. These methylation assays correlate well with sulfate reduction and methane production. However, high concentrations of MeHg can be present in areas of the wetland when methylation assays reveal no measurable activity suggesting a pool of recalcitrant MeHg exists in wetlands. We hypothesize that the hydrologically interconnected areas of the wetland are most important in producing and exporting MeHg. However, the slow release of Hg isotope from the 658 wetland indicates Hg retention, thus response to changes in Hg deposition, is at least on the order of years and probably decades.
B11B-0411
A Coupled Biogeochemical Reactive Transport Model in Bed Sediments and Water Column of Riverine Systems
ABSTRACT: A multi-scale, quasi-two-dimensional, biogeochemical reactive theoretical and numerical model is presented, able to simulating sediment associated transport and transformations of contaminants in the water column and bed sediments of riverine systems as a result of sediment associated transport, as well as resuspension, deposition and burial. The model considers contaminant mass exchange between sediments and aqueous phase both in benthic sediments and water column as a kinetically controlled process. It also takes into account the effect of microbially-mediated redox reactions affecting the speciation of chemicals. Transport of species in the sediments is modeled using a set of vertical one-dimensional sub-models which take into account the reactive transport of chemicals, burial, sorption/desorption to/from the solid phase, and diffusive transport of aqueous species. An innovative multi-time step approach is used to model the fully kinetic nonlinear reaction terms using a non-iterative explicit method. This approach enables the model to handle fast and near- equilibrium reactions without a significant increase in computational burden. Ongoing and planned applications of this multiscale modeling strategy to two cases, multiple metal transport in Lake Coeur d'Alene, Idaho, and Mercury Cycling in Walker Creek, California, are discussed.
B11B-0412
Competitive binding between mercury and copper for reduced sulfur binding sites on dissolved organic matter from the Florida Everglades
The interaction of mercury and dissolved organic matter (DOM) strongly influences the biogeochemistry of mercury in the Florida Everglades. Previous laboratory-based studies of simple systems at environmentally relevant concentrations of mercury(II) (a soft Lewis acid) and DOM found strong conditional binding constants (log KHgL' = 28-31). These large constants result from the interaction of mercury(II) with reduced sulfur (a soft Lewis base) sites on DOM. Reported conditional binding constants for other metals with DOM (e.g. log KCuL' = 11-14), suggest that metals of borderline Lewis acidity would not compete with mercury(II) for the strongest binding sites at environmentally relevant concentrations. However, the small proportion of strong binding sites responsible for mercury(II) binding have proven to be susceptible to competitive effects from borderline metals. Equilibrium dialysis experiments using organic matter isolated from the Florida Everglades were designed to determine the effects of competitive binding between copper(II) and mercury(II) on DOM binding sites. These experiments demonstrated that copper(II), a borderline Lewis acid, effectively competed for strong DOM sites at concentrations only 1-2 orders of magnitude greater than experimental mercury(II) concentrations (which ranged from 0.05 to 0.2nM). Our results indicate that the reduced sulfur sites responsible for Hg(II) binding on DOM also have high affinities for borderline metals. Interactions of copper(II) and DOM were also investigated in the absence of mercury(II). These results further substantiate the significance of a small concentration of strong binding sites on DOM. At low copper(II) to DOM ratios, preliminary results indicate that the binding interactions between copper(II) and DOM are significantly greater than previously reported and are close to those measured for DOM-mercury(II) binding. We conclude that currently available binding constants for metals of interest (borderline Lewis acids) are inadequate for assessing competitive effects with mercury(II)-DOM binding at low metal to DOM ratios. In the environment, copper(II) may be found at concentrations several orders of magnitude greater than mercury(II) concentrations and the concentration of copper(II) may significantly exceed the concentration of strong binding sites on DOM. Potential competition between mercury and borderline metals may influence mercury speciation and significantly affect the biogeochemical modeling of mercury in aquatic systems.
B11B-0413
Adding to the Mercury Speciation Toolbox
Mercury was used to separate lithium-6 isotope for weapons production at the Y-12 Plant in Oak Ridge, TN in the 1950s and 1960s. A large portion of the waste Hg entered the environment and continues to move throughout the sub-surface and surface waters in the area. Environmental management of Hg contamination within this complex hydrologic system, where Hg speciation and the mobile fraction have been found to vary widely, will require ongoing characterization and predictive modeling of Hg speciation. State-of-the-art spectroscopic tools that can directly probe Hg speciation in preserved aqueous and sediment samples with greater sensitivity, however, are required to determine rates and mechanisms of biogeochemical reactions. We will present the first results demonstrating the use of x-ray absorption spectroscopy (XAS) at the Hg M5 edge (2295 eV) to fingerprint Hg species. Heavy-metal M5 absorption edges can have very sharp features due to local electron transitions, and therefore, we are developing this edge as a tool for quantitative measurement of Hg species. In addition, sulfur speciation using the sulfur K absorption edge, which is at a similar energy (2472 eV), can be measured in the same scan as the Hg M5 edge. Potentially important organic and inorganic sulfur species (sulfide, disulfide, elemental sulfur, sulfite and sulfate) are readily differentiated, and thereby, provides an independent method for monitoring the redox state of the system along with changes in S-Hg bonding. We will also present x-ray microprobe 2-D concentration maps of Hg and other elements at the grain and pore scales to identify its microscopic distribution and chemical associations. When used in combination with established sequential extraction and direct spectroscopic methods, the addition of XAS at the Hg M5 edge should provide a significant advancement in the determination of Hg speciation in complex biogeochemical environments.
B11B-0414
Isotopic Methods for Determining the Relative Importance of Bioavailability Versus Trophic Position in Controlling Mercury Concentrations in Everglades Mosquitofish
The concentration of mercury in fish tissues is widely used as an indicator of the magnitude of mercury contamination in aquatic ecosystems. Eastern mosquitofish (Gambusia holbrookii) is an important sentinel species used for this purpose in the varied environments of the Florida Everglades, because mosquitofish are abundant, have a short lifespan, and migrate little. Like other freshwater fish, the primary route of mercury uptake into mosquitofish tissues is through diet as bioavailable methylmercury. Yet, it is unclear whether variations in mosquitofish mercury observed across the Everglades are due primarily to differences in bioaccumulation (i.e., trophic position) or abundance of methylmercury available to the food web base. We use isotopic methods to investigate the importance of these two controls on mosquitofish mercury at the landscape scale. As part of the USEPA REMAP project, mosquitofish and periphyton were collected during September 1996 from over one hundred sites throughout the Everglades and analyzed for mercury concentration. The USGS analyzed splits of the samples for nitrogen (d15N), carbon (d13C), and sulfur (d34S) isotopic composition, to investigate the causes of mercury variations. The d15N value of tissues is often used to estimate the relative trophic positions of organisms in a food web, and should correlate positively with tissue mercury if bioaccumulation is an important control on mosquitofish mercury concentration. The d13C value can be useful for detecting differences in food web base (e.g., algal versus detrital), and thus the entry point of contaminants. Tissue d34S potentially indicates the extent of dissimilatory sulfate reduction in sediments, a process used by sulfate-reducing bacteria (SRB) during conversion of inorganic Hg(II) to bioavailable methylmercury. Because this process increases the d34S value of remaining sulfate, which enters the food web base, mosquitofish sulfur isotopes should show positive correlations with SRB activity, methylmercury production, and mosquitofish mercury concentrations. The d15N, d13C, and d34S values of mosquitofish and periphyton are significantly correlated, indicating that a component of the bulk periphyton analyzed in this study is part of the mosquitofish food web. Mosquitofish mercury does not correlate significantly with tissue d15N or the d15N difference between mosquitofish and periphyton. Thus, differences in trophic level (and bioaccumulation) among the fish do not contribute a detectable influence on mercury variations in the samples studied. In contrast with the d15N results, mosquitofish mercury levels show significant, positive correlations with mosquitofish d34S and the d34S difference between mosquitofish and periphyton. This suggests that during the period studied, mosquitofish mercury concentrations in the Everglades were primarily influenced by the bioavailability of mercury, rather than by differences in trophic position. This study demonstrates that isotopic measurements, especially d34S, can be useful tools for determining causes of high mercury concentrations in fish populations.
B11B-0415
Mercury cycling in agricultural and non-agricultural wetlands in the Yolo Bypass Wildlife Area, California: bioaccumulation in small fish
We examined the bioaccumulation of mercury in small fish within white rice, wild rice, and permanent wetland habitats at the Yolo Wildlife Area during the 2007 rice growing season. We introduced 30 mosquito fish in each of four cages placed at the inlet, center, and outlet (two cages) of each wetland in June, immediately after the white rice fields were re-flooded after being seeded. All fish were removed from their cages 60-days after their introduction, with the exception that ten fish from each of the second cages at the outlets were removed 30-days after introduction to assess temporal trends in mercury exposure. Mercury concentrations will be compared between fish that were introduced into cages and reference fish that originated from the same fish stock (Sacramento County Vector Control). We also measured fish length and mass both when they were introduced and collected to 1) control for growth effects on mercury bioaccumulation and 2) examine whether wetland habitat influenced growth rates. Fish are currently being analyzed for mercury and results will be available by the conference.
B11B-0416
Translating Research on Mercury in the Environment into High School Curriculum through Teacher Professional Development
Traditional science disciplines taught in high school just scratch at the surface of the complex natural world, especial biogeochemical cycling. Teachers are challenged to go beyond the traditional perspectives and to link current scientific research with classroom experiences. Through professional development workshops from Stanford University's Environmental Molecular Science Institute (EMSI), high school science teachers learn about the EMSI research findings on environmental mercury. Mercury is the focus of the workshop because it is a significant contaminant in the local San Francisco Bay region. Equally as important, teachers learn approaches to science language instruction from a science education professor. The instructional approaches attempt to simplify science discourse and provide students with a richer conceptual and linguistic repertoire. Using the EMSI research on mercury, teachers develop lessons to integrate biogeochemistry into their classroom curriculum, guided by EMSI scientists. In the second year of offering the workshop, more time was spent on designing lessons which led to an increase in the number of high school students learning about mercury in their classrooms. A web-based learning center provides an interactive learning environment including standards- based lesson plans, materials, and video of the lessons taught by workshop participants. http://pangea.stanford.edu/research/emsi/