Final Report: Microbiological and Physicochemical Aspects of Mercury Cycling in the Coastal/Estuarine Waters of Long Island Sound and Its River-Seawater Mixing Zones

EPA Grant Number: R827635
Title: Microbiological and Physicochemical Aspects of Mercury Cycling in the Coastal/Estuarine Waters of Long Island Sound and Its River-Seawater Mixing Zones
Investigators: Fitzgerald, William F. , Visscher, Pieter T.
Institution: University of Connecticut
EPA Project Officer: Hiscock, Michael
Project Period: October 1, 1999 through September 30, 2002
Project Amount: $592,035
RFA: Mercury: Transport and Fate through a Watershed (1999) RFA Text |  Recipients Lists
Research Category: Water and Watersheds , Mercury , Water , Safer Chemicals


Consumption of marine fish and seafood products is the principal pathway by which humans are exposed to the very toxic organomercurial, monomethylmercury (MMHg). Consequently, there is an urgent need for increased knowledge and understanding of the marine biogeochemical cycling of mercury (Hg) and the impact of anthropogenically related Hg inputs. Biologically productive, nutrient-rich near-shore regions, which support major commercial and recreational fisheries, are of special interest. Accordingly, our U.S. Environmental Protection Agency Science to Achieve Results (STAR) Hg research was focused on Long Island Sound (LIS), its watershed, and river-seawater mixing zones. This major natural resource provides a valuable analog for other near-shore/urban marine ecosystems. Our process reaction-focused investigations will allow the results to be applied in other marine regions. Such an approach was essential, given the complexity and variability of fertile estuaries and adjacent coastal waters, which are major repositories for natural and pollutant riverborne/watershed-derived substances such as Hg. The specific objectives of this research project were concerned with several major features of the aquatic biogeochemistry of Hg, particularly elemental mercury (Hg0) cycling and emissions, MMHg production in sediments, interactions between terrestrial watersheds, rivers, and near-shore marine waters, and the role of organic matter (OM) in governing the availability of Hg for competing methylation/reduction reactions.

Our work was conducted in the local coastal waters of LIS, a large (3,200 km2) embayment in the northeastern United States. LIS is the subject of numerous biogeochemical investigations and a long-term monitoring program of its waters (Connecticut Department of Environmental Protection [CT DEP], 2003). Current and historic pollution, including sewage (Buchholtz ten Brinck, et al., 2000), has perturbed LIS significantly. As a consequence, it has longitudinal gradients in pollutant Hg (Varekamp, et al., 2000; Hammerschmidt and Fitzgerald, 2004), dissolved oxygen and nutrients (CT DEP, 2003), as well as sediment geochemistry and microbial activities (Knebel and Poppe, 2000; Mecray and Buchholtz ten Brinck, 2000; Poppe, et al., 2000). Such gradients in LIS are expected to encompass the range of water column and sediment characteristics found in most other coastal regimes. Thus, information on the biogeochemistry of Hg and MMHg in LIS is directly applicable to comparable coastal marine sediments and systems.

Previous measurements of sources and sinks of Hg in LIS have been validated by several independent measurements, resulting in well-constrained mass balances for total Hg and MMHg in LIS (Vandal, et al., 2002; Balcom, et al., submitted, 2003). The principal sources of total Hg (241 kg yr-1) to LIS are rivers (~136 kg yr-1; 56 percent of total inputs), water pollution control facilities (WPCFs) (~11 kg yr-1; 5 percent), the East River (~68 kg yr-1; 28 percent), and direct atmospheric deposition (~26 kg yr-1; 11 percent). Principal external sources of MMHg to LIS (~5 kg yr-1) include rivers (~3 kg yr-1), the East River (~1.4 kg yr-1), and direct atmospheric deposition (~0.7 kg yr-1). In situ sedimentary production was predicted to be the major source of MMHg in LIS (Langer, et al., 2001), and Hammerschmidt, et al. (submitted, 2003) have estimated a sediment-water flux of 11 ± 4 kg MMHg yr-1 (65 percent of total inputs). Although direct atmospheric Hg deposition to LIS is small (~26 kg yr-1), modest leaching (25-30 percent watershed delivery; 90-108 kg Hg yr-1) of the LIS-wide atmospheric deposition normalized to its watershed area accounts for 65-80 percent of river Hg inputs (Balcom, et al., submitted, 2003).

Summary/Accomplishments (Outputs/Outcomes):

Hg-Organic Interactions

Spring runoff contributes large amounts of Hg to rivers (watershed leaching) that is tightly bound to dissolved and colloidal organic ligands and particulate matter, which are largely unreactive (not reducible with Sn[II]; Rolfhus, et al., 2003; Lamborg, et al., 2003). Complexation of inorganic mercury cations (Hg[II]) by natural organic compounds has been posited as an influential and often controlling feature of the aquatic biogeochemical cycling of this toxic metal and was one of the working hypotheses for the present study. The high affinity of Hg for OM is characterized by stability constants that are typically five or more orders of magnitude greater than most other metals (e.g., Mantoura, et al., 1978). Complexation of Hg by organic ligands exerts control on important, speciation-dependent, biogeochemical transformations such as methylation, reduction/evasion, and solubility/adsorption (e.g., Barkay, et al., 1997; Benoit, et al., 1999a; Benoit, et al., 2001a; Rolfhus and Fitzgerald, 2001; Turner, et al., 2001; Lamborg, 2003). Although many studies suggest that the majority of Hg present in natural waters is complexed with organic ligands, little quantitative information currently exists regarding the abundance and strength of such Hg-complexing agents in natural waters. We have developed a new method for the determination of the concentration and conditional stability constants of dissolved organic matter (DOM) towards Hg using an in vitro reducible-Hg titration approach (Lamborg, et al., 2003).

Long Island Sound. We found the concentration of Hg-binding organic ligands in LIS and its environs to range from less than 1 to greater than 60 nN, and that the conditional stability constants (affinities of the OM for Hg) are very high (logK' = 21-24; Lamborg, et al., 2003). Only one ligand class was found in the natural waters tested (i.e., rivers, seawaters, bog waters, sewage, and sedimentary porewaters). Concentrations, affinities, and kinetics implicate multidentate binding sites as the principal chelation moieties for Hg. Recent spectroscopic investigations of Hg binding to soil organic material have pointed to multidentate associations involving sulfur and oxygen bonds to Hg (Xia, et al., 1999; Hesterberg, et al., 2001). In freshwaters, greater than 99.9 percent of Hg is found in organic complexes (Lamborg, et al., 2003), and although the fraction of Hg in organic complexes varies in salt waters, coastal waters also are dominated (> 50 percent) by organic forms. These findings are significant, as the organically complexed pool is likely to have much different biogeochemical reactivity, and can, therefore, affect Hg biogeochemistry on local, regional, and global scales.

Ligand activity through the salinity gradient of the Connecticut River (CTR) indicated that a majority of the ligands in LIS would be of terrestrial origin. Ligand distributions through the CTR estuary suggest pseudoconservative mixing (higher concentrations in fresher waters) of ligand derived from the CTR watershed (Lamborg, et al., 2003). Furthermore, the ligand:dissolved organic carbon (DOC) ratios for a variety of end member waters for LIS indicate that offshore (continental shelf) waters and sewage (East River) possess very ligand poor DOC. Therefore, a substantial percentage of the Hg binding compounds present in the coastal waters of LIS are allochtonous in origin (Lamborg, et al., 2003). We have constructed a first-order mass balance for ligand and DOC in LIS (Lamborg, et al., submitted, 2003), based on measurements of ligand concentrations, DOC analyses, and some estimated DOC fluxes. The principal sources of ligands to LIS are riverwater (47 percent; terrestrial OM) and phytoplankton DOC exudation (31 percent), and the only significant loss term identified is tidal exchange with the low DOC/low ligand waters of the continental shelf. The seasonal variations in ligand abundance (lowest during winter and highest during summer and spring) are a reflection of the importance of river flow and primary production, as these sources are strongest in the spring and summer in LIS (Lamborg, et al., submitted, 2003).

Methylmercury Production in Sediments

Cycling of toxic MMHg in biologically productive coastal marine systems is affected by geochemical and macro/microbiological factors that control its production and mobilization from sediment. Despite the paucity of information concerning the sources, in situ production, biogeochemistry, and bioaccumulation of MMHg in near-shore marine sediments, they appear to be potentially significant sources of MMHg to food webs in the coastal zone, and possibly the open ocean via hydrological or biological transport. Such sediments often are a major repository of pollution-derived Hg that has accumulated over the past 150 years ("legacy Hg"; Fitzgerald and Lamborg, 2003). Additionally, they host active communities of sulfate-reducing bacteria (SRB)—the principal group of organisms mediating transformation of inorganic Hg to MMHg (Compeau and Bartha, 1985; Gilmour, et al., 1992). The activity of SRB in coastal marine sediments is extraordinarily large; they mineralize most of the organic carbon (Capone and Kiene, 1988). Given the combination of potential reactants (SRB, large burdens of "legacy Hg," and modern Hg inputs), we posited considerable production of MMHg in near-shore sediments. Our three-part working hypothesis consisted of the following postulates: (1) sedimentary Hg methylation by SRB is an important source of MMHg in the coastal zone; (2) bioturbation enhances Hg methylation in marine sediments; and (3) reworking of sediments by benthic infauna makes a portion of potentially immobile "legacy Hg" (e.g., Hg sequestered in solid sulfide phases) available for microbial MMHg production.

Long Island Sound. Sediment-phase concentrations of MMHg and Hg(II)(Hg[II] = total Hg - MMHg) increased from east to west in LIS surface sediments, and the ratio of MMHg:Hg(II) was relatively proportional throughout LIS (about 0.8 percent MMHg; Hammerschmidt and Fitzgerald, 2004). Both MMHg and total Hg (i.e., organically bound Hg, inorganic Hg, and MMHg) were related positively with OM in surface sediment, which also increases from east to west in LIS. In contrast to the trends in Hg species in LIS surface sediments, potential rates of Hg methylation (measured with an added isotope tracer, 200Hg) decreased from east to west in LIS and were related inversely to OM (Hammerschmidt and Fitzgerald, 2004). In other words, although comparatively more MMHg was present in organic-rich western LIS substrate, the rate of sedimentary Hg methylation was greater in the eastern LIS. Potential rates of Hg methylation were enhanced in August relative to March and June, illustrating the role of methylating bacteria (i.e., SRB) in utilizing available substrate Hg(II) (Hammerschmidt and Fitzgerald, 2004). Artifact MMHg can substantially bias measurements of MMHg in natural samples, especially sediments. Therefore, we also evaluated the potential for formation of artifact MMHg and found that little or no MMHg was produced artifactually during analysis of LIS sediments (Hammerschmidt and Fitzgerald, 2001).

We found that sedimentary OM and acid-volatile sulfide are the principal controls on the partitioning of MMHg and Hg(II) between dissolved and particle phases (Hammerschmidt and Fitzgerald, 2004; Hammerschmidt, et al., submitted, 2003). 200Hg methylation varied inversely with the distribution coefficient (KD, L kg-1) of Hg(II) and positively with the concentration of Hg(II) in porewater (Hammerschmidt and Fitzgerald, 2004), which exists, mostly as HgS0, in porewater. Therefore, more dissolved inorganic Hg is available to methylating bacteria in sediment where levels of OM are lower (e.g., eastern LIS). The observation of coincident sediment-water partitioning of Hg species and organic carbon suggests organic ligands may affect the speciation of dissolved inorganic Hg complexes in anoxic low-sulfide sediments such as those in LIS. This is in marked contrast to chemical speciation models that show sulfide is the major ligand of both dissolved MMHg (Dyrssen and Wedborg, 1991) and Hg(II) (Benoit, et al., 1999b) in natural porewaters. Knowledge of Hg(II) and MMHg speciation in porewaters is key to understanding the production (bioavailability) of MMHg and associated fluxes of MMHg from sediment.

Most Hg methylation occurs at the surface in undisturbed sediment (i.e., central and western LIS; Gilmour, et al., 1998; Langer, et al., 2001). However, benthic infauna can affect the biogeochemical cycling of MMHg in coastal marine systems. Physical mixing/irrigation of marine sediments by infauna appears to enhance rates of MMHg production and extend zones of active Hg methylation in sediment (Hammerschmidt, et al., submitted, 2003). Subsurface peaks in 200Hg methylation potentials coincide with anomalies in a bioturbation index (change in organic carbon normalized to change in depth in sediment) that indicate localized physical disturbance of sediment. Bioturbation may introduce labile OM to depths where active sulfate reduction occurs, or it may promote chemical conditions that favor the bioavailability of inorganic Hg substrate, both of which may result in increased methylation in sediment (Hammerschmidt, et al., submitted, 2003). Bioturbation can redistribute "legacy Hg" within the sedimentary column to zones of active biological methylation, creating the potential for methylation, mobilization, and bioaccumulation of pollutant Hg that was buried during the past 150 years. Our results with 200Hg isotope show that a significant potential for MMHg production exists at depth in coastal marine sediment, where "legacy Hg" is buried, sequestered in solid sulfide complexes, and presumed unavailable for microbial Hg methylation (Hammerschmidt and Fitzgerald, 2004).

Flux from LIS Sediments. Accumulation of MMHg in surface sediments of LIS is not directly related to potential rates of bacterial Hg methylation. Much of the MMHg produced in sediments is lost to overlying water (Hammerschmidt and Fitzgerald, 2004). The estimated diffusive sediment-water flux of MMHg in LIS (55 ± 20 mol yr-1 or 11 kg yr-1) exceeds inputs from external sources (26 mol yr-1; Balcom, et al., submitted, 2003). This indicates that in situ production is the major source of MMHg to LIS, and by extension, other comparable near-shore systems. Anthropogenic sources have enhanced total Hg in LIS sediments about sevenfold since the Industrial Revolution (Varekamp, et al., 2000; Fitzgerald, et al., 2000), and we have found that MMHg production in such sediments is related to the availability of inorganic Hg (Hammerschmidt and Fitzgerald, 2004). Thus, we infer that MMHg synthesis in LIS sediments has increased temporally, relative to pollutant Hg enrichment. The toxicological significance of MMHg in the food web of near-shore systems is unknown, but it is likely that the biotic MMHg burden has increased in recent history. Our results from LIS indicate a link between sedimentary production, mobilization, and bioaccumulation of MMHg. Sedimentary production and subsequent mobilization of MMHg can account for most of the MMHg in primary producers of LIS (Hammerschmidt, et al., submitted, 2003). Hence, through dietary bioaccumulation, much of the MMHg in higher trophic levels within LIS may be attributed to Hg methylation in the sediments.

River-Seawater Mixing Zones

The most significant river inputs to LIS are the East River, with its large sewage loadings, and the CTR, which contributes about 70 percent of annual input of freshwater, and whose extensive watershed and potential for leaching of atmospherically derived Hg extends northward into Canada. We hypothesized that the processes associated with estuarine mixing (e.g., ion exchange, ligand competition, metal scavenging) are forming labile Hg from riverine Hg-DOM complexes in river-seawater mixing zones. It is well known that, as outlined, particulate and DOM significantly alter the speciation of Hg in aquatic systems, with complex natural organic ligands (e.g., S-rich humic and fulvic acids) generally exhibiting larger conditional stability constants for Hg-complex formation than inorganic ligands (e.g., Cl- and major seawater cations; Lamborg, et al., 2003; Benoit, et al., 2001b; Babiarz, et al., 2000; Ravichandran, et al., 1999). However, organically bound metals undergo dramatic changes in speciation, concentration, and distribution as the complex encounters high-ionic strength media during estuarine mixing. These include ion exchange of major seawater cations (particularly Mg2+ and Ca2+) for trace metals associated with clays, organic material, and Fe3+-oxyhydroxide complexes. These processes are complicated by metal adsorption/desorption from phase boundaries (particle/colloid surfaces), sediment resuspension, and speciation changes mediated by changing pH, ionic strength, and DOC (Santschi, et al., 1997). Thus, for many dissolved and particulate metal fractions, several varieties of nonconservative behavior are observed in association with sources and sinks during estuarine mixing (Benoit, et al., 1994; Stordal, et al., 1996). Mechanisms that shift Hg speciation to more labile forms (i.e., participating in redox transformations, methylation/demethylation) may significantly alter the rates and extent of such reactions, and may, therefore, potentially increase the availability of MMHg to the aquatic food web (Rolfhus, et al., 2003). Therefore, the river-coastal water mixing regime is one of the most critical parts of the watershed.

Connecticut River. Reactive Hg has been used as an operationally defined proxy for the labile Hg(II) reactant that participates in methylation, reduction, and particle scavenging in coastal waters (Rolfhus and Fitzgerald, 2001). This study examined the role of estuarine mixing on formation of labile Hg complexes (reactive Hg) from relatively refractory Hg-organic associations in river water and examined the behavior and distribution of Hg species in the CTR estuary. Results indicated that although total Hg partitioning (KD) and concentrations remained fairly constant with increasing salinity, the fraction present as reactive Hg increased, primarily in the particulate phase (Rolfhus, et al., 2003). Linearly increasing trends in reactive Hg and reactive Hg/total Hg (reactive normalized to total Hg) with increasing salinity may be explained by conservative mixing of properties from the salt and freshwater end members. Riverine organic ligands rapidly scavenge reactive Hg from natural waters, but samples free of riverine influence remained much more "reactive" (Rolfhus, et al., 2003). Our observations, coupled with a simple competitive ligand model, support the notion that dilution of a dominant organic ligand class and competition with chloride, followed by coagulation/adsorption onto suspended particles, is primarily responsible for the enhanced reactive Hg. Enhanced Hg lability may support increased rates of methylation in estuarine and coastal ecosystems, potentially enhancing MMHg exposure to humans and wildlife.

East River. In addition to estuarine reactions, we hypothesized that direct WPCF discharges (sewage) increase the labile Hg fraction available for reduction and methylation reactions. The waters of the East River are similar to WPCF effluent with respect to total Hg concentrations, and elevated as compared to LIS (Vandal, et al., 2002; Balcom, et al., submitted, 2003). The highest total Hg, reactive Hg, and Hg0 concentrations in East River surface waters were measured in both spring and summer near the largest municipal WPCF discharge (Wards Island). The concentrations of Hg species show a negative correlation with salinity, decreasing eastward toward LIS because of mixing with LIS water. Even after mixing, however, reactive and total Hg were high in both spring and summer at the mouth of the East River as compared to LIS. We have documented an increase in bottom water reactive and total Hg between spring and late summer in western/central LIS. We hypothesize that the East River is supplying labile Hg to the waters of LIS that, in turn, supports much Hg0 production in western/central LIS.

Hg0 and Hg Speciation in Long Island Sound

In situ Hg0 (dissolved gaseous mercury [DGM]; approximately 99 percent elemental Hg in seawater) production in the waters of LIS and emissions to the local/regional atmosphere are major processes (Rohlfus and Fitzgerald, 2001; Rolfhus, 1998). We hypothesized that the Hg0 distribution in LIS is spatially/temporally variable, related to the distribution of labile Hg and the in situ supply of reducing agents (bacterial activity and solar radiation). Our DGM surveys have elucidated spatial/seasonal patterns in the distribution of Hg0 in LIS and their correlation with hydrographic conditions. We used an automated aqueous gaseous elemental mercury sampling and analysis system (AGEMS), designed by our laboratory for shipboard use, which allowed for direct analysis of Hg0 in surface waters. Field measurements were supported by laboratory analyses using a semiautomatic dissolved elemental mercury analyzer ([DEMA]; Tseng, et al., 2003), which has been developed as part of our STAR research program. Earlier (1995-1997) DGM measurements in LIS (Rolfhus and Fitzgerald, 2001) showed maxima in central LIS and elevated concentrations during the warm months. DGM sometimes decreased with decreasing salinity west of the CTR (salinity decreases from east to west in LIS), particularly during the spring. As suggested by our hypothesis, these spring distributions were attributable to enhanced Hg0 production associated with a major reactive Hg source (e.g., CTR), with the distribution maintained by biological production and simple mixing of reactive Hg (i.e., reactant) in LIS (Rolfhus and Fitzgerald, 2001).

Our DGM surveys have further elucidated spatial/seasonal patterns in the distribution of Hg0 in LIS and their correlation with hydrographic conditions. Surface maxima have commonly been observed along the central axis of western/central LIS in the region between two bottom sills (Stratford Shoal and Anchor Reef) that traverse LIS. Examination of the hydrographically generated supply of labile Hg reveals inputs from deep-water mixing (e.g., degradation of OM at depth), which may supply Hg reactant for DGM production at the surface between the sills (e.g., August/September breakdown of thermal stratification). Both in the spring and late summer, measured surface water concentrations of labile Hg and nitrate (used as a tracer of labile inputs) in western/central LIS are supported by bottom water concentrations. Conversely, reactant for DGM production in western LIS is likely supplied by simple mixing from the East River. Diurnal Hg0 measurements using AGEMS and/or DEMA during the fall and summer indicate relatively uniform concentrations over a 24-hour period. Therefore, even in the summer, photoreduction of labile Hg to Hg0 does not fully account for the surface peaks in DGM. Mixing in the surface mixed layer and deep-water mixing in the absence of thermal stratification may be the important control on surface Hg0 concentrations in central/western LIS.

Role of OM. Using information from the ligand titration studies, experiments were conducted to examine the effect of Hg speciation on the important biogeochemical process of in situ reduction of Hg(II) to Hg0. The addition of a common form of DOC (humic acid) to synthetic seawater solutions increased the rate of reduction. This finding was not new (e.g., Rolfhus, 1998). However, the effect of adding competitive ligands (ethylenediaminetetraacetic acid [EDTA] and Cl-) at high enough concentrations to shift the Hg speciation away from the humic acid was to lower the reduction rate to almost zero (Lamborg, 2003). This indicates that Hg must be bound to organic material to be reduced in natural waters by abiological processes. These results explain certain aspects of Hg cycling in LIS (Lamborg, 2003). First, higher Hg0 concentrations in summer are supported by the higher concentrations of DOC and ligand, which likely bring Hg speciation and DOC values to the point of optimal reduction rates. This phenomenon, coupled with low wind speeds, leads to a buildup of Hg0 during the summer. Second, DOC may at times be high enough to prevent reduction to Hg0 even when there is excess Hg(II) (labile Hg) available for reduction. Third, the results also suggest that Hg-organic associations can explain reduction below the photic zone, and this flux is likely to be the dominant reduction term on a depth-integrated basis. Therefore, the important dark reductions of Hg may be abiological and organically mediated (Lamborg, 2003).

Hg0 Fluxes from LIS. Supersaturation of Hg0 in all seasons indicates that Hg is lost from LIS to the atmosphere via evasion. There is agreement in the average calculated Hg0 flux (Wanninkhof, 1992) is between the earlier 1995-1997 (334 pmoles m-2 d-1, range = 68-531; Rolfhus and Fitzgerald, 2001) and later 1998-2002 LIS surveys (280 pmoles m-2 d-1, range = 75-822; present study). General trends include increased Hg0 flux with increased Hg0 concentrations during warmer months and at higher wind velocities. Annual emissions are estimated at 80 kg (Rolfhus and Fitzgerald, 2001; present study), which indicates remobilization of approximately 30 to 35 percent of the Hg inputs (219 kg/yr) to LIS (Fitzgerald, et al., 2000; Balcom, et al., submitted, 2003). Because most Hg entering LIS has an anthropogenic origin (> 70 percent), a substantial pollution component is being remobilized and its lifetime extended in active reservoirs. The aqueous production of Hg0 competes for reactant (i.e., labile Hg) with the in situ biological synthesis of MMHg such that water bodies with a large production of Hg0 may have smaller amounts of MMHg in biota and accumulation in the sediment.


Connecticut Department of Environmental Protection. The Long Island Sound Water Quality Monitoring Program, 2003.

Buchholtz ten Brinck MR, Mecray EL, Galvin EL. Clostridium perfringens in Long Island Sound sediments: an urban sedimentary record. Journal of Coastal Research 2000;16:591-612.

Varekamp JC, Buchholtz ten Brink MR, Mecray EL, Kreulen B. Mercury in Long Island Sound sediments. Journal of Coastal Research 2000;16:613-626.

Knebel HJ, Poppe LJ. Sea-floor environments within Long Island Sound: a regional overview. Journal of Coastal Research 2000;16:533-550.

Mecray EL, Buchholtz ten Brink MR. Contaminant distribution and accumulation in the surface sediments of Long Island Sound. Journal of Coastal Research 2000;16:575-590.

Poppe LJ, Knebel HJ, Mlodzinska ZJ, Hastings ME, Seekins BA. Distribution of surficial sediment in Long Island Sound and adjacent waters: texture and total organic carbon. Journal of Coastal Research 2000;16:567-574.

Mantoura RFC, Dickson A, Riley JP. The complexation of metals with humic materials in natural waters. Estuarine and Coastal Marine Science 1978;6:387-408.

Barkay T, Gillman M, Turner RR. Effects of dissolved organic carbon and salinity on bioavailability of mercury. Applied and Environmental Microbiology 1997;63(11):4267-4271.

Benoit JM, Gilmour CC, Mason RP, Heyes A. Sulfide controls on mercury speciation and bioavailability to methylating bacteria in sediment pore waters. Environmental Science and Technology 1999a;33:951-957.

Benoit JM, Mason RP, Gilmour CC. Estimation of mercury-sulfide speciation in sediment pore waters using octanol-water partitioning and implications for availability to methylating bacteria. Environmental Toxicology and Chemistry 1999b;18:2138-2141.

Benoit JM, Gilmour CC, Mason RP. The influence of sulfide on solid-phase mercury bioavailability for methylation by pure cultures of Desulfobulbus propionicus. Environmental Science and Technology 2001a;35:127-132.

Benoit JM, Mason RP, Gilmour CC, Aiken GR. Constants for mercury binding by dissolved organic matter isolates from the Florida Everglades. Geochimica et Cosmochimica Acta 2001b;65(24):4445-4451.

Turner A, Millward GE, Le Roux SM. Sediment-water partitioning of inorganic mercury in estuaries. Environmental Science and Technology 2001;35(23):4648-4654.

Xia K, Skyllberg UL, Bleam WF, Bloom PR, Nater EA, Helmke PA. X-ray absorption spectroscopic evidence for the complexation of Hg(II) by reduced sulfur in soil humic substances. Environmental Science and Technology 1999;33:257-261.

Hesterberg D, Chou JW, Hutchison KJ, Sayers DE. Bonding of Hg(II) to reduced organic sulfur in humic acid as affected by S/Hg ratio. Environmental Science and Technology 2001;35(13):2741-2745.

Compeau G, Bartha R. Sulfate-reducing bacteria: principal methylators of mercury in anoxic estuarine sediment. Applied and Environmental Microbiology 1985;50:498-502.

Gilmour CC, Henry EA, Mitchell R. Sulfate stimulation of mercury methylation in freshwater sediments. Environmental Science and Technology 1992;26:2281-2288.

Capone DJ, Kiene RP. Comparison of microbial dynamics in marine and freshwater sediments: contrasts in anaerobic carbon metabolism. Limnology and Oceanography 1988;33:725-745.

Dyrssen D, Wedborg M. The sulfur-mercury(II) system in natural waters. Water, Air, and Soil Pollution 1991;56:507-519.

Gilmour CC, Riedel GS, Ederlington MC, Bell JT, Benoit JM, Gill GA, Stordal MC. Methylmercury concentrations and production rates across a trophic gradient in the Northern Everglades. Biogeochemistry 1998;40:327-345.

Babiarz CI, Hoffmann SR, Shafer MM, Hurley JP, Andren AW, Armstrong DE. Critical evaluation of tangential-flow ultrafiltration for trace metal investigations in freshwater systems. 2. Total mercury and methylmercury. Environmental Science and Technology 2000;34(16):3428-3434.

Ravichandran M, Aiken GR, Ryan JN, Reddy MM. Inhibition of precipitation and aggregation of metacinnabar (mercuric sulfide) by dissolved organic matter isolated from the Florida Everglades. Environmental Science and Technology 1999;33:1418-1423.

Santschi PH, Lenhart JJ, Honeyman BD. Heterogeneous processes affecting trace contaminant distribution in estuaries: the role of natural organic matter. Marine Chemistry 1997;58:99-125.

Benoit G, Oktay-Marshall SD, Cantu A, Hood EM, Coleman CH, Corapcioglu MO, Santschi PH. Partitioning of Cu, Pb, Ag, Zn, Fe, Al, and Mn between filter-retained particles, colloids, and solution in six Texas estuaries. Marine Chemistry 1994;45:307-336.

Stordal MC, Gill GA, Wen L-S, Santschi PH. Mercury phase speciation in the surface waters of three Texas estuaries: importance of colloidal forms. Limnology and Oceanography 1996;41(1):52-61.

Rolfhus KR. The production and distribution of elemental mercury in a coastal marine environment. Ph.D. Dissertation. University of Connecticut, Storrs, CT, 1998.

Wanninkhof R. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research 1992;97(C5):7373-7382.

Hoppe H-G. Use of fluorescent model substrates for extracellular enzyme activity (EEA) measurement of bacteria. In: Kemp PF, Sherr BF, Sherr EB, Cole JA, eds. Handbook of Methods in Aquatic Microbial Ecology. Boca Raton: Lewis Publishers, 1993, pp. 423-431.

Lamborg CH. Mercury speciation and reactivity in the coastal and estuarine waters of Long Island Sound. Ph.D. Dissertation, University of Connecticut, 2003.

Xia K, Skyllberg UL, Bleam WF, Bloom PR, Nater EA, Helmke PA. X-ray absorption spectroscopic evidence for the complexation of Hg(II) by reduced sulfur in soil humic substances. Environmental Science and Technology 33:257-261.

Journal Articles on this Report : 11 Displayed | Download in RIS Format

Other project views: All 35 publications 13 publications in selected types All 11 journal articles
Type Citation Project Document Sources
Journal Article Balcom PH, Fitzgerald WF, Vandal GM, Lamborg CH, Rolfhus KR, Langer CS, Hammerschmidt CH. Mercury sources and cycling in the Connecticut River and Long Island Sound. Marine Chemistry 2004; 90(1-4): 53-74. R827635 (Final)
not available
Journal Article Fitzgerald WF, Vandal GM, Rolfhus KR, Lamborg CH, Langer CS. Mercury emissions and cycling in the coastal zone. Journal of Environmental Science 2000;12(1):92-101. R827635 (Final)
not available
Journal Article Hammerschmidt CR, Fitzgerald WF. Formation of artifact methylmercury during extraction from a sediment reference material. Analytical Chemistry 2001;73(24):5930-5936. R827635 (2001)
R827635 (Final)
not available
Journal Article Hammerschmidt CR, Fitzgerald WF, Lamborg CH, Balcom PH, Visscher PT. Biogeochemistry of methylmercury in sediments of Long Island Sound. Marine Chemistry 2004; 90(1-4): 31-52. R827635 (Final)
not available
Journal Article Hammerschmidt CR, Fitzgerald WF. Geochemical controls of the production and distribution of methylmercury in near-shore marine sediments. Environmental Science and Technology 2004; 38(5): 1487-1495. R827635 (Final)
not available
Journal Article Lamborg CH, Tseng C-M, Fitzgerald WF, Balcom PH, Hammerschmidt CR. Determination of the mercury complexation characteristics of dissolved organic matter in natural waters with "reducible Hg" titrations. Environmental Science & Technology 2003;37(15):3316-3322. R827635 (2002)
R827635 (Final)
  • Full-text: ACS Full Text
  • Other: ACS PDF
  • Journal Article Lamborg CH, Fitzgerald WF, Skoog A, Visscher PT. The abundance and source of mercury-binding organic ligands in Long Island Sound. Marine Chemistry 2004; 90(1-4): 151-163. R827635 (Final)
    not available
    Journal Article Langer CS, Fitzgerald WF, Visscher PT, Vandal GM. Biogeochemical cycling of methylmercury at Barn Island Salt Marsh, Stonington, CT, USA. Wetlands Ecology and Management 2001;9(4):295-310. R827635 (Final)
    not available
    Journal Article Rolfhus KR, Fitzgerald WF. The evasion and spatial/temporal distribution of mercury species in Long Island Sound, CT-NY. Geochimica Cosmochimica Acta 2001; 65(3): 407-418. R827635 (Final)
    not available
    Journal Article Rolfhus KR, Lamborg CH, Fitzgerald WF, Balcom PH. Evidence for enhanced mercury reactivity in response to estuarine mixing. Journal of Geophysical Research-Oceans 2003;108(C11):3353. R827635 (2001)
    R827635 (Final)
    not available
    Journal Article Tseng CM, Balcom PH, Lamborg CH, Fitzgerald WF. Dissolved elemental mercury investigations in Long Island Sound using on-line Au amalgamation-flow injection analysis. Environmental Science & Technology 2003;37(6):1183-1188 R827635 (2002)
    R827635 (Final)
    not available

    Supplemental Keywords:

    Long Island Sound, LIS, East River, Connecticut River, CTR, New York, NY, physicochemical aspects, aquatic, biogeochemical cycling, coastal, emissions, fate and transport, fish consumption, marine environment, mass balance studies, mercury cycling, microbiological aspects, microbiology, risk assessment, river-seawater mixing zones, mercury, Hg, monomethylmercury, MMHg, watershed, dissolved organic carbon, DOC, organic matter, OM, sediments, coastal marine sediment, toxic metals., RFA, Scientific Discipline, Waste, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Bioavailability, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Fate & Transport, Ecological Effects - Environmental Exposure & Risk, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, Mercury, fate and transport, microbiology, risk assessment, aquatic, Long Island Sound, river-seawater mixing zones, mass balance studies, emissions, fish consumption, mercury cycling, biogeochemical cycling, water quality, Physicochemical aspects, marine environment, solar radiation, coastal, microbiological aspects

    Relevant Websites:

    Synthesis Report of Research from EPA’s Science to Achieve Results (STAR) Grant Program: Mercury Transport and Fate Through a Watershed (PDF) (42 pp, 760 K)

    Progress and Final Reports:

    Original Abstract
  • 2000 Progress Report
  • 2001 Progress Report