Estuaries are dynamic ecosystems which vary widely in loading of the contaminant methylmercury (MeHg), and in environmental factors which control MeHg exposure to the estuarine foodweb. Inputs of ...organic carbon and rates of primary production are important influences on MeHg loading and bioaccumulation, and are predicted to increase with changes in climate and land use pressures. To further understand these influences on MeHg levels in estuarine biota, we used a field study approach in sites across different temperature regions, and with varying organic carbon levels. In paired comparisons of sites with high vs. low organic carbon, fish had lower MeHg bioaccumulation factors (normalized to water concentrations) in high carbon sites, particularly subsites with large coastal wetlands and large variability in dissolved organic carbon levels in the water column. Across sites, MeHg level in the water column was strongly tied to dissolved organic carbon, and was the major driver of MeHg concentrations in fish and invertebrates. Higher primary productivity (chlorophyll-a) was associated with increased MeHg partitioning to suspended particulates, but not to the biota. These findings suggest that increased inputs of MeHg and loss of wetlands associated with climate change and anthropogenic land use pressure will increase MeHg concentrations in estuarine food webs.
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•Dissolved organic carbon drives dissolved methylmercury levels in the intertidal zone.•Fish levels of methylmercury are positively associated with water column concentrations.•Methylmercury bioaccumulation is lower in environments with high organic carbon content in sediment.•Increased water column methylmercury from watersheds will increase levels in fish.
Wetland areas temper the bioaccumulation of methylmercury in estuaries, yet increased watershed inputs of methylmercury associated with climate change and land disturbances are predicted to increase mercury levels in fish.
The fate and mobility of mercury, and its bioaccumulation primarily as methylmercury (MeHg), in marine ecosystems are influenced by climate related environmental factors, including increased ...temperature and carbon loading. To investigate the interactions between sediment organic carbon and temperature MeHg bioaccumulation, mesocosm experiments were conducted examining relationships between sediment, water column and biota (sediment-dwelling amphipod and juvenile oyster) MeHg concentration. Experimental treatments consisted of a two by two design of high and low temperature (15 & 25 °C) and high and low sediment organic carbon (4–5% and 13% LOI, pre-experiment). Sediment organic carbon had significant individual effects on MeHg concentration in water and biota, with higher carbon associated with lower MeHg. Temperature individual effects were significant for sediment, water, and only amphipod MeHg concentration, with higher temperature treatments indicating higher MeHg concentration. There were significant temperature × carbon interactions observed for sediment, dissolved, and oyster MeHg concentration. Sediment carbon reduction had greater influence than temperature on increasing MeHg concentrations in both the water column and biota. MeHg concentrations in the bulk sediment were not correlated with MeHg in the water column or in the biota, indicating that even when sediments are the only source of MeHg, bulk sediment measurements do not provide a good proxy for bioaccumulation and that the concentration in bulk sediments is not the primary determinant of MeHg entry into the food web.
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•Climate change is predicted to influence carbon loading and temperature in estuaries.•Estuaries are important areas for methylmercury production and bioaccumulation.•Mesocosms examined effect of temperature and sediment organic carbon on MeHg.•Water column MeHg, not sediment concentration, related to biota MeHg•Sediment carbon influenced MeHg bioaccumulation more than temperature
Using two different natural archiving media from remote locations, we have reconstructed the atmospheric deposition of mercury (Hg) over the last 800–1000 years in both hemispheres. This effort was ...designed (1) to quantify the historical variation and distributional patterns of atmospheric Hg fluxes in the midlatitudes of North America at Nova Scotia (N.S.) and at a comparable midlatitude region in the Southern Hemisphere at New Zealand (N.S.), (2) to identify and quantify the influence of anthropogenic and natural Hg contributions to atmospheric Hg fluxes, (3) to further investigate the suitability and comparability of our two selected media (lake sediments and ombrotrophic peat) for Hg depositional reconstructions, and (4) to assess the relative importance of wet and dry deposition to the study areas. Significant findings from the study include the following: (1) The lake sediments examined appear to faithfully record the contemporary flux of Hg from the atmosphere (e.g., 1997: N.S. Lakes: approximately 8 ± 3 μg m−2 yr−1; N.S. Rain: 8 μg m−2 yr−1). The upper 10 cm (approximately 10 yr) of ombrotrophic peat cores from Nova Scotia were dated using a biological chronometer (Polytrichum) and were also consistent with the flux data provided by current direct sampling of precipitation. These observations place limits on the contribution of dry deposition (40 ± 50% of wet flux). Unfortunately, the peat samples could not be dated below 10 cm. This was due to the apparent diagenetic mobility of the geochronological tracer (210Pb). (2) There is no evidence of a significant enhancement in the atmospheric Hg flux as a result of preindustrial (<1900 c.e. (Common Era)) activities such as the extensive Au and Ag mining in the Americas. (3) A factor of 3 and 5x increase in the deposition of Hg to the lake sediment archives was observed since the advent of the industrial revolution in New Zealand and Nova Scotia respectively, suggesting a worldwide increase in the atmospheric deposition of Hg. Furthermore, this increase is synchronous with increases in the release of CO2 from combustion of fossil fuels on a global scale. The magnitude of increase since industrialization appears larger in Nova Scotia than in New Zealand. This may be due to enhanced deposition of Hg as a result of either regional emission of Hg or enhanced regional oxidation of Hg°.
A novel semiautomatic dissolved elemental mercury analyzer (DEMA) was developed for investigating dissolved elemental Hg (DEM) in natural waters. This on-line setup couples the main analytical steps ...from sample introduction, gas-liquid separation, and Au amalgamation/separation to final detection/data acquisition using flow injection techniques. This approach provides ease of operation and high analytical performance and is suitable for shipboard use. The analyzer can be fully automated and also be modified to examine other Hg species (e.g., reactive and total Hg and monomethyl-Hg). Here, we present the results of laboratory performance tests and make a comparison with a traditional manual method. DEM measured by both manual and the DEMA show good agreement. Representative field DEM data from spring and summer 1999 in Long Island Sound, U.S.A. (LIS) are presented. Spatial and temporal DEM variations were evident. Rapid and accurate determinations of DEM are necessary to observe its distribution dynamics, evaluate emissions, and assess its role in the aquatic biogeochemical cycling of Hg.
An examination of the distribution of mercury and methylmercury across estuarine ecosystems in the northeast USA was completed under a number of projects. Sites ranged from Maine to the Chesapeake ...Bay and included both pristine and contaminated sites. In addition to measurements of bulk sediment and porewater, methylation and demethylation rates were also measured. Results showed that the relationships between sediment-porewater partitioning and methylation potential with sediment organic content are complex and that sediment organic content alone is not always a good predictor of the potential for a system to produce methylmercury. Modeling and correlations between variables suggest that the sulfur content of the system needs to be considered and for high organic content sediments, both sulfur and organic content.
Estuaries are a conduit of mercury (Hg) from watersheds to the coastal ocean, and salt marshes play an important role in coastal Hg cycling. Hg cycling in upland terrestrial ecosystems has been well ...studied, but processes in densely vegetated salt marsh ecosystems are poorly characterized. We investigated Hg dynamics in vegetation and soils in the Plum Island Sound estuary in Massachusetts, USA, and specifically assessed the role of marsh vegetation for Hg deposition and turnover. Monthly quantitative harvesting of aboveground biomass showed strong linear seasonal increases in Hg associated with plants, with a 4-fold increase in Hg concentration and an 8-fold increase in standing Hg mass from June (3.9 ± 0.2 µg kg.sup.-1 and 0.7 ± 0.4 µg m.sup.-2, respectively) to November (16.2 ± 2.0 µg kg.sup.-1 and 5.7 ± 2.1 µg m.sup.-2, respectively). Hg did not increase further in aboveground biomass after plant senescence, indicating physiological controls of vegetation Hg uptake in salt marsh plants. Hg concentrations in live roots and live rhizomes were 11 and 2 times higher than concentrations in live aboveground biomass, respectively. Furthermore, live belowground biomass Hg pools (Hg in roots and rhizomes, 108.1 ± 83.4 µg m.sup.-2) were more than 10 times larger than peak standing aboveground Hg pools (9.0 ± 3.3 µg m.sup.-2).
Sediments of New York/New Jersey (NY/NJ) Harbor are contaminated with Hg from modern discharges and the pollution legacy of the Industrial Revolution, and there is concern related to the ...bioavailability, transformation, and mobilization of monomethylmercury (MMHg) from these deposits. We investigated the production and distribution of MMHg in sediments of NY/NJ Harbor across wide and contrasting ranges of inorganic Hg (Hg(II)), sulfide, and organic matter in August 2002 and February and May 2003. Organic material largely controls the geographical distribution of Hg(II) and MMHg. Partitioning coefficients (
K
D) for MMHg and Hg(II) are related positively to the organic content of deposits with less than 10 µM dissolved sulfide.
K
D values for MMHg and Hg(II) in sediments of NY/NJ Harbor are about 10× greater than those in deposits of Long Island Sound (LIS) and the continental shelf, suggesting differences in the affinity of Hg species for allochthonous (Harbor) and planktonic organic matter (LIS, shelf). Dissolved sulfide enhances the solubility of MMHg and Hg(II) and inhibits MMHg production. Potential gross rates of Hg methylation, assayed by experimental addition of
200Hg to intact cores, are related positively to the level of Hg(II), presumably as HgS
0, in 0.2-µm filtered pore fluids of sediments having less than 10 µM sulfide, and are reduced greatly in deposits with greater levels of dissolved sulfide. MMHg:Hg(II) concentration ratios, potential rates of
200Hg methylation, and diffusional sediment–water MMHg fluxes vary seasonally. The estimated whole-basin sediment–water flux of MMHg (i.e., net production at steady state) is about 1% relative to Hg(II) burial, a percentage much less than that in LIS and at three sites on the continental shelf (8%). Thus, it appears that allochthonous organic material (terrestrial and/or sewage) and dissolved sulfide reduce bioavailability of Hg and attenuate gross and net rates of MMHg production in the Harbor. Accordingly, changes in allochthonous organic inputs and microbial respiration of this material (i.e., sulfide production) could affect the production and mobilization of MMHg by altering the bioavailability of modern inputs and some portion of the large reservoir of “legacy Hg” buried in the sediment.
Mercury (Hg) contamination, which includes its toxic byproduct monomethylmercury (MMHg), is ubiquitous and often severe in estuarine and near-shore systems of industrialized countries. However, Hg ...cycling is not well studied in anthropogenically impacted systems such as New York/New Jersey Harbor Estuary (NY/NJ Harbor), and more generally, knowledge concerning the biogeochemical cycling of toxic metals is limited for estuaries and coastal regions. Here, we are reporting results from a 1-year seasonally focused field investigation on the behavior and fate of Hg and MMHg in NY/NJ Harbor. Filtered (<
0.2-μm) and unfiltered reactive (labile) and total Hg, as well as filtered and particulate MMHg, were measured in surface and bottom waters (5–9 stations) in August 2002, February 2003, and May 2003. Scavenging by particulate matter is a major control on the partitioning of total Hg in the vertically well-mixed waters of the Harbor; 89–99% of total Hg (log
K
D
=
5.3–6.5) and 56–89% of MMHg (log
K
D
=
4.5–5.6) were in the particle phase. Mean levels of unfiltered total Hg (30–550 pM) and total MMHg (0.2–1.8 pM; filtered
+
particulate) were greater and more variable seasonally at the sites in Newark Bay and the Upper Harbor, as compared to the Lower Harbor and Jamaica Bay, consistent with fluvial inputs (Hudson River yields 90% of freshwater input) as a principal source of total Hg to the Harbor. Water-column particle-specific concentrations (mean
±
SE) of total Hg (4.8
±
0.5 nmol g
−
1
) and MMHg (20
±
2 pmol g
−
1
; 0.4% of total Hg) are comparable to levels in surface sediment, suggesting significant sediment suspension and deposition. The major sources of total Hg (∼
2440 mol y
−
1
) to NY/NJ Harbor are rivers (∼
1640 mol y
−
1
; 67% of total inputs), the East River (∼
630 mol y
−
1
), water pollution control facilities (WPCFs; ∼
140 mol y
−
1
), and direct atmospheric deposition (∼
30 mol y
−
1
). Although direct atmospheric deposition to NY/NJ Harbor is small, leaching (ca. 25–30% watershed delivery) of atmospheric Hg deposition to the NY/NJ Harbor watershed is a significant source (22–69%), but additional unknown sources also appear to contribute to fluvial Hg loadings. The MMHg flux to the Harbor from internal and external sources is estimated as 33 mol y
−
1
with 18 mol y
−
1
from rivers (55%), and 8 mol y
−
1
(25%) from
in situ sedimentary production and mobilization. While fluvial MMHg inputs are dominant, the relative source strength of watershed versus sedimentary riverine production is not yet clear.
We reconstruct from lake-sediment archives atmospheric Hg deposition to Arctic Alaska over the last several centuries and constrain a contemporary lake/watershed mass-balance with real-time ...measurement of Hg fluxes in rainfall, runoff, and evasion. Results indicate that (a) anthropogenic Hg impact in the Arctic is of similar magnitude to that at temperate latitudes; (b) whole-lake Hg sedimentation determined from 55 210Pb-dated cores from the five small lakes demonstrates a 3-fold increase in atmospheric Hg deposition since the advent of the Industrial Revolution; (c) because of high soil Hg concentrations and relatively low atmospheric deposition fluxes, erosional inputs to these lakes are more significant than in similar temperate systems; (d) volatilization accounts for about 20% of the Hg losses (evasion and sedimentation); and (e) another source term is needed to balance the evasional and sedimentation sinks. This additional flux (1.21+/-0.74 microg m(-2) yr(-1)) is comparable to direct atmospheric Hg deposition and may be due to some combination of springtime Arctic depletion and more generalized deposition of reactive gaseous Hg species.
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