Mercury Fluxes Research Articles

Predicting mercury concentrations and fluxes in the water column and sediment of lakes with a limited dataset

The purpose of the present study was to evaluate the mercury (Hg) Environmental Ratios Multimedia Ecosystem Sources (HERMES) model on two Ontario, Canada lakes (Harp and Dickie) and to include modifications to enable the model to estimate the major model input variables that tend to be missing for lakes with limited datasets. No significant differences were found for either sediment solid or bulk water total mercury (THg) when the HERMES model was applied to the two Ontario lakes, regardless of whether all available data were altered during application or only the 10 variables that tend to cause the most variation in model output (i.e., concentration of THg in atmosphere, water inflow THg concentration, water inflow rate, water volume, surface area, mean depth, suspended particulate matter concentration, settling rate of solids in water column, water temperature, and precipitation rate). Since measured sediment and water THg values do not exist for most lakes removed from industrial activities, empirical relationships were incorporated into the HERMES model framework to provide a method to double-check model output for lakes where this information is unavailable.

Release of mercury from intertidal sediment to atmosphere in summer and winter

The release of mercury from intertidal sediment to atmosphere was studied based on the simulated experiment. The experiment samples were collected from the Haibo Estuary (S1) and the Licun Estuary (S2) of the Jiaozhou Bay in China, which are seriously polluted with mercury. The results show that the mercury in sediment releases rapidly to atmosphere under solar radiation. After 8 hours of solar radiation, mercury concentrations decrease from 5.62 μg/g and 2.92 μg/g to 2.34 μg/g and 1.39 μg/g in S1 and S2 sediments respectively in summer, and decrease from 5.62 μg/g and 2.92 μg/g to 4.58 μg/g and 2.13 μg/g respectively in winter. The mercury species in the sediment change markedly under solar radiation. The concentrations of mercury bound to organic matter decrease significantly from 2.73 μg/g to 0.31 μg/g in S1 and from 2.07 μg/g to 0.31 μg/g in S2, and the released mercury mainly comes from mercury bound to organic matter. Mercury flux shows distinguishing characteristic of diurnal change, and it increases rapidly in the morning with the rising of solar radiation intensity, but decreases in the afternoon. The mercury flux increases with sediment temperature and solar radiation intensity. The rapid release of mercury in intertidal sediment plays an important role in the regional mercury cycle.

Seasonal variability in gaseous mercury fluxes measured in a high-elevation meadow

Seasonal patterns of atmospheric mercury (Hg) fluxes measured over vegetated terrestrial systems can provide insight into the underlying process controlling emission and deposition of Hg to vegetated surfaces. Gaseous elemental Hg fluxes were measured for week-long periods in each season (spring, summer, fall, and winter) over an uncontaminated high-elevation wetland meadow in Shenandoah National Park, Virginia using micrometeorological methods. Mean net deposition was observed in the spring (−4.8 ng m −2 h −1), emission in the summer (2.5 ng m −2 h −1), near zero flux in the fall (0.3 ng m −2 h −1), and emission in the winter (4.1 ng m −2 h −1). Nighttime deposition (when stomata are closed) and the poor correlation between Hg fluxes and canopy conductance during periods of active vegetation growth suggest that stomatal processes are not the dominant mechanism for ecosystem-level GEM exchange at this site. The strong springtime deposition relative to summer implies that young vegetation is better at scavenging Hg, with the highest deposition occurring at night possibly via a cuticular pathway. These results suggest that spring is a period of GEM deposition while other seasons exhibit net emission, emphasizing the importance of capturing GEM flux seasonality when determining total Hg budgets.

Wet deposition mercury fluxes in the Canadian sub-Arctic and southern Alberta, measured using an automated precipitation collector adapted to cold regions

This paper reports mercury (Hg) concentrations and fluxes in precipitation that was collected from 2006 to 2008 at three sites in Canada: sub-Arctic boreal forest, sub-Arctic coast, and southern Alberta, using cold-adapted precipitation collectors which operated reliably at temperatures below −30 °C during the study. The southern Alberta site (Crossfield) may be influenced by Calgary urban air, whereas the sub-Arctic coastal (Churchill, Manitoba) and boreal forest (Fort Vermilion, Alberta) sites are in more remote northern areas. Annual mean Hg concentrations in precipitation (5.0–9.2 ng L −1) at the study sites were in the lower half of the range reported for southern Canada and the USA by the Mercury Deposition Network (MDN). But owing to typically low precipitation rates, gross wet Hg fluxes (0.54–2.0 μg m −2 yr −1) were among the lowest reported by MDN, with Crossfield having about twice the flux in 2007 of the other two sites. Flux was significantly correlated with precipitation, and thus was highest in summer (June–August) and lowest during winter, a pattern typical of other temperate continental locations. There was no evidence of higher wet Hg fluxes or concentrations in springtime at Churchill where atmospheric mercury depletion events (AMDEs) occur. Measured gross deposition fluxes at the study locations were ∼2–8 times lower than estimated by GEOS-Chem and GRAHM atmospheric models. The largest discrepancy occurred for Churchill, which raises the question of how well Hg deposition from AMDEs is described by current models. Better agreement between measurements and models was obtained from MDN stations in Alberta and Alaska, where wet Hg fluxes were 2–10 times higher than the study sites either because of power plant emissions (Alberta), or because of high precipitation rates (Alaska).

Mercury transport between sediments and the overlying water of the St. Lawrence River area of concern near Cornwall, Ontario

Contaminated sediments in the St. Lawrence River remain a difficult problem despite decreases in emissions. Here, sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and diffusion from the sediment to the overlying water was 17.5 + or - 10.6 SE ng cm(-2) yr(-1) for THg and 3.8 + or - 1.7 SE ng cm(-2) yr(-1) for MeHg. These fluxes were very small when compared to the particle-bound mercury flux accumulating in the sediment (183 + or - 30 SE ng cm(-2) yr(-1)). Studies have reported that fish from the westernmost site have higher Hg concentrations than fish collected from the other two sites of the Cornwall Area of Concern, which could not be explained by differences in the Hg flux or THg concentrations in sediments, but the highest concentrations of sediment MeHg, and the greatest proportions of MeHg to THg in both sediment and pore water were observed where fish had highest MeHg concentrations.

Protocol to Reconstruct Historical Contaminant Loading to Large Lakes: The Lake Michigan Sediment Record of Mercury

Samples of opportunity from Pb-210 dated sediment cores collected from Lake Michigan between 1994 and 1996 were analyzed for mercury. The storage of anthropogenic and total (post-1850) mercury in the lake is calculated to be 186 and 228 t, respectively. By setting the sum of mercury stored in a representative core equal to the mercury storage within the entire lake, the time variation of annual mercury loading to the lake is calculated. The modern (1980-2002) mercury flux to the lake represented by the surface of the core at the time of collection in 1994 was 21.4 microg/m(2)/y. The preindustrial flux (< or =1850) was 3.09 microg/m(2)/y, and the peak flux in 1946 was 53.3 microg/m(2)/y. These yield modern and peak enrichment factors of 6.92 and 17.2, respectively. Modern fluxes exceed published atmospheric deposition estimates and, therefore, include terrestrial point sources, atmospheric deposition to watersheds, and atmospheric deposition to the lake. The modern net mercury load to the lake's sediments was 1157 kg/y in 1994. The atmosphere is estimated to contribute 91% of this load directly to the lake.

Mercury Flux to Sediments of Lake Tahoe, California–Nevada

We report estimates of mercury (Hg) flux to the sediments of Lake Tahoe, California–Nevada: 2 and 15–20 µg/m2/year in preindustrial and modern sediments, respectively. These values result in a modern to preindustrial flux ratio of 7.5–10, which is similar to flux ratios recently reported for other alpine lakes in California, and greater than the value of 3 typically seen worldwide. We offer plausible hypotheses to explain the high flux ratios, including (1) proportionally less photoreduction and evasion of Hg with the onset of cultural eutrophication and (2) a combination of enhanced regional oxidation of gaseous elemental Hg and transport of the resulting reactive gaseous Hg to the surface with nightly downslope flows of air. If either of these mechanisms is correct, it could lead to local/regional solutions to lessen the impact of globally increasing anthropogenic emissions of Hg on Lake Tahoe and other alpine ecosystems.

The influence of dynamic chamber design and operating parameters on calculated surface-to-air mercury fluxes

Dynamic Flux Chambers (DFCs) are commonly applied for the measurement of non-point source mercury (Hg) emissions from a wide range of surfaces. A standard operating protocol and design for DFCs does not exist, and as a result there is a large diversity in methods described in the literature. Because natural and anthropogenic non-point sources are thought to contribute significantly to the atmosphere Hg pool, development of accurate fluxes during field campaigns is essential. The objective of this research was to determine how differences in chamber material, sample port placement, vertical cross sectional area/volume, and flushing flow rate influence the Hg flux from geologic materials. Hg fluxes measured with a Teflon chamber were higher than those obtained using a polycarbonate chamber, with differences related to light transmission and substrate type. Differences in sample port placement (side versus top) did not have an influence on Hg fluxes. When the same flushing flow rate was applied to two chambers of different volumes, higher fluxes were calculated for the chamber with the smaller volume. Conversely, when two chambers with different volumes were maintained at similar turnover times, the larger volume chamber yielded higher Hg fluxes. Overall, the flushing flow rate and associated chamber turnover time had the largest influence on Hg flux relative to the other parameters tested. Results from computational fluid dynamic (CFD) modeling inside a DFC confirm that the smaller diffusion resistance at higher flushing flows contributes to the higher measured flux. These results clearly illustrate that differences in chamber design and operation can significantly influence the resulting calculated Hg flux, and thus impact the comparability of results obtained using DFC designs and/or operating parameters. A protocol for determining a flushing flow rate that results in fluxes less affected by chamber operating conditions and design is proposed. Application of this protocol would provide a framework for comparison of data from different studies.

Dynamic exchange of gaseous elemental mercury during polar night and day

From February 29 until June 15 2008 gaseous elemental mercury (GEM) fluxes above a snow covered surface was measured in Ny-Ålesund, Svalbard using a GEM flux gradient method. A clear seasonal pattern in the meteorological variables associated with the GEM flux was observed. For the first time in Ny-Ålesund a net deposition of GEM was recorded during polar night, despite the lack of Atmospheric Mercury Depletion Events (AMDE). 7500 ng m −2 GEM was emitted from the surface snow to the air during the entire study. The depositions of GEM and reactive gaseous mercury (RGM) were calculated to be 1500 and 1000 ng m −2, respectively, during the same time period. The GEM fluxes reported in this study were found to be comparable to GEM fluxes measured at other Arctic locations (i.e. Alert and Barrow), suggesting that GEM acts in a similar way throughout the Arctic. An assessment of the GEM flux gradient method used discovered a non-linear GEM concentration profile. The nonlinearity was explained by a non-stationary turbulence regime. The GEM flux calculated was not found to be representative for the entire surface boundary layer.

Growing season total gaseous mercury (TGM) flux measurements over an Acer rubrum L. stand

Relaxed eddy accumulation (REA) measurements of the total gaseous mercury (TGM) flux measurements were taken over a deciduous forest predominantly composed of Red Maple ( Acer rubrum L.) during the growing season of 2004 and the second half of the growing season of 2005. The magnitudes of the flux estimates were in the range of published results from other micrometeorological mercury fluxes taken above a tall canopy and larger than estimates from flux chambers. The magnitude and direction of the flux were not static during the growing season. There was a significant trend ( p < 0.001), from net deposition of TGM in early summer to net evasion in the late summer and early fall before complete senescence. A growing season atmosphere-canopy total mercury (TGM) compensation point during unstable daytime conditions was estimated at background ambient concentrations (1.41 ng m −3). The trend in the seasonal net TGM flux indicates that long term dry deposition monitoring is needed to accurately estimate mercury loading over a forest ecosystem.

Mercury Sources to Lake Ozette and Lake Dickey: Highly Contaminated Remote Coastal Lakes, Washington State, USA

Mercury concentrations in largemouth bass and mercury accumulation rates in age-dated sediment cores were examined at Lake Ozette and Lake Dickey in Washington State. Goals of the study were to compare concentrations in fish tissues at the two lakes with a larger statewide dataset and examine mercury pathways to the lakes. After accounting for fish length, tissue concentrations at the lakes were significantly higher than other Washington State lakes. Wet deposition and historical atmospheric monitoring from the area show no indication of enhanced local or regional deposition. Sediment core records from the lakes indicate rising sedimentation rates coinciding with logging in the lakes’ drainages has greatly increased the net flux of mercury to the waterbodies.

Dynamics of mercury fluxes and their controlling factors in large Hg-polluted floodplain areas

Environmental pollution by mercury (Hg) is a considerable environmental problem world-wide. Due to the occurrence of Hg volatilization from their soils, floodplains can function as an important source of volatile Hg. Soil temperature and soil water content related to flood dynamics are considered as important factors affecting seasonal dynamics of total gaseous mercury (TGM) fluxes. We quantified seasonal variations of TGM fluxes and conducted a laboratory microcosm experiment to assess the effect of temperature and moisture on TGM fluxes in heavily polluted floodplain soils. Observed TGM emissions ranged from 10 to 850 ng m −2 h −1 and extremely exceeded the emissions of non-polluted sites. TGM emissions increased exponentially with raised air and soil temperatures in both field ( R 2: 0.49–0.70) and laboratory ( R 2: 0.99) experiments. Wet soil material showed higher TGM fluxes, whereas the role of soil water content was affected by sampling time during the microcosm experiments.

Mercury fluxes through the sediment water interface and bioavailability of mercury in southern Baltic Sea sediments

Mercury fluxes through the sediment water interface and bioavailability of mercury in southern Baltic Sea sediments

Mercury degassing from forested and open field soils in Rondônia, Western Amazon, Brazil

A Teflon ® dynamic flux chamber was used to characterize Gaseous Elemental Mercury (GEM) flux from forested and open field soils in a highly changing environment in Rondônia State, western Amazon. We simultaneously analyzed meteorological parameters at the soil level relating GEM fluxes to soil temperature, air humidity, soil moisture, solar radiation, and speed and wind direction. We also examined variations of atmospheric GEM concentration. GEM fluxes during the day and night in the open field site were significantly different (17 ± 14 ng m −2 h −1 and 0.9 ± 1.9 ng m −2 h −1, for day and night, respectively), but were similar within the forest site (4.8 ± 1.4 ng m −2 h −1 and 4.4 ± 1.8 ng m −2 h −1 for day and night periods, respectively). A comparison between 24-h periods averages in the two sites showed much larger emission from the open field site. GEM fluxes at the open field site were positively correlated with soil moisture, solar irradiation and soil temperature and inversely correlated with air humidity. At the forest site GEM fluxes showed no correlation with meteorological variables. At the open field site GEM concentrations significantly correlated with GEM flux, at least during the day. At night in the open field site and during the day and night at the forest site no correlation was found between GEM fluxes and GEM concentrations in the ambient air. Higher emissions from the open field site support earlier studies showing larger Hg remobilization following forest conversion to pasture.

Towards a sediment and organic carbon budget for Hudson Bay

A preliminary sediment and organic carbon budget is constructed for the Hudson Bay marine system based on published literature and new data collected from nine rivers and 13 sediment boxcores. The budget considers the main inputs of terrestrial and marine components of sediment and organic carbon and the main sinks (sediment burial) and losses (oxidation, export to Hudson Strait). Sedimentation rates (0.032–0.23 g cm − 2 yr − 1 ) were estimated from 210Pb profiles and a sediment advection–diffusion model in our cores and in two cores collected previously by Lockhart et al. [Lockhart, W.L. et al., 1998. Fluxes of mercury to lake sediments in central and northern Canada inferred from dated sediment cores. Biogeochemistry 40, 163–173]. Sedimentation rates implied by the 210Pb profiles were verified against profiles of 137Cs and, for some of the cores, contaminant Pb. The sediment sink in Hudson Bay was estimated at 138 (± 64) × 10 6 t a − 1 by applying the average sedimentation rate to the area of active sedimentation in the Bay (~ 15% of the seafloor), calculated according to a regional sedimentation map developed from seismic data [Josenhans, H.W. et al., 1988. Preliminary seismostratigraphic and geomorphic interpretations of the Quaternary sediments of Hudson Bay, Natural Resources Canada]. The known sediment sources to Hudson Bay include river input (11.6 (± 6) × 10 6 t a − 1 ), subaerial coastal erosion (8 (± 4) × 10 6 t a − 1 ), marine primary production (24.2 (± 17) × 10 6 t a − 1 ), and atmospheric deposition (0.5 × 10 6 t a − 1 ). Based on the available data, the modern sediment input (44.3 (± 18) × 10 6 t a − 1 ) represents only about one-third of the apparent sediment sink in Hudson Bay. Resuspension and lateral transport of shallow-water deposits (primarily glacigenic) and winnowing from topographic highs, likely consequences of the exceptional, continuous relative sea-level (RSL) fall in Hudson Bay, provides a plausible source for the ~ 116 × 10 6 t a − 1 imbalance. Using organic carbon and δ 13C values in the cores, we estimate the burial of particulate organic carbon (POC) in sediments at 1.3 (± 0.6) × 10 6 t C a − 1 , of which ~ 80% is marine. The importance of reworked glaciomarine carbon to the burial flux is difficult to estimate because modern (autochthonous) primary production provides a large source of POC to the system (16.1 (± 7) × 10 6 t C a − 1 ) and its degradation is not well-constrained. The 0.58 × 10 6 t C a − 1 terrestrial carbon, estimated to be transported as part of the redistributed sediment load, accounts for almost one-half the total terrigenous POC inputs to the Bay. If sediment and OC supply and burial in the Hudson Bay system are presently responding to the history of isostatic rebound, as proposed here, the task of predicting and measuring the additional consequences of river diversions and climate change (e.g., sea ice, permafrost, runoff) is rendered considerably more difficult.

Submarine Groundwater Discharge of Total Mercury and Monomethylmercury to Central California Coastal Waters

Fluxes of total mercury (Hg(T)) and monomethylmercury (MMHg) associated with submarine groundwater discharge (SGD) at two sites onthe central California coast were estimated by combining measurements of Hg(T) and MMHg in groundwater with the use of short-lived, naturally occurring radium isotopes as tracers of groundwater inputs. Concentrations of Hg(T) were relatively low, ranging from 1.2 to 28.3 pM in filtered groundwater, 0.8 to 11.6 pM in filtered surface waters, and 2.5 to 12.9 pM in unfiltered surface waters. Concentrations of MMHg ranged from < 0.04 to 3.1 pM in filtered groundwater, < 0.04 to 0.53 pM in filtered surface waters, and 0.07 to 1.2 pM in unfiltered surface waters. Multiple linear regression analysis identified significant (p < 0.05) positive correlations between dissolved groundwater concentrations of Hg(T) and those of NH4+ and SiO2, and between dissolved groundwater concentrations of MMHg and those of Hg(T) and NH4+. However, such relationships did not account for the majority of the variability in concentration data for either mercury species in groundwater. Fluxes of Hg(T) via SGD were estimated to be 250 +/- 160 nmol day m(-1) of shoreline at Stinson Beach and 3.0 +/- 2.0 nmol m(-2) day(-1) at Elkhorn Slough. These Hg(T) fluxes are substantially greater than net atmospheric inputs of Hg(T) reported for waters in nearby San Francisco Bay. Calculated fluxes of MMHg to coastal waters via SGD were 10 +/- 12 nmol day(-1) m(-1) of shoreline at Stinson Beach and 0.24 +/- 0.21 nmol m(-2) day at Elkhorn Slough. These MMHg fluxes are similar to benthic fluxes of MMHg out of surface sediments commonly reported for estuarine and coastal environments. Consequently, this work demonstrates that SGD is an important source of both Hg(T) and MMHg to coastal waters along the central California coast.

Mercury volatilization from salt marsh sediments

In situ volatilization fluxes of gaseous elemental mercury, Hg(0), were estimated for tidally exposed salt marsh sediments in the summer at the urban/industrial Secaucus High School Marsh, New Jersey Meadowlands (Secaucus, New Jersey) and in the early autumn at a regional background site in the Great Bay estuary (Tuckerton, New Jersey). Estimated daytime sediment‐air mercury volatilization fluxes at the Secaucus High School Marsh ranged from −375 to +677 ng m−2 h−1 and were positive (land to air flux) in 16 out of 20 measurement events. At the Great Bay estuary, mercury fluxes measured continuously over a 48‐h period ranged from −34 to +81 ng m−2 h−1 and were positive during the day and negative at night. At both sites, mercury volatilization fluxes peaked at midday, and cumulative mercury fluxes exhibited strong positive correlations with cumulative solar radiation (r2 = 0.97, p &lt; 0.01) consistent with a light‐driven mercury volatilization efficiency of about 15 ng Hg mol PAR−1 or about 0.06 ng Hg kJ−1. No significant correlations were found between mercury fluxes and wind speed, air temperature, or tide height at either site. Thus despite a tenfold difference in sediment mercury concentration, photochemistry appears to be the dominant factor controlling mercury volatilization from these salt marsh sediments. The average mercury volatilization flux estimated for the Great Bay salt marsh in this study (17 ng m−2 h−1) compares well with other micrometeorological mercury fluxes for nonpoint source contaminated salt marsh and forest soils (8–18 ng m−2 h−1) and is more than 10 times higher than the average mercury emission flux from land (∼1 ng m−2 h−1). Annual mercury emissions from salt marsh wetlands may be comparable to individual industrial emissions sources in coastal states of the eastern United States.

Anthropogenic impacts recorded in recent sediments from Otisco Lake, New York, USA

Geochemical analysis of 210Pb-dated sediment cores from Otisco Lake (New York) combined with analysis of recent land cover change in the watershed revealed the history of land use change, lake management, and industrial pollution since European settlement in the northeastern US. Clearance of forestland for agriculture characterized the early settlement era that was marked in the Otisco Lake sediments by a decline in organic carbon (OC) and OC:N ratios, which indicate a change in the sources of organic matter to the lake. Agricultural land use reached its greatest areal extent in the Otisco watershed around 1900, followed by field abandonment and reforestation over the last century. In the 1920s sediment accumulation rates began to increase coincident with residential development along the lake shore. Nitrogen and organic carbon, which are transported from the watershed, show increased fluxes to the lake in response to this change. Deposition of inorganic carbon increased markedly over a short period from the 1940s to the 1980s, which is consistent with enhanced mobilization of watershed calcium by increased acidic deposition, followed by alkalinization of the lake waters and calcite precipitation. An increase in copper content in the sediments reflects application, since 1942, of the algicide copper sulfate to the lake waters to control algal blooms. This CuSO4 marker confirmed the accuracy of the 210Pb chronology. Atmospheric mercury (Hg) fluxes to the lake were affected by increased sediment transport from the watershed. The maximum Hg peak in the sediment record, however, was dated to the early 1970s and coincides with maximum Hg emissions to the atmosphere in the Great Lakes region.

Evaluation of Potential for Mercury Volatilization from Natural and FGD Gypsum Products Using Flux-Chamber Tests

Synthetic gypsum produced by flue-gas desulfurization (FGD) in coal-fired power plants (FGD gypsum) is put to productive use in manufacturing wallboard. FGD gypsum wallboard is widely used, accounting for nearly 30% of wallboard sold in the United States. Mercury is captured in flue gas and thus is one of the trace metals present in FGD gypsum; raising questions about the potential for mercury exposure from wallboard. Mercury is also one of the trace metals present in "natural" mined gypsum used to make wall board. Data available in the literature were not adequate to assess whether mercury in wallboard from either FGD or natural gypsum could volatilize into indoor air. In this study, mercury volatilization was evaluated using small-scale (5 L) glass and Teflon flux chambers, with samples collected using both iodated carbon and gold-coated sand traps. Mercury flux measurements made using iodated carbon traps (n=6) were below the detection limit of 11.5 ng/m2-day for all natural and synthetic gypsum wallboard samples. Mercury flux measurements made using gold-coated sand traps (n=6) were 0.92 +/- 0.11 ng/m2-day for natural gypsum wallboard and 5.9 +/- 2.4 ng/m2-day for synthetic gypsum wallboard. Room air mercury concentrations between 0.028 and 0.28 ng/m3 and between 0.13 and 2.2 ng/m3 were estimated based on the flux-rate data for natural and synthetic gypsum wallboard samples, respectively, and were calculated assuming a 3 m x 4 m x 5 m room, and 10th and 90th percentile air exchange rates of 0.18/hour and 1.26/hour. The resulting concentration estimates are well below the U.S. Environmental Protection Agency (EPA) reference concentration for indoor air elemental mercury of 300 ng/m3 and the Agency for Toxic Substances and Disease Registry minimal risk level (MRL) of 200 ng/m3. Further, these estimates are below background mercury concentrations in indoor air and within or below the range of typical background mercury concentrations in outdoor air.

Mercury dynamics and transport in two Adirondack Lakes

We investigated the chemistry and fluxes of mercury (Hg) species for two Adirondack lakes with contrasting landscape, physical, and chemical attributes. Samples were collected monthly at the lake inlets and outlets over 2 yr, and evasion of elemental Hg was measured at one lake (Arbutus). Concentrations of total Hg (THg) and methyl Hg (MeHg) in watershed runoff were highly variable throughout the year, increasing markedly during summer months. The proportion of THg as MeHg ranged from &lt;5% at Arbutus Lake up to 10% at Sunday Lake. Concentrations of Hg species increased with increases in dissolved organic carbon concentrations and percentage wetland coverage. The estimated rate of volatilization loss of elemental mercury (Hgo) from Arbutus Lake surface (7.8 µg m−2 yr−1) was comparable to the rate of direct atmospheric Hg deposition to the lake surface (8.6 µg m−2 yr−1). Dry deposition to Arbutus Lake amounted to ca. 26% of total wet THg deposition. Hydraulic residence time (HRT) played a critical role in controlling Hg dynamics in the lakes. Negligible removal of THg inputs was observed at Sunday Lake, which has a short HRT (0.02 yr), compared with approximately 60% removal at Arbutus Lake, which has a longer HRT (0.6 yr). This pattern of increasing net Hg retention in lakes with increasing HRT was consistent with other mass balance studies in the literature. Both Arbutus and Sunday lakes were net sinks of MeHg.