Dissolved gaseous mercury concentrations and mercury volatilization in a frozen freshwater fluvial lake.
ABSTRACT In situ mesocosm experiments were performed to examine dissolved gaseous mercury (DGM), mercury volatilization, and sediment interactions in a frozen freshwater fluvial lake (Lake St. Louis, Beauharnois, QC). Two large in situ mesocosm cylinders, one open-bottomed and one close-bottomed (no sediment diffusion), were used to isolate the water column and minimize advection. Mercury volatilization over the closed-bottom mesocosm did not display a diurnal pattern and was low (mean = -0.02 ng m(-2) h(-1), SD = 0.28, n=71). Mercury volatilization over the open-bottom mesocosm was also low (mean = 0.24 ng m(-2) h(-1), SD = 0.08, n=96) however a diurnal pattern was observed. Low and constant concentrations of DGM were observed in surface water in both the open-bottomed and close-bottomed mesocosms (combined mean = 27.6 pg L(-1), SD = 7.2, n=26). Mercury volatilization was significantly correlated with solar radiation in both the close-bottomed (Pearson correlation = 0.33, significance = 0.005) and open-bottomed (Pearson correlation = 0.52, significance = 0.001) mesocosms. However, DGM and mercury volatilization were not significantly correlated (at the 95% level) in either of the mesocosms (significance = 0.09 in the closed mesocosm and significance = 0.9 in the open mesocosm). DGM concentrations decreased with depth (from 62 to 30 pg L(-1)) in the close-bottomed mesocosm but increased with depth (from 30 to 70 pg L(-1)) in the open-bottomed mesocosm suggesting a sediment source. DGM concentrations were found to be high in samples of ice melt (mean 73.6 pg L(-1), SD = 18.9, n=6) and snowmelt (mean 368.2 pg L(-1), SD = 115.8, n=4). These results suggest that sediment diffusion of mercury and melting snow and ice are important to DGM dynamics in frozen Lake St. Louis. These processes may also explain the lack of significant correlations observed in the DGM and mercury volatilization data.
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ABSTRACT: The biogeochemical cycling of elemental Hg has important effects on the global and regional mobility and reactivity of the metal, and has not been well characterized in coastal marine systems. Five sets of measurements examining the spatial/temporal distribution of dissolved gaseous Hg (DGM), total Hg (HgT), and reactive Hg (HgR) in the waters of Long Island Sound (LIS) indicate that Hgo evasion is geochemically significant, and an estimated 35% of the total annual Hg inputs to the system (average flux: 342 pmol m−2 d−1 to the atmosphere, based on a gas exchange model). DGM concentrations ranged from 0.04 to 0.55 pM (81–1167% saturation relative to atmospheric equilibrium), and show maxima in the surface mixed layer. Distinct seasonal patterns were observed, including higher DGM concentrations and percentage saturations during the warmer months. Seasonally averaged unfiltered HgT concentrations decreased by an order of magnitude from western LIS to the east, whereas the percent of unfiltered total as HgR increased from 14% in the west to 71% in the east. Relationships between filtered HgR, DOC, and DGM suggest that the DGM distribution within LIS is related to the supply and distribution of labile Hg reactant, which is in turn controlled by the distribution and nature of DOM.Geochimica et Cosmochimica Acta. 01/2001;
Article: Mercury in Lake MichiganEnvironmental Science & Technology - ENVIRON SCI TECHNOL. 02/1997; 31(3).
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ABSTRACT: To investigate relationships between mercury speciation and site-specific factors in temperate freshwaters, we measured the concentration of seven Hg species along with 18 environmental variables in the surface waters of 23 northern Wisconsin lakes during spring and fall. The lakes spanned relatively wide gradients in Hg(0.15-4.8 ng liter â»Â¹) and methylmercury (MeHg: 0.04-2.2 ng literâ»Â¹). Over the range of measured variables, Hg and MeHg were most strongly correlated with each other (rÂ² = 0.83-0.88) and with dissolved organic C (DOC) (rÂ² = 0.64-0.92). Multiple regression models containing DOC and a (DOC x pH) interaction term accounted for 85-90% of the variability in Hg and MeHg between lakes. Observed differences between lakes reflected internal cycling processes and external transport pathways. Internally, high DOC and low pH favored Hg methylation and retention over Hg evasion across the air-water interface. Externally, watershed mapping suggested that the cotransport of DOC, Hg, and MeHg from riparian wetland was also a potentially important process. Observed seasonal differences indicated a 30% increase in MeHg across lakes during summer due to internal or external processes. The effects of DOC, seston-water partition coefficients tended to decrease, indicating disproportionately more Hg in the dissovled phase. These observations are consistent with previous data on bioaccumulation factors for zooplankton and fish. 43 refs., 5 figs., 5 tabs.Limnology and Oceanography - LIMNOL OCEANOGR. 01/1995; 40(3):556-565.