Sulfate Addition Increases Methylmercury Production in an Experimental Wetland

Abstract

Atmospheric mercury is the dominant Hg source to fish in northern Minnesota and elsewhere. However, atmospherically derived Hg must be methylated prior to accumulating in fish. Sulfate-reducing bacteria are thought to be the primary methylators of Hg in the environment. Previous laboratory and field mesocosm studies have demonstrated an increase in methylmercury (MeHg) levels in sediment and peatland porewaters following additions of sulfate. In the current ecosystem-scale study, sulfate was added to half of an experimental wetland at the Marcell Experimental Forest located in northeastern Minnesota, increasing annual sulfate load by approximately four times relative to the control half of the wetland. Sulfate was added on four separate occasions during 2002 and delivered via a sprinkler system constructed on the southeast half (1.0 ha) of the S6 experimental wetland. MeHg levels were monitored in porewater and in outflow from the wetland. Prior to the first sulfate addition, MeHg concentrations (filtered, 0.7 microm) were not statistically different between the control (0.47 +/- 0.10 ng L(-1), n = 12; mean +/- one standard error) and experimental 0.52 +/- 0.05 ng L(-1), n = 18) halves. Following the first addition in May 2002, MeHg porewater concentrations increased to 1.63 +/- 0.27 ng L(-1) two weeks after the addition, a 3-fold increase. Subsequent additions in July and September 2002 did not raise porewater MeHg, but the applied sulfate was not observed in porewaters 24 h after addition. MeHg concentrations in outflow from the wetland also increased leading to an estimated 2.4x increase of MeHg flux from the wetland. Our results demonstrate enhanced methylation and increased MeHg concentrations within the wetland and in outflow from the wetland suggesting that decreasing sulfate deposition rates would lower MeHg export from wetlands.

Common Loon Reproductive Success in Canada: the West is Best but Not for Long

“…Methylmercury concentrations are higher (e.g., Bodaly et al 1993) and pH (e.g., Eilers et al 1983) and abundance of forage fish (e.g., Piper et al 2012) are lower in smaller than in larger lakes, which likely explains why reproductive success in this study was lower in smaller than in larger lakes. Also, methylmercury concentrations are higher where pH is lower (e.g., Jeremiason et al 2006), which combined with the direct negative effects of low pH on food supply, likely explains why reproductive success in this study was lower where pH was lower.…”

“…The amount of methylmercury in lake water available to enter food chains is governed by multiple biotic and abiotic methylation and demethylation pathways; thus, uptake is greatest where the methylation rate exceeds the demethylation rate (Celo et al 2006). Sulfur oxides from acid precipitation favor methylation because they increase the activity of sulfur-reducing bacteria, which convert large amounts of mercury to methylmercury (Jeremiason et al 2006). Higher water temperatures also increase the activity of the bacteria and favor methylation over demethylation (Shin and Krenkel 1976, Wright and Hamilton 1982, Ramlal et al 1993.…”

“…Moreover, some smaller lakes receive relatively larger inputs from acid precipitation and hold fewer substances that neutralize acids compared to larger lakes (Eilers et al 1983), which means that smaller lakes generally have lower pH than larger lakes (e.g., Rago and Wiener 1986, Matuszek and Beggs 1988, McNicol et al 1995. Thus, smaller lakes typically are warmer and have lower pH than larger lakes, which likely explains why methylmercury is more abundant in smaller lakes (Bodaly et al 1993, Jeremiason et al 2006. All of these factors in turn likely explain why Common Loon reproductive success and survival of young declines with decreasing lake area (Alvo 2009, McNicol et al 1995, Piper et al 2012).…”

Linking landscape development intensity within watersheds to methyl-mercury accumulation in river sediments

“…The KruskalWallis test confirmed that watersheds with mining as prevalent activities had significantly higher (p\0.05) concentrations of sulfate than the other identified land-use types. Although both sulfate and organic matter can stimulate microbial methylation of ionic Hg (Jeremiason et al 2006), they also do have optimum values beyond which Hg methylation becomes limited due to reduced Hg bioavailability through both binding to organic ligands and precipitation as insoluble Hg sulfide minerals. Finally, agricultural and urban activities within the MARB could impact MeHg production/accumulation in sediments through nutrient inputs as reported for other watersheds by Balogh et al (2002Balogh et al ( , 2003.…”

Development of an Enhanced Hydro-geochemical Model to Address Mercury-speciation Fate and Transport in Aquatic Environments

“…The Hg complexation in the mixtures was then investigated. The Hg species distribution plotted against salinity content (‰) in the mixtures is shown , is the parameter that triggers the production of MeHg (Bates et al, 2002;Jeremiason et al, 2006;Wang et al, 2009;Weaver et al, 2008;Wnalin et al, 2007). In order to understand the water quality conditions that favor the complexation between Hg and Sulfur, which can lead to the methylation of Hg, the Hg species distribution at various redox values in ENP water was evaluated (using the water quality data at P33 station, which is shown in Table 50); the results are depicted in Figure 72.…”