Article

Mercury Cycling in Stream Ecosystems. 1. Water Column Chemistry and Transport

U.S. Geological Survey, 2280 Woodale Drive, Mounds View, Minnesota 55112, USA.
Environmental Science and Technology (Impact Factor: 5.33). 05/2009; 43(8):2720-5. DOI: 10.1021/es802694n
Source: PubMed

ABSTRACT

This paper is freely available via Open Access: http://pubs.acs.org/doi/abs/10.1021/es802694n

We studied total mercury (THg) and methylmercury (MeHg) in eight streams, located in Oregon, Wisconsin, and Florida, that span large ranges in climate, landscape characteristics, atmospheric Hg deposition, and water chemistry. While atmospheric deposition was the source of Hg at each site, basin characteristics appeared to mediate this source by providing controls on methylation and fluvial THg and MeHg transport. Instantaneous concentrations of filtered total mercury (FTHg) and filtered methylmercury (FMeHg) exhibited strong positive correlations with both dissolved organic carbon (DOC) concentrations and streamflow for most streams, whereas mean FTHg and FMeHg concentrations were correlated with wetland density of the basins. For all streams combined, whole water concentrations (sum of filtered and particulate forms) of THg and MeHg correlated strongly with DOC and suspended sediment concentrations in the water column.

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    • "The speciation of Hg(II) recently deposited in organic-rich soils is dominated by complexation with thiol groups in soil organic matter (SOM) (Skyllberg et al., 2006; Nagy et al., 2011). Similarly, complexation of Hg(II) with thiol groups in dissolved organic matter (DOM) (Haitzer et al., 2002) in soil pore waters is thought to be responsible for the co-mobilization of mercury with DOM from riparian soils to streams (Mierle and Ingram, 1991; Shanley et al., 2008; Brigham et al., 2009; Dittman et al., 2009, 2010). In particular, the hydrophobic organic acid fraction of DOM, compared to other DOM fractions, contains greater thiol group content (Haitzer et al., 2003) and has been observed to correlate positively with the filter-passing total mercury (Hg T ) concentration in streams (Shanley et al., 2008; Dittman et al., 2009, 2010). "
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    ABSTRACT: Riparian soils are an important environment in the transport of mercury in rivers and wetlands, but the biogeochemical factors controlling mercury dynamics under transient redox conditions in these soils are not well understood. Mercury release and transformations in the Oa and underlying A horizons of a contaminated riparian soil were characterized in microcosms and an intact soil core under saturation conditions. Pore water dynamics of total mercury (HgT), methylmercury (MeHg), and dissolved gaseous mercury (Hg0(aq)) along with selected anions, major elements, and trace metals were characterized across redox transitions during 36 d of flooding in microcosms. Next, HgT dynamics were characterized over successive flooding (17 d), drying (28 d), and flooding (36 d) periods in the intact core. The observed mercury dynamics exhibit depth and temporal variability. At the onset of flooding in microcosms (1–3 d), mercury in the Oa horizon soil, present as a combination of ionic mercury (Hg(II)) bound to thiol groups in the soil organic matter (SOM) and nanoparticulate metacinnabar (β-HgS), was mobilized with organic matter of high molecular weight. Subsequently, under anoxic conditions, pore water HgT declined coincident with sulfate (3–11 d) and the proportion of nanoparticulate β-HgS in the Oa horizon soil increased slightly. Redox oscillations in the intact Oa horizon soil exhausted the mobile mercury pool associated with organic matter. In contrast, mercury in the A horizon soil, present predominantly as nanoparticulate β-HgS, was mobilized primarily as Hg0(aq) under strongly reducing conditions (5–18 d). The concentration of Hg0(aq) under dark reducing conditions correlated positively with byproducts of dissimilatory metal reduction (∑(Fe,Mn)). Mercury dynamics in intact A horizon soil were consistent over two periods of flooding, indicating that nanoparticulate β-HgS was an accessible pool of mobile mercury over recurrent reducing conditions. The concentration of MeHg increased with flooding time in both the Oa and A horizon pore waters. Temporal changes in pore water constituents (iron, manganese, sulfate, inorganic carbon, headspace methane) all implicate microbial control of redox transitions. The mobilization of mercury in multiple forms, including HgT associated with organic matter, MeHg, and Hg0(aq), to pore waters during periodic soil flooding may contribute to mercury releases to adjacent surface waters and the recycling of the legacy mercury to the atmosphere.
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    • "The predominant source of MeHg to many streams is production in wetlands and subsequent transfer during times of high hydrological connectivity (Brigham et al. 2009). While it is well known that beaver-induced channel alterations change the way materials flow through streams (Naiman et al. 1986, 1988), only recently has the enhancement of landscape hydrological connectivity by beaver damming been considered in the Hg literature. "
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    Full-text · Article · Oct 2015 · Ecosphere
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    • "The U.S. Geological Survey (USGS) has conducted extensive studies of national and regional fish-tissue contaminant data by combining results of several separate targeted studies conducted over time, analyzing the data and characterizing contaminant levels on the basis of region and watershed type, including propensity for methylation and fish characteristics (Schmitt, 2002; Scudder et al., 2009; Chalmers et al., 2011). These studies have led to identification of patterns and mechanisms of Hg accumulation in fish including the propensity for methylation to occur in watersheds with abundant wetlands (Brigham et al., 2009; Scudder et al., 2009). USGS continues to emphasize locally-focused studies which are national in their distribution (Brigham et al., 2014; Feaster et al., 2014; Chalmers et al., 2014) and explore causative mechanisms for the observed variations in Hg concentrations in a variety of media and settings. "
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