Mercury Cycling in Stream Ecosystems. 2. Benthic Methylmercury Production and Bed Sediment−Pore Water Partitioning

Abstract

Mercury speciation, controls on methylmercury (MeHg) production, and bed sediment-pore water partitioning of total Hg (THg) and MeHg were examined in bed sediment from eight geochemically diverse streams where atmospheric deposition was the predominant Hg input. Across all streams, sediment THg concentrations were best described as a combined function of sediment percent fines (%fines; particles < 63 µm) and organic content. MeHg concentrations were best described as a combined function of organic content and the activity of the Hg(II)-methylating microbial community and were comparable to MeHg concentrations in streams with Hg inputs from industrial and mining sources. Whole sediment tin-reducible inorganic reactive Hg (Hg(II) R ) was used as a proxy measure for the Hg(II) pool available for microbial methylation. In conjunction with radiotracer-derived rate constants of 203 Hg(II) methylation, Hg(II) R was used to calculate MeHg production potential rates and to explain the spatial variability in MeHg concentration. The %Hg(II) R (of THg) was low (2.1 ( 5.7%) and was inversely related to both microbial sulfate reduction rates and sediment total reduced sulfur concentration. While sediment THg concentrations were higher in urban streams, %MeHg and %Hg(II) R were higher in nonurban streams. Sediment pore water distribution coefficients (log K d 's) for both THg and MeHg were inversely related to the log-transformed ratio of pore water dissolved organic carbon (DOC) to bed sediment %fines. The stream with the highest drainage basin wetland density also had the highest pore water DOC concentration and the lowest log K d 's for both THg and MeHg. No significant relationship existed between overlying water MeHg concentrations and those in bed sediment or pore water, suggesting upstream sources of MeHg production may be more important than local streambed production as a driver of water column MeHg concentration in drainage basins that receive Hg inputs primarily from atmospheric sources.

Mercury bioaccumulation and biomagnification in Ozark stream ecosystems

“…Incorporation of invertebrates and fish into crayfish diets, which would increase Hg biomagnification over what would be expected from consumption of streamconditioned detritus alone, represents a plausible explanation for among-site differences in crayfish HgT. At BGR, we suspect that low HgT concentrations in biota reflect the combined effects of FPOM dilution by mine tailings and other inorganic sediments from construction and agriculture, biodilution by algal blooms (e.g., Chen and Folt, 2005), reduced flux of terrestrial detritus from the more heavily developed watershed, and lower bioavailability and possibly methylation rates due to sulfides in the lead-zinc mine wastes (e.g., Suchanek et al, 2008a;Marvin-DiPasquale et al, 2009). The comparative uniformity of the HgT accumulation patterns among taxa and sites also indicates that once incorporated into the food web, differences among sites (including BGR) in the proportion of HgT represented by MeHg are small.…”

“…1). HgT concentrations in Missouri lead-zinc ores are comparatively low (Leach et al, 1995), but mine wastes represent significant sources of sulfides and sulfates to surface and groundwater Kleeschulte, 2008;Schumacher, 2008) that could either facilitate Hg methylation or bind Hg and reduce its availability (Compeua and Bartha, 1985;Krabbenhoft et al, 1998;Marvin-DiPasquale et al, 2009). The BGR collection site was downstream of the Old Lead Belt, a population center, and a sewage treatment plant.…”

Mercury Cycling in Stream Ecosystems. 3. Trophic Dynamics and Methylmercury Bioaccumulation

“…Hg concentrations in biota were evaluated relative to integrated streambed sediment MeHg production potential (42), atmospheric depositional Hg loading (15,43) (not shown), and wetland abundance as a percent of the watershed area in the stream basin (16). Mercury in biota was not significantly correlated to either in-stream MeHg production potential or depositional loading (τ < 0.5, p > 0.1); however, Hg concentrations in invertebrates, forage fish, and predators were significantly and positively correlated to percent wetland ( Figure 3).…”

Characterization of the Deltaproteobacteria in contaminated and uncontaminated stream sediments and identification of potential mercury methylators

“…Hg methylation is an important biogeochemical process that generates the potent human neurotoxin monomethylmercury (MeHg) (Clarkson 1998). Net MeHg production in aquatic ecosystems is linked to environmental and geochemical parameters along with electron donor and acceptor availability (Marvin-DiPasquale et al 2009). Previously, wetlands and floodplain lakes have been associated with MeHg production in aquatic ecosystems, but recent work in stream sediments has found significant in situ MeHg production that warrants further examination of streambed Hg methylation and the associated microbial communi-ties (Tsui et al 2010).…”