Methyl mercury hotsports and sources in the Great Salt Lake, Utah, Adjacent freshwater bays and impounded wetlands

Water column, sediment and pore water samples were collected from multiple locations of the Great Salt Lake (GSL), Utah to examine the spatial and temporal distribution of total mercury (THg) and methyl mercury (MeHg) concentrations and MeHg production potentials (MPPs). Sampling locations included multiple transects in the south arm of the GSL, adjacent freshwater influenced bays, and multiple impounded and sheet flow freshwater wetland sites during the period of summer 2009-summer 2012. Select water column and sediment subsamples were spiked with inorganic mercury (I204Hg) and methyl mercury (Me204Hg) to examine net production of methyl mercury (Me204Hg ) and net loss of Me201Hg. First order methylation (kmeth) and demethylation (kdemeth) rate constants were determined from changes in isotope dilution corrected concentrations and/or changes in isotope ratios as a function of time. Tin reducible inorganic Hg (Hg(II)R) was used as a proxy for bioavailable Hg(II) in GSL samples. MeHg production potentials (MPPs) were calculated as the time integrated product of kmeth and Hg(II)R to compare methylation in deep brine layer (DBL) versus underlying sediment slurry (SSL) samples of the GSL. A large range of methylation rate constants (1.4E-6 to 1.1E-3 hr-1) was observed across the region, whereas demethylation was only significant in the DBL. Positive correlation of kmeth to organic matter content was observed in sediment of the freshwater influenced bays and impounded wetlands, while this trend was not observed in DBL and SSL of the GSL. These results further indicate that sediment organic matter, as well as other factors (e.g., organic matter lability and sulfide concentrations) contribute to production of MeHg. Spatially, higher MeHg concentrations in the GSL and sheet flow freshwater wetlands present the possibility of ‘hot spots' for MeHg introduction into the food web. Greater and temporally constant MPPs in SSL relative to DBL may explain the persistence of high MeHg concentrations in the DBL.