Role of the deep brine layer in the production of methylmercury in the Great Salt Lake

Westminster University, Salt Lake City UT

Investigators

Abstract

The Great Salt Lake in Utah is a major stop over for millions of migratory birds each year. These birds feed on brine shrimp and brine flies that live in the Lake, putting them at risk of mercury toxicity due to the very high concentrations of methylmercury in the Great Salt Lake. Methylmercury is one form of the toxic heavy metal mercury, and it is the only form that is readily accumulated to increasing concentrations moving up the food chain. It is currently unknown why the Great Salt Lake has some of the highest methylmercury concentrations ever measured in a natural water body. The goal of this research is to determine the primary locations of methylmercury production in the Great Salt Lake. Such information could help scientists and government regulators to develop ways to decrease mercury exposure to humans and animals at the Great Salt Lake. This research will support multiple students from backgrounds underrepresented in the geosciences, in particular multiple women. This project will also support the development of new science curriculum by teachers at both the high school and university levels. The hypersaline Great Salt Lake (GSL) is a major stop over for millions of migratory birds each year. It is also home to some of the highest concentrations of methylmercury (MeHg) ever reported for a natural water body. The highest concentrations of MeHg are found in the South Arm's anoxic deep brine layer, which is created by the flow of denser, more saline water from the North Arm into the South Arm. While the high levels of MeHg throughout this ecosystem have been well documented, the primary source of MeHg and the underlying reasons for the exceptionally elevated concentrations of MeHg here are not known. The closure of two culverts in the causeway separating the North Arm and South Arm of the GSL has resulted in the recent disappearance of the deep brine layer, while the completion of a new bridge on the causeway in the second half of 2016 is expected to lead in the redevelopment of the deep brine layer in the South Arm. This unique and transient event provides the conditions for an unintended regional-scale natural experiment and opportunity to track the possible sources of MeHg (either the anoxic deep brine layer or sediment underlying this layer). The investigators will use a multifaceted approach to test these hypotheses, including the measurement of MeHg concentrations, Hg methylation and demethylation rates, and naturally occurring stable Hg isotope ratios in water and sediment collected before, during, and after the reestablishment of the deep brine layer.