TOTAL MERCURY AND METHYLMERCURY RESPONSE IN WATER, SEDIMENT, AND BIOTA TO DESTRATIFICATION OF THE GREAT SALT LAKE, UTAH, USA
Environmental science & technology | 13 Apr 2017
C Valdes, FJ Black, B Stringham, JN Collins, JR Goodman, HJ Saxton, CR Mansfield, JN Schmidt, S Yang and WP Johnson
Measurements of chemical and physical parameters made before and after sealing of culverts in the railroad causeway spanning Great Salt Lake in late 2013 documented dramatic alterations in the system in response to the elimination of flow between the Great Salt Lake’s north and south arms. The flow of denser, more saline water through the culverts from the north arm (Gunnison Bay) to the south arm (Gilbert Bay) previously drove the perennial stratification of the south arm and the existence of oxic shallow brine and anoxic deep brine layers. Closure of the causeway culverts occurred concurrently with a multiyear drought that resulted in a decrease in the lake elevation and a concomitant increase in top-down erosion of the upper surface of the deep brine layer by wind-forced mixing. The combination of these events resulted in replacement of the formerly stratified water column in the south arm with one that is vertically homogeneous and oxic. Total mercury concentrations in the deep waters of the south arm decreased by approximately 81%, and methylmercury concentrations in deep waters decreased by roughly 86%, due to destratification. Methylmercury concentrations decreased by 77% in underlying surficial sediment whereas there no change was observed in total mercury. The dramatic mercury loss from deep waters and methylmercury loss from underlying sediment in response to causeway sealing provides new understanding of the potential role of the deep brine layer in the accumulation and persistence of methylmercury in the Great Salt Lake. Additional mercury measurements in biota appear to contradict the previously implied connection between elevated methylmercury concentrations in the deep brine layer and elevated mercury in avian species reported prior to causeway sealing.
* Data courtesy of Altmetric.com