Geology and Geophysics Department

University of Utah

Bio:

William Johnson is a Professor in the Geology & Geophysics Department and an Adjunct Professor in the Civil & Environmental Engineering Department at the University of Utah. His research group research examines fate and transport in water of contaminants ranging from particles and pathogens to trace elements such as mercury as well as organic compounds. Their work and spans field to laboratory settings and experimental to advanced computing numerical simulations. Research contexts include developing theory for predicting nano- and micro-particle transport in porous media, selenium and mercury cycling in the Great Salt Lake, impacts from tar sand mining/processing in eastern Utah, and gold mining processing impacts to rivers in southern Ecuador. Dr. Johnson strives to sustain an interactive synergistic learning community of undergraduates through PhD candidates. 

Title: Total Mercury and Methylmercury Response in Water and Sediment to De-stratification and Re-Stratification of Great Salt Lake

Wednesday, May 9th, 2:05 PM

Abstract: The recent closing and re-opening of culverts in the railroad causeway separating the north and south arms of Great Salt Lake constitute a large scale experiment for which we monitored the response of total mercury and methylmercury in water and underlying unconsolidated sediment. Related aquatic chemical parameters demonstrated that de-stratification of the lake occurred in response to elimination of flow from the higher salinity north arm into the south arm in December 2013. Specifically, prior to elimination of flow, oxic and anoxic conditions characterized the shallow and deep brine layers, respectively. After elimination of flow, the south arm became vertically homogenous and oxic, with consequent loss of sulfide (99.7%). Concurrently, reduction of total mercury (81%) and methyl mercury (86%) in the water column, and reduction of methyl mercury (77%) in underlying unconsolidated sediment occurred, suggesting that the deep brine layer promoted the accumulation of methyl mercury in both phases. In the period prior to re-establishment of north-to-south flow, periodic anoxia at depth under quiescent conditions indicated respiration of underlying sediment organic matter, with consequent increase in sulfide, methyl mercury, and total mercury. Following re-establishment of north-to-south flow in July 2017, density stratification progressed from north to south with consequent stable increases in sulfide, methylmercury and total mercury. Our results confirm that the denser deep brine layer promotes methylmercury accumulation in bottom waters and underlying unconsolidated sediment.