OXIDATION OF SEQUESTERED SELENIUM INTO THE WATER COLUMN OF GREAT SALT LAKE, UTAH, USA

In order to develop a selenium budget for the Great Salt Lake, the movement of selenium in the water column must be understood. Sediment flux in the water column includes deposition of transported sediment and re-suspension of deposited sediment. The water column of the Great Salt Lake is complicated by the presence of a chemocline that is persistent over annual to decadal time periods. The water below the chemocline is referred to as the deep brine layer and has a high salinity (22%) and is anoxic. The water above the chemocline is known as the upper brine layer and has lower salinity (14%) and is oxic. Mixing or displacement of the deep brine into the upper less saline water may involve selenium movement within the water column due to changes in oxidation state. Evidence of mixing in the water column has been observed at two fixed stations on the lake using detailed temperature profiling and hydroacoustics. Mixing events occur over periods of 12 to 24 hours and are associated with strong wind events. Laboratory equilibration tests simulating the observed sediment re-suspension were conducted to understand the effect of transporting anoxic bottom sediments into oxic water and the associated effect of selenium desorption and (or) dissolution. Results from the laboratory simulations indicate that selenium associated with anoxic bottom sediments is periodically recycled into the upper brine layer where it can potentially be incorporated into the biota utilizing the oxic part of Great Salt Lake.