TOTAL- AND METHYL-MERCURY RESPONSE TO CAUSEWAY CLOSURE IN THE GREAT SALT LAKE, UTAH

In 2007, high mercury (Hg) concentrations were measured in various waterfowl species residing at the Great Salt Lake (GSL), Utah. During this time high monomethylmercury (MMHg, the toxic bioaccumulative form of Hg) concentrations were also determined in the anoxic deep brine layer (DBL) of the GSL, ranging from 0.8 to >30 ng-L^-1. The DBL is therefore suspected as a source of MMHg to the surrounding ecosystem; however, the pathways by which MMHg is able to propagate from the DBL upward into the higher trophic levels of the GSL ecosystem is unknown. The DBL has recently retreated from the southernmost basin of the GSL following the closure of culverts in the causeway separating the north and south arms of the lake. Anoxic, reductive conditions and high dissolved organic matter (DOM) content in the DBL allow the persistence of MMHg, thus the retreat of the DBL could affect total mercury (THg) and MMHg concentrations in brine and sediment, as well as the Hg burdens in invertebrates and waterfowl. Because the extent of the DBL depends on flux of north arm brine through causeway openings, this temporary closing of flow provides a unique opportunity to monitor the response of Hg concentrations in the DBL, sediment, and biota during this transient. Waterfowl and invertebrate tissues, plant, sediment, and brine samples were collected before and after the culvert closure. Biota and sediment samples were digested, and all samples were analyzed using cold vapor adsorption atomic fluorescence spectroscopy (CVAFS). The samples from pre- and post-closure will be compared and described in order to deduce the role of the DBL as a potential reservoir of MMHg in the GSL.