SPATIAL VARIATION OF MERCURY METHYLATION POTENTIAL IN SEDIMENTS AND OVERLYING WATER COLUMN IN THE FARMINGTON BAY OF THE GREAT SALT LAKE, UTAH

The Great Salt Lake and the surrounding wetlands in Northern Utah are an important ecosystem for millions of migratory birds and waterfowl. A consumption advisory for several species of waterfowl was recently released due to findings of toxic mercury levels in those species. Farmington Bay (FB) lies in the southeast end of the lake and receives high volumes of effluent from surrounding water treatment facilities. About three kilograms of mercury flow into the main body of the Great Salt Lake (GSL) each year from FB through a bridge in an automobile causeway that divides FB from the main body. The bioavailable form of mercury, monomethyl mercury (MMHg), is also shown by previous studies to be relatively high in the main body of the GSL. Sediment and water column samples were collected from 10 sites along two transects located at the northern and southern ends of Farmington Bay. Sub-samples of the sediment and water from each site were spiked to approximately 25% and 15% of the average ambient total mercury concentration, respectively, with ²⁰⁴Hg²⁺ and were incubated for 12, 24, 48, and 72 hours. Mercury concentration and isotopic signals were detected using cold vapor atomic fluorescence spectrometry inductively coupled plasma mass spectrometry (CV-AFS-ICP-MS). Isotopic signals were used to develop first order rate of formation constants for MMHg for each sample. Rate constants, which describe methylation potential for each site, vary between the two transects and within the sites of the individual transects. Methylation potential was found to be higher in the sediments than in the water column above.