| Description |
Aquatic and trace element chemistry parameters in the Great Salt Lake (GSL), Utah, USA were monitored to address the system response to density restratification. Six months following the engineered breach of the causeway separating the North and South Arms of the lake, restratification progressed from north to south, with associated sustained anoxia, robust sulfide (3-15 mg/L), elevated methyl-mercury (14-23 ng/L), and total mercury (17-55 ng/L) concentrations in deep water. These observations demonstrate that the system is reverting to its previous stratified condition wherein density stratification drove accumulation of high methyl mercury concentrations in the lake's deep brine waters (layers) (ranging 20-30 ng/L). Percent spiked inorganic mercury methylated (%204iHg) in both deep water and underlying sediments were examined to understand the role of the deep brine layer. The observed lack of significant difference of %204iHg under stratified versus destratified conditions indicated that the deep brine layer promotes accumulation (rather than generation) of methyl-mercury and total mercury at depth. Under destratified conditions, hydrologic (snowmelt runoff) forcing yielded stratification with temporal anoxia, concomitant with elevated concentrations of sulfide (2-6 mg/L), methyl-mercury (8-13 ng/L), and total mercury (20-40 ng/L) in deep water, highlighted the role of organic carbon in underlying sediment. Frequent and co-located water and brine shrimp samples were collected for a 2- year period to investigate the transfer routes of trace elements from water to biota. iv Temporal correspondence between brine shrimp and water concentrations were observed for selenium and mercury, with repeated year-to-year timing of peak concentrations for mercury but not selenium. Temporal correspondence was strong between brine shrimp and shallow filtered water, suggesting exposure of biota to both elements occurred mainly in surface water although mercury concentrations were much greater in deep water. |
