Hydrogen Sulfide in Farmington Bay and the Great Salt Lake: A Potential Odor-Causing Agent

Odors from Farmington Bay and/or the Great Salt Lake frequently impact residents of Salt Lake and Davis counties, but the agent causing the problem and the origin of the odor is uncertain. Hydrogen sulfide (H2S) gas is produced in the deeper layers of water in Farmington Bay and Gilbert Bay in the Great Salt Lake, but these deeper waters are generally part of high salinity deep-brine layers that are resistant to wind mixing. Hydrogen sulfide has a rotten-egg odor and is a likely component contributing to the lake stink. The goals of this study were to determine (1) whether wind driven mixing events drove mixing of the deep-brine layers in Farmington and Gilbert Bays, (2) determine the amount of hydrogen sulfide present in each of these bays, and (3) determine the potential of each area of the lake to release hydrogen sulfide from those deep-brine layers and cause odor events. We found that in Farmington Bay, which was \u3c1.5 m (5 ft) deep during the study, the deep-brine layer was entrained (mixed) four times in three months during high-wind events. By contrast, in Gilbert Bay, which has a deeper water column and more stable deep-brine layer, the brine layer was never completely entrained. However, the top 0.9 m (3 ft) of the deep brine layer eroded between July and October. Hydrogen sulfide concentrations in the surface mixed layers of both bays were insignificant on each sampling date, but concentrations in the deep-brine layers were significant. In Farmington Bay H2S concentrations reached 8 mg/L in the deep-brine layer. In Gilbert Bay H2S concentrations in the deep-brine layer ranged from 11 mg/L in late July to 4 mg/L in November 2003. The higher concentrations in Gilbert Bay are likely due to decreased mixing and therefore increased time intervals of hydrogen sulfide accumulation in Gilbert Bay. Both bays may release H2S into the airshed, and thus contribute to odor problems. Large releases of H2S into the water columns could result in rapid deoxygenation and toxicity to aquatic organisms. Detailed whole water column monitoring of oxygen, salinity, and H2S concentrations in both bays should be undertaken to assess these potential threats. It will necessary to do these studies at a variety of lake levels in order to fully understand the driving mechanisms creating H2S and allowing it to be released from the lake