Hydrogen sulfide production and volatilization in a polymictic eutrophic saline lake, Salton Sea, California

The Salton Sea is a large shallow saline lake located in southern California that is noted for high sulfate concentrations, substantial algal productivity, and very warm water column temperatures. These conditions are well-suited for sulfide production, and sulfide has been implicated in summer fish kills, although no studies have been conducted to specifically understand hydrogen sulfide production and volatilization there. Despite polymictic mixing patterns and relatively short accumulation periods, the amount of sulfide produced is comparable to meromictic lakes. Sulfide levels in the Salton Sea reached concentrations of 1.2 mmol L−1 of total free sulfide in the hypolimnion and 5.6 mmol L−1 in the sediment pore water. Strong winds in late July mixed H2S into the surface water, where it depleted the entire water column of dissolved oxygen and reached a concentration of 0.1 mmol L−1. Sulfide concentrations exceeded the toxicity threshold of tilapia (Oreochromis mossambicus) and combined with strong anoxia throughout the water column, resulted in a massive fish kill. The mixing of sulfide into the surface waters also increased atmospheric H2S concentrations, reaching 1.0 μmol m−3. The flux of sulfide from the sediment into the water column was estimated to range from 2–3 mmolm−2 day−1 during the winter and up to 8 mmol m−2 day−1 during the summer. Application of the two-layer model for volatilization indicates that up to 19 mmolm−2 day−1 volatilized from the surface during the mixing event. We estimate that as much as 3400 Mg year−1 or approximately 26% of sulfide that diffused into the water column from the deepest sediments may have been volatilized to the atmosphere.