Submitted to: Chemical Geology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2005
Publication Date: 3/30/2006
Citation: Ryu, J., Zierenberg, R.A., Dahlgren, R.A., Gao, S. 2006. Chemical and biological processes of evaporation ponds. Chemical Geology. 229:257-272. Interpretive Summary: Sulfur biogeochemistry is an important regulator of redox chemistry especially under anoxic and hypersaline conditions and has strong linkages with nutrient cycling, groundwater chemistry, trace-metal redox behavior, microbiological energetics, and mineralogical composition of sediments. This study investigated sulfur biogeochemistry of shallow groundwater and sediments at Owens Dry Lake by determining the aqueous speciation of sulfur and the fractionation of sulfur isotopes in aqueous and solid phases (from oxic to anoxic layers). Pyrite was the predominant sulfur-bearing phase in the capillary fringe and groundwater zones where anoxic conditions developed but limited when high concentrations of dissolved sulfide was associated with low concentrations of dissolved Fe. Bacterial sulfate reduction resulted in the enrichment of '34S-sulfate and the presence of 34S depleted sulfides in the groundwater/sediments. Findings suggest that NaCl concentration may be a factor controlling sulfate reduction rate. This study provides important isotopic information on sulfur biogeochemistry and valuable to many scientists worldwide who are dealing with issues associated with hypersaline conditions.
Technical Abstract: Processes regulating sulfur biogeochemistry of hypersaline, strongly alkaline groundwaters and sedimentary layers at Owens Dry Lake were investigated as part of an effort to help guide mitigation efforts for attenuating dust generation from the dry lakebed. Groundwater and subsurface sediment samples (~ 1m depth) at sites representative of different groundwater pathways were collected to determine the aqueous speciation of sulfur and the fractionation of sulfur isotopes in aqueous and solid phases. In addition, selected sediment samples at 5 different depths (from oxic to anoxic layers) were collected to investigate the processes controlling sulfur biogeochemistry in sedimentary layers. Pyrite was the predominant sulfur-bearing phase in the capillary fringe and groundwater zones where anoxic conditions developed. Low concentration of pyrite (<0.59 %) coupled with high concentrations of dissolved sulfide (4.81 to 134.7 mg/L) and low concentrations of dissolved Fe (generally <1 mg/L) indicate that the availability of Fe limits pyrite formation. The enrichment of '34S-sulfate and the presence of 34S depleted sulfides are evidence of bacterial sulfate reduction in the groundwater/sediments. The uniformity of down-core isotopic trends for sulfur bearing mineral phases in the sedimentary layers suggests that diffusion is rapid relative to sulfate reduction rates. Shallow groundwater is connected to the atmosphere through capillary rise, and evaporation is an important factor regulating sulfur dynamics in the sediment layers. The shallow groundwater is a relatively open system with respect to sulfate. Sulfate reduction is influenced by strong evaporation and surface/subsurface inflow near the lakebed margins and Owens River. The strong correlation of 'D with dissolved sulfate concentrations indicates the important role of evaporation in concentrating sulfate in groundwater. The increase in '34S of sulfate and total reduced sulfur as salt concentration increases in groundwater suggests that the NaCl concentration may be a factor controlling sulfate reduction in hypersaline conditions.