HR: 16:00h
AN: B24B-01 INVITED     [Abstracts]
TI: Salinity Effects on the Biogeochemical Cycles of Sulfate, Arsenate, Nitrate, and Methane in Anoxic Sediments of Mono Lake and Searles Lake, California.
AU: * Kulp, T R
EM: trkulp@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 480, Menlo Park, CA 94025 United States
AU: Hoeft, S E
EM: sehoeft@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 480, Menlo Park, CA 94025 United States
AU: Miller, L G
EM: lgmiller@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 480, Menlo Park, CA 94025 United States
AU: Oremland, R S
EM: roremlan@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 480, Menlo Park, CA 94025 United States
AB: Mono Lake and Searles Lake are two members of a chain of hypersaline and alkaline soda lakes that occur in closed basins along the arid eastern escarpment of the Sierra Nevada in California. These lakes are alkaline (pH = 9.8), highly saline, and As-rich due to hydrothermal input and evaporative concentration. Mono Lake is characterized by a salinity of 90 g/L and contains 200μM dissolved As. Searles Lake, a partially-dry residual playa, exhibits salt concentrations >300 g/L (near saturation) and 3.9 mM dissolved As. We utilized ³⁵SO₄ and ⁷³As(V) as radioactive tracers to compare sulfate and arsenate [As(V)] reductase activities at in-situ concentrations in sediment cores (25 cm depth) from Mono and Searles Lakes. Sulfate reduction activity was detected in sediments from Mono Lake, with the highest rates occurring in the upper 2 cm sediment depth. No sulfate reduction activity was observed in Searles Lake sediments, suggesting that this metabolic process may not provide sufficient energy to cope with the demands of osmoadaptation at saturated salt concentrations. Anaerobic pathways that utilize As(V) or nitrate as terminal electron acceptors are bioenergetically more favorable than sulfate reduction. Dissimilatory reduction of As(V) occurred in sediments from both lakes, with the fastest rates of As(V) reduction occurring at 3 cm sediment depth. We conducted additional experiments with As- or nitrate-amended slurries of Searles Lake sediment prepared in artificial media that mimicked lake water chemistry over a range of total salinities. Slurries were sampled periodically and analyzed to determine the rate of As(V) reduction or denitrification at each salinity. Methane production was also monitored in the headspace of As(V)-amended and non-amended slurries. As(V) and nitrate reduction rates, as well as methane production, demonstrated an inverse relationship with total salinity over the range of 50 - 346 g/L. These data suggest that halophilic bacteria capable of anaerobic respiration using As(V) or nitrate as terminal electron acceptors, as well as methanogenic organisms, tolerate but do not prefer the salt saturated conditions of Searles Lake.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0448 Geomicrobiology
DE: 0456 Life in extreme environments
DE: 0488 Sulfur cycling
SC: Biogeosciences [B]
MN: Fall Meeting 2005