HR: 17:15h
AN: H24C-06    [Abstracts]
TI: The Arsenic Cycle in Searles Lake, California: An Arsenic-Rich, Salt-Saturated Soda Lake: I. Sediment Experiments.
AU: * Kulp, T R
EM: trkulp@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, ms 480, Menlo Park, CA 94025 United States
AU: Hoeft, S E
EM: sehoeft@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, ms 480, Menlo Park, CA 94025 United States
AU: Miller, L G
EM: lgmiller@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, ms 480, Menlo Park, CA 94025 United States
AU: Baesman, S M
EM: sbaesman@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, ms 480, Menlo Park, CA 94025 United States
AU: Oremland, R S
EM: roremlan@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, ms 480, Menlo Park, CA 94025 United States
AB: Searles Lake is a residual playa of what once was the end-member of a series of soda lakes that were connected during the Pleistocene. Brinewaters are saturated (300 g/L), alkaline (pH = 9.8), and rich in arsenic (3.9 mM). Porewater profiles (max. depth = 25 cm.) show the speciation of arsenic changes from arsenate [As(V)] in the slightly oxic (DO = 6.2 uM) surface to predominantly arsenite [As(III)] in the sediments. Porewaters also contained ammonia (0.4 - 1.2 mM), sulfide (0.1 - 0.2 mM), and methane (0.05 - 0.6 uM). Sediment slurries incubated with artificial brinewater (salinity = 346 g/L) demonstrated reduction of As(V) to As(III). The rate of As(V) reduction (40 umol/L/day) increased 50 percent with addition of lactate. Addition of sulfide or hydrogen to slurries stimulated this rate by 2.4- and 4.1-fold, respectively. This suggests that chemoautotrophs are important agents of As(V)-respiration in this system. The rate of As(V)-reduction responded inversely with increased salinity, decreasing from 470 umol/L/day at 50 g/L to 40 umol/L/day at 346 g/L. A similar relationship to salinity was found for methane production. Slurries incubated under aerobic conditions showed a rapid biological oxidization of As(III) (rate = 220 umol/L/day). These results show that a microbiological arsenic cycle occurs in this extreme environment. The anaerobes in this ecosystem, however, seem best adapted to lower salinities. Nonetheless, significant dissimilatory As(V) reduction still occurs at the condition of salt-saturation.
DE: 4805 Biogeochemical cycles (1615)
DE: 4802 Anoxic environments
DE: 1065 Trace elements (3670)
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting