HR: 0800h
AN: B11B-0157    [Abstracts]
TI: Microbial Community Structure Responses to Long-Term Acid-Mine Drainage Contamination in a Coastal Salt Marsh
AU: * Moreau, J W
EM: moreau@eps.berkeley.edu
AF: Department of Earth and Planetary Science, University of California-Berkeley 307 McCone Hall, Berkeley, CA 94709-4767 United States
AU: Zierenberg, R A
EM: zierenberg@geology.ucdavis.edu
AF: Department of Geology, University of California-Davis One Shields Avenue, Davis, CA 95616-8605 United States
AU: Banfield, J F
EM: jill@eps.berkeley.edu
AF: Department of Earth and Planetary Science, University of California-Berkeley 307 McCone Hall, Berkeley, CA 94709-4767 United States
AU: Banfield, J F
EM: jill@eps.berkeley.edu
AF: Department of Environmental Science, Policy and Management, University of California-Berkeley 151 Hilgard Hall #3110, Berkeley, CA 94720-3110 United States
AB: Constructed wetlands for in situ bioremediation of metals and acid mine drainage (AMD) require the activity of sulfate-reducing bacteria (SRB) to sequester dissolved metals into metal-sulfide precipitates (e.g. Webb et al. 1998). Factors such as low pH and high dissolved [Cu] will constrain the growth of SRB (Sani et al. 2001). Unintentional stimulation of the growth of sulfuric acid-generating microbes, such as Thiomicrospira, would also decrease bioremediation efficiency. Few studies of natural wetlands under long-term forcing by AMD and metals have been performed. We characterized the microbial diversity, mineralogy and geochemistry of a contaminated salt marsh at the Richmond Field Station along the East San Francisco Bay. For over 50 years, this marsh has received pH$\sim$2, metal-rich groundwaters from near-surface pyrite tailings and paint and explosives manufacturers. Sediment cores (30-40 cm long) were taken from contaminated sites with pH $\sim$2 and $\sim$8. Whole-sediment analyses showed As, Cd, Cu, Se, Zn, and Pb are present at 100s of ppm (URS Corp. 2001). ICP-AES analyses of pore waters showed 10-50 ppb As. All cores contained fine-grained black muds and exhibited a noticeable sulfide odor. Transmission electron microscope studies of marsh sediments support the sequestration of metals into aggregates of nanocrystalline sulfides. Isotopic analyses of pore-water sulfate taken at several depths within cores of AMD pool (SMR-1) and tidal slough sediments (SM148-1) at pHs 2-3 and 7-8, respectively, all yielded significant negative $\delta$34S values (-25 to -35 $\permil$) consistent with bacterial sulfate reduction. However, values of the upper 10 cm of SMR-1 are roughly 10 $\permil$ heavier than seawater and support a significant contribution of dissolved sulfate from direct oxidation of pyrite tailings. 16S gene clone libraries revealed significantly different microbial community structures in cores SMR-1 and SM148-1. Roughly 40% of the library from SMR-1 consisted of {\it Thiomicrospira denitrificans} (22%) and several other bacteria capable of oxidizing reduced sulfur species (18%). SRB were present (15%), however, and probably reflect contributions from core depths at which acidity is attenuated by tidal flushing. In contrast, SM148-1 contained $\sim$25% SRB, and aero- and halo-tolerant SRB were enriched from this core by cultivation. The dominance of {\it Thiomicrospira} and other sulfur-/sulfide-oxidizing bacteria, in combination with isotopic results, showed microbially-mediated pyrite oxidation in SMR-1. In contrast, {\it Desulfobacterium} spp. dominated the community in SM148-1 and reduced dissolved metals to near or below EPA action levels. References: Webb et al. 1998, J. Appl. Microbio., 84, 240-248; Sani et al. 2001, Applied Env. Microbio., 67, 4765-4772; URS Corp. 2001, Report 51.09967067.00.
DE: 4805 Biogeochemical cycles (1615)
DE: 4840 Microbiology
DE: 1890 Wetlands
DE: 1040 Isotopic composition/chemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting