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Geological Society, London, Special Publications; 1988; v. 40; p. 59-75;
DOI: 10.1144/GSL.SP.1988.040.01.06
© 1988 Geological Society of London

Part I Tectonic, Geological, Geochemical and Biological Framework

Microbial and biogeochemical processes in Big Soda Lake, Nevada

R. S. Oremland, J. E. Cloern, R. L. Smith, C. W. Culbertson, J. Zehr, L. Miller, B. Cole & R. Harvey

Water Resources Division, U.S. Geological Survey, Menlo Park, Ca. 94025, USA

Z. Sofer & N. Iversen

Cities Service Co., Tulsa, Okla. 74102, USA
Institute of Water, Soil and Environmental Technology, Aalborg, Denmark

M. Klug

Kellogg Biological Station, Hickory Corners, Mi. 49060, USA

D. J. Des Marais & G. Rau

NASA Ames Research Center, Moffett Field, Ca. 94035, USA

Meromictic, alkaline lakes represent modern-day analogues of lacustrine source rock depositional environments. In order to further our understanding of how these lakes function in terms of limnological and biogeochemical processes, we have conducted an interdisciplinary study of Big Soda Lake. Annual mixolimnion productivity (ca. 500 g m–2) is dominated by a winter diatom bloom (600f annual) caused by upward transport of ammonia to the epilimnion. The remainder of productivity is attributable to chemoautotrophs (30%) and photosynthetic bacteria (10%) present at the oxic-anoxic interface from May to November. Studies of bacterial heterotrophy and particulate fluxes in the water column indicate that about 900f annual productivity is remineralized in the mixolimnion, primarily by fermentative bacteria. However, high rates of sulphate reduction (9–29 mmol m–2 yr–1) occur in the monimolimnion waters, which could remineralize most (if not all) of the primary productivity. This discrepancy has not as yet been fully explained. Low rates of methanogenesis also occur in the monimolimnion waters and sediments. Most of the methane is consumed by anaerobic methane oxidation occurring in the monimolimnion water column. Other bacterial processes occurring in the lake are also discussed. Preliminary studies have been made on the organic geochemistry of the monimolimnion sediments. Carbon-14-dating indicates a lower depositional rate prior to meromixis and a downcore enrichment in 13C of organic carbon and chlorophyll derivatives. Hydrous pyrolysis experiments indicate that the sediment organic matter is almost entirely derived from the water column with little or no contribution from terrestrial sources. The significance of the organics released by hydrous pyrolysis is discussed.