Control of Denitrification in a Permanently Ice Covered Antarctic Lake: Potential for Regulation By Bioactive Metals

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AbstractOPP97-25345P.I. Mark L. WellsDenitrification is the main loss term for fixed nitrogen from ecosystems, and thus its rate and regulation may directly affect primary production and carbon cycling over short and long time scales. The proposed research investigates the role of bioactive metals in regulating denitrification by exploiting a natural experimental system that occurs in a permanently ice-covered lake in the Taylor Valley of East Antarctica. Chemical distributions in the two lobes of Lake Bonney imply that denitrification occurs in one lobe but not the other. Most of the obvious biological and chemical variables that usually influence denitrification, and might account for the difference between the two lobes, have been ruled out by previous study. Denitrifiying bacteria are present in both lobes of the lake and isolates derived from the lake show temperature and salinity optima consistent with their persistence in this environment. The proposed research represents a combination of culture experiments and field work to examine this paradox, and include: (1) Experiments to determine the metal tolerances and requirements for growth and denitrification by the denitrifying isolates, (2) Measurement of metal concentrations and metal speciation in surface transects and depth profiles, and (3) Experiments to determine how denitrifying bacteria respond to alterations in metal availability. This approach allows examination of the relationship between microbial activity and metal distributions in Lake Bonney and has implications for elemental cycling in other aquatic systems. Moreover, the insights will be useful for evaluating the proposed used of paleo-denitrification indicators for past climate reconstructions, as well as the potential significance of the global marine denitrification/nitrogen fixation ratio on atmospheric carbon dioxide levels.