Water Column Transformations of Nitrogen in a Perennially Ice-Covered Antarctic Lake

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Permanently ice-covered Lake Bonney, an Antarctic lake with two distinct lobes, presents a special situation where turbulence and upper trophic levels are virtually non-existent. This unusual environment yields a system where microbially-mediated processes dominate biogeochemical reactions. Current information on nitrogen dynamics in Lake Bonney indicates that phytoplankton are nitrogen-deficient, that nitrous oxide concentration in the chemocline of the east lobe is the highest recorded in nature, that bulk denitrification does not exist in the east lobe and that nitrogen values in the west lobe are the highest ever measured in an aquatic system. It is hypothesized that 1) both ammonia and oxidized nitrogen are significant regenerated nutrients in the upper trophogenic zone, 2) nitrous oxide is a product of nitrification and 3) bulk denitrification acts as a sink for nitrous oxide in the west lobe, regulating its accumulation. These hypotheses will be addressed by measuring microbial regeneration and utilization of ammonia, nitrite and nitrate, nitrous oxide production, and the distribution of nitrifying and denitrifying bacteria. This study will be one of the first to examine nitrogen dynamics in a system lacking "top- down" regulation and will provide important clues regarding microbial nitrous oxide production. This project is jointly supported by the National Science Foundation and the National Aeronautics and Space Administration.