Interactions Among Dissolved 0rganic Matter, Genetic Structure, and Denitrification in an Agriculturally-influenced Stream Ecosystem

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Denitrification is a critical, natural environmental process carried out by various groups of bacteria. Denitrification removes reactive nitrogen from aquatic ecosystems and has important implications for water quality. Quantifying the factors that control denitrification rates in streams, and their spatial and temporal variability, has long been a challenge. The goal of this study is to determine the extent to which patterns in denitrification can be explained by the genetic structure of bacterial communities and the interactions between bacteria and other environmental factors, such as the chemistry of dissolved organic matter. This project will be conducted in an agricultural landscape in the midwestern U.S. where nitrogen pollution is a pressing concern. The study will combine modern molecular biology with recent advances in use of isotopic tracers to measure in-stream denitrification rates. Nitrogen enrichment of aquatic ecosystems is a persistent environmental problem, particularly in agricultural areas. However, current understanding of nitrogen cycling in streams and rivers is based largely on studies in watersheds with low levels of nitrogen pollution. By focusing on a nitrogen-rich agricultural landscape, this study will expand understanding of nitrogen cycling in human-dominated ecosystems. This project will advance scientific understanding of how bacterial communities interact with the environment to produce an important ecosystem function (denitrification). It will also contribute to a growing body of knowledge addressing the question of how ecosystem function is related to biodiversity, and promote interdisciplinary graduate research training and undergraduate education.