RAPID: The missing anthropogenic N - assessing denitrification at the watershed scale

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Lakes, estuaries, and coastal marine waters throughout the world have been degraded by over-enrichment with plant nutrients such as nitrogen (N) that cause algal blooms, and eventually deplete dissolved oxygen. Nitrogen exports to aquatic ecosystems have been increased by agricultural runoff, sewage discharges, and air pollution. Studies of these nitrogen sources have found less N exported by rivers than is expected from the amount of N added to the rivers by human activities. The N that does not enter rivers is either stored within the watersheds as soil or plant materials or converted to N gases by the microbial process of denitrification and lost to the atmosphere. The research supported by this award will involve development of new methods to improve measurements of gas fluxes from streams and soils to the atmosphere. Building on previous research, this project will apply new methods to assess denitrification in agricultural watersheds. Denitrification consumes nitrate, the main form of N exported from N-enriched watersheds, and produces dinitrogen (N2) and nitrous oxide (N2O) gases. The project will measure accumulations of N2 and N2O gases in groundwater and soils, and changes in the isotopic composition of nitrate that are indicative of denitrification. The study will identify locations within watersheds where denitrification is hypothesized to have high rates, primarily in damp areas such as stream buffers and wetlands. The NSF-funded project will collaborate with a USDA-funded project in assisting farmers to select better agricultural practices by supplying information on areas with high denitrification potential for capturing N lost from croplands. Knowing the fate of agricultural N will help improve the management of the Choptank River watershed and other basins. The research efforts will also include participation of local high school, undergraduate, and graduate students.