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

该奖项由2009年《美国复苏和再投资法案》(公法111-5)资助。世界各地的湖泊、河口和沿海海域由于过度富含氮(N)等植物营养物质而退化，这些营养物质会导致藻类水华，并最终耗尽溶解氧。农业径流、污水排放和空气污染增加了对水生生态系统的氮出口。对这些氮源的研究发现，河流输出的氮比人类活动增加到河流中的氮量预期的要少。没有进入河流的N要么作为土壤或植物材料储存在流域内，要么通过反硝化的微生物过程转化为N气体并流失到大气中。更好地了解氮在生态系统中的去向将有助于管理氮污染，但从来没有在整个流域内充分衡量氮的储存和反硝化作用。在以往研究的基础上，该项目将应用新的方法来评估农业流域的反硝化作用。反硝化作用消耗硝酸盐，硝酸盐是富氮流域输出的氮的主要形式，并产生氮素(N2)和一氧化二氮(N2O)气体。该项目将测量地下水和土壤中氮气和N2O气体的累积，以及指示反硝化作用的硝酸盐同位素组成的变化。这项研究将确定流域内假设反硝化率较高的地点，主要是在河流缓冲区和湿地等潮湿地区。NSF资助的项目将与美国农业部资助的一个项目合作，通过提供有关具有高反硝化潜力的地区的信息来帮助农民选择更好的农业措施，以捕获农田中流失的氮。了解农业氮素的命运将有助于改善对乔普坦克河流域和其他流域的管理。研究工作还将包括当地高中、本科生和研究生的参与。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).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 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. A better understanding of the fate of N in ecosystems would help manage N pollution, but N storage and denitrification have never been adequately measured within an entire watershed. 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.