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

世界各地的湖泊、河口和沿海海水都因过度富集植物营养物质而退化，如氮(N)，导致藻华，并最终耗尽溶解氧。农业径流、污水排放和空气污染增加了向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向河流添加的氮量所预期的要少。没有进入河流的氮要么作为土壤或植物材料储存在流域内，要么通过微生物反硝化过程转化为氮气体，然后损失到大气中。该奖项支持的研究将涉及开发新方法，以改进从溪流和土壤到大气的气体通量的测量。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，这是从富氮流域输出的氮的主要形式，并产生二氮（N2）和氧化亚氮（N2O）气体。该项目将测量地下水和土壤中N2和N2O气体的积累，以及表明反硝化作用的硝酸盐同位素组成的变化。该研究将确定流域内反硝化速率较高的地点，主要是在河流缓冲带和湿地等潮湿地区。美国国家科学基金会资助的项目将与美国农业部资助的项目合作，通过提供有关具有高反硝化潜力的地区的信息，帮助农民选择更好的农业实践，以捕获农田损失的氮。了解农业氮素的命运将有助于改善Choptank河流域和其他流域的管理。研究工作还将包括当地高中生、本科生和研究生的参与。

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.