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Urbanization has negative environmental impacts, including increasing the export of eutrophying pollutants, such as nitrogen, that reach downstream water bodies. In response, efforts are underway to use “green” stormwater infrastructure (GSI) that enhances infiltration of stormwater and increases retention and removal of pollutants. However, the effectiveness of GSI regarding nitrogen is questionable: there is evidence that some GSI provides no more nitrogen (or sometimes, less) retention than traditional stormwater management. The reason for this apparent limitation of GSI is uncertain and is the focus of the proposed research. We hypothesize that there is a tradeoff between hydrological and biogeochemical processes that allows GSI to effectively reduce concentrations and loads of nitrate from atmospheric deposition, as well as particulate nitrogen, while increasing loads of terrestrial nitrate with little reduction in total nitrogen loads. Alternatively, if GSI functions as designed, there is the potential for removal of nitrate via denitrification, which may cause GSI to reduce export of both atmospheric and terrestrial nitrate resulting in declines in total nitrogen. We propose to address this issue by assessing the controls of streamwater nitrogen export from a pair of gaged watersheds in Ellicott City, Maryland. One watershed was developed using traditional stormwater management, whereas the other is presently being developed using GSI. We plan to analyze nitrogen and oxygen stable isotopes of nitrate on newly-collected and archived surface water (and rainfall) samples collected from these watersheds to investigate the influence of hydrology and biogeochemistry on export of atmospheric and terrestrial nitrate, as well as particulate nitrogen and total nitrogen. Insights gained through the proposed comparative analysis regarding the effectiveness of GSI at processing and reducing nitrogen loads from different sources will support county, state and federal efforts to control water pollution and, ultimately, contribute to restoration of the Chesapeake Bay.