Reactive Transport of Nitrogen in Lowland Agricultural Watersheds
While intensively managed watersheds are known to retain a high percentage of net N inputs (e.g., >70%), accurately quantifying the sources, fates, and transport of reactive nitrogen in heterogeneous watershed systems continues to be a conundrum due to the nonlinear interactions between hydrological and biogeochemical processes at the watershed scale. In the intensively tile-drained Upper Embarras River watershed, east-central Illinois, we are combining StorAge Selection (SAS) functions, water and nitrate isotope analyses, and continuous nitrate sensing to examine the transport and transformation of nitrogen under variable hydrological regimes. This combination of novel analytical and modeling tools will allow for better characterization of flow generation pathways and elucidate how nitrogen cycling and export are controlled by watershed functions and climate variability across different scales. The results from this research show that time-variant water age is a concise description of watershed hydrological transport, highlighting the dominant controls of a shallow groundwater table and subsurface tile drains on flow generation in this lowland watershed. Combining water age modeling with isotope analysis revealed coherent variations between discharge, water age, and nitrate isotopic imprints, which offer a novel lens through which to examine flow paths variations and their interactions with subsurface nitrate storage and reactivity. We are currently extending the SAS approach by coupling it with biogeochemical and isotopic modeling to quantify nitrogen cycling rates and source/sink strengths at the watershed scale. |
Flow through pipe hosting a in-stream nitrate sensor in Upper Embarras River at Camargo, Illinois
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