INFEWS N/P/H20: Nitrogen and Phosphorus Dynamics in Restored Floodplains of Intensively Managed Watersheds

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1706612 (McMillan). Excess nitrogen and phosphorus in receiving waters (streams, rivers, lakes, etc.) is associated with high nutrient inputs (e.g., fertilizer, food and animal waste, sewage overflows) in watersheds that are unsustainably and intensively managed for agriculture and urban uses. Sustainably restoring floodplains shows great promise to improve water quality and multiple ecosystem (e.g., floodplain soils) services, however a clear understanding and quantification of the cumulative effects of inundation on nitrogen and phosphorus dynamics is critically needed. Therefore, the goal of this research is to determine the functional relationships that exist between sources and sinks of nutrients (e.g., denitrification, phosphorus release) and natural system drivers (e.g., hydrodynamic and biogeochemical). To achieve this goal, this project seeks to (1) quantify how hydrologic connectivity varies across spatial and temporal scales in a river floodplain system, (2) characterize the relative role of hydrodynamic versus biogeochemical processes on the rates of nitrogen and phosphorus inputs, removal and release in floodplain soils, and (3) determine the cumulative effect on the retention or release of nitrogen and phosphorus at the river-floodplain system scale. The research will consist of three major components to link physical and biogeochemical controls of nitrogen and phosphorus dynamics in restored riverine floodplains. The first component will apply a 2-dimensional model of the Wabash-Tippecanoe River confluence to predict the time and lateral extent of inundation as well as magnitude and direction of surface velocity and groundwater flow to quantify hydraulic residence time and lateral water flux. The second component will quantify key processes responsible for nutrient flux in the floodplain system, including nitrogen removal via denitrification, phosphorus uptake/release, and the soil properties that could help predict these processes. Nitrogen and phosphorus response variables and potential predictors variables will be linked in the third component to identify the controls on processes using a multivariate statistical approach. A systems analysis approach will be used to apply these relationships to aggregate fluxes at the monthly scale and determine net floodplain function (e.g., source/sink behavior). Through this research, critical information will be provided that is needed to sustainably restore floodplain ecosystems that maximize water quality improvements for both nitrogen and phosphorus. Impacts of this research are potentially far-reaching as communities and regulatory agencies invest in mitigation projects to reduce nutrient loads to downstream lakes and coastal zones where eutrophication impacts are occurring.