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How Landscape Source, Sink, and Transport Interactions Mediate Nitrogen and Phosphorus Across a Large River Basin
Citation:
Golden, H., C. Lane, S. Leibowitz, J. Christensen, J. Compton, E. D'Amico, A. Prues, M. Weber, AND R. Hill. How Landscape Source, Sink, and Transport Interactions Mediate Nitrogen and Phosphorus Across a Large River Basin. 2018 AGU Fall Meeting, Washington, DC, December 09 - 14, 2018.
Impact/Purpose:
Current information is limited on how to detect watershed status for nutrient challenges.Statistical watershed models that include water storage and transport improve our ability to manage the surface water quality and quantity for swimmable, fishable, and drinkable goals. Attainment of these end goals important to EPA’s mission of protecting human health and the environment. Outputs from this research will allow states, tribes, and regions to make informed water quality and quantity decisions in watersheds with eutrophication issues.
Description:
A watershed’s hydrologic landscape can, in part, be conceptualized as a series of storage nodes (e.g., wetlands, floodplains) and edges (e.g., flowpaths). These nodes and edges interact to influence nutrient transport to aquatic systems – and these interactions can be site specific, scale dependent, and/or nutrient specific. At present, there is a limited understanding of how these edges and nodes interact with sources to affect stream nutrient loadings at regional scales, which is important for managing drinking water sources, harmful algal blooms, and water quality in general. Specifically, there is a need to understand how such edges, i.e., hydrological transport metrics, mediate water quality across a range of land use and environmental gradients at regional scales. This study therefore examines the role of node (here, surface depression and wetland) related landscape metrics in mediating nitrogen and phosphorus dynamics in streams across the 490,000 km2 Upper Mississippi River Basin (UMRB). An initial 13-yr dataset from nearly 88 and 122 federal, state, and local gages throughout the UMRB with total nitrogen (TN) and total phosphorus (TP) records, respectively, were obtained and summarized for seasonal and annual analyses. Nationally available high resolution spatial datasets were used to delineate the UMRB sub-watersheds draining to the selected gages and build new datasets to help explain surficial hydrologic transport. We calculated spatial predictors describing surface depression attributes and other landscape characteristics using a crop data layer, point-source data, and ancillary nationally available datasets. Preliminary findings suggest that nutrient source, node, and edge interactions play a role in TN and TP concentrations across this large river basin. Specifically, we found that cultivated areas are a major source of elevated TN, while point sources from developed landscapes were the major source of TP concentration in streams across the UMRB watersheds. Preliminary analyses also revealed statistically significant indirect linear relationships between surface depressions (nodes) and aquatic TN and TP concentrations. Furthermore, the increase in the slope of the relationship between surface depressions and nutrient concentrations for watersheds with a higher proportion of cultivated area suggests the contribution of these systems in mediating the effects of agriculture on in-stream nutrient concentration. Our analysis will further explore the specific effects of edges (transport) on TN and TP concentrations. The outcomes of the study will bring improved understanding of the interactive role source, sink, and transport on aquatic nutrient concentrations across the regionally diverse UMRB.
