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Wetland Flowpaths Mediate Nitrogen and Phosphorus Concentrations across the Upper Mississippi River Basin
Citation:
Mengistu, S., H. Golden, C. Lane, J. Christensen, M. Wine, E. DAmico, A. Prues, S. Leibowitz, J. Compton, M. Weber, AND Ryan A Hill. Wetland Flowpaths Mediate Nitrogen and Phosphorus Concentrations across the Upper Mississippi River Basin. JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION. American Water Resources Association, Middleburg, VA, 59(5):1162-1179, (2023). https://doi.org/10.1111/1752-1688.12885
Impact/Purpose:
An extended body of research confirms wetlands as beneficial for capturing non-point source nutrients from landscape sources (e.g., excess fertilizers, atmospheric deposition) and thus removing them from downstream flows. What remains uncertain is the influence of wetland characteristics in mediating water quality across watershed scales. We developed a large, novel set of spatial variables that characterize the hydrological flowpaths from wetlands to streams, i.e., “wetland hydrological transport variables,” to explore how wetlands affect downstream water quality. We first built multilinear regression models for total nitrogen (TN) and total phosphorus (TN) concentrations across a large river basin (Upper Mississippi River Basin [UMRB], US), to examine how traditionally used wetland variables (e.g., percent wetlands) assessed alongside other landscape variables (e.g., land cover) explain the variability in TN and TP concentrations. We then constructed statistical models with the newly developed wetland transport variables to interrogate the extent to which wetland flowpath characteristics mediate TN and TP across the UMRB. We found that wetland flowpath variables improved landscape-to-aquatic nutrient multilinear regression models (from R2=0.89 to 0.91 for TN; R2=0.53 to 0.84 for TP) and provided insights into potential processes governing how wetlands influence watershed-scale TN and TP concentrations. Specifically, flowpath variables describing flow-attenuating environments, e.g., subsurface transport compared to overland flowpaths, were related to lower TN and TP concentrations. Frequent hydrological connections from wetlands to streams were also statistically linked to low TP concentrations, which likely suggests a nutrient source - rather than hydrological transport - limitation in some areas of the UMRB. Consideration of wetland flowpaths could inform management and conservation activities designed to reduce nutrient export to downstream waters.
Description:
Eutrophication, harmful algal blooms, and human health impacts are critical environmental challenges resulting from excess nitrogen and phosphorus in surface waters. Yet we have limited information regarding how wetland characteristics mediate water quality across watershed scales. We developed a large, novel set of spatial variables characterizing hydrological flowpaths from wetlands to streams, that is, “wetland hydrological transport variables,” to explore how wetlands statistically explain the variability in total nitrogen (TN) and total phosphorus (TP) concentrations across the Upper Mississippi River Basin (UMRB) in the United States. We found that wetland flowpath variables improved landscape‐to‐aquatic nutrient multilinear regression models (from R2 = 0.89 to 0.91 for TN; R2 = 0.53 to 0.84 for TP) and provided insights into potential processes governing how wetlands influence watershed‐scale TN and TP concentrations. Specifically, flowpath variables describing flow‐attenuating environments, for example, subsurface transport compared to overland flowpaths, were related to lower TN and TP concentrations. Frequent hydrological connections from wetlands to streams were also linked to low TP concentrations, which likely suggests a nutrient source limitation in some areas of the UMRB. Consideration of wetland flowpaths could inform management and conservation activities designed to reduce nutrient export to downstream waters.
URLs/Downloads:
DOI: Wetland Flowpaths Mediate Nitrogen and Phosphorus Concentrations across the Upper Mississippi River Basin