title: Contrasting nitrogen and phosphorus budgets in urban watersheds and implications for managing urban water pollution.
abstract: Managing excess nutrients remains a major obstacle to improving ecosystem service benefits of urban waters. To inform more ecologically based landscape nutrient management, we compared watershed inputs, outputs, and retention for nitrogen (N) and phosphorus (P) in seven subwatersheds of the Mississippi River in St. Paul, Minnesota. Lawn fertilizer and pet waste dominated N and P inputs, respectively, underscoring the importance of household actions in influencing urban watershed nutrient budgets. Watersheds retained only 22% of net P inputs versus 80% of net N inputs (watershed area-weighted averages, where net inputs equal inputs minus biomass removal) despite relatively low P inputs. In contrast to many nonurban watersheds that exhibit high P retention, these urban watersheds have high street density that enhanced transport of P-rich materials from landscapes to stormwater. High P exports in storm drainage networks and yard waste resulted in net P losses in some watersheds. Comparisons of the N/P stoichiometry of net inputs versus storm drain exports implicated denitrification or leaching to groundwater as a likely fate for retained N. Thus, these urban watersheds exported high quantities of N and P, but via contrasting pathways: P was exported primarily via stormwater runoff, contributing to surface water degradation, whereas N losses additionally contribute to groundwater pollution. Consequently, N management and P management require different strategies, with N management focusing on reducing watershed inputs and P management also focusing on reducing P movement from vegetated landscapes to streets and storm drains.
authors.affiliation: Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108; shobbie@umn.edu.
authors.forename: Sarah E
authors.identifier: 0000-0001-5159-031X
authors.initials: SE
authors.lastname: Hobbie
authors.affiliation: Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108.
authors.forename: Jacques C
authors.identifier: 0000-0002-7968-7030
authors.initials: JC
authors.lastname: Finlay
authors.affiliation: Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Janke
authors.affiliation: Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Nidzgorski
authors.affiliation: Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN 55108.
authors.forename: Dylan B
authors.initials: DB
authors.lastname: Millet
authors.affiliation: Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, MN 55108.
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Baker
mesh_terms: D017753:Ecosystem; D004784:Environmental Monitoring; D060587:Groundwater; D009584:Nitrogen / Q000032:analysis / Q000737:chemistry*; D010758:Phosphorus / Q000032:analysis / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D014876:Water Pollution
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus; D009584:Nitrogen
keywords: eutrophication; nitrogen; phosphorus; stormwater; urban watershed