Sources and mechanisms of nitrate and orthophosphate transport in urban stormwater runoff from residential catchments

Abstract

Nutrients export from residential catchments contributes to water quality impairment in urban water bodies. We investigated the concentrations, transport mechanisms, and sources of nitrate-nitrogen (NO₃-N) and orthophosphate-phosphorus (PO₄-P) in urban stormwater runoff generated in residential catchments in Tampa Bay, Florida, United States. Street runoff samples, collected over 21 storm events, were supplemented with rainfall and roof runoff samples from six representative residential catchments. Samples were analyzed for N and P forms, N and oxygen (O) isotopes of nitrate (δ¹⁸O-NO₃^- and δ¹⁵N-NO₃^-), and δ¹⁸O and hydrogen (δD) isotopes of water (H₂O). We found that the main NO₃-N source in street runoff was atmospheric deposition (range: 35-64%), followed by chemical N fertilizers (range: 1-39%), and soil and organic N (range: 7-33%), whereas PO₄-P in the street runoff likely originated from erosion of soil particles and mineralization from organic materials (leaves, grass clippings). The variability in the sources and concentrations of NO₃-N and PO₄-P across catchments is attributed to different development designs and patterns, use of various fill materials during land development, and landscaping practices. This data can be useful to develop strategies to offset the impacts of urban development (e.g., designs and patterns resulting in variable impervious areas) and management (e.g., fertilizer use, landscaping practices) on NO₃-N and PO₄-P transport in urban residential catchments.

Keywords: Nitrate; Orthophosphate; Residential catchments; Stable isotopes; Urban stormwater runoff.