Organic nitrogen in residential stormwater runoff: Implications for stormwater management in urban watersheds

Mary G Lusk; Gurpal S Toor; Patrick W Inglett

doi:10.1016/j.scitotenv.2019.135962

Organic nitrogen in residential stormwater runoff: Implications for stormwater management in urban watersheds

Sci Total Environ. 2020 Mar 10:707:135962. doi: 10.1016/j.scitotenv.2019.135962. Epub 2019 Dec 7.

Authors

Mary G Lusk¹, Gurpal S Toor², Patrick W Inglett³

Affiliations

¹ University of Florida/Institute of Food and Agricultural Sciences, Gulf Coast Research and Education Center, Soil and Water Sciences Department, 14625 CR 672, Wimauma, FL 33598, United States. Electronic address: mary.lusk@ufl.edu.
² Department of Environmental Science and Technology, University of Maryland, College Park, MD 20742, United States.
³ University of Florida, Soil and Water Sciences Department, Wetland Biogeochemistry Laboratory, Gainesville, FL, United States.

PMID: 31863977
DOI: 10.1016/j.scitotenv.2019.135962

Abstract

Stormwater runoff containing organic nitrogen (N) is a source of potentially bioavailable N in water bodies. Characterization and concentrations of dissolved organic N (DON) and particulate organic N (PON) in urban stormwater runoff are rarely reported and considered in stormwater management. Our objectives were to (1) characterize the organic (DON, PON) and inorganic (NO₃^- and NH₄⁺) N pools in residential stormwater runoff and (2) determine the rainfall driven landscape sources of runoff PON using an isotopic mixing model with ¹³C and ¹⁵N during a wet season (June-September). We instrumented a 13 ha (0.13 km²) residential catchment located in Florida, United States with an ISCO autosampler and collected stormwater runoff samples (n = 52) over 11 individual stormwater runoff events. Mean concentration of total N in runoff during the wet season was 1.61 mg L^-1, of which 37% was DON and 25% was PON. A strong seasonal first flush of PON, giving rise to a large PON:TN ratio, was observed as the wet season progressed from June (PON:TN = 0.39;) to September (PON:TN = 0.12), whereas DON did not display any seasonal variability (mean: 0.66 mg L^-1). The isotope mixing model estimated that 76% of PON in the runoff originated from oak detritus (leaves: 50%, acorns: 26%) and the remaining 24% from lawn grass clippings. The dominance of organic N fractions in the urban stormwater runoff suggests that landscape controls on PON and DON are needed to reduce N loading in the urban stormwater runoff. The seasonal first flush of PON indicates that monitoring strategies should focus on how nutrient concentrations in runoff may respond to seasonal drivers such as leaf litterfall and that there may be optimal times for N management, such as after a prolonged dry season in which materials accumulate and pose the risk for later mobilization.

Keywords: Dissolved organic nitrogen; Grass clippings; Leaf litter; Particulate organic nitrogen; Residential stormwater runoff; Urban watersheds.