Nitrogen in Residential Stormwater Runoff.

Nitrogen in Residential Stormwater Runoff Jariani Jani a, Gurpal S. Toor b,* a Soil and Water Quality Laboratory, Gulf Coast Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, 14625 CR 672, Wimauma, FL 33598, USA b Department of Environmental Science and Technology, University of Maryland, College Park, MD 20742, USA Nitrogen (N) input from residential stormwater runoff has been recognised causing nutrient enrichment in coastal water which leads to eutrophication. Our study objectives were to investigate composition, loading, and sources of N in residential stormwater runoff that travels into stormwater retention pond. Runoff water samples (n=220) were collected during wet season (May to September 2016) from an inlet of stormwater wet pond that has been installed with autosampler. Samples were analyzed for various N forms [ammonium (NH3–N), nitrate (NO3–N), dissolved organic nitrogen (DON), and particulate organic nitrogen (PON)]. A total of 26 storm events were captured during the wet season. Total rainfall recorded in 26 events were 40 cm or 38% of total rainfall throughout the study period (105.5 cm). Total flow over wet season was 21.54 million L and total flow of stormwater runoff throughout the 26 storm events was 6.68 million L and carried 14.9 kg of TN with DON as the dominant form (72%). Out of the 26 events, 4 major events was recorded loading a total of 11.4 kg of TN which accounted 78% of total TN loads in the whole wet season. Organic N forms were dominant at 18 events as compared to inorganic N forms (8 events). Stable isotope data (?15N and ?18O) showed that NO3-N originated from mixing of multiple sources [atmospheric deposition (mean: 41%), NH4 fertilizers (mean: 13.4%), NO3 fertilizer (mean: 33.2%), nitrification (mean: 7.8%), and soil and organic N sources (mean: 4.5%)]. This result showed that organic N forms are the major contributor of N in urban runoff and inorganic fertilizer contributed only 47% runoff of NO3-N which are less than 10% of total N suggesting that policy should consider management of all N forms to ensure the effectiveness of the stormwater best management practice (BMP).