Transport and sources of nitrogen in stormwater runoff at the urban catchment scale

Revealing the transport and sources of nitrate in urban stormwater runoff can effectively manage nitrate pollution in urban areas. This study used the chemical properties of stormwater along with delta N-15-NO3- and delta O-18-NO3- isotopes to identify the transport and sources of nitrate within an urban catchment. The results showed that the NO3-N concentration and total dissolved nitrogen (TDN) composition differed among roof runoff, road runoff, and drainage runoff. The highest NO3-N concentration was found in roof runoff and NH3-N dominated the TDN composition. However, the erosion of pervious surfaces and litter may have led to higher DON/TDN values in road runoff. The TDN composition of drainage runoff was consistent with that of roof runoff. Furthermore, among the various rainfall characteristics, the depth and intensity of rainfall were significantly correlated with the NO3-N concentrations in roof runoff and road runoff, while antecedent dry days had little effect. According to a Bayesian mixing model, the average contributions of the nitrate load in drainage runoff were ranked as road runoff (51.6%) > rainwater (292%) > and roof runoff (15%), which is consistent with the results of previous studies. Rainwater nitrate may have ranked second due to the confluence time, pollution level, and other factors that made rainwater reduce the pollution characteristics of roof runoff. The dominant contribution of road runoff to the NO3-N concentration of drainage runoff could be attributed to the large runoff volume. Hence, effective measures should be taken to minimize the NO3-N concentration in roof runoff, while runoff volume reduction should be the primary concern for controlling road runoff pollution. This work is helpful for obtaining a better understanding of the transport and sources of nitrate that vary dynamically within different hydrological flow pathways, and the outcomes are expected to enhance targeted measures to mitigate nitrate pollution in urban water systems. (C) 2021 Elsevier B.V. All rights reserved.