Increased nitrogen (N) from urban stormwater runoff aggravates the deterioration of aquatic ecosystems as urbanisation develops. The sources and transport of nitrate (NO3-) in urban stormwater runoff were investigated by analysing different forms of N, water isotopes (δD-H2O and δ18O-H2O), and NO3- isotopes (δ15N-NO3- and δ18O-NO3-) in urban stormwater runoff in a residential area in Hangzhou, China. The results showed that the concentrations of total N and nitrate N in road runoff were higher than those in roof runoff. Moreover, high concentrations of dissolved organic N and particulate N led to high total nitrogen (TN) concentrations in road runoff (mean: 3.76 mg/L). The high δ18O-NO3- values (mean: + 60 ± 13.1‰) indicated that atmospheric deposition was the predominant NO3- source in roof runoff, as confirmed by the Bayesian isotope mixing model (SIAR model), contributing 84-98% to NO3-. Atmospheric deposition (34-92%) and chemical fertilisers (6.2-54%) were the main NO3- sources for the road runoff. The proportional contributions from soil and organic N were small in the road runoff and roof runoff. For the initial period, the NO3- contributions from atmospheric deposition and chemical fertilisers were higher and lower, respectively, than those in the middle and late periods in road runoff during storm events 3 and 4, while an opposite trend of road runoff in storm event 7 highlighted the influence of short antecedent dry weather period. Reducing impervious areas and more effective management of fertiliser application in urban green land areas were essential to minimize the presence of N in urban aquatic ecosystems.
Keywords: Nitrogen; Road runoff; Roof runoff; SIAR model; Stable isotopes; Urban Residential area.
© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.