Comparative analysis of nitrogen concentrations and sources within a coastal urban bayou watershed: A multi-tracer approach

Fate and transport of nitrogen (N) in urban coastal watersheds continues to draw research interest due to serious impacts of N pollution and complexities with N sources and transport pathways. In this study, we used multiple tracers for source identification of N pollution (N-15 isotope in nitrate and chemical sewage tracers in water) and waters (using isotopes of O-18 and H-2 in water) in a coastal northwest Florida U.S.A. urban bayou fed by two contrasting streams, namely Jackson Creek traversing a dense residential area and Jones Creek flowing mainly through a wetland preserve. Results showed that the slightly higher delta N-15-NO3- values in Jones Creek and the bayou were insufficient to distinguish N sources; yet the different chemical sewage tracer concentrations (e.g., sucralose, carbamazepine and sulfamethoxazole) clearly demonstrated the major N source from leaking septic tanks in the Jackson Creek sub-basin but not in the Jones Creek sub-basin. The higher concentrations of nitrate, which constituted over 98% of dissolved inorganic N in Jackson Creek, support active nitrification in sandy soils and steep terrain while higher delta N-15-NO3- and much lower nitrate in Jones Creek are likely associated with denitrification in dense vegetative wetland and riparian zones. Episodic high nitrate concentrations and delta O-18 values in Jackson Creek preceded by periods of little rainfall indicated that the creek was sustained by subsurface flow with a steady input of nitrate. This study demonstrated the connection of land use and stormwater runoff generation to the forms of N entering urban waterways, the utility of N sourcing approaches, and the value of watershed-scale assessments for developing strategies to limit N loadings in urban settings. Published by Elsevier B.V.

Automated summary

This study in urban coastal watersheds of northwest Florida, USA, demonstrated the influence of land use and stormwater runoff on nitrogen sources and transport in urban waterways. The study highlighted the importance of nitrogen sourcing approaches in understanding nitrogen pollution in urban settings.