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Deterioration of urban waterways has become a major environmental concern as management and recreational goals are often hampered by poor water quality. The San Antonio River (TX, USA), whose upper reaches, including its headwaters, pass through a highly urbanized community, is vulnerable to pollution from a myriad of anthropogenic activities within its initial 17-km stretch. This investigation applied a dual-isotope approach to characterize water samples collected during the wet season (May–June, 2019) in order to assess the potential sources of nitrate in the urban stretch of river. The δ15N-NO3 and δ18O-NO3 values ranged from + 5.56 to + 10.89‰ and + 3.26 to + 5.90‰, respectively. The ranges of these values suggest that urban sewage and effluent coupled with denitrification were the major sources of nitrate being introduced into the San Antonio River. Biological assimilation and denitrification resulted in the consumption of residual NO3 downstream and caused a positive shift in the isotopic compositions of NO3. Furthermore, shifts in δ15N-NO3 by about + 2.0‰ between a zoo and downtown San Antonio indicated that sewage and urban wastes were major sources of nitrate in the San Antonio River.

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This is the author accepted manuscript version of the final publication:

Abongwa, P.T., Den, W. & Teague, A. Dual Isotopic (O & N) Approach in the Assessment of NO3 Pollution in an Urban River. Water Air Soil Pollut 233, 280 (2022).