We investigated the distribution of nitrogen compounds in Han River as well as two tributaries of Tancheon and Jungrangcheon. Particularly, we observed the significant releases of NH4 (+)-N from effluent of wastewater treatment plants (WWTPs) in two tributaries that has resulted in the increases of ammonium nitrogen (NH4 (+)-N) in Han River as well as in Tancheon and Jungrangcheon. Due to the increases of NH4 (+)-N in two tributaries, the larger distribution of δ(15)N-NH4 (+) was observed than those of δ(15)N-NO3 (-) in downstream. We calculated the contribution rate of ammonium nitrogen and nitrate nitrogen from effluent to downstream according to the results of stable isotope. The contribution rates of δ(15)N-NH4 (+) from effluent to downstream were significant that ranged between 53 and 100 % in Tancheon and between 27 and 100 % in Jungrangcheon. While the contribution of δ(15)N-NO3 (-) was not significant in Tancheon, it was occasionally observed in Jungrangcheon. These results demonstrated that WWTPs are the major sources of NH4 (+)-N in two tributaries, which caused the distinguishable stable isotope of δ(15)N-NH4 (+). Therefore, the stable isotope of δ(15)N-NH4 (+) could be a useful parameter or tracer for the evaluation of NH4-N released from WWTPs in rivers.
Keywords: Ammonium nitrogen; Nitrate nitrogen; Stable isotope; WWTPs.