Stable isotope on the evaluation of water quality in the presence of WWTPs in rivers.

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.