Analysis of isotope tracing of domestic sewage sources in Taihu Lake—A case study of Meiliang Bay and Gonghu Bay

Due to the difficulty of quantifying the temporal and spatial variations of the sewage sources of Taihu Lake, this paper collected water samples from Gonghu Bay and Meiliang Bay, in the northeast of Taihu Lake and from the inflow river of Wangyu River from January to December in 2012 and applied stable isotope techniques to trace the sources of the nitrogen pollutants. At the same time, a two-end-member mixing model of isotopes was used to determine the sources of domestic sewage. According to the results of nitrogen isotope values in the sampling points, the annual proportion of the sewage sources of the Meiliang Bay, Gonghu Bay and Wangyu River is 17.2%, 15.3% and 19.7%, respectively. More than 80% of the nitrogen pollution sources are from non-domestic sewage, which indicates that domestic sewage is not the primary source of nitrogen pollution in Taihu Lake. In addition, these three regions have demonstrated higher ratios of sewage sources during the winter season than during other seasons. Therefore, domestic sewage that flows into Taihu Lake during the winter season should be strictly limited. In the meantime, it is necessary to strengthen the treatment of nitrogen sources other than domestic sewage sources.