WATER POLLUTION CHARACTERISTICS AND NITROGEN SOURCE APPOINTMENT OF THE MAOBANQIAO RESERVOIR ON THE MAINSTREAM OF THE LONGCHUAN RIVER CHINA

The situation of water pollution in the Maobanqiao Reservoir is not optimistic, and the cause of pollution is not clear. In order to identify the present situation of water environment and pollution sources of the Maobanqiao Reservoir, combined with historical data collection and on-site investigation, this study analyzed the main over-standard factors of the water body. The contribution of different pollution sources to nitrate were quantitatively calculated through the analysis of nitrate-nitrogen and oxygen isotope (delta N-15-NO3- and delta O-18-NO3-). The results show that the ratio up to the standard of water quality was 60.5% in Maobanqiao Reservoir national control section, based on class III standard of the National Surface Water Environmental Quality Standards (GB3838-2002) in China, while the main over-standard factors of water quality were TP, BOD5, and COD. With the on-site investigation in July 2019, the TN concentrations fluctuated between 0.91 and 1.96mg/L, with an average value of 1.29mg/L, and the nitrogen pollution was relatively serious. With IsoSource model analysis, the nitrate in the Maobanqiao Reservoir mainly comes from soil nitrogen (68%), followed by chemical fertilizer (18%) and domestic sewage (14%). Therefore, the agricultural planting and domestic sewage input by non-point source pollution should be controlled in the upper reaches of the Longchuan River to effectively reduce the pollution load of pollutants into the Maobanqiao Reservoir.