[Impact analysis of Xi'an to the water quality of Weihe River].

Based on the water quality inspection results of Weihe River in the Xi'an section and the runoff at the watershed in different representative years, it was found through the pollution load calculated from the mean concentration method that Weihe River's main stream was dominated by point source pollution and non-point source pollution was more serious in tributaries. The input amount of pollutant to Weihe River' main stream from Xi'an which is located within the Xianyang and Lintong section was calculated from the material balance algorithm based on the pollutant concentrations measured in 2009 and 2011. The percentage of the pollution load of Xi'an area on Lower reaches' monitoring section of Lintong was analysed and the impact of Xi'an area on the water quality of Weihe River was quantified. The computational results showed that the upstream of the Xianyang section was the main source of the pollution load of the Lintong section in Weihe River, followed by Xi'an area. More than 40% of TN, COD and NH4+ -N of the Lintong section came from the upstream of the Xianyang section and more than 30% came from Xi'an area, in addition, 53% of TP came from Xi'an area. The non-point source pollution in Xi'an was more serious than in its upstream and downstream areas while point source pollution load accounted for 63% of the total.