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Single factor water quality identification index (SFWQII) and Comprehensive water quality identification index (CWQII) were applied to the data of 6 parameters for water quality of West Lake at 10 different sites and 4 main inflows in the West Lake basin, generated during March 2012 to February 2013. This study evaluated and elucidated the temporal and spatial variation of each parameter on water quality and the main pollution factor of West Lake by SFQII. CWQII based on the SFQII was applied to evaluate the eutrophication level of West Lake and substantiated mesotrophic waters. Stable isotopes of nitrate were used to identify the nitrate sources of West Lake. The δ15NNO3 values in samples from the West Lake and inflows had a range of 2.6‰ to 12.0‰, while the δ15NNO3 values in Qiantang River was 5.3‰, in rainfall was 5.2‰ and in runoff was 3.6‰, respectively. Animal wastes, commercial fertilizer and domestic sewage were the main nitrate sources. The groundwater and denitrification might increase the levels of NO3- in West Lake.

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