Temporal and spatial variation of main pollutants in Baihexi River,the western inflow river of Erhai Lake

To explore the impacts of the inflow rivers on the water quality of Erhai Lake, a continuous survey of water quality for the Baihexi River, the inflow river of west Erhai Lake, was carried out from September 2013 to August 2014. The spatial and temporal variations of the pollutant concentrations and sources were studied, the pollutant loads into the lake estimated, and their main sources analyzed. The results indicated that the water quality of the upstream and the midstream of the Baihexi River were relatively good, with an average of Grade Ⅲ (Environmental Quality Standards for Surface Water (GB 3838-2002)); followed by the estuary and downstream regions, which were in Grade Ⅳ. The COD_Mn ((5.10±1.38)mg/L) and concentration of N {\mathrm{H}}_4^{+} -N ((0.87±0.76)mg/L) in Baihexi River was relatively low, while the concentration of TN ((2.81±1.24)mg/L) and TP ((0.26±0.12)mg/L) was high, TN and TP are the main indicators of water pollution. The main pollutant loads were the highest during July to October, accounting for about 70% of the total annual pollutant loads, followed by December to February, accounting for 18% or so, and the pollutant loads were relatively low in other months. The COD_Mn and N {\mathrm{O}}_3^{-} -N concentrations in the wet season were obviously higher than those in the dry season (P<0.05), while the concentrations of N {\mathrm{H}}_4^{+} -N, TN and TP in the wet season had no significant difference with those in the dry season. These indicated that COD_Mn and N {\mathrm{O}}_3^{-} -N mainly derived from non-point sources, while N {\mathrm{H}}_4^{+} -N, TN and TP were affected by both point sources and non-point sources.