Variation of surface water quality based on crop-livestock structure change and its pollution assessment in Sichuan Hilly Area

Abstract: In order to analyze the influence of crop-livestock structure to the seasonal change and spatial variation characteristics of surface water in Sichuan Hilly Area, the water quality indexes including CODC r,TN, NO3--N, NH4+-N and TP were investigated from March 2013 to February 2015 in Zhongjiang county of Sichuan province, based on seven monitoring sections in Xiangtan river and four research points in Zhenggouwan small watershed, and the water quality pollution status was also evaluated by using single factor evaluation method and the comprehensive pollution index method. The outcomes showed that in low flow period, CODcr, NH4+-N and TP were major pollutants of surface water in seven monitoring sections in Xiangtan river, and their concentrations were 15.67% ,59.35% and 12.83% higher than that of the annual average value respectively. In high water period, the major pollutant was TN, and its concentration value increased by 19.27 % comparing with that of the annual average value. The concentrations of TN, NO3--N, NH4+-N and TP of surface water in different areas followed the order that Livestock Farms > Planting Regions & Livestock Farm > Planting Regions in Xiangtan river, and Large-scale pig farming's waste emissions was the root cause of surface water pollution in Planting Regions & Livestock Farm area, and the CODcr, TN, NO3--N, NH4+-N and TP concentrations of surface water in this area increased by 17.79%, 198.15%, 132.10%, 219.85%, 567.57% respectively, comparing with that of Planting Regions. Both the Large scale pig farming in Xiangtan river and below designated size pig farming in Zhenggouwan small watershed significantly increased the total surface water pollution index, it also changed the type of surface water pollution, and in Planting Regions, the surface water pollution type was TN - CODcr pollution, but that was TN - TP pollution in both of Livestock Farms and Planting Regions & Livestock Farm area. According to the results of single factor evaluation method, the surface water pollution was serious in seven monitoring sections in Xiangtan river and four research points in Zhenggouwan small watershed, and their water quality all reached inferior V class water quality standard, on the basis of "surface water environment quality standard (GB 3838-2002)". The crop-livestock structure also changed the degree of surface water pollution, and the Nemerow Pollution Indexes of surface water in Planting Regions in both Xiangtan river and Zhenggouwan small watershed were 2.95and 2.89, but that were 8.93 and 5.56 in Planting Regions & Livestock Farm respectively, so centralized Pig breeding particularly large scale pig farming's waste emissions exacerbated degree of surface water pollution to its downstream receiving waters. From the perspective of water pollution control, it is essential to launch control of water loss ,soil erosion and soil nutrient loss, especially nitrogen loss in Planting Regions in Sichuan Hilly Area, at the same time, urgently need to strengthen technology research about harmless treatments and resource recycling utilization of livestock residues, to promote the healthy development of Sichuan hilly area and ensure ecological environment of the upper reaches of the Yangtze river.