Water quality evaluation in Qingyang city by GIS

Based on the survey data of water pollutant contents in 2006, the present paper gives the results of comprehensive evaluation in the form of pollution index, and the distribution map of water quality in Qingyang, through spatial analysis of GIS. The main pollutants in the rivers determined are COD, chloride, petroleum, sulfide, total hardness, ammonia nitrogen, nitrate nitrogen and total phosphorus. The results are as follows: COD, sulfide, and petroleum were the pollutants which polluted the rivers more heavily. The seriously-polluted area was distributed in the reaches between Huancheng Town in Huanxian County and the urban area of Ningxian County, which took up 4.8% of the gross area. The heavily-polluted area was mainly in the lower reaches of the Malian River, the section below the urban area of Ningxian County, and occupied 0.3% of the studied region. The moderately polluted area located in the oil production areas in Huanxian County, Qingcheng County, Huachi County and Heshui County, taking up 18.4% of the studied region. The slightly-polluted area included Yanwu in Huanxian County, Xinji and Tunzi in Zhenyuan County,Taibai and Pangu in Heshui County, Nanyi in Ningxian County and towns around the southwest of Qingyang, and accounting for 10% of the region. The unpolluted area took up 66.4% of the studied region.