| In recent years, the Xiangjiang River and Dongting Lake water quality has beendeteriorating. Seting seven sampling cross sections in Xiangjiang River and Dongting Lake,taking nitrogen, phosphorus and organic pollutants as main objective, the water quality wasmeasured and evaluated monthly from Apr.2006 to Mar.2007, and the water quality variationwas analyzed. The following achievements were obtained:1. In the 36 times measurement of the Xiangjiang River water quality, 21 times wereinferior to theⅢlevel of water quality standard, accounting for 58.3% of the total. The times ofNemero index between 1.0～2.0, which was in lightly polluted water quality level, reached 10,accounting for 27.8% of the total. The indices exceeding the standard mostly were totalphosphorus (TP) and ammonia nitrogen (NH3-N).2. In the 12 times measurement of Aozhou (the upriver sampling cross section inXiangjiang River) water quality, the times inferior to theⅢlevel of water quality standard upto 6, accounting for 50% of the total 12. The times of Nemero index between 1.0～2.0, whichwas in lightly polluted water quality level, was 1, accounting for 8.3% of the total 12. In the 12times measurement of Qiaokou (the sampling cross section in middle reaches of XiangjiangRiver) water quality, the times inferior to theⅢlevel of water quality standard up to 8,accounting for 66.7% of the total 12. The times in lightly polluted water quality level were 7,accounting for 58.3% of the total 12. The times inferior to theⅢlevel of water quality standardof Lujiao,which was the sampling cross section in the lower reaches of Xiangjiang River, up to7, accounting for 58.3% of the 12 times measurement. The times in lightly polluted waterquality level were 4, accounting for 33.3% of 12 times measurement.3. In the 45 times measurement of the Dongting Lake water quality, 41 times were inferiorto theⅢlevel of water quality standard, accounting for 91.1% of the total; the times inferior totheⅤlevel of water quality standard reached 30, accounting for 66.7% of the total. The times ofNemero index between 1.0～2.0, which was in lightly polluted water quality level, reached 13,accounting for 28.9% of the total. The times of Nemero index higher than 2.0, which was in polluted water quality level, reached 23, accounting for 51.1% of the total. The indicesexceeding the standard mostly were total nitrogen (TN), total phosphorus (TP) and ammonianitrogen (NH3-N).4. There were 12 times measurement of Junshan sampling cross section in the EastDongting Lake, all of them were inferior to theⅢlevel of water quality standard, 9 times wereinferior to theⅤlevel of water quality standard, accounting for 75.0% of the total. The times ofNemero index between 1.0～2.0, which was in lightly polluted water quality level, were 3,accounting for 25.0% of the total 12. The times of Nemero index higher than 2.0, which was inpolluted water quality level, were 7, accounting for 58.3% of the total 12. The times inferior totheⅢlevel of water quality standard of Guihuayuan, which was the exit of Dongting Lake, upto 11; 7 times were inferior to theⅤlevel of water quality standard, accounting for 58.3% of 12times measurement. There were 2 times in lightly polluted water quality level and 6 times inpolluted water quality level, accounting for 16.7% and 50.0% of the total 12 separately. Therewere 11 times measurement of Wanzihu sampling cross section in the South Dongting Lake, thetimes inferior to theⅢlevel of water quality standard up to 10, and 8 times were inferior to theⅤlevel of water quality standard, accounting for 72.7% of the total 11. There were both 5 timesin lightly polluted water quality level and polluted water quality level, accounting for 45.5% ofall 11. There were 10 times measurement of Mupinhu sampling cross section in the WestDongting Lake, the times inferior to theⅢlevel of water quality standard up to 8, and 6 timeswere inferior to theⅤlevel of water quality standard, accounting for 60.0% of the total 10.There were 3 times in lightly polluted water quality level and 5 times in polluted water qualitylevel, accounting for 30.0% and 50.0% of the total 10 separately.5. The contribution of total phosphorus of the Xiangjiang River and Dongting Lake wasmainly due to particulate phosphorus cause. The main causes of nitrogen pollution wereprecipitation and agricultural activities. Surface runoff was the main channel of nitrogen andphosphorus entering the water in a certain degree. Agricultural Non-point source pollution wasone of the main sources of nitrogen and phosphorus pollutants of the Xiangjiang River andDongting Lake. The main channel of organic pollutants entering the water was surface runoff inDongting Lake. Along with organic pollutants into the water, salt entered the water, sonon-point source pollution was one of the important sources of organic pollutants. 6. The correlations of TN, dissolved oxygen (DO) and electric conductivity (EC) in allsections were the best; ammonia nitrogen (NH3-N) and redox potential (Eh) were the second.These showed that the nitrogen pollutants, dissolved oxygen and salinity had similarcharacteristics of accumulation and digestion. When the water quality of upriver reaches ofXiangjiang River was improved, the water quality of lower reaches of Xiangjiang River wouldbe improved; the water quality of Dongting Lake would be improved also in a certain degree.7. There was a same characteristic in Xiangjiang River and Dongting Lake pollutionindices' emporal variation. It was that the pollutants concentration would be significantlyincreased in the rainy and dry season. The spatial variation of pollution indices showed that thepollutants concentration in upriver of Xiangjiang River was generally lower than which inmiddle and lower reaches. The changes of the pollutants concentration in the East DongtingLake were bigger than which in the South and West Dongting Lake.
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