Water Quality Assessment Of Three Gorges Reservior Mainstream Based On Different Analysis

In order to effectively protect the water environment, control the water pollution, firstly, the water quality evaluation of water body is needed to carry on. Water quality evaluation can determine the level of water quality of water unit, assess the pollution extent and clarify the change law of water quality, so as to provide scientific and rational basis for the water environment function zoning, water pollution control, as well as the planning and management of water environment. In this paper, based in the water quality monitoring data in2008-2012of the eight monitoring sections in the main stream of Three Gorges Reservoir, the principal component analysis method, single factor evaluation method and cluster analysis method were used to analyze the water pollution characteristics of the Three Gorges Reservoir from the time and space. Through the water quality evaluation, we can judge the water pollution trends with time of the Three Gorges Reservoir accurately, and obtain the pollution changes of the water with the water flow direction in the reservoir, as well as obtain the water quality variations characteristics under different water level in space through the difference among the water level change within a year in the Three Gorges Reservoir. The results of the evaluation, which are of a great practical significance, can provide basic guidelines for the prevention and control of water pollution and water environmental management.In the introduction, a variety of existing and used more water quality evaluation methods were described, also the pros and cons of the different water quality evaluation methods were analyzed. Compared with different methods, and combined the actual situation of own research, ultimately, the research program was determined with the principal component analysis, single factor analysis, cluster analysis as the main research means. The basic conclusions of the paper are as follows:(1) Single factor evaluation method was used in the section of the Yangtze River of2008-2012. The results shown that all water quality categories were V water, which was due to the total nitrogen and total phosphorus in all sections are in a excessive state. In addition to the total nitrogen and total phosphorus, single factor evaluation was applied to the reservoir, the results shown that the annual average water quality compliance rate in the important section of the Yangtze River in Reservoir was62.5%. The water quality of the Cuntan, Changshou, Qingxichang sections from2008to2012were lower than Ⅲ criteria, and the exceeding factor was fecal coliforms, which can illustrated that sanitary sewage had serious influence on the water pollution in the Three Gorges Reservoir upstream.In the period of2008-2012, the total nitrogen content level of all sections in the Yangtze River is belong to V class, and the content is in the range of1.5mg/L-2.0mg/L. For total phosphorus, the phosphorus pollution of the Qingxichang section within2008-2012is more serious than the other sections, and the total phosphorus concentrations is of the decreasing trend from upstream to downstream. The Guandukou Padang, Miaohe sections were assessed as the standards in lakes and reservoirs, the results shown that the total phosphorus content is in a state of excessive and goes on an upward trend over time.(2) In2012, Qingxichang section is the most polluted of the eight sections in the reservoir and Fengjie section is of the better water quality relative to the other sections. The BOD5, ammonia-nitrogen, and potassium permanganate index make the biggest contribution to water pollution in Fengjie and its upstream section. From the section following Fengjie to the Miaohe section, the prominent pollution is the total nitrogen and total phosphorus, which appears to the eutrophication trend.(3)From2008to2012, nitrate nitrogen, total phosphorus, BOD5, total nitrogen pollution in Qingxichang section are of the exacerbated trend, and the pollution level of permanganate index and fecal coliforms are with no major changes; but the ammonia pollution has reduced to some extent. In the Fengjie section of2008-2012, the overall water quality declined in fluctuations, where the pollution levels of nutritional substances have increased.(4) The Three Gorges Reservoir mainstream sections were roughly divided into three classes through the cluster analysis. The first kind is the three sections of Cuntan, Changshou, Qingxichang located in the upstream of the reservoir. The second kind is the sections of Fengjie and Wanxian located in the middle of the reservoir. The third kind is the sections of Miaohe, Badang and Guandukou located in the head of the reservoir. To study the variation characteristics of TN and TP pollution in the reservoir in space, the cluster analysis also could be used in the eight sections of the main stream.(5) The spatial characteristics of the reservoir water pollution under different water level condition are studied. During the water level regulation period, BOD5and ammonia nitrogen pollution of the Wanxian and Fengjie sections in the mainstream located in the middle of the reservoir are more serious than other sections. The nutritional substances in the reservoir appears a downward trend from upstream to downstream overall, in which the Qingxichang section reach the maximum value and Cuntan section is seriously polluted affected by sanitary sewage. During the low water level operating period, there are a number of pollution indicators in the reservoir can have significant impact on the water quality. The water quality in the upstream of the reservoir was significantly worse than these in the midstream and downstream. The important indicator affected the water quality of the downstream in the reservoir is TN. During the high water level operating period, the nutritional substances are the major pollutants of the Cuntan to Fengjie sections in the upstream, and the nutritional substances appears a downward trend overall. Aerobic organic pollutants in the sections of the upstream and downstream in the reservoir are of higher concentrations and of lower in the middle sections. In the downstream of the reservoir, the aerobic organic matter is the main pollutant.