The Study Of The Function Change And The Assessment And Analysis Of The Wetland Of Nansihu Lake

Nansihu Lake is one of the biggest fresh water lakes in China, whose area is 1266 km2 and average water depth is 1.46 meter. According to the general index of the wetland -whose water level is below 2 meters in depth, the whole wetland in this area is a typical lake wetland. So it is classified as a protective area of the national wetland.The formation and evolution of Nansihu Lake has a close relation with the overflow and the silt stagnation of The Yellow River, which have a prodigious effect on the degeneration of the wetland of Nansihu Lake. With the increasing economic development in lately 30 years, various functions of the wetland in Nansihu Lake have assumed obvious degeneration and destruction. The study and protection of the national wetland are very important to the construction of the ecological environment. But now there have had almost no researches on the lake as wetland. This article studies this question comprehensively and systemically.Based on the brief introduction and analysis of the conception and the research status quo of the wetland, the sedimentological method, the technology of remote sensing, the quality model of polluted water and the method of the artificial neural network are used to discuss and analyze the functions of the wetland. These functions include the storage of the floodwater, the purification of polluted water and the production force. According to these analyses, the reason of the wetland degeneration is studied and the countermeasures of the sustainable development are put forward.The main contents of the research include:l.The Status of Reclamation and Deposition of the WetlandDue to the effect of the overflowed plain of the west of the lake, the quantity of sandiness of the rivers is very high and the deposition depth reaches 0.4 centimeter per year. The rapid expansion of the population and the shortage of the land accelerate the reclamation of the wetland. So the range and the speed of the reclamation have an increasing tendency.in2.The Analysis to the Function Change of the StorageCombined with the interpretative data of the satellite photographs, the article analyzes the changes of the area and shows that the corresponding curve of the water level in the area is not suitable to the present condition. On this basis, the curve is mended according to the interpretative data.3.The Polluted Status Quo of the Water Quality of the WetlandAccording to the data of 23 monitor points of the water quality, with the method of the comprehensive appraisal of the single factor, the water quality is quantitatively analyzed. On this basis, the water is distributed into three regions.4.The Analysis to the Production Force of the WetlandOn the basis of the analysis to the present data, combined with the data of drill hole of Dushan Lake, the change of the production force of the wetland is analyzed since the formation of Nansihu Lake.5.The Comprehensive Appraisal of the Quality of the Ecological Environment of the WetlandThe article selects six indexes as the layer of inputting. The six indexes are the accumulated temperature higher than 10 Centigrade degree, the average of annual precipitation, the water quality of the rivers flowing into the lake, the water quality of the lake, the proportion of silt to the lake volume, the degree of the eutrophication. Then by the method of back neural network, comprehensively appraise the quality of the ecological environment of Nansihu Lake.6.The Analysis of the Function Degeneration of the Wetland and the Countermeasures of the Sustainable UtilizationBased on the comprehensive appraisal of the quality of the ecological environment, the reasons of the degeneration are discussed. Finally the countermeasures and measures of the sustainable development are brought forward, combined with the theories and methods of the resumption.