Study On Non-point Source Pollution Control In Taihu Lake Basin Based On Landscape Pattern Analysis In YiXing

With rapid socio-economic developement in Taihu Lake Basin, the pollution of watersource in Taihu Lake is increasingly getting serious. Thus the governments at all levels spend amass of resource （money and manpower） on the issue in the basin of Taihu Lake. With theefforts the point source pollution has been better controlled around the basin. But the non-pointsource pollution is still serious due to its dispersion, concealment, random and difficultmonitoring. So it still is the key and difficult points to be paid attention to in the current andfuture. The non-point source pollution is the result of multiple factors such as soil, topography,hydrology, socio-economic development, management methods and land use, and it is closelyrelated to the landscape distribution pattern. Reasonable landscape distribution can improvewater quality by reducing the output of non-point source pollution, and hindering transformingwatershed pollutants into the waters.Landscape pattern index can also be a good description of the landscape heterogeneity,and location-weighted landscape contrast index（LCI） can quantify the non-point sourcepollution. Now little work has been done on the concrete relationship between the water qualityindex to the landscape index. Taihu lake is the third largest freshwater lake in our country.Meanwhile it is the water source area of Shanghai, Jiangsu, Zhejiang and other provinces andcities. And the water quality may directly affect the social economic development ofneighboring regions. But there is few of systematic research on the effects and the mechanismbetween landscape pattern and the water quality.In order to cope with the situation of non-point source pollution getting worsen and landuse system changing greatly in Taihu lake watershed, we performed the study to approach thespatio-temporal variation of non-point source pollution in the area based on “source-sink”landscape change. Test plot was located in the Yixing city of west bank, and ten typicalchannels connected with Taihu lake were selected to be sampling plots. During the study ‘source-sink’ landscape constrast index（LCI） of these chanels was calculated based onsource-sink landscape theory, in addition to water sample collection and water qualityanalysis.And we chosen some indicators such as source-sink landscape location-weightedLandscape Contrast Index （LCI）, Number of Patches （NP）, Edge Density （ED）, ContagionIndex （CONT）, Shannon’s Diversity Index （SHDI） and Aggregation Index（AI） were analyzedwhich could reflect landscape characteristics. Some parameters such as Total Nitrogen （TN）,Total Phosphorus （TP）, Chemincal Oxygen Demand (COD_Mn) were measured which reflectwater quality. By employing the way of correlation analysis and path analysis between thelandscape pattern and stream water quality. The main conclusions in this thesis have beensummarized as follows.（1） In general, the non-point source pollution was improved in Yixing city. The‘Sink’landdscape pattern area increased8.75%, including the forest land area increased4.03%.And LCI decreased0.098. These show that the ecological restoration have remarkable effectafter2007. ED decreased and CONT, AI increased. SHDI reduced to1.474from1.697. Theresult shows: the complexity of the landscape elements decreased. The landscape heterogeneityof the watershed decreased. The concentration of NH₄⁺decreased by29.1%, and otherindicators did not change significantly.（2） On the spatial dimention, LCI was mainly influenced by landscape patterns,and LCI was positively related with comprehensive water quality identification index. Thus bythe test it implied that landscape pattern change in the channels connected with Taihu lakecould influence water quality. Generally spoken, LCI was closely related to the content ofNH₄⁺-N and TN. LCI and water quality of the channels had the same change trends. The‘source-sink’ landscape constrast index responsed well.（3） Among LCI and TN, TP, COD_Mnthey had a positive significant correlation, the directaction coefficients were0.266,1.512and0.979respectively. While ED had a significant effecton TN、COD_Mnand NH₄⁺-N, and direct action coefficients were0.740,-0.189and0.852. ForCONT with TN and NH₄⁺-N, they were positive significant correlation. But for SHDI with TNand NH₄⁺-N, the relationship all were negative. Moreover among the other indexes the relationship was not significant. It was concluded that landscape pattern had a certain influenceon the stream water quality. Reasonable allocation of landscape pattern was able to effectivelycombat non-point source pollution, and improve water quality in the watershed.（4） Moreover N and P absorption by2clones of Salix integra （‘Yizhibi’ and ‘Weishanhu’）in artificial eutrophic water was approached. The results showed that2clones of S. integracould effectively remove TN （90%） at the low level of treatment, which was2times as that ofhigh concentration treatment. While for removal efficiency of TP, it reached80%at thetreatment of low level, whilst at high concentrations of artificial eutrophic water it attained92%.