| Since the reform and opening up,due to the rapid development of socio-economy and the accelerate of urbanization,the per capita availability of land resources have become increasingly scarce,and the area of enclosure aquaculture of lakes in China increased significantly.The intensive enclosure aquaculture is an effective way to cope with the increasing demand for aquaculture products,however,it brings serious water environment problems,such as landscape fragmentation,water quality degradation and lake eutrophication,leading to great pressure and challenge in the water ecosystem health of lakes in China.Therefore,the water ecosystem health assessment of the lake and the spatial pattern optimization of the lake have become an urgent task.In this study,the multi-temporal remote sensing data,hydrology,water quality and water ecology data of 41 lakes in Lixia River area of Jiangsu Province were selected to analyze the landscape pattern evolution of lake group and its driving factors,as well as the influence mechanism of landscape pattern evolution of lake group on water environment.In addition,a water ecosystem health comprehensive evaluation model was established based on the “Pressure-State-Response”(PSR)model,and the optimization scheme of spatial pattern of lake group was proposed.The main results are as follows:(1)Landscape pattern evolution of lake group and its influence on water environment: The landscape fragmentation of lake group increased dramatically during the period of 1985-2018,with the highest growth rate from 1995 to 2000.With the emergence of the economic form of fishery stock cooperative system in 1995,the development of enclosure aquaculture became large-scale and intensive.In recent years,due to the promulgation of lake protection policy and the implementation of special plan about conversion of enclosure aquaculture to lake,the fragmentation growth rate of lake group decreased.The Chlorophyta density and the diversity index in non-flood season and the comprehensive nutrient status index in flood season were significantly correlated with the patch density,with the correlation coefficient were 0.66,-0.28 and0.33,respectively.It indicated that the higher fragmentation,the worse water environment.(2)Water ecosystem health comprehensive assessment of lake group: Based on the PSR model,a water ecosystem health comprehensive evaluation model of lake group was established.The Pressure included driving factors,and the State included water safety,aquatic organisms,aquatic habitats,landscape patterns,and the Response included water space and policy planning.The result showed that the water ecosystem health comprehensive index(H)of lake group was between 1.37-4.83.The Lvyanghu had the smallest H(1.37)and the Xiquehu had the largest H(4.83).The increasing fragmentation caused the lake group ecosystem to be a sub-healthy state,while the Lvyanghu water ecosystem with the greatest fragmentation was in an unhealthy state.(3)Optimization scheme of the spatial pattern of lake group: Based on the needs of the ecological service functions(i.e.flood water storage,water purification,wetland conservation,germplasm resources protection,natural and human landscape supply)of lake group in the Lixia River area,the ecological restoration of lakes group was carried out in spatial and temporal scale.It is recommended to give priority of pattern optimization to the 6 lakes with high fragmentation and poor health,such as Lvyanghu,Deshenghu,Chenbaocaodang,Gengjiadang,Cuiyindang and Caihuadang.Spatially,lakes with the ecological function of germplasm resources protection,which can be carried out ecological aquaculture.However,the water area of other lakes should be banned or withdrawn from enclosure aquaculture.The study showed that combination of remote sensing data and water ecological environment monitoring data,using landscape ecology theories and methods,which can effectively establish a quantitative relationship between the spatial pattern of lake group and the ecological health of the water environment of lake group.It is important for human beings to guide the ecological restoration of lake group in spatial-temporal pattern and to provide an effective method for the regional restoration planning of lakes in the future. |
