The Impacts Of River Dam Construction On Land Use,Vegetation Cover And Vegetation Productivity At Catchment And Landscape Scales

Dam construction is widely used for flooding control,cropland irrigation and hydropower,which promotes the economic and social development as well as a series of social and ecological environmental problems.After dam construction,it will not only change of the surrounding land use and coverage,but also brings problems such as inhabitant resettlement,which change regional land use/land cover type in river catchment and landscape scale.These changes will react on net primary productivity of plant,further affect sediment yield,sediment transport and carbon transport intensity in the catchment scale.Therefore,it is very important to study the impact of dam construction on surrounding ecological environment,which can provide a reference for the protection and construction of water environment in the dam construction area.Taking cascade reservoir constructed river — Wujiang River,and none hydropower development in main stream river — Chishuihe River as examples,study based on the data of land use contrast the change of land use characteristics both in catchment scale and landscape scale before and after dam construction.Land use transfer matrix was used to quantify land use change and change direction in different scale and discuss the influence of dam construction on land use change around reservoir area.Land use change leads to the change of vegetation cover.Taking Wujiang River and Chishuihe River as examples,based on MOD17A3 H NPP data,the variation trend and sustainability of NPP in Wujiang River and Chishuihe River in catchment scale were analyzed.Some results were shown as follows:Based on the analysis of land use change and transfer matrix,it is found that land use change in Wujiang River catchment occurred mainly from 2010 to 2020 after the completion of most reservoirs,while the land use change in Chishuihe River catchment shows more significant from 2000 to 2010.On the spatial scale,dam construction has the greatest influence on land use within 0-1 km buffer zone,mainly due to the change of water body and building type.After dam construction,the water level in the reservoir area rises and submerges the original cultivated land and grassland.At the same time,under the influence of urbanization,the original cultivated land type is transferred to the building type.Sen-MK trend test and Hurst index analysis based on NDVI data showed that NDVI in Wujiang River catchment and Chishuihe River catchment both showed a fluctuating upward trend,and the main variation type is significantly increased.Hurst Index average in Wujiang River catchment is less than 0.5,which means the variation trend of NDVI at the scale of Wujiang River catchment is anti-sustainable,while the Hurst index in Chishuihe River catchment is higher than 0.5,the variation trend of NDVI is persistent,the variation trend of NDVI in Wujiang River and Chishuihe River in catchment scale is different in the future.At the sub-catchment scale of reservoir region,except Hongjiadu and Dongfeng reservoirs in the upper reaches of Wujiang River,Hurst index of other main stream sub-catchment is less than 0.5,indicating an anti-sustainable development of NDVI.Through the Mann-Kendall mutation test on the variation trend of NDVI at the sub-catchment scale,it can be seen that the mutation in the interannual variation of NDVI is basically consistent with the dam construction time,which confirms that dam construction has an impact on NDVI.Sen-MK trend test and Hurst index analysis based on NPP data showed that NPP value of Wujiang River catchment is higher than that of Chishuihe River catchment at the watershed scale,mainly because the proportion of woodland types in Wujiang River catchment is more dominant.Compared with Chishuihe River catchment,the anti-sustainability trend of NPP in Wujiang River catchment is stronger,and the anti-sustainability region is mainly in the middle and downstream in Wujiang River catchment where cascade reservoirs set.Compared reservoirs with different regulation types,it is found that the seasonal and daily regulation reservoirs have stronger anti-sustainability than the annual regulation reservoirs.At the same time,Zhikong reservoir located in Lhasa River was considered as the research object to verify the above results and conclusions.Through the analysis of land use change and transfer matrix,it is found that the land use change around Zhikong reservoir area mainly occurred in the second stage of dam construction(2010-2020),and the land use change mostly occurred within the 0-1 km buffer zone,which was consistent with the previous studies.