The Three Gorges Project is the largest water conservancy project in the world. To cope with the ecological problems of the subsidence zone in the Three Gorges Reservoir area, the Kaizhou water-level-regulating dam was built, forming a model of nested water conservancy projects. The Pengxi River Basin is affected not only by this project but also by human activities in the reservoir area and changes in the substratum and hydro-meteorology, which exert influences on the water connotation function and its ecological value through complex mechanisms. In addition, the response mechanism of the changes in the environment is unclear. Therefore, based on the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model and a spatial interpolation method, in this study, two time nodes (2005 and 2018) before and after the operation of the nested water conservancy projects began were selected, and seven simulation scenarios with different water levels, precipitations, and temperatures were created to explore the evolution of the water conservation service function in the nested water conservancy project operation area under the complex changes in the environment. The results reveal that the operation of the water conservancy projects has had some influence on the water content, but the response of the water content function to the precipitation conditions has been more significant. In colder and rainier years, the water content was higher. In contrast, the lowest value occurred in a year with high temperatures and low rainfall. The highest and lowest values were quantitatively different. Therefore, the influences of the complex environmental factors on the regional water connotation service function deserve more attention. The results of this study provide a scientific basis for research on the ecological service function and the value of water conservation in the Three Gorges Reservoir subsidence zone and the nested operation area of the related water conservancy projects, as well as a data reference for the optimal allocation of regional water resources.
This study was conducted in the Qinghai-Tibet Plateau which is a typical less-favored ecologically fragile area. First, we constructed a GIS-based spatial gridding structure over the study area, the Yarlung Zangbo river basin in China’s Tibet, and used a value-assessment model to measure supply, support, regulation, and culture ecosystem services in each study grid. We then analyzed the spatiotemporal patterns of different ecosystem services in the region from 2000 to 2020. In addition, we conducted a spatial visualized analysis of the trade-off and synergies of multiple ecosystem services in each study grid. We found that: (1) On the temporal scale, from 2000 to 2020, the values of the four ecosystem services for supply, support, regulation, and culture along the basin demonstrated an upward trend. (2) On the spatial scale, the values of ecosystem services showed an uneven distribution, with a decline trend from east to west along the basin. (3) From the perspective of land use types, due to the large areas of water, grassland, and forest along the river basin, the ecosystem service values of the three types of land use ranked among the top levels. (4) The trade-offs and synergies between different ecosystem services and their spatial distribution along the river basin showed an uneven distribution pattern. The ecosystem services zoning revealed that the policies in guiding rural sustainability in the less-favored areas should adjust the measures to local conditions, it's necessary to establish multiple targets across the entire region.
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