Research On Ecological Environmental Effects Of Hydropower Projects In The Upper Yellow River Based On The InVEST Model

With the rapid development of hydropower projects in China,the increasing human activities have changed the original landscape structure and brought serious damage to the local ecological environment.The upper reaches of the Yellow River have the earliest and most welldeveloped terrace hydropower stations,with unique conditions for hydropower development and rich ecological functions.To this end,in this paper,the spatial heterogeneity of landscape pattern and ecosystem service evolution in the upstream reservoir area of the Yellow River were taken as the entry point in the context of the development of the upstream Yellow River step hydropower project.The InVEST model was used as a technical tool to assess the ecosystem service function,and the pre-,mid-and post-construction periods of the upstream Yellow River step hydropower plant were taken as the study periods to systematically analyze the landscape pattern caused by human activities before and after the construction of the step hydropower plant.And further analyze the impact on changes in ecosystem services in the study area.The main results are as follows:(1)The analysis of land use and landscape patterns in the study area yielded that the grassland area in the upper reaches of the Yellow River accounts for about two-thirds of the total area.The order of area size of various land types is grassland>forest land>unused land>cultivated land>water area>construction land.In general,except for the decrease of arable land and unused land,other land types increased,the construction land and unutilized land had the largest change range,and the transfer of unutilized land,grassland and forest land had obvious advantages.During the construction of the hydropower project,various landscape types had undergone complex changes.Some cultivated land was converted into construction land and unused land was converted into pasture,cropland and woodland after development and management.The fluctuation of each index is obvious.After the completion of cascade hydropower stations,a series of ecological protection and restoration measures had been taken.Therefore,the landscape pattern index fluctuates little,and the ecological environment gradually recovers and tends to be stable.(2)Simulation analysis by the InVEST model yielded that carbon reserves,water yield and soil conservation capacity in the upstream of the Yellow River had been enhanced.Changes in carbon stocks were mainly due to changes in the basin above Lanzhou,especially from river source to Maqu.The water production depth in the northwest region of the upstream of the Yellow River was relatively low,and the water production depth gradually increased from northwest to southeast in space.The high values were mainly in the southeast of the study area.The distribution of soil retention in the upper reaches of the Yellow River is uneven,and the spatial distribution changes are comparatively apparent,the soil conservation was relatively high in the south-central and northeast areas of the study area,because there were many forest lands and high vegetation coverage.Land use change had a greater impact on carbon storage and soil conservation,and precipitation had a greater impact on water production function.(3)The comparative analysis of the buffer zone showed that the moisture conditions improved with the increasing distance from the reservoir and the gradual increase in elevation.The vegetation coverage,carbon storage,water yield and water and soil conservation slowly increased with the increase of the distance from the bank,and the closer to the reservoir,the greater the change.The hydropower development had increased the fragmentation of the landscape,weakened the heterogeneity of the landscape,and reduced the richness and diversity,and the landscape pattern evolution within the 500 m buffer zone had the greatest impact.(4)The comparative analysis of the Lijiaxia,Jishixia and Laxiwa reservoirs yielded that with the increase of the distance from the bank,the change range of vegetation coverage,carbon storage,water yield and soil conservation before and after the construction of the three hydropower stations decreased.The change range of vegetation coverage,carbon storage,water yield and soil retention after and before the construction of the three hydropower stations decreased with the increase of the distance from the bank.The closer to the reservoir,the greater the change range,indicating that the impact of reservoir construction is more significant.In terms of ecological service functions,the Laxiwa Hydropower Station was the weakest,and the correlation coefficient of ecosystem service in the reservoir area of each hydropower station was significantly different.Reservoir construction will promote the trade-off/synergy between different service functions In Laxiwa and Jishixia reservoirs,carbon storage – water yield and water yield – soil conservation are tradeoffs,and carbon storage – soil conservation is a synergistic relationship.The carbon storage – soil conservation and water yield – soil conservation of Lijiaxia Reservoir presents a trade-off relationship,while the carbon storage –water yield present a synergistic relationship.The above analysis can provide a further understanding of the current situation of the ecological environment in the region in recent years and possible changes in the future.To some extent,it provides some thoughts and suggestions for studying the environmental benefit evaluation of cascade hydropower stations in the upper reaches of the Yellow River,and prepares for the current and future ecological protection in the source area of the Yellow River.