Impact Assessment Of Trans Water Project In Arid Area On Terrestrial Vegetation In Water Diversion Area

Arid area is an important part of terrestrial ecosystem.Due to the lack of rainfall and water resources,the ecosystem in arid areas of Northwest China is particularly fragile,which seriously restricts the healthy development of the ecological environment.In order to meet the needs of water in social production,life and ecological,people changed the uneven spatial and temporal distribution of water resources by building an inter-basin water transfer project.The influence of water diversion on the ecological environment is very complicated.Through the study at home and abroad water diversion project,the general effects of water transfer on terrestrial vegetation in arid regions have been summarized.This paper takes the Yinhajidang project as a case to predict the degree of influence of engineering water supply on the natural land vegetation of the Sugan Lake wetland in the lower reaches of the water transfer area.Sugan Lake wetland is an important ecological unit of the Qaidam Basin,which is the inland arid area,the natural vegetation plays an important role in maintaining the ecological function and protecting the ecological environment.From the perspective of protecting the wetland ecological environment in arid area,this study establish reasonable water diversion of the Yinhajidang project initially according to the effect of the Processing MODFLOW model on the area of the big Sugan Lake and the groundwater level of the wetland.According to the quantitative relationship of natural vegetation and the groundwater in arid area and on the basis of each water transfer scheme,this paper predicts the impact of the decline of groundwater level on natural vegetation type and area in wetland after water transfer for 5 years,10 years,20 years,30 years and 50 years.In addition,on the basis of the changes of vegetation stability,changes in vegetation biomass and wetland vegetation landscape were predicted and analyzed.(1)Considering the demand of water in Dunhuang basin and Sugan Lake,the initial set of water diversion scheme is 1.0×108m~3for wet year,and 0.8×108m~3for normal year,and 0.3×108m~3 for low water year.(2)After 50 years of different schemes of water diversion,the area of big Sugan Lake will not decrease by more than 8%,in addition to 0.4×108m~3for low flow year.The decrease of groundwater level is less than 1m,and the area of 0-1m of wetland groundwater level will continue to decline.(3)The part natural vegetation succession of wetland will occur,mainly by the wetland vegetation to xerophytic vegetation,and the influence will be concentrated on the wetland of the two lakes and the marginal area of the wetland.As follow:(1)The swamps in the 0-1m area of shallow groundwater will be partially degraded or disappearing,and the degraded area will reach 12 km2 after 50 years,accounting for 2.14% of the current marsh vegetation area.(2)After water transferred,the area of Saline meadow in the 1-3m area of groundwater level will decrease by about 1%.When the groundwater level continues to drop to more than 2m,some wet reeds will evolve into alt reeds,which will be increased by 0.34% after 50 years.(3)The area of 3-5m in groundwater shallow-buried areas will increase year by year.The changed areas will be concentrated in the outer edge of the Sugan Lake wetland,and the forecast will increase by more than 4% compared with the current situation.(4)After water transferred,the area of swamp is decreasing and the area of shrub is increasing.Due to the difference of unit biomass,the biomass of the wetland in the Sugan lake will increase after the water diversion.(5)After 50 years of operation of the Yinhajidang project,the Shannon-diversity index of wetland vegetation landscape increased from 1.6149 to 1.6597,the Shannonevenness index will increase from 0.7766 to 0.7982,and the dominance index will decrease.It shows that the degree of landscape fragmentation and spatial heterogeneity increase,however,the existing dominant species still have the absolute advantage,and the wetland landscape structure is still stable.In general,the project will have a certain impact on the ecological environment of Sugan Lake wetland,but its impact in the controllable range.