Research On The Transformation Of Surface Water And Groundwater And Its Ecological Effects In The Main Stream Of Tarim River Under Land Use Change

The main stream of the Tarim River has experienced serious water resources crisis and ecological degradation,Under the influence of global warming and intensified human activities.Since 2000,the comprehensive improvement project of the Tarim River Basin has alleviated some of the water-ecological contradictions,and the desert riparian forests on the mainstream of the Tarim River have regained their vitality.However,as climate change intensifies,uncertainties in upstream inflows and other factors have led to a serious challenge to the mainstream use of external water to supplement groundwater in order to maintain the sustainability of ecological restoration.The related issues such as the transformation mechanism of surface water and groundwater and its ecological effects have become frontier and hot issues in environmental science research.This study takes the transformation relationship between surface water and groundwater in the mainstream of the Tarim River as the main line of research.Based on the existing comprehensive monitoring of ecological cross-sections,water,soil,gas,and ecology of the mainstream of the Tarim River,long-term monitoring data of points,lines,and areas have been obtained.Using multidisciplinary and comprehensive research methods,the characteristics of the aquifer boundary,hydrogeological units,source and sink terms,etc.of the transformation of surface water and groundwater in the mainstream of the Tarim River were studied,and a Visual MODFLOW model was constructed.Carried out the simulation of the transformation relationship between surface water and groundwater under different land use modes,and the research on the synergistic relationship between land use change and riparian vegetation distribution.Explored the interaction mechanism and ecological effects of surface water and groundwater in the mainstream of the Tarim River under different land use patterns.A joint regulation strategy of surface water and groundwater is proposed to maintain the ecological and water security of the mainstream of the Tarim River under different hydrological years and land use change scenarios.The main conclusions are as follows:(1)Based on the hydrogeological characteristics and groundwater flow characteristics of the study area,a Visual MODFLOW model of the transformation between surface water and groundwater in the mainstream of the Tarim River was constructed.The results show that the average absolute error of the simulated and observed groundwater depths during the simulation and verification periods is 0.44 m,respectively.0.46 m,both are less than 0.50 m,the root mean square error is 1.53 m,1.47 m,and the water balance difference is-0.241×10~8 m~3,-0.015×10~8m~3,the hydrogeological parameters are relatively accurate,and the model simulation effect is good.The numerical model of surface water and groundwater transformation constructed in this study can reflect the regularity and characteristics of groundwater flow in the mainstream of the Tarim River.The hydrogeological conditions are similar to the actual conditions of the study area,which can better reflect the movement characteristics and dynamic trend of the groundwater in the study area.The model and optimized hydrogeological parameters can be used to numerically transform the surface water and groundwater of the main stream of the Tarim River under different conditions.simulation.(2)In the past 30 years,the area of grassland in the mainstream of the Tarim River has been continuously decreasing,and the area of desert and arable land has been continuously increasing;the land use structure changed the most from 2005 to 2010,and the land use structure was the most stable from 2010 to 2015;The transformation of surface water and groundwater in 1990 and 2000 showed negative equilibrium,and the transformation of surface water and groundwater in 2005 and 2010 showed positive equilibrium;as the area of arable land increased,the amount of irrigation infiltration increased;river leakage The change trend of recharge,canal leakage and runoff is the same.(3)The conversion between surface water and groundwater in the mainstream of the Tarim River in wet years is in positive equilibrium,and the conversion between surface water and groundwater in normal and dry years is in negative equilibrium.As the inflow of water decreases,the depth of groundwater continues to decline,the conversion of surface water and groundwater gradually shifts from a positive equilibrium to a negative equilibrium,and the area of vegetation degradation continues to expand.In wet years,runoff increases and groundwater levels rise,which is conducive to vegetation growth and the restoration of the ecological environment.The woodland area increases by 134.80 km~2;in dry years,the water volume decreases,the groundwater level drops,vegetation degrades,and the desert expands to forests and grasslands by 3105.90 km~2.(4)The density of Populus euphratica seedlings on both sides of the Tarim River,the coverage and abundance of trees,shrubs and grasses showed a significant downward trend with the increase of groundwater depth.Emergency ecological water transportation has made the value of ecosystem services in the lower reaches of the Tarim River show a trend of "increasingdecreasing-rising",with a total increase of 299 million yuan;Water resources are of great significance to the stability and improvement of the ecosystem service value in arid areas.Based on path analysis,it is found that the internal relationship between water body area changes and ecosystem service value is the largest,with a direct effect of 0.610 and an indirect effect of 0.345.Based on the multi-year average inflow of water,the proportion of grassland,woodland,arable land,desert,and wetland area is 39.59%,10.03%,3.13%,45.23%,and 0.98%,respectively.When the land use structure is optimal,the corresponding ecosystem service value is the largest 52.436 billion yuan.