Interaction Of Water-Vegetation And Inversion Of Groundwater Under Changing Environment In Semiarid Farming-pastoral Ecotone

In recent decades,significant changes have taken place in China and in the global environment as well,such as climate change,water shortage,desertification and the sharp decline in biodiversity,which seriously threaten the ecological environment,the quality of ecological services,and service functions.The relationship between vegetation change and water problem has become one of the most urgent problems with respect to social sustainable development and ecological construction.However,due to the influence of global environmental changes such as LUCC and climate change,regional water cycle has also changed.There is a general interaction between vegetation change and eco-hydrology,which is more complex and uncertain.Tongliao Plain in the West Liaohe River Basin is a typical agro-pastoral ecotone in semi-arid areas of China.It is a vast area where agriculture and animal husbandry coexist in space and alternate in time.In recent decades,the problems of groundwater overexploitation,surface water drying up,vegetation degradation and desertification etc.have been aggravating,which has become a serious ecological environment problem restricting the sustainable development of local economy,society and people's lives.This paper studied the process of vegetation evolution and eco-hydrological change in Tongliao Plain area of West Liaohe River Basin from 1980 to 2015.On the basis of reviewing the previous research results,the regional eco-hydrological characteristics in the changing environment are monitored and analyzed by means of field investigation,laboratory experiments,theoretical analysis and model simulation.The regional climate change and water resources change were analyzed.The spatial and temporal evolution processes laws of land use dynamic change and vegetation change had been evaluated.The characteristics and laws of environmental factors had been revealed.The inversion simulation of water resources has been carried out by using multi-source remote sensing data.The spatial and temporal variation law of regional water resources had been explored.The effects of changes in hydrological conditions on vegetation and vegetation change on nature and human beings had been quantitatively analyzed.The eco-hydrological effects of vegetation evolution in changing environment were analyzed.The main conclusions are as follows:(1)The vegetation species decreased sharply in the area and the patchy trend of vegetation community was serious,which was in the process of the early to mid-term development of community succession.Under the influence of regional natural and human factors,the eco-hydrological conditions of the area had changed,which has promoted the reverse succession of vegetation.The evolution process of grassland types was as follows:the natural landscape between meadow grassland,sparse forest grassland,and forest grassland had changed to the natural landscape between desert grassland,meadow grassland,sparse forest grassland and forest grassland.The evolution process of vegetation community was as follows:from Pinus Linn,Artemisia Linn,Quercus,Chenopodiaceae,Cyperaceae,and Graminaceae to Artemisia Linn,Pinus Linn,Chenopodiaceae,Graminaceae,Cyperaceae,and Quercus;aftertoward to Artemisia Linn,Chenopodiaceae,Pinus Linn,Quercus,Graminaceae,and Cyperaceae;furthermore to Artemisia Linn,Chenopodiaceae,Cyperaceae,Pinus Linn,Graminaceae,and Ephedra Tourn.ex L.;until the present Artemisia Linn,Cyperaceae,and Graminaceae community.(2)The mean annual NDVI of vegetation in the area showed a slight fluctuated increase trend in the time series with a change rate of 0.004/yr.but had a strong spatial differentiation that mainly affected by human activities.On the time scale,P and T were the main limiting factors of NDVI change,and P was more sensitive to the response of T to NDVI change.On the spatial scale,vegetation NDVI change was the result of a combination of climate change and human activities.In the early period(1982-1993),the human activities impact was 75.07%,and risen to 98.08%in the recent period(1994-2015).(3)The groundwater depth in the area continued to increase significantly.The impact on NDVI was more obvious.Affected by cultivated land,the grassland was more prominent,showing the succession process from non-zonal meadow vegetation to zonal typical grassland vegetation.With the increase of groundwater depth,two large groundwater funnels had been gradually formed in the central part of the region.Human activities are the dominant factor in this phenomenon,and climate change is a secondary factor.(4)Based on the different GRACE satellite data,the changes of total water resources(TWS)and groundwater reserves(GW)in the study area with different scales showed a fluctuating downward trend in time series and obvious spatial heterogeneity at spatial scale.The results of JPL data inversion could better reflect the spatial and temporal variation characteristics of water resources in the study area.(5)Estimation models of groundwater depth change based on regional multiple stepwise regression and multiple linear regression were constructed.Although both models could not ideally meet the dynamic changes of groundwater depth.The fitting results showed that the multiple linear regression model could be used for better prediction of groundwater depth change.In conclusion,influenced by both natural and man-made factors,precipitation in Tongliao Plain of West Liaohe River Basin showed a decreasing trend.Since 1980s,the scale of land use of irrigated land had been increased dramatically.The use of groundwater had resulted in a continuous downward trend of groundwater level which lead to a decrease or even discontinuity of surface runoff and a change in total terrestrial water resources reserves(TWSC).Although the area mean annual NDVI showed a slight fluctuating upward trend,it had a strong spatial differentiation.The groundwater depth was continually increased significantly in some parts in the area.The multi-linear regression model could better simulate the groundwater depth change.The human activities had increasingly become the dominant driving factors for the spatial differentiation of vegetation and the change of eco-hydrological conditions.