Study On The Evolution Of Groundwater Environment In Semi-arid Region

Groundwater is an important part of water resources in arid and semi-arid areas.In recent years,with the intensification of human activities,the groundwater environment has been damaged and brought about a series of environmental problems.Therefore,it is of great theoretical and practical significance to carry out relevant research on the evolution of groundwater environment in semi-arid areas for correctly handling the relationship between humans and nature,scientifically planning and protecting groundwater resources,and realizing the improvement and sustainable development of groundwater environment in semi-arid areas.This paper is based on the project "Regional Water Resources Survey Method and Groundwater Ecological Threshold Survey" of Shenyang Geological Survey Center,China Geological Survey(No.DD20190340-W09)and "Groundwater Resources Investigation and Evaluation of Shuangliao City".Taking Shuangliao as an example to study the evolution of the groundwater environment in a semi-arid region.A research system of groundwater environment evolution in semi-arid regions is constructed,including "groundwater environment assessment-spatio-temporal evolution– evolution pattern-regulation".The DAPSIR groundwater environment assessment system including Drivers(D),Activities(A),Pressures(P),States(S),Impacts(I),and Responses(R)was constructed and the groundwater environment was evaluated by it.Based on spatial analysis and spatial statistics,the spatial and temporal evolution of the groundwater environment and its influencing factors are revealed.The evolution pattern of the groundwater environment is divided by the coupling coordination model and decoupling model,and the evolution mechanism of different evolution patterns was studied by the partial least squares structural equation model.The regulation of groundwater environment evolution is studied by groundwater numerical simulation.The main results are as follows:(1)A groundwater environment evolution research system integrating "groundwater environment assessment-spatio-temporal evolution-evolution patternregulation" in semi-arid areas has been constructed.This system combines the mathematical modeling method,spatial analysis and spatial statistics method,secondgeneration statistical method,and numerical simulation method.From the two aspects of the time change and space difference,the spatial-temporal evolution characteristics and influencing factors of the groundwater environment in semi-arid regions are clarified,and the understanding level of groundwater environment evolution is improved.The evolution pattern and mechanism of the groundwater environment under the comprehensive influence of the natural environment and human activities are analyzed quantitatively.(2)The improved DAPSIR evaluation system considering Activities(A)was used to evaluate the groundwater environment in Shuangliao.The results show that the overall situation of the groundwater environment in Shuangliao presents a spatial situation of "high in the south and low in the north".The Dongliaohe River valley plain has better resource endowment,less negative impact from human activities,and higher groundwater environmental assessment value,which reflects its relatively good groundwater environment.The Xiliaohe River valley plain has a good resource endowment,but the negative impact of human activities in the urban area is strong,and its evaluation value is lower than that of the Dongliaohe River valley.The resource endowment and ecological environment of the tableland are poor,and the evaluation value is the lowest,which reflects that the groundwater environment is relatively poor.(3)The evolution characteristics and influencing factors of the groundwater environment in Shuangliao from 1982 to 2018 were comprehensively and systematically revealed.The groundwater environment in Shuangliao city showed an obvious trend of deterioration.The Dongliaohe River valley plain had the smallest deterioration,while the Xiliaohe River valley plain was in the middle,and the tableland deteriorated the most.The spatial polarization trend of the groundwater environment was increasing.Its evolution can be divided into two stages: 1982-1997 and 1998-2018.With the enhancement of human activities,the spatial situation of "high in the south and low in the north" of the groundwater environment has been further strengthened since 1998.The towns with high-quality groundwater environments are mainly concentrated in the Dongliaohe River valley plain,and the towns with low quality are located in the north of the platform.With the evolution of the groundwater environment,the decrease in high-quality areas and the increase in the poor-quality area reflect the deterioration trend of the groundwater environment.In terms of influencing factors of evolution,the natural endowment is the basic factor determining the initial pattern state of the groundwater environment from 1982 to 1997.From 1998 to 2018,the damage to the groundwater environment caused by human activities was prominent.The influencing factors in the high-quality area of the groundwater environment focus on water quantity,the influencing factors in the transition area focus on groundwater quantity and quality,and the influencing factors in the poor-quality area and the risk area focus on water quantity,water quality,and ecology.(4)Five kinds of groundwater environmental evolution patterns in Shuangliao were divided and their evolutionary mechanisms were analyzed.The evolution patterns include: coordinate-strong decoupling rapid deterioration pattern(the town of Wohu,Yongjia,Xinglong,Fuxian,Bolishan,Maolin),transition-weak decoupling slow deterioration pattern(the urban area),coordinate-recession decoupling continuing recession pattern(the town of Namusi,Hongqi),coordinate-negative decoupling of expansion continual optimization pattern(the town of Xinli,Wangben,Liutiao)and coordinate-weak decoupling slow deterioration pattern(the town of Dongming and Shuangshan).The results of evolutionary mechanism research show that: the changes in water quantity factors are mainly reflected in the decrease in water level and the increase in the degree of development and utilization.Except for urban areas,the effect intensity of natural environmental pressure on water quantity factors is greater than that of social-economic pressure.In terms of water quality factors,different evolution patterns have different severity of water quality problems,and the pressure of water quality factors is reflected in the use of chemical fertilizers and sewage discharge.In terms of ecological and environmental factors,some evolutionary patterns have different degrees of ecological and environmental problems.The natural environmental pressure is reflected in the change of land use type,and the social and economic pressure is reflected in the reclamation rate and livestock production.The difference in the natural endowment of the groundwater environment is the fundamental reason for the evolution difference.(5)Based on the analysis of the evolution and mechanism of the groundwater environment,this study puts forward the corresponding regulation scheme of the groundwater environment.The dry land on tableland will be irrigated with a watersaving pattern by relying on the national high-standard farmland construction and the black land consolidation project.Combined with the water diversion project in the eastern part of Jilin Province,water source substitution is implemented in the urban area of the Xiliaohe River,popularizing scientific fertilization in Shuangliao city,improving urban sewage collection and treatment rate,and reduction of sewage discharge were implemented.The prediction results of the control scheme show that after the new water diversion project,the overexploitation problem will be completely alleviated,the landing funnel will disappear,and the water level will rise by 2～4 m.After the implementation of a water-saving irrigation project on the platform,the groundwater level will rise by about 0.5 m.In terms of water quality,the high concentration of nitrate and TDS can be effectively controlled under the conditions of scientific fertilization and increasing the rate of urban sewage collection and treatment.The main innovation points of this study are:(1)A groundwater environment evolution research system integrating "groundwater environment assessment,spatio-temporal evolution,evolution pattern and regulation" in semi-arid areas has been constructed.The temporal and spatial evolution of groundwater environment and its influencing factors in semi-arid areas were revealed.The evolution pattern and mechanism of the groundwater environment under the comprehensive influence of the natural environment and human activities are analyzed quantitatively.(2)The DAPSIR groundwater environmental assessment system is improved and put forward.In the evaluation system,the Activities(A)is fully considered,clearly reflecting the influence and disturbance of human activities on the evolution of groundwater environment,and providing a basis for the regulation of groundwater environment.(3)A classification method of groundwater environment evolution pattern was put forward to quantitatively analyze the effects of natural environment and socioeconomic factors on groundwater environment and the key driving factors in different evolution patterns,so as to effectively quantify the causality of groundwater environmental evolution.