Study On Characteristics Of Groundwater System And Evolution Of Eco-environment In The Plain Area Of Kashgar River Basin

Climate change brings new challenges to the survival and development of humanbeings.The impact of human activities could develop driving factors to the nature.Therefore,under the great influences brought by human activities,the research on changes,trends,laws and their driving mechanisms of the eco-geology is particularly necessary.The Kashgar River Basin is located in the western edge of the Tarim Basin,the northwest arid and semi-arid area of China.The ecological environment is relatively fragile and the ecological capacity is limited.Groundwater is an important water source for maintaining the production,life and ecology in the plain of the Kashgar River Basin.Long-term and large-scale mining hasinduced a series of eco-environmental and geological problems.These quantitative changes turned into qualitative changes and caused the evolution of eco-environment.The exploring of its internal mechanisms has practical significance for the rational utilization and protection of environmental resources.This paper takes the plain area of the Kashgar River Basin as the study area,aims to investigate and evaluate the water resources,comprehensively using multi-disciplinary techniques such as groundwater dynamics,remote sensing interpretation analysis,statistics,and numerical model simulation.The research reveals the characteristics of groundwater flow system and analyses the evolution of eco-environment in the plain area of the Kashgar River Basin,especially the causes and trends of its salinization situation.From a practical perspective,the research also optimizes the division of the two-level groundwater functional zones,delimites and rechecks the over-extraction areas.The main conclusions of this research are as follows:(1)According to the similarity and relevance of the characteristics such as geomorphology,aquifer characteristics,water-rich characteristics,groundwater flow field characteristics,hydrochemical characteristics and river distribution,we divide the Quaternary groundwater flow system in the plain area into the groundwater flow sub-region of the Kezilesu River(?₁),the groundwater flow sub-region of the Gaizi River-Kushan River-Yigziya River(I_2-3-4),and the Qiakemake River-Buguzi River groundwater flow sub-region(I_5-6).These classifications are the theoretical basis for the following investigating and evaluating of groundwater resources in the study area;(2)The equilibrium calculations indicate that the total amount of groundwater resources in the plain area of the Kashgar River Basin(M?2g/L)is 14.60×10⁸m³/a.The amount of groundwater resources in the plain area of the Kezilesu River Basin,the Gaizi River Basin,the Kushan River Basin,the Yigeziya River Basin,the Qiakemake River Basin and the Buguzi River Basin is 5.02×10⁸m³/a,5.20×10⁸m³/a,2.48×10⁸m³/a,0.82×10⁸m³/a,0.21×10⁸m³/a and 0.88×10⁸m³/a respectively;(3)According to the practical experience of groundwater resources management,the division of groundwater two-level functional areas is optimized and improved considering the function orientation,water quality factors,priority protection,backup water source and the convenience for grass-roots management.The first level function is divided into living function area(L),ecological function area(E)and production function area(P).On the basis of the first level functional areas,we divide the second level functional areas into eight sub-areas,namely,centralized water supply source area(L1),water treatment and water supply source area(L2),standby high-quality water source area(L3)in living function area(L),water conservation area(E1),ecologically fragile area(E2),ecologically protection area(E3)in ecological function area(E),development area(P1)and emergency water source area(P2)in production function area(P).According to the optimized division system of groundwater function areas,the Kashgar River Basin is divided into 4 L1 areas(49.86km²),7 L2 areas(75.49km²),2 L3 areas(1952.54km²),8 E1 areas(45302.54km²),14 E2 areas(3949.56km²),7 E3 areas(3457.97km²),11 P1 areas(9104.73km²),and no P2area is identified;(4)The six counties in the downstream of the Kashgar River Basin have no large-scale and relatively serious eco-environmental and geological problem.However,the lowering of groundwater level due to the over exploitation has caused the shrinkage of natural water areas such as wetlands and the degradation of local vegetation.The over exploitation of groundwater has also occurred in some areas;(5)From 2000 to 2010 and from 2010 to 2017,the dominant change type is all the transformation from extremely severe saline soil to severe saline soil.The relative change rate of salinization severity index was-6.68%from 2000 to 2010,and-8.05%from 2010 to 2017.The speed of remediating saline soil showed an increasing trend,indicating that the problem of soil salinization was generally getting better.There was a significant linear regression relationship between the variation of salinization severity and that of ET,NDVI and LST(P<0.01).?ET and?NDVI could effectively explain the variation of salinization severity,in which?ET showed the strongest explanation ability for the dynamics of soil salinization severity.In addition,the decreased groundwater level in this area might also contributed the alleviation of soil salinization;(6)For Jiashi county,a typical area in the plain area of Kashgar River Basin,base on the current scheme of groundwater exploitation,the groundwater level will continue to decline rapidly.The over-exploitation of groundwater will eventually cause the shrinkage of natural water areas such as wetlands and the degradation of natural vegetation,and may cause more serious eco-environmental problems.Base on the scheme of moderate groundwater exploitation,the groundwater level will become stable and rise slightly,and the eco-environment of the basin will be improved gradually.Base on the relatively less groundwater exploitation,the groundwater level of the basin will rise slowly.Under this situation,although the eco-environment shows a better tendency,the risk of secondary salinization will exit.For protecting eco-environment effectually and utilizing groundwater sustainably,a moderate groundwater exploitation plan should be formulated.