Study On The Process And Mechanism Of Atmospheric Precipitation-Surface Water-Groundwater-Mine Water Transformation Driven By Coal Mining In The Maguan River Basin

Northwest China is deep inland,arid and semi-arid areas,with poor water resources and very fragile ecological environment but rich in mineral resources.The mining of coal promotes the development of regional economy,but in the process of mining is bound to change the hydrodynamic conditions of groundwater system,change the conversion process of atmospheric precipitation,groundwater and surface water,which affects the development and utilization of water resources.Therefore,it is of practical reference significance to understand the process and mechanism of atmospheric precipitation-surface water-groundwater-mine water conversion driven by coal mining for the development and utilization of water resources and improvement of ecological environment.This paper takes the Ma Guan River basin as the study area,adopts continuous monitoring,regular sampling and indoor experiments to obtain conventional water chemical indexes,heavy metal element indexes,hydrogen and oxygen isotope test data,and meteorological data,and uses Piper trilinear diagram,Gibbs diagram,ion ratio method,correlation analysis,multivariate linear mixed model and other methods to deeply analyze the atmospheric precipitation-surface water-groundwater transformation relationship in natural state,and reveal the atmospheric precipitation-surface water-groundwater transformation process and mechanism under the influence of coal mining.-The relationship between atmospheric precipitation-surface water-groundwater transformation under the influence of coal mining is revealed,and the mutual transformation mechanism of atmospheric precipitation-surface water-groundwater and mine water is clarified and expressed quantitatively.The main conclusions are as follows.1.During the five periods of abundant,flat,dry and transitional periods in the natural basin,surface water and groundwater water chemistry types,hydrogen-oxygen isotope characteristics,and hydrogen-oxygen isotope fitting equations are similar,indicating that the recharge source properties of both are closely related,and groundwater chemistry types evolve from HCO₃-Ca·Mg type to HCO₃·SO₄-Ca·Mg type along the direction of surface water runoff.And the hydrogen and oxygen isotopes of surface water and groundwater are all located below the national atmospheric precipitation line,indicating that atmospheric precipitation is the main source of recharge.Surface water exhibited isotopic enrichment compared with groundwater in all periods..2.The transformation relationship of the natural basin in the five periods of abundance,flat,dry and transition are groundwater to surface water,the transformation of atmospheric precipitation to surface water and groundwater increases during the period of abundance,the contribution of groundwater to surface water in May 2019(flat period)is 45.75%,followed by the recharge of atmospheric precipitation to surface water with 27.05%;August 2019(abundant period)the contribution of atmospheric precipitation to recharge of surface water and groundwater increases(36.05%);October 2019(abundant and dry excess period)the contribution of atmospheric precipitation to surface water is 41.95%and to groundwater is31.45%;July 2020(abundant period)and November 2020(dry period)is mainly the recharge of atmospheric precipitation to surface water and groundwater,and surface water is recharged to groundwater through seepage.The conversion of groundwater to surface water decreases and the conversion of atmospheric precipitation to surface water increases,and atmospheric precipitation depletes the?D and?18O of surface water.3.The water chemistry types of surface water and groundwater in the mine area and the following watersheds are consistent,which proves the close hydraulic connection,and the elevation of calcium ions,magnesium ions and sulfate ions in the water chemistry of the mine area is related to sulfate minerals;the slopes of the fitted equations of hydrogen and oxygen isotopes of surface water and groundwater are smaller than the local precipitation line,which indicates that the recharge source of surface water and groundwater is atmospheric precipitation.The mining activity has changed the original circulation pattern,as the extraction disturbs the groundwater to form a new deposit form-mine pit water,the transformation relationship between atmospheric precipitation-surface water-groundwater and the transformation amount are changed;the coal mining drains the groundwater to lower the groundwater level in the mine watershed,forming a landing funnel centered on the mine,which reduces the mutual transformation amount between surface water;the surface fissures and collapse caused by the extraction,which makes the transformation amount between atmospheric precipitation and mine pit water decrease.The surface fissures and collapse caused by mining have changed the conversion relationship between precipitation and mine water from indirect to direct conversion.4.The conversion of atmospheric precipitation to surface water and groundwater during the period of abundant water and the transition period between abundant and dry in the mine area and the following watersheds,and the conversion of groundwater to surface water is reduced by 10.9%compared with the natural watersheds;the conversion of groundwater to surface water during the period of flat water and dry water,and the conversion of atmospheric precipitation to surface water is reduced by 20.25%.The coal mining changed the sink conditions of atmospheric precipitation,and the mining process produced damage to the surface,which accelerated the conversion capacity of atmospheric precipitation and surface water to groundwater and reduced the surface runoff of atmospheric precipitation;the conversion of groundwater to surface water decreased from 36.85%to 25.38%.5.Mining activities have changed the original circulation pattern,as extraction disturbs groundwater to form a new form of deposit-mine pit water,the transformation relationship between atmospheric precipitation-surface water-groundwater and the amount of transformation has changed,coal mining drains groundwater to lower the groundwater level in the mine basin,forming a landing funnel centered on the mine,which reduces the contribution of groundwater to surface water,and the contribution of groundwater to surface water during the flat,abundant,dry and transitional water periods The contribution of groundwater to surface water is reduced by 4%,8%,6%and 9%respectively.The coal mining changed the sink conditions of atmospheric precipitation,and the mining process produced damage to the surface,which accelerated the conversion capacity of atmospheric precipitation and surface water to groundwater,and increased by 3%,2%,4.5%,and 2%during the flat,abundant,dry,and transitional water periods,respectively;reduced the amount of atmospheric precipitation to surface runoff conversion,and the contribution of atmospheric precipitation to surface water decreased by 2%,14%,10%,and 2%,respectively6.The water chemistry types of groundwater and surface water are similar to those of the same period.Mine water conventional water chemistry indicators,heavy metal indicators and?D and?18O variation range are smaller than surface water and groundwater,mine water and?D and?18O distribution is concentrated and not obvious seasonalization,mainly distributed in the lower left of the atmospheric precipitation line,indicating that mine water receives recharge from atmospheric precipitation;groundwater to mine water transformation in May 2019(flat water period),August 2019(abundant water period),October 2019(abundant and dry transition period),July 2020(abundant water period),and November2020(dry water period)are 73%,62%,69%,64%,and 77%,respectively;the average contribution of atmospheric precipitation to mine water is 0.65%,3.2%,0.7%,2.9%,and0.05%;the average contribution of surface water to mine water is 15.9%,28.5%,16.8%,26.4%,and 12.3%.The conversion ratio of atmospheric precipitation to mine water increases during the abundant water period and decreases during the flat and dry water periods,while the lateral recharge of groundwater to mine water increases during the flat and dry water periods and decreases during the abundant water period.The contribution varies among periods,but the main source of recharge is still groundwater,followed by surface water,and the least direct conversion of mine water by atmospheric precipitation.