Characteristics Of The Movement Of Reclaimed Soil Water And Its Water Source Study Using Stable Isotope Technology In Mining Subsidence Area With High Phreatic Water Level

China is the largest producer of coal in the world,and its coal production accounts for approximately half of the global production and underground(well)mining is the major coal mining way,which produces approximately 95% of the raw coal in China.The resulted land subsidence has emerged as the most prominent problem in coal mining areas.Land subsidence destroys large areas of arable land and threatens the national food security,and water logging in the subsided land area.Consequently,a large amount of land reclamation and ecological reconstruction work have been done in collapse area.The deep understanding of the change of stable isotope of soil water to regional water cycle is extremely important.Stable hydrogen and oxygen isotopes of water(?D and ?18O)as natural tracers for water cycle,having characteristics of rapid reaction to water environmental change,have been widely applied to hydrological processes and climatological studies.In this study,we chose reclamied soil in mining subsidence area with high phreatic water level.Based on the background level and its seasonal changes of precipitation,river,water of collapse area and underground water concluded by using isotope tracer technology,we do further analysis of the characteristics of seasonal change and vertical change of reclamied soil in the study area.Besides,we compare the characteristic of reclamied soil and its possible water source to research the pattern of soil water movement and the contribution rate of all types of water source affected by different reclamation time and its ways.In addition,we can conclude the main source of collapse water,which is beneficial to control the further enlargement of subsidenced area by taking suitable measures.Main results and conclusions are shown below:(1)The variations of ?D and ?18O in the study area were within the range of values of global and Chinese rainfall.?D,?18O in these areas showed seasonal change,which was lower in summer half year but higher in winter half year.The local meteoric water line(LMWL)in the district is ?D = 8.11?18O+14.48(R2=0.9),n=38,P<0.01,and its slope and intercept are both higher than that of the Global meteoric water line(GMWL).In addition,d-excess values were relative higher.All of these could be concluded to the fact that the humid climate condition in the area.Similar pattern was also seen in the values of ?D,?18O of regional river,water in the collapse area.But the variation rates of these two water types were smaller,compared with that of precipitation.Underground water in the district remained stable all year round because it’s rarely affected by outside factors.Seasonal change was also seen in underground water,too.(2)Soil moisture content increased with the increase of reclamied period,and finally remained stable.It was found that soil moisture was higher in 15 years than other reclaimed lands of shorter reclamation period.Seasonal pattern was seen in soil moisture of lands with different land use.Generally,rainy season was higher than dried season,but soil water content was higher in forest even in dried half year considering its strong function of water conservation.(3)The variation of ?D and ?18O of soil water was lower than that of precipitation.Generally,the values of δD and δ18O decreased with the increase of soil layer.The values of δD and δ18O of soil water remained stable and were much closer to that of underground water.It could be concluded that values of ?D and ?18O in soil water were higher with the increase of reclamation year.Apart from that,obvious fluctuation rate was normally seen in the topsoil(10-30cm)caused by the strong evaporation effect,but it decreased with depth and remained at a small level below 70 cm.Trees and crop have significant impacts on infiltration and mixture.Therefore,growing trees and crop is a good way to improve the cycling of soil moisture content and nutrition.(4)Precipitation is the main source of soil in collapse area(cropland: 0~30 cm;or forest: 0~40 cm).Below the depth of 70 cm,soil water mainly received underground water.In the middle of soil layer,approximately in the depth from 30/40 cm to 70 cm,mainly recharge by mixture soil water,infiltration from surface soil layer,root absorption and the upward movement of underground water caused by water potential.