| The Kashgar Delta is located in the western Kashi Prefecture of Xinjiang,and plays an important strategic role in the national regional development and the opening up of the western region.Water resources in this area are relatively scarce,groundwater as the main water supply source,the shortage of groundwater caused by poor water quality(sulfate,chloride,total dissolved solids and total hardness generally exceed the standard)has seriously hindered the economic development of the region.At present,there is no research on groundwater circulation patterns in Kashgar Kelta.Therefore,it is very important to study the groundwater circulation patterns in this area.This study can provide scientific basis for groundwater resource evaluation,management,utilization and ecological environment protection.Based on the regional groundwater circulation theory and the analysis of regional hydrogeology condition and groundwater flow field,hydrogeochemistry and environmental isotopes were comprehensively applied to study the current circulation characteristics of groundwater in the study area,and the typical groundwater circulation pattern was established.The main research results were as follows:(1)The groundwater depth of single structure unconfined groundwater area was 5 to 100 m,and groundwater depth of multilayer structure unconfined groundwater-confined groundwaterarea was 0 to 50 m.The groundwater level was approximately 1170 to 2465 m,and direction of groundwater generally moved from west to east.Groundwater hydraulic gradient decreased from west to east.(2)The groundwater in the study area was weak alkaline,SO42-was the main anion in the groundwater,followed by Cl-,Na+ was the main cation,and the concentration of Ca2+ and Mg2+ were not significantly different.The ion concentration of groundwater was characterized by unconfined groundwater in river alluvial plain>confined groundwater in river alluvial plain>unconfined groundwater in piedmont sloping alluvial-diluvial plain.Groundwater salinity accumulated from upstream to downstream.The unconfined groundwater were mainly SO4 and SO4·Cl types,confined groundwater were mainly SO4·HCO3,SO4·Cl and SO4 types.The evolution trend of groundwater chemical types was HCO3·SO4?SO4?SO4·Cl(Cl·SO4).(3)The groundwater ions were mainly derived from the dissolution of evaporates such as halite and gypsum,and the dissolution ability was characterized by unconfined groundwater in piedmont sloping alluvial-diluvial plain>confined groundwater in river alluvial plain>unconfined groundwater in river alluvial plain.Piedmont sloping alluvial-diluvial plain was the main dissolution-runoff zone and the river alluvial plain was main runoff-accumulation salt zone.Unconfined groundwater in the river alluvium plain was affected by evaporation,and the confined groundwaterwas affected by reverse cation exchange and mixing.(4)The groundwater in the study area was mainly derived from atmospheric precipitation,and was affected by evaporation.The groundwater recharge elevation was from 2447 to 4419 m,with the increase of recharge elevation,the isotopic of groundwater tends to be depleted,and the isotopic elevation effect was obvious.The north groundwater system groundwater recharge area was located in the high mountains of northwest Tianshan,and the groundwater recharge area of the southern groundwater system was located in the middle-low and high mountains of southwest Kunlun Mountains.(5)In the northern groundwater system,99.38%of the area of unconfined groundwater and 92.48%of the area of confined groundwater SO42-exceeded standard,and 56.97%of the area of unconfined groundwater and 89.89%of the area of confined groundwater SO42-exceeded standard in the southern groundwater system.The sources of sulfate in the unconfined groundwater in the northern and southern piedmont sloping alluvial-diluvial plain were the dissolution of terrestrial and marine-terrestrial deposit evaporates,respectively.The sources of sulfate in the unconfined groundwater in the river alluvium plain were the dissolution of terrestrial deposit evaporates and pollution from fertilizer leaching.The confined groundwater was affected by the dissolution of evaporates,and was also affected by the bacterial sulfate reduction and mixing effect of the unconfined groundwater.(6)The results of 3H age estimation of groundwater in the study area were 8-49a and>50a.The 3H age of unconfined groundwater in piedmont sloping alluvial-diluvial plain in northern and southern groundwater systems were 30a and 29a,respectively.The age of unconfined groundwater in downstream river alluvial plain and confined groundwater in river alluvial plain were>50 a.The results of renewal rate estimation of groundwater in the study area were 0.03?16.35%·a-1.In the northern groundwater system,the average renewal rate of unconfined groundwater in piedmont sloping alluvial-diluvial plain,unconfined groundwater in river alluvial plain and confined groundwater in river alluvial plain were 6.13%·a-1?5.80%·a-1 and 0.19%·a-1,respectively.In the southern groundwater system,the average renewal rate of unconfined groundwater in piedmont sloping alluvial-diluvial plain,unconfined groundwater in river alluvial plain and confined groundwater in river alluvial plain were 5.21%·a-1?1.98%·a-1 and 0.20%·a-1,respectively.The results of 14C age estimation of groundwater were 476?34 578 a.The average 14C ages of unconfined groundwater in river alluvial plain in northern and southern groundwater systems were 10 682a and 5 529a,respectively.The average 14C ages of confined groundwater in river alluvial plain were 31 197a and 27 967a,respectively.(7)Inverse hydrogeochemical simulation results showed that along the unconfined groundwater and confined groundwater path,halite,dolomite,and gypsum were dissolved,and calcite was precipitated.In the middle and lower reaches,the unconfined groundwater depth became shallower and CO2 escaped,which was affected by evaporation.Confined groundwater was affected by reverse cation exchange and along the flow path,and the reverse cation exchange was stronger.(8)Northern and Southern groundwater systems in the study area were divided into two local circulation systems(?1 and ?2)and a regional circulation system(?).Local circulation system ?1 mainly existed in the unconfined groundwater in piedmont sloping alluvial-diluvial plain and upstream river alluvial plain,groundwater was younger with higher renewal rate.Local circulation system ?2 mainly existedin the unconfined groundwater in middle and lower river alluvial plain.Groundwater was mainly horizontal flow,and along groundwater,with chemical compositions and age of water increased gradually,the renewal rate decreased gradually,and the renewal rate decreased gradually.Regional circulation system? refered to deep circulation system,and it existed in deep buried unconfined groundwater in piedmont and confined groundwater,groundwater was mainly horizontal flow.This system,contained deep circulation depth,long runoff pathway,old groundwater age,and weak renewal ability. |
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