Groundwater Chemical Characteristics And Controlling Factors In Jilantai Salt Lake Basin,Inner Mongolia

Jilantai Salt Lake is located in the southeastern part of Inner Mongolia Alxa League.It is an important salt production base in China,but it is located in the desert edge of the northwest dryland area.The ecological environment is fragile.Groundwater is the main source of water for local residents to live and produce.In recent years,there have been many problems such as water reduction,water quality deterioration,and the complexity of pollutant types and sources.Therefore,research on the chemical characteristics and pollution assessment of groundwater is extremely urgent.In this paper,the Jilantai Salt Lake Basin was selected as research object.The Shukalev classification,Piper trilinear diagram,Gibbs diagram and ion ratio method were used to analyze groundwater chemical characteristic and influencing factors in study area.The quality evaluation of groundwater in study area was carried out by single factor evaluation method,Nemerow comprehensive evaluation method and health risk evaluation method.using factor analysis method and absolute principal component score multiple linear regression extracts groundwater pollution sources,and analyzes the sources and causes of pollutants.Provides scientific basis for rational development and utilization of groundwater and ater environmental protection.The results showed that:(1)Groundwater environment was weakly alkaline as a whole in study area,and groundwater quality was brackish water.The groundwater hydrochemistry type was dominated by Cl--Na+type.The groundwater chemical type in northern part of the study area was relatively simple,which was relatively abundant in southern part of the study area.Evaporation and concentration is an important mechanism for controlling the main ions of groundwater in Jilantai Salt Lake Basin.The chemical composition of groundwater in study area was most affected by weathering of evaporite,followed by the weathering of silicate rock minerals.Cl-was mainly produced by evaporating salt deposits,Na+was not a single source,and Na+other than the dissolution of evaporated salt deposits was mainly produced by weathering and dissolution of sodium aluminosilicate.The weathering and dissolution of silicate rock was the primary factor affecting groundwater Ca2+and Mg2+ in study area.The alternating adsorption of cations has little effect on the chemical composition of groundwater in study area.(2)The single factor evaluation results showed that groundwater pollution in Jilantai Salt Lake Basin was very serious,there is no groundwater of Class I,II and III,and there are 10%IV water and 90%V water.The spatial distribution characteristics of single-factor index of groundwater quality indicators were more complicated.Most of the over-standard areas were distributed in parts such as Tugrigolla Valley,Bayinwula Mountains,Ulanbuh Desert in form of spots,islands and patches.The Helan Mountain and Piedmont alluvial plains had fewer single indicators over-standard areas.Nemerow comprehensive evaluation results showed that 20%of groundwater was poor water,and the remaining 80%of groundwater was very poor water in study area,and the extremely poor water was mainly distributed in the west of study area.The evaluation of the heavy metal Nemero index showed that the heavy metal pollution was small,and only 5.6%of the samples were slightly polluted.The contaminated area was concentrated in the Tugrigolla Valley in the southwest of salt lake.Health risk assessment results showed that health risk value of chemical carcinogens through the drinking water pathway was much higher than health risk value of non-chemical carcinogens.The average chemical carcinogenic risk value is lower than the US EPA maximum acceptable risk level,and there was a local or local area that exceeds the US EPA maximum acceptable risk level in the Salt Lake Basin.(3)The 6 common factors influencing groundwater quality were screened out by the method of factor analysis,which were F1(leached-enrichment factor,contribution rate of 24.61%),F2(agricultural activity factor,contribution rate of 20.38%),F3(original geological-agricultural production and living pollution factor,contribution rate of 11.72%),F4(industrial production pollution factor,contribution rate of 10.38%),F5(geological environment background factor,contribution rate of 10.78%)and F6(original geological factor,contribution rate of 10.61%)respectively.F1,F5 and F6 were environmental factors,and F2,F3 and F4 were human activity factors.The factor scores were obtained from factor function,which showed that the overall pollution factor score in the Bayinwula Mountains was higher,and point-like high-value areas existed in Ulanbuh desert.There was certain degree of pollution in the upper reaches of Tugrigolla Valley,while the water quality in most parts of the southeastern salt lake basin was better.These kinds of distribution and change were affected by both natural factors and human activities.The R2 between the calculated water quality index by APCS-MLR and observed values were greater than 0.7,which could be used to evaluate the contribution rate of factor to water quality.The study showed that the method by combining factor analysis and APCS-MLR was better in effectively identifying and quantitatively analyzing the chemical components of groundwater.