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Groundwater is one of the major water sources for production, living, and agricultural irrigation in the Yinchuan Plain. Owing to the influence of the regional environmental background and long-term effects of human activities, groundwater quality is generally inferior. To deeply analyze the formation mechanism and source of hydrochemical components in groundwater in the Yinchuan Plain, the traditional hydrochemical graphic method and mathematical statistics and principal component analysis-multivariate linear statistical model were used. Based on inorganic component contents of 100 phreatic water samples and 46 confined groundwater samples, the hydrochemical characteristics and quality status, spatial distribution of over-limit toxicological components, and contribution rate of hydrochemical components were analyzed. The results showed that the chemical components of groundwater were controlled by rock weathering and evaporation concentration. Dissolution-enrichment （F1）, original geological environment （F2）, and human activities（F3） were the principal factors that influenced groundwater hydrochemistry with the contribution rates of 73.67%, 14.45%, and 11.88%, respectively. The major over-limit toxicity indices in groundwater were NO 3 - -N and F - . High NO 3 - -N phreatic water was mainly influenced by agriculture activities, followed by the discharge of domestic sewage. Enrichment of groundwater F - was mainly caused by leaching of F-bearing minerals and cation exchange adsorption.

Groundwater pollution early warning is an effective means for regional groundwater pollution prevention. The groundwater pollution early warning model coupled with the current situation of groundwater quality, groundwater quality variation trend, and groundwater pollution risk were applied to the plain area of Barkol-Yiwu Basin, and the regional scale groundwater pollution early warning was realized by combining the early warning of groundwater quality status and trend. The TOPSIS method based on comprehensive weight was used to evaluate the current situation of groundwater quality. The variation trend of groundwater quality was analyzed by calculating the trend interpolation results of 18 in-situ groundwater quality monitoring wells. The groundwater vulnerability map, groundwater pollution load map, and groundwater function value map were superimposed using the superposition index method to evaluate groundwater pollution risk. The results showed that the groundwater quality was good and relatively good, and the poor groundwater quality in some areas was mainly affected by the shallow groundwater depth and the large porosity of the vadose zone. Groundwater quality was stable from 2011 to 2022, mainly due to the leakage of wastewater generated by industries and agriculture into groundwater, resulting in the deterioration of groundwater quality in some areas. Groundwater pollution risk was generally low, and the dual effects of high vulnerability and high pollution load of groundwater led to local areas with high pollution risk. The early warning level of groundwater pollution was generally low, and the heavy and highly heavy warning areas accounted for 16.4% and 17.5% of the study area, respectively, mainly distributed in Xiamaya Township of Yiwu County and northern Santanghu Town, Dahongliuxia Township, and Dahe Town of Barkol County. The quaternary sediments exposed were mainly sandy pebbles, with developed pores and strong water permeability. The interception and adsorption capacity of pollutants were weak. Pollutants produced by industries, agriculture, and life easily leaked into groundwater aquifers, resulting in poor groundwater quality and high risk of groundwater pollution, which ultimately led to a high early warning level of groundwater pollution in some areas. The research on early warning of groundwater pollution provided an important theoretical basis for the development of groundwater pollution remediation.

The accurate prediction of spatial variation trends in groundwater SO 4 2- is of great significance for improving groundwater quality and regional groundwater management level. The multi-source spatio-temporal data such as land cover data, soil parameter data, digital elevation data, and groundwater pH value in the plain area of the Yarkant River Basin in 2011, 2014, 2017, and 2020 were used as characteristic variables to analyze their correlation with groundwater SO 4 2- concentration. To enhance the prediction accuracy, the Bayesian optimization algorithm (BOA) was used to optimize the random forest regression (RFR). Based on the BOA-RFR model, the importance of the characteristic variables was analyzed, the prediction accuracy of the model was evaluated, and the groundwater SO 4 2- prediction map was generated. The results showed that pH value, ground elevation (GE), and percentage of bare land (BAR) in the contribution area were important parameters influencing groundwater hydrochemical composition, which were significantly negatively correlated with groundwater SO 4 2- concentration, and the importance of impact factors for predicting groundwater SO 4 2- concentration exceeded 25 %. The geostatistical interpolation method was used as an auxiliary tool for the predictive modeling of spatial distribution. After adding auxiliary samples, the R 2 of groundwater SO 4 2- concentration prediction of the BOA-RFR model was greater than 0.96, and the maximum values of RMSE and MAE were reduced by 4.7 % and 23.8 %, respectively, compared with the minimum values of the model with fewer samples. The SO 4 2- concentration prediction map showed that high SO 4 2- groundwater was enriched in the northeast of the plain area of the Yarkand River Basin, an area that was expanding.

Groundwater is a vital resource for local human life and production in the oasis zone of the Cherchen River Basin of Xinjiang. Understanding the controlling factors of groundwater salinization and pollution is of great significance for the sustainable utilization of groundwater resources and protection of the ecological environment in desert oasis areas. In light of this, a total of 36 single structure unconfined groundwater samples and 54 multi-layered structure unconfined and confined groundwater samples were collected from the oasis zone of the Cherchen River Basin and evaluated for the distribution characteristics and pollution status of major ions. Hydrogeochemical methods (e.g., Piper diagram, multivariate statistics, Gibbs model, and relationships among ions) were used to determine the main controlling factors of groundwater salinization and pollution. Differences in hydrogeochemical zonation were found from the single structure unconfined aquifers in sloping plains of piedmont areas to the multi-layered structure unconfined and confined aquifers in alluvial-proluvial plain areas, and Cl-Na (87.8%) was the main hydrochemical type in the groundwater of the study area. The quality of single structure unconfined groundwater was starkly better than that of the multi-layered unconfined and confined groundwater, which was mainly caused by Na + (mean value of 9 969 mg·L -1 ), Cl - (13 687 mg·L -1 ), and SO 4 2- (5 840 mg·L -1 ). Moreover, the natural hydrogeochemical process was the main reason for the deterioration of groundwater quality. The hydrochemistry was mainly controlled by the water-rock interaction and evaporation processes. The mineral dissolution of silicates and evaporites was an important source of chemical ions in the groundwater. Furthermore, the chemical weathering of evaporites combined with the processes of evaporation and cation exchange had a significant influence on the salinization of multi-layered unconfined and confined groundwater in alluvial-proluvial plain areas. In addition, synthetic fertilizers were the main pollution sources of NO 3 - in groundwater in the intensive agricultural zones.

Groundwater pollution risk assessment is an important part of groundwater pollution prevention and control. Taking groundwater in the plain area of Barkol-Yiwu Basin as the research object, the DRSTIW model was constructed to evaluate groundwater vulnerability. According to the survey data of contaminated sites and land use types, point source and non-point source pollutions were classified, and the groundwater pollution load was evaluated. The primary value, economic value, and ecological value of groundwater were considered to evaluate the functional value of groundwater. The groundwater pollution risk assessment map was generated by using the map algebra function of ArcGIS software. The ROC curve was used to verify the risk assessment results of groundwater pollution. The spatial distribution of cold and hot spots of groundwater pollution risk was obtained by calculating the G index, and the change in hot spots was quantitatively analyzed by combining the center of gravity and standard deviation ellipse. The results showed that the groundwater vulnerability was generally low. The gentle terrain slope, shallow groundwater depth, and strong aquifer permeability made it easy for pollutants to enter the aquifer, resulting in high groundwater vulnerability in the northwest of Santanghu Town, the southeast of Dahongliuxia Township, and Kuisu Town in Barkol County. The groundwater pollution load and groundwater functional value were generally low, whereas the point source and non-point source pollution caused by industrial and agricultural production and life would increase the groundwater pollution load in local areas, and the human economic activities and habitat quality levels would affect the distribution of high groundwater function value areas. Groundwater pollution risk was generally low; very high and high pollution risk areas only accounted for 6.8% of the study area, mainly distributed in Naomaohu Town and Yanchi Town of Yiwu County, Kuisu Town, Shirenzi Township, Huayuan Township of Barkol County, and Hongshan Farm of Corps. The shallow groundwater depth, strong permeability of soil surface and vadose zone media, poor adsorption capacity, and concentrated distribution of pollution sources made it easy for pollutants to migrate and enrich in these areas. Under the dual influence of high vulnerability and high pollution load of groundwater, the risk of groundwater pollution in local areas increased. Affected by human activities, there was a certain spatial agglomeration of groundwater pollution risk, and the overall trend was from northwest to southeast. The results of groundwater pollution risk assessment provided a scientific reference for the division of groundwater pollution prevention and control areas.

Groundwater is an important water supply source for production and life in arid and semi-arid areas. This study revealed the hydrochemical characteristics of groundwater in the Barkol-Yiwu Basin of Xinjiang and analyzed the pollution sources, which is of great significance in the sustainable utilization of local groundwater. Four spring water samples, 20 unconfined groundwater samples, and 11 confined groundwater samples collected in August 2022 were analyzed using mathematical statistics, a graphic method, and the PCA-APCS-MLR model. The results showed that the chemical types of groundwater in the study area were complex and diverse. The spring water was mainly HCO 3 ·SO 4 -Na·Ca type groundwater, the chemical types of unconfined groundwater were mainly HCO 3 ·SO 4 -Na·Ca and HCO 3 ·SO 4 -Ca, and the chemical types of confined groundwater were HCO 3 ·SO 4 -Na·Ca and HCO 3 ·Cl·SO 4 -Na·Ca. The hydrochemical type of confined water in unused land was single(Cl·SO 4 -Na·Ca), and the hydrochemical types of confined groundwater in cultivated land and urban and rural residential land were complex, indicating that groundwater was affected by human activities. The evolution process of groundwater was mainly affected by water-rock interactions and cationic exchange. The cation exchange from spring water to unconfined groundwater to confined groundwater was gradually enhanced, the weathering and dissolution of gypsum and anhydrite was gradually weakened, and the weathering and dissolution of rock salt was gradually strengthened. Leaching-enrichment(mainly the dissolution of evaporite), human activities(industrial, agricultural, and domestic pollution), and the primary geological environment were the main factors affecting groundwater in the study area.

Groundwater contamination risk assessment is an effective tool for groundwater pollution prevention and control. The evaluation system mainly includes three parts:groundwater contamination source load assessment, groundwater vulnerability assessment, and groundwater function value evaluation. Taking the plain area of southern Turpan Basin as an example, based on the survey data and land use data, point source pollution and non-point source pollution were divided to evaluate the load of groundwater pollution sources, the classical DRASTIC model was selected to evaluate the vulnerability of groundwater, and the functional value of groundwater was evaluated from the point of view of water quality and quantity. The three factors were weighted and superimposed via GIS platform to generate the risk zoning map of groundwater contamination. The results showed that the overall risk of groundwater contamination in the study area was low. The area of high-risk and relatively high-risk areas accounted for 15.5% of the total study area, which were mainly distributed in L1, L2, and L3 of the study area. L1 was mainly affected by high pollution source load and high groundwater vulnerability. L2 was mainly the result of the joint action of high groundwater function value and domestic non-point source pollution. Non-point source pollution dominated by agricultural activities and high functional value of groundwater were the main reasons for the high risk of groundwater pollution in the L3 area. The results of the groundwater contamination risk assessment serve as an important reference for decision-makers to delineate the prevention and control area of groundwater pollution.

Groundwater pollution risk assessment is an effective method to manage groundwater resources and prevent groundwater pollution. The DRSTIW model was used to evaluate the groundwater vulnerability in a plain area of the Yarkant River Basin, and factor analysis was used to identify pollution sources for pollution loading evaluation. The functional value of groundwater was estimated by considering both the mining value and the in-situ value. The entropy weight method and the analytic hierarchy process (AHP) were used to determine the comprehensive weight, and a groundwater pollution risk map was generated based on the overlay function of ArcGIS software. The results showed that the natural geological factors such as large groundwater recharge modulus, wide recharge sources, strong permeability of soil surface and unsaturated zone, and shallow groundwater depth facilitated pollutant migration and enrichment, resulting in a higher overall groundwater vulnerability. Very high vulnerability and high vulnerability areas were mainly distributed in Zepu County, Shache County, Maigaiti County, Tumushuke City, and the eastern part of Bachu County. The pollution loading of groundwater was generally low, the main pollution sources were point source pollution caused by water-rock interaction, non-point source pollution caused by pesticides and fertilizers, and point source pollution caused by industry and life. The overall functional value of groundwater was low because of human economic activities, fine water quality, and good habitat quality. Groundwater pollution risk was generally low, and very high and high pollution risk areas accounted for 20.7% of the study area, mainly distributed in Shache County, Zepu County, Maigaiti County, Tumushuke City, and the western part of Bachu County. Natural conditions such as strong aquifer permeability, weak groundwater runoff conditions, large groundwater recharge modulus, low vegetation coverage, and strong water-rock interaction, coupled with frequent human activities such as application of agricultural fertilizers and discharge of industrial and domestic sewage, made the groundwater pollution risk higher in these areas. Groundwater pollution risk assessment provided strong data support for the optimization of the groundwater monitoring network and the prevention of groundwater pollution.

To analyze spatial-temporal variation in groundwater quality and contamination sources in the Shihezi-Changji area in Xinjiang, a Bayesian water quality evaluation model based on Shannon entropy, Spearman rank correlation coefficient, principal component analysis, and an absolute principal component scores-multiple linear regression receptor model (APCS-MLR) were comprehensively used in this study. Groundwater samples in 23 in-situ wells were collected from 2016 to 2021 for quality analysis. The results showed that ① groundwater quality was generally good, with most samples having a phreatic water quality of Class Ⅰ and Class Ⅱ and most confined groundwater quality being of Class Ⅰ. ② Temporally, 2016 and 2017 were the key time nodes of water quality variation in phreatic water and confined groundwater, respectively. Class Ⅳ and Class Ⅴ groundwater was observed only before the key time nodes, whereas after those time nodes the groundwater quality fluctuated within Class Ⅰ to Class Ⅲ. ③ Spatially, the order of phreatic water quality in descending order was Shihezi City, Hutubi county, Manas county, and Changji City, whereas that of confined groundwater quality was:Shihezi City and Changji City, Hutubi county, and Manas county. ④ The spatial-temporal variations in groundwater quality and that in major related indices were basically similar and highly heterogeneous. ⑤ Phreatic water quality was mainly affected by leaching (67.30%), leaching-migration (10.89%), and agricultural-domestic pollution (9.44%); by contrast, unconfined groundwater quality was mainly affected by leaching-enrichment (52.08%), agricultural-domestic pollution (16.06%), and ion exchange under an alkaline environment (12.64%). Although groundwater quality was improved over the years, more attention should be paid to groundwater salinization in the 149 Regiment in northern Manas County.

This study revealed the distribution characteristics and formation mechanism of groundwater salinization in the plain area of the lower Kashgar River in Xinjiang, which can provide scientific basis for a local sustainable groundwater exploitation plan and practical significance for local water supply security and social stability. Fifteen phreatic water samples, 38 shallow confined groundwater samples, and 16 deep confined groundwater samples were collected in September 2018. Mathematical statistics, a Duorv diagram, PCA-APCS-MLR model, ion ratios, and hydrogeochemical simulations were comprehensively used for sample analysis. The results showed that groundwater was weakly alkaline in general (pH ranged between 6.48 and 8.60 with an average of 7.57), with total dissolved solids (TDS) ranging from 573.0 to 16700.0 mg·L -1 . Groundwater was mainly composed of Cl - , SO 4 2- , Na + , and Ca 2+ . The main groundwater hydrochemical types included were HCO 3 ·SO 4 ·Cl, SO 4 , and SO 4 ·Cl. No brine was observed in the study area, phreatic water was mainly composed of brackish water and saline water, and confined groundwater was mainly composed of saline water. The salinization coefficient calculation results showed that the salinization degree gradually increased from phreatic water to deep confined groundwater. Evaporation concentration and lixiviation were the main factors leading to the salinization of groundwater. The dissolution and cation exchange of carbonate and silicate rocks gradually weakened from phreatic water to deep confined groundwater, whereas the dissolution of evaporite rock always dominated and was gradually strengthened, which was also the primary factor that caused the salinity of deep groundwater to be higher than that of shallow groundwater. Human activities such as agricultural fertilization, unreasonable use of surface water for irrigation, and improper treatment of domestic sewage had a certain impact on groundwater salinization. The leaking recharge of salt water from adjacent aquifers aggravated the groundwater salinization.

The geological conditions of the Bortala River basin are complex, and the transformation of surface water and groundwater is frequent. It is great significance to study the hydrochemical characteristics and transformation relationship of surface water and groundwater for the reasonable development and allocation of water resources in the basin. Based on 15 surface water samples and 39 groundwater samples collected in April and May 2021, the APCS/MLR model and the combination of stable hydrogen and oxygen isotopes with hydrochemistry were used in this study to analyze the hydrochemical types and the distribution characteristics of hydrogen and oxygen isotopes, the source contribution of chemical components, and the transformation relationship between surface water and groundwater. The results showed that the surface water was mainly HCO 3 ·SO 4 -Ca type and HCO 3 -Ca type, and the groundwater was mainly HCO 3 ·SO 4 -Ca·Na type, HCO 3 -Ca type, and HCO 3 ·SO 4 -Ca type. The contribution rates of the dissolution-migration-enrichment factor, human activities factor, environment factor, and native geological factor to the chemical components were 28.8%, 17.7%, 12.0%, and 6.5%, respectively. Bortala River water D and 18 O was enriched along the distance, and groundwater D and 18 O in the north bank was generally more enriched than groundwater in the south bank as a whole. Under the control of geological conditions such as geological structure and hydrogeological conditions, the transformation of river water and groundwater was concentrated in the middle reaches of the Bortala River, which was generally manifested in both unconfined groundwater and spring overflow in the sides of the recharge river water, and the recharge proportion ranged from 1.0% to 70.9%.

In this study, the hydrochemical characteristics of surface water in the Yarkant River Basin of Xinjiang and their controlling factors were analyzed using a Piper trilinear diagram, Gibbs diagram, saturation index, ion proportional relationship, and other methods. The study has significance to the surface water resources in the basin for development and utilization. The results indicated that the pH of the surface water ranged from 7.40 to 8.33, with a mean value of 7.92, which was weakly alkaline. The mean value of the total dissolved solids (TDS) of the river, canal, and reservoir water exhibited an increasing trend. The TDS mean of the river was 429.24 mg·L -1 , higher than the average value of rivers worldwide (115 mg·L -1 ). The hydrochemical types of the river water were predominantly HCO 3 ·SO 4 -Ca·Na and SO 4 ·HCO 3 ·Cl-Ca·Na·Mg types, of the canal water was mainly HCO 3 ·SO 4 ·Cl-Ca·Na type, and of the reservoir water was mostly the SO 4 ·Cl-Na·Ca type. The TDS of the river water along the Yarkant River and Tiznap River demonstrated a continuous increase and fluctuation trend, respectively, while the variation of the primary ions was relatively complex. The primary ions of surface water were mostly influenced by rock weathering, evaporation crystallization, and cation exchange, in which gypsum and rock salt were predominantly dissolved in the process of rock weathering. In addition, human activities had significant effects on the chemical composition of the surface water downstream.

We use 3487 surface soil samples, 35 soil profile samples, and 93 agricultural products and root soil samples obtained from the southeastern Tarim basin, Xinjiang, northwestern China (Ruoqiang County and Qiemo County, Bayingguo Mongolia Autonomous Prefecture, and Minfeng County and Yutian County, Hetian Prefecture) to assess As contamination. Multivariate statistical analysis, geostatistics, and global information system (GIS) techniques are used to study:the spatial distribution characteristics of soil As, the effects of various agricultural products on As enrichment, and to compare the characteristics of the As content of agricultural products and root soils in spatially significantly and non-significantly autocorrelated regions. The As content of soil samples were relatively low, and the average As contents determined for agricultural land and non-agricultural land were 9.81 mg·kg -1 and 7.94 mg·kg -1 , respectively. We found that 568 surface soil samples (16.3% of all samples) had an As content that exceeded Xinjiang soil background values (11.2 mg·kg -1 ) and that five samples exceeded the risk screening values (25 mg·kg -1 ). The Moran's indexes of spatial autocorrelation were>0, and the main aggregation types of spatial autocorrelation of soil As were high-high and low-low types, with the zone of the high-high type being mainly located in the agricultural land of each county. A GIS spatial distribution map showed that the high value area of soil As content presented a flaky or island-like scattered distribution. The standard deviation ellipses showed that the trend direction of soil As content in:Ruoqiang County was from north to south, Qiemo County and Minfeng County were both from southwest to northeast, and Yutian County was from northwest to southeast. The As content of the vertical profiles of the agricultural land in Ruoqiang County fluctuated from the surface to depth, whereas those of other counties were relatively stable. The As enrichment ability of crops was ranked as:root vegetables > walnuts > wheat > corn > red dates. The As contents of corn and red dates showed a significant positive correlation with that of the root soil. There was no significant difference in the As content of agricultural products between significant autocorrelation zones and non-significant autocorrelation zones, whereas there was a significant difference in the As content of root soils.

Pollution-induced water shortage problems have severely hindered the economic development of Kashi Prefecture in Xinjiang. In order to study the chemical characteristics and main ion sources of groundwater in the Kashgar River Delta of Western Kashi Prefecture, 402 groundwater samples and 114 groundwater hydrogen and oxygen isotope samples were collected and tested in June to October 2016. Based on the methods of mathematical statistics, Gibbs diagram, ion ratio, Schoeller diagram, and hydrogeochemical simulation, the hydrogeochemical characteristics of the groundwater were analyzed, and the hydrochemical evolution law and the main ion sources were discussed. The following results were noted. ①SO 4 2- was the main anion in the groundwater, followed by Cl - . Na + was the main cation, and the groundwater was mainly SO 4 ·Cl-Na type. ②The groundwater ion components were controlled by dissolution of rocks and evaporation. The groundwater ions were mainly derived from the dissolution of evaporites, followed by the dissolution of carbonates. Unconfined groundwater in the river alluvium plain was affected by evaporation, and the confined groundwater was affected by reverse cation exchange and mixing. ③Along the groundwater flow direction, the concentration of ion components in the groundwater increased. Halite, dolomite, and gypsum were dissolved, and calcite was precipitated.

Poor water quality is one of the main reasons for a shortage of water resources in the Kashi Prefecture of Xinjiang. The area of the Kashgar Delta is located in the western Kashi Prefecture and covers an area of 13329 km 2 . Sulfate concentrations exceed the groundwater quality class Ⅲ standard in 73.2% of the unconfined groundwater area and 53.2% of the confined groundwater area. In addition, the TDS content and the hardness of the water are high. The chemical characteristics and sources of groundwater sulfate were analyzed using the isotope method of δ D, δ 18 O-H 2 O, and δ 34 S-SO 4 2- . The results showed that:① The dissolution of salt minerals such as calcareous siltstone, calcareous sandstone, and gypsum in denuded mountainous areas controlled the hydrochemical compositions in the basin, and formed surface water and groundwater dominated by SO 4 . The evolution trend of groundwater chemical types was HCO 3 ·SO 4 →SO 4 →SO 4 ·Cl. Alluvial-proluvial gravel plains on the piedmont slopes were the main dissolution-runoff zones and the fluvial plain was main runoff accumulation zone. The chemical composition of the groundwater tended towards salinization, from upstream to downstream; ② The groundwater was mainly derived from atmospheric precipitation, and was affected by evaporation. The distribution of δ D and δ 18 O in the groundwaters of different hydrogeological units was clear; from upstream to downstream, isotope values varied from low to increasingly higher, and evaporation varied from weak to strong, respectively. The distribution of isotopes in the confined groundwater in the river alluvium plain was relatively discrete, which was affected by the mixing effect of unconfined groundwater; ③ The sources of sulfate in the unconfined groundwater in the southern and northern alluvial-proluvial gravel plains on the piedmont slopes were the dissolution of marine-terrestrial and 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 the mixing effect of the unconfined groundwater and bacterial sulfate reduction.