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To investigate the chemical characteristics of groundwater and material sources in a typical karst hill (valley) depression, 41 groundwater samples were systematically collected in the Shiqi River basin. The statistical analysis of the conventional ion content in the groundwater shows that pH of the groundwater in the study area is between 6.06-8.07, the total solid solubility is between 18.21 mg ·L-1 and 336.28 mg ·L-1, and the charges of anions and cations in the water body are balanced. Ca2+, Mg2+, and HCO3- are the main ions in groundwater, with concentrations of 2.61-108.7 mg ·L-1, 0.54-27.61 mg ·L-1, and 8.1-370.74 mg ·L-1, respectively. The groundwater characteristics in the study area are consistent with the high calcium and weak alkalinity characteristics of karst water. By using the Gibbs diagram, piper diagram, end-member analysis, and ion proportional coefficient, hydrochemical characteristics and material sources of groundwater were further analyzed. The results show that Ca2+ and Mg2+ are mainly controlled by the weathering of limestone and dolomite in which carbonic acid is involved. Na+ mainly comes from the dissolution of silicate rocks. At the same time, Ca2+ and Na+ undergo cationic exchange adsorption in the groundwater flow process. K+, Cl-, and NO3- are mainly affected by agricultural fertilizer application and domestic wastewater discharge. The hydrogen and oxygen isotope analysis of groundwater shows that atmospheric precipitation is the main recharge source of groundwater in this region, which impacts the chemical characteristics and material sources of local groundwater. The results of this study show that the geological background of groundwater is the main factor that affects its hydrochemical characteristics and material sources in areas with relatively little anthropogenic activity.Groundwater resources are important sources of water in the arid region of northwestern China, but their overexploitation and utilization has led to a series of ecological and environmental problems. Exploring the characteristics and mechanism of groundwater chemical evolution is important for the rational use of groundwater resources. #link# The characteristics of groundwater chemical evolution were studied in the Yongji Irrigation Area of Hetao Irrigation District and the formation mechanism of the chemical compounds in groundwater were investigated using cluster analysis, factor analysis, and other statistical methods. The influence degree of different factors was calculated. The results showed that the major cations in groundwater in the study area were Na+ and K+, and the major anions were Cl- and HCO3-. Moreover, Na+, K+, and Cl- showed high spatial variability and were the main factors contributing to groundwater salinization. The major chemical compounds in the groundwater in the study area were Cl-Na, HCO3 ·Cl ·SO4-Na, and HCO3-Na. Based on the cluster analysis results, the groundwater was divided into four categories (A1, A2, B1, and B2), of which A1 was highly mineralized by Cl-Na type water, while A2, B1, and B2 were mainly HCO3 ·Cl ·SO4-Na and HCO3-Na type water. Principal component analysis results suggest that groundwater chemistry was mainly affected by salinization, carbonate karstification, and human activities with the influence degrees of 45.976%, 23.853% and 16.678%, respectively. Evaporation, salt rock dissolution, and cation exchange were important sources of Na+ and Cl- accumulation in the irrigation area. find more (leaching of soil salts) and drought (intense transpiration) were the key drivers of groundwater salinization in the irrigation area.To study the chemistry of surface water and potential control measures in the Ranwu Lake basin, 19 samples were collected from Ranwu Lake in 2019. Conventional hydrochemical techniques and statistical analysis methods (descriptive statistics, the Gibbs figure, ion ratio, Piper triangular diagrams) were applied to better understand the solute geochemistry and surface water hydrochemistry in the Ranwu Lake catchment. Surface water in the Ranwu catchment is slightly alkaline (pH of the samples ranged from 7.54 to 8.48 with an average value of 8.06). The concentrations of total dissolved solids (TDS) in the water range from 59.89 to 96.75 mg ·L-1 with an average of 79.98 mg ·L-1, the total dissolved solids of all samples are less than 100 mg ·L-1 and belong to fresh water. The TDS are dominated by Ca2+, Mg2+, HCO3-, and SO42- in the Ranwu Lake. The ion concentrations in the lake water samples are in the order of Ca2+ > Mg2+ > Na+ > K+. The concentrations of Na+and K+are very low. Ranging from 0.5 to 1.21 mg ·L-1,on the lake are found to be weak.To better understand the isotope variations on a short time scale, this study focused on a long-term rainfall event with light precipitation (June 26-27) and a short-term one with heavy precipitation (July 28) in Lanzhou City in the summer of 2019. Combined with HYSPLIT model, samples collected during a continuous precipitation event every 10 min and 30 min were analyzed to explore the characteristics and mechanism of stable hydrogen and oxygen isotopes in precipitation. The results indicate that the effect of sub-cloud secondary evaporation makes the slope of the sequential meteoric water line (SMWL) smaller at the beginning of the rainfall event. Most of the continuous sampling points are distributed above the global meteoric water line (GMWL) and local meteoric water line (LMWL). Moreover, the deuterium excess is larger than the local average annual deuterium (8.13), indicating that the samples have experienced moisture recycling to a certain extent. During two consecutive days (June 26-27) of rainfall, the variations in oxygen isotope δ18O did not follow the effect of precipitation amount; the precipitation δ18O of the first day was "L" shaped, and it fluctuated the next day. On July 28, δ18O steadily decreased, and the range of δ18O exceeded 9‰. On June 26, the moisture transport path was short at the height of 500 m and on June 27 local evaporation was the main pathway. On July 28, with a relatively stable air mass, the moisture source of the entire precipitation event did not change significantly, neither did the isotope value. Therefore, for a single precipitation event on a short time scale, the difference in moisture sources is one of the reasons for isotope variations.
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