Hydrogeochemical Characteristics and Controlling Factors of Groundwater in a Typical Oasis in Arid Regions

Hydrogeochemical Characteristics and Controlling Factors of Groundwater in a Typical Oasis in Arid Regions | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hydrogeochemical Characteristics and Controlling Factors of Groundwater in a Typical Oasis in Arid Regions Xing WEI, Qingmei ZHANG, yulin zhou, Libo RAN, Delun CHEN, Xueting DOU, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8100581/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Feb, 2026 Read the published version in Acta Geophysica → Version 1 posted 5 You are reading this latest preprint version Abstract In arid regions, oases are critical to human survival and development, relying heavily on groundwater to sustain ecological balance and support socio-economic growth. This study focuses on a representative oasis city, where 198 groundwater samples were systematically collected in September 2022. A suite of analytical methods—including statistical analysis, Piper and Gibbs diagrams, ion-ratio analysis, and hydrogeochemical modeling—was used to characterize groundwater chemistry and identify its controlling factors. The results indicate that groundwater in the area is slightly alkaline. Unconfined groundwater is dominated by HCO₃·SO₄–Ca and HCO₃·SO₄–Na·Ca types, whereas confined groundwater is mainly HCO₃·SO₄–Na·Ca and HCO₃·SO₄·Cl–Na·Ca. Groundwater ion composition is influenced by water–rock interaction, with major ions primarily derived from the dissolution of halite, evaporites, and carbonates; cation exchange processes further affect confined groundwater. Halite and gypsum dissolve, while calcite and dolomite are near dissolution–precipitation equilibrium; overall dissolution propensity is higher in unconfined than in confined groundwater. Hydrogeochemical modeling quantitatively corroborates the primary water–rock interactions inferred from qualitative analyses of groundwater flow. These findings improve understanding of hydrogeochemical evolution in oasis groundwater within arid regions. Arid Region Oasis Groundwater Hydrogeochemistry Hydrogeochemical Modeling Controlling Factors Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Arid regions cover a substantial portion of global land, and their unique climatic conditions and fragile ecosystems have attracted considerable interdisciplinary attention (Yao et al., 2024 ; Tang et al., 2024 ). Within these environments, oases function as relatively humid refugia that support human survival and development, playing an essential regional role (Liu et al., 2023 ; Ju et al., 2023 ). Their existence relies on multiple natural resources, with groundwater being the most critical. Groundwater provides indispensable water for vegetation growth and agricultural irrigation and is central to maintaining ecological balance (Sheng et al., 2022 ; Gobashy et al., 2021 ; Ullah et al., 2024 ). Yet groundwater in arid regions is particularly vulnerable to environmental change because of limited recharge and high evaporative losses, making its sustainable management a global challenge (Yan et al., 2025 ). In recent years, climate change and intensifying human activities have caused groundwater degradation in more than 20% of oasis irrigated areas worldwide (Mao et al., 2020 ). Problems such as persistent groundwater-level decline and progressive water-quality deterioration have emerged (Palma et al., 2023 ), placing unprecedented pressure on aquifer systems. For instance, excessive irrigation pumping has driven salinization and nitrate pollution in many arid oases, threatening ecosystem health and water security. As a crucial component of water resources in oasis systems, the hydrogeochemical characteristics of groundwater reveal its formation and evolution; however, the relative contributions of controlling factors to groundwater chemistry are often poorly quantified (Wang et al., 2024 ; Liu et al., 2020 ; Koncsos et al., 2024). Recent studies highlight the value of integrating hydrochemical and isotopic techniques to disentangle complex interactions between natural processes (e.g., rock weathering, evaporation) and anthropogenic influences (e.g., irrigation return flow, wastewater discharge) on groundwater quality (Preethi et al., 2025 ). A comprehensive understanding of groundwater hydrogeochemistry and its controlling factors in typical arid-region oases is therefore of great theoretical and practical significance for sustainable use and protection of groundwater resources, maintaining ecological balance, and ensuring safe water supplies. Despite substantial progress, several knowledge gaps remain. First, the relative roles of natural processes (e.g., mineral dissolution, evaporation) and human activities (e.g., agricultural practices, urbanization) in shaping groundwater chemistry are still not well constrained (Li et al., 2024 ). Second, the spatial and temporal variability of groundwater quality in oasis systems—particularly under a changing climate—remains insufficiently understood (Guo et al., 2019 ). Third, there is a lack of integrated frameworks that couple traditional hydrochemical methods with advanced modeling to predict future groundwater evolution (Kumar et al., 2017 ). In China, Xinjiang is a typical arid region with numerous oases, among which the Changji Hui Autonomous Prefecture stands out as a representative area. The unique geographical location and geological conditions of this region contribute to the complexity and distinctiveness of its oasis groundwater system. For example, the interaction between surface water and groundwater, coupled with the high evaporation rates, creates a dynamic hydrogeochemical environment that is highly sensitive to external perturbations. In recent years, the growing reliance on groundwater has resulted in excessive extraction, significantly altering its chemical composition. Therefore, this study focuses on a typical oasis in this arid region. Using field surveys, water sample collection, and analytical testing, a comprehensive approach was adopted, integrating statistical analysis, Piper diagrams, Gibbs diagrams, ion ratios, and hydrogeochemical modeling to reveal the groundwater’s chemical characteristics and controlling factors in the area. Insights into groundwater circulation processes from this study provide scientific evidence and references for the sustainable utilization of groundwater resources and environmental protection in arid-region oases. 2. Materials and Methods 2.1. Study Area The Changji Hui Autonomous Prefecture is situated on the northern slope of the Tianshan Mountains and the southeastern edge of the Junggar Basin, between latitudes 43°20′–45°00′ N and longitudes 85°17′–91°32′ E, covering a total area of 73,900 square kilometers (Fig. 1 ). The topography gradually descends from higher altitudes in the southern region to lower areas in the north, with a southeast-to-northwest gradient. The region's landforms can be divided into four types: the Tianshan Mountains, sloping plains, desert basins, and the Beita Mountains. The central plains lie between the southern mountains and northern desert, forming a flat, fertile oasis zone with favorable water and soil conditions created by alluvial and fluvial deposits. The study area has a typical continental arid climate, marked by low precipitation and high evaporation. Annual precipitation ranges from 160 to 190 mm, while evaporation reaches 1,900 to 2,700 mm. The average annual temperature is 6 to 7.5°C, indicating a typical arid oasis environment. Geologically, the study area is divided from south to north into the Bogda Anticline, the Junggar Central Depression, the Qitai Uplift, and the Almant-Karamay Mountain Uplift. The exposed strata in this area consist primarily of the Quaternary, Carboniferous, and Devonian systems, with lithology becoming progressively finer from south to north, characterized by cobble, gravel, sand, and silty sand. The piedmont sloping plain serves as the main groundwater recharge zone, with replenishment primarily through river valley underflow, infiltration from storm runoff, and return flow from irrigation canals and fields. This process forms an unconfined aquifer with a single-layer structure, where groundwater depth exceeds 5 meters. The general groundwater flow direction is from south to north, with a hydraulic gradient of 3–4‰. In the alluvial and aeolian plains, the aquifer medium is composed of fine-grained or weakly permeable layers, resulting in poor groundwater flow conditions where vertical alternating movement predominates. This creates an upper unconfined-lower confined multilayered aquifer structure, with groundwater depths ranging from 5 to 200 meters. Discharge occurs mainly through spring outflow, evaporation, lateral runoff, and artificial extraction. 2.2. Sample Collection and Chemical Analysis of Groundwater In September 2022, groundwater samples were methodically collected from boreholes across the study area, comprising a total of 198 samples—133 from unconfined aquifers and 65 from confined aquifers (Fig. 1 ). Samples were collected in 500 mL polyethylene bottles, which were rinsed three times with deionized water before sampling and then rinsed three times with the water to be collected. All water samples were filtered using a 0.45 µm microporous membrane. For anion analysis, samples were sealed immediately after filtration, while for cation analysis, high-purity nitric acid was added to acidify the samples to a pH of ≤ 2. GPS was used to record the latitude, longitude, and elevation of each sampling location. On-site measurements of pH, temperature, conductivity, TDS, and redox potential were conducted using a pH meter (pH818), a portable conductivity/TDS meter (AR8011), and an oxidation-reduction potential meter (AZ8552), with accuracies of 0.01, 0.1°C, 1 µS•cm⁻¹, 1 mg•L⁻¹, and 1 mV, respectively. Ion analysis was performed by the Changji Prefecture Institute of Water Science and Technology, testing for pH, K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻, SO₄²⁻, HCO₃⁻, total hardness (TH), and TDS, along with other indicators. Concentrations of K⁺, Na⁺, Ca²⁺, and Mg²⁺ were measured using an inductively coupled plasma optical emission spectrometer (iCAP6300); Cl⁻, SO₄²⁻, and NO₃⁻ were determined using an ion chromatograph (ICS1100); and HCO₃⁻ was measured by acid-base titration. The detection limit for all ions was 0.01 mg•L⁻¹. The cation-anion charge balance error for all water samples was maintained within ± 5%. 2.3. Analytical Method Using the hydrogeological conditions and groundwater chemistry data from the study area, the chemical characteristics of groundwater and their controlling factors were analyzed through a combination of statistical analysis, Piper trilinear diagrams, Gibbs diagrams, ion ratios, and hydrogeochemical modeling. Excel was used for statistical analysis of hydrochemical parameters, while Grapher 10.0 was employed to generate Piper trilinear diagrams, Gibbs diagrams, and ion relationship plots. The saturation index and inverse hydrogeochemical modeling were conducted using PHREEQC 2.8, and other figures were created with Photoshop and ArcGIS 10.2. 3. Results 3.1. Statistical Results The statistical results of groundwater hydrochemical parameters in the study area are presented in Table 1 . The pH of unconfined groundwater ranges from 7.08 to 8.52, with an average of 7.69, while the pH of confined groundwater ranges from 7.19 to 8.30, with an average of 7.81, indicating weak alkalinity in both cases. The TDS of unconfined groundwater varies from 182.45 to 3255.81 mg/L, with an average of 551.44 mg/L, whereas TDS in confined groundwater ranges from 241.20 to 3886.37 mg/L, with an average of 640.02 mg/L. The total hardness of unconfined groundwater ranges from 88.12 to 1261.76 mg/L, with an average of 273.64 mg/L, while in confined groundwater, it ranges from 79.11 to 1472.06 mg/L, with an average of 276.62 mg/L. Ion concentrations of both cations and anions are higher in confined groundwater than in unconfined groundwater. The average cation concentration in unconfined groundwater follows the trend Ca²⁺ >Na⁺ + K⁺ >Mg²⁺, while the average anion concentration follows HCO₃⁻ >SO₄²⁻ >Cl⁻. In confined groundwater, the average cation concentration trend is Na⁺ + K⁺ >Ca²⁺ >Mg²⁺, and the anion concentration follows SO₄²⁻ >HCO₃⁻ >Cl⁻. Table 1 Statistical results of hydrochemical parameters of groundwater Parameters Unconfined groundwater (n = 133) Confined groundwater (n = 65) Max Min Mean SD CV Max Min Mean SD CV pH 8.52 7.08 7.69 0.27 0.03 8.30 7.19 7.81 0.20 0.03 TDS 3255.81 182.45 551.44 378.00 0.69 3886.37 241.20 640.02 556.46 0.87 TH 1261.76 88.12 273.64 182.59 0.67 1472.06 79.11 276.62 231.12 0.84 Na + +K + 587.86 1.75 51.71 66.00 1.28 941.64 12.61 84.89 124.18 1.46 Ca 2+ 566.00 21.10 83.63 64.71 0.77 447.16 27.27 73.63 59.51 0.81 Mg 2+ 125.00 0.24 17.61 19.28 1.09 170.03 1.22 22.68 27.00 1.19 Cl - 830.57 8.51 71.07 92.70 1.30 830.57 12.00 86.31 121.44 1.41 HCO 3- 440.05 90.45 180.78 78.34 0.43 510.94 100.23 184.30 76.07 0.41 SO 4 2- 989.05 30.45 149.67 142.49 0.95 1545.29 28.53 188.20 231.26 1.23 Note: In the table, SD represents standard deviation; VC represents coefficient of variation; pH represents a dimensionless quantity; the rest of the water chemical indicators are in mg/L, and the coefficient of variation is in %. 3.2. Hydrochemical Types The Piper diagram is a widely adopted tool for illustrating the composition and evolution of major ions in groundwater chemistry, offering the benefit of being independent of human-induced impacts. (Wang et al., 2023 ; Yang et al., 2016 ). As shown in the Piper trilinear diagram for the study area (Fig. 2 ), in the cation triangle (left triangle), most unconfined and confined groundwater samples are categorized as calcium-type with mixed sodium-type, with a higher proportion of sodium-type in confined groundwater, indicating the influence of ion accumulation in confined water. In the anion triangle (right triangle), both unconfined and confined groundwater are primarily bicarbonate-type and sulfate-type, with a small fraction of unconfined water showing chloride-type characteristics. The Piper diamond-shaped diagram further shows that the hydrochemical types of unconfined groundwater are predominantly HCO₃•SO₄-Ca and HCO₃•SO₄-Na•Ca, while confined groundwater is mainly of the HCO₃•SO₄-Na•Ca and HCO₃•SO₄•Cl-Na•Ca types. 3.3. Mechanisms Controlling Groundwater Geochemistry 3.3.1. Dominant Factors The Gibbs diagram provides a qualitative framework for evaluating hydrochemical evolution processes, which are influenced by atmospheric precipitation (Marandi&Shand, 2018 ), evaporative concentration, and rock weathering. Although initially developed for surface water, the Gibbs diagram requires contour adjustments for groundwater analysis, as groundwater has a much longer residence time in aquifers. This extended residence time leads to extensive water-rock interactions, which expand the “rock weathering control” range (Marandi & Shand, 2018 ). The Gibbs diagram for groundwater in the study area shows that both unconfined and confined groundwater are predominantly located within the rock weathering zone (Fig. 3 ), indicating that groundwater in this area is primarily influenced by rock dissolution, with minimal influence from evaporation concentration or atmospheric precipitation. Some confined groundwater samples show a distinct clustering in γ (Na⁺)/ γ (Na⁺+Ca²⁺), while γ (Cl⁻)/ γ (Cl⁻+HCO₃⁻) displays no clear pattern. 3.3.2 . Cation Exchange Cation exchange is typically assessed by examining the relationship between γ (Mg²⁺ + Ca²⁺ − SO₄²⁻ − HCO₃⁻) and γ (Na⁺ − Cl⁻). If cation exchange occurs, the ratio between these two values should be approximately − 1(Xiao et al., 2015 ). As shown in Fig. 4 a, confined groundwater exhibits a strong negative correlation ( R ² = 0.91) between γ (Mg²⁺ + Ca²⁺ − SO₄²⁻ − HCO₃⁻) and γ (Na⁺ − Cl⁻), with the ratio close to -1, indicating the occurrence of cation exchange in confined groundwater. In contrast, unconfined groundwater shows a ratio that deviates significantly from − 1, with a weaker correlation ( R ² = 0.29), suggesting that cation exchange is not prominent in unconfined groundwater. This observation is consistent with the findings of Ma et al., who reported cation exchange in confined groundwater within alluvial fan systems (Ma et al., 2022 ). The chloro-alkaline indices (CAI-1 and CAI-2) are used to characterize the direction and intensity of ion exchange during groundwater chemical evolution (Singh et al., 2015 ; Nematollahi et al., 2018 ). When CAI-1 and CAI-2 are less than 0, it indicates forward cation exchange, where Ca²⁺ or Mg²⁺ in groundwater displaces Na⁺ from aquifer minerals. Conversely, when CAI-1 and CAI-2 are greater than 0, it suggests reverse cation exchange, where Na⁺ in groundwater displaces Ca²⁺ or Mg²⁺ from aquifer minerals (Wang et al., 2015 ). Figure 4 b shows the relationship between the chloro-alkaline indices and TDS for confined groundwater, where most CAI-1 and CAI-2 values are less than 0, indicating forward cation exchange. This suggests that Ca²⁺ and Mg²⁺ in confined groundwater have exchanged with Na⁺ and K⁺ from the surrounding rock, consistent with previous analyses. The larger absolute values of CAI-2 further indicate stronger ion exchange. Along the groundwater flow path, the particle size of confined aquifer media in the alluvial plain gradually becomes finer, with an increase in clay minerals. This enhances cation exchange, as surface-adsorbed Na⁺ is replaced by Ca²⁺ and Mg²⁺ in the water. 3.3.3. Dissolution Processes The primary minerals in the study area’s strata include sulfates, carbonates, silicates, and halite. Sulfate minerals consist mainly of gypsum and mirabilite, carbonate minerals include calcite and dolomite, and silicate minerals are primarily quartz, mica, and feldspar. Through weathering and water-rock interactions, these minerals dissolve into the groundwater, contributing to its chemical composition (Mahamuda et al., 2024 ; You et al., 2024 ). Ion ratio relationships are used to analyze these dissolution processes. Unconfined groundwater sampling points are located near the line γ (Na⁺ + K⁺)/ γ (Cl⁻) = 1 (Fig. 5 a), indicating that the hydrochemical composition of unconfined groundwater is primarily influenced by halite dissolution. In contrast, most confined groundwater sampling points are positioned above γ (Na⁺ + K⁺)/ γ (Cl⁻) = 1, suggesting that, in addition to halite dissolution, the hydrochemical composition of confined groundwater may also be affected by the dissolution of other sodium salts. In the confined groundwater of the river alluvial plain, Na⁺ + K⁺ concentrations deviate significantly from the 1:1 line, likely due to cation exchange, resulting in Na⁺ + K⁺ concentrations exceeding those of Cl⁻. Both unconfined and confined groundwater sampling points are positioned above the line γ (Ca²⁺ + Mg²⁺)/ γ (HCO₃⁻) = 1 (Fig. 5 b), indicating that, in addition to the weathering and dissolution of calcite and dolomite, other Ca²⁺-bearing minerals are also dissolving (Wang et al., 2024 ). A significant linear relationship is observed between γ (Ca²⁺ + Mg²⁺) and γ (HCO₃⁻ + SO₄²⁻) (Fig. 5 c), with most groundwater sampling points falling below the line γ (Ca²⁺ + Mg²⁺)/ γ (HCO₃⁻ + SO₄²⁻) = 1. The relationship between γ (SO₄²⁻ + Cl⁻) and γ (HCO₃⁻) can be used to evaluate the contributions of sulfate and carbonate minerals to groundwater ions (Liu et al., 2023 ). Most unconfined and confined groundwater sampling points are located above the line γ (SO₄²⁻ + Cl⁻)/ γ (HCO₃⁻) = 1 (Fig. 5 d), indicating that sulfate dissolution is the dominant contributor to ions in the water, with Ca²⁺ primarily sourced from the dissolution of gypsum and mirabilite. A linear relationship between γ (Ca²⁺) and γ (SO₄²⁻) (Fig. 5 e) further suggests that gypsum dissolution is the main source of both Ca²⁺ and SO₄²⁻ in the groundwater. In addition to the increase in Na⁺ concentration in confined groundwater due to cation exchange, the primary sources of Na⁺ in groundwater are the weathering and dissolution of halite and mirabilite, while Ca²⁺ mainly originates from gypsum dissolution and, to a lesser extent, the weathering of carbonates. The parameter γ (Ca²⁺ + Mg²⁺ − HCO₃⁻) represents the Ca²⁺ concentration derived from gypsum dissolution, and γ [SO₄²⁻ − (Na⁺ − Cl⁻)] represents the SO₄²⁻ concentration from gypsum dissolution. If all SO₄²⁻ in the water samples is derived from gypsum dissolution, the value of γ (Ca²⁺ + Mg²⁺ − HCO₃⁻)/ γ [SO₄²⁻ − (Na⁺ − Cl⁻)] should equal 1. As shown in Fig. 5 f, groundwater sampling points in the study area are located near or below the y = x line, further confirming that SO₄²⁻ in groundwater primarily originates from gypsum dissolution. PHREEQC software was used to calculate the saturation indices (SI) of various minerals to assess their dissolution and precipitation states (Liu et al., 2021 ; Kim et al., 2008 ). Generally, when SI 0.5, the mineral is in a saturated state (Rouabhia et al., 2011 ). In the groundwater environment of the study area, the saturation index (SI) of calcite ranges from − 0.69 to 1.43(Fig. 6 ), with an average of 0.25, indicating an overall state of equilibrium. The SI of dolomite ranges from − 2.13 to 2.52, averaging 0.09; most dolomite in unconfined groundwater is in equilibrium, with a small portion in a dissolution state, while dolomite in confined groundwater is generally in a saturated or equilibrium state. The SI of gypsum ranges from − 2.29 to − 0.49, with an average of − 1.60, indicating a general dissolution state. Halite has an SI range of − 8.54 to − 4.81, with an average of − 7.27, also indicating dissolution. Overall, these minerals show a higher dissolution capacity in unconfined groundwater than in confined groundwater. The saturation indices of minerals gradually increase from upstream to downstream, trending toward saturation. 3.4. Hydrogeochemical Modeling PHREEQC software enables quantitative simulation of water-rock interactions influenced by various natural processes and human activities (You et al., 2024 ). Along the groundwater flow direction, the unconfined groundwater pathway Q45 → Q49 → Q50 and the confined groundwater pathway C49 → C45 → C40 were selected for hydrogeochemical modeling. In the model, primary minerals in the Quaternary aquifer of the study area—quartz, halite, calcite, dolomite, and gypsum—are designated as “potential mineral phases.” Since unconfined groundwater is in an open system, CO₂ is also included as a “potential mineral phase” along the unconfined groundwater pathway. In contrast, confined groundwater, being relatively deep and in a semi-closed system, does not involve CO₂ in hydrogeochemical processes. However, cation exchange occurs in confined groundwater, and this process is added as an additional “potential mineral phase” along the confined groundwater pathway. The model’s uncertainty factor is set at 0.05. The simulation results (Table 2 ) indicate that along the unconfined groundwater pathway Q45 → Q49 → Q50, halite, dolomite, and gypsum undergo dissolution. As gypsum dissolves, the Ca²⁺ concentration in unconfined groundwater increases, leading to calcite precipitation (with a precipitation amount of 5.280 × 10⁻⁴ mmol/L). Along the confined groundwater pathway C49 → C45 → C40, calcite precipitates while halite, dolomite, and gypsum remain in a dissolved state. Forward cation exchange occurs in confined groundwater, with the intensity of this exchange increasing along the flow path (from 1.268 × 10⁻³ mmol/L to 1.872 × 10⁻³ mmol/L), maintaining a relatively low Ca²⁺ concentration. Consequently, the hydrochemical type evolves from HCO₃•SO₄-Ca•Na to HCO₃•SO₄•Cl-Na•Ca. Table 2 Reverse simulation results of unconfined groundwater and confined groundwater flow paths Molar Transfer Amount /mmol·L -1 Unconfined Groundwater Pathway Confined Groundwater Pathway Mineral Phase Chemical Formula Q45→Q49 Mineral Phase Chemical Formula Q45→Q49 Halite NaCl 2.402×10 − 4 Halite NaCl 2.402×10 − 4 Calcite CaCO 3 2.427×10 − 4 Calcite CaCO 3 2.427×10 − 4 Dolomite CaMg(CO 3 ) 2 1.001×10 − 5 Dolomite CaMg(CO 3 ) 2 1.001×10 − 5 Gypsum CaSO 4 ·2H 2 O 1.177×10 − 4 Gypsum CaSO 4 ·2H 2 O 1.177×10 − 4 CO 2 CO 2 3.355×10 − 4 CO 2 CO 2 3.355×10 − 4 Cation Exchange CaX 2 — Cation Exchange CaX 2 — NaX — — NaX — Note: In the table, a positive value indicates dissolution; a negative value indicates precipitation; and “—” indicates that the mineral did not participate in the reaction. 4. Discussion 4.1. Hydrochemical Characteristics and Evolution The weakly alkaline nature of groundwater in the study area is consistent with findings in other arid regions, such as the Tarim Basin and the Yinchuan Plain (Li et al., 2024 ). The higher TDS and ion concentrations in confined groundwater compared to unconfined groundwater suggest longer residence times and more extensive water-rock interactions, as observed in similar alluvial systems (Marandi & Shand, 2018 ). The dominance of Ca²⁺ and HCO₃⁻ in unconfined groundwater reflects the influence of carbonate weathering, which is typical in recharge zones where fresh water interacts with carbonate-rich sediments (Katz et al., 2011 ). In contrast, the shift to Na⁺ and SO₄²⁻ dominance in confined groundwater indicates the increasing role of silicate weathering and cation exchange processes, as reported in the Hexi Corridor. This evolution of hydrochemical types along the flow path is a common feature in arid regions, where groundwater chemistry is strongly influenced by the mineralogy of aquifer materials and the intensity of water-rock interactions. 4.2. Mechanisms Controlling Groundwater Chemistry The Gibbs diagram results confirm that rock weathering is the primary control on groundwater chemistry, consistent with findings in other arid regions (Gibbs, 1970; Marandi & Shand, 2018 ). However, the distinct clustering of confined groundwater samples in the γ (Na⁺)/ γ (Na⁺+Ca²⁺) plot suggests additional influences from cation exchange, as reported in the North China Plain (Xiao et al., 2015 ). Cation exchange is particularly significant in confined aquifers due to the presence of clay minerals, which provide abundant exchange sites for Na⁺, Ca²⁺, and Mg²⁺. This process not only alters the ionic composition of groundwater but also affects its suitability for irrigation, as high Na⁺ concentrations can lead to soil sodicity and reduced agricultural productivity (Singh et al., 2015 ). The strong negative correlation between γ (Mg²⁺ + Ca²⁺ − SO₄²⁻ − HCO₃⁻) and γ (Na⁺ − Cl⁻) in confined groundwater ( R ² = 0.91) indicates significant cation exchange, a phenomenon also observed in the Nile Delta (Mostafa & Abdel, 2016). In contrast, the weaker correlation in unconfined groundwater ( R ² = 0.29) suggests limited cation exchange, likely due to shorter residence times and coarser aquifer materials (Ma et al., 2022 ). This difference highlights the importance of aquifer lithology and groundwater flow dynamics in controlling hydrochemical processes. For example, the finer-grained sediments in confined aquifers promote more extensive cation exchange, while the coarser materials in unconfined aquifers favor rapid recharge and limited water-rock interactions (Liu et al., 2021 ). 4.3. Mineral Dissolution and Precipitation The dissolution of halite and gypsum, along with the equilibrium state of calcite and dolomite, is consistent with findings in the Loess Plateau (Liu et al., 2023 ) and the Arabian Peninsula (Rouabhia et al., 2011 ). The higher dissolution capacity in unconfined groundwater compared to confined groundwater reflects the influence of recharge processes and open-system conditions, as observed in the Badain Jaran Desert. In unconfined aquifers, the continuous influx of fresh water enhances the dissolution of soluble minerals such as halite and gypsum, while the semi-closed nature of confined aquifers limits dissolution and promotes mineral saturation (Kim et al., 2008 ). This spatial variability in mineral dissolution has important implications for groundwater quality, as it influences the concentrations of major ions such as Na⁺, Ca²⁺, and SO₄²⁻, which are critical for assessing water suitability for drinking and irrigation. 4.4. Implications for Groundwater Management The evolution of hydrochemical types from HCO₃•SO₄-Ca•Na to HCO₃•SO₄•Cl-Na•Ca along the flow path highlights the need for targeted management strategies. For example, the high Na⁺ and SO₄²⁻ concentrations in confined groundwater may pose risks for irrigation and drinking water supplies, as reported in the Indus Basin (Singh et al., 2015 ). Elevated Na⁺ levels can lead to soil degradation and reduced crop yields, while high SO₄²⁻ concentrations may cause health issues such as gastrointestinal discomfort. To mitigate these risks, it is essential to implement measures such as controlled groundwater extraction, artificial recharge, and the use of alternative water sources for irrigation. Furthermore, the findings of this study have broader implications for sustainable groundwater management in arid regions. The integration of hydrochemical and isotopic techniques, as demonstrated here, provides a robust framework for understanding groundwater evolution and identifying contamination sources (Calvi et al., 2022 ). Future studies should focus on quantifying the impacts of climate change and human activities on groundwater quality, particularly in vulnerable oasis systems. For example, the increasing intensity of agricultural practices and urbanization in arid regions is likely to exacerbate groundwater degradation, necessitating the development of adaptive management strategies. 5. Conclusions This study investigated the hydrochemical characteristics and controlling factors of groundwater in a typical oasis city in an arid region using statistical analysis, Piper diagrams, Gibbs diagrams, ion ratios, and hydrogeochemical modeling. The main findings are as follows: (1) Groundwater in the study area is weakly alkaline, with higher TDS, total hardness, and ion concentrations in confined groundwater compared to unconfined groundwater. The hydrochemical types of unconfined groundwater are predominantly HCO₃•SO₄-Ca and HCO₃•SO₄-Na•Ca, while confined groundwater is mainly HCO₃•SO₄-Na•Ca and HCO₃•SO₄•Cl-Na•Ca. (2) Rock dissolution is the primary control on groundwater chemistry, with minimal influence from evaporation and atmospheric precipitation. Major ions (Na⁺, Ca²⁺, HCO₃⁻, Cl⁻, and SO₄²⁻) are derived from the dissolution of evaporites (halite, gypsum, and mirabilite) and carbonates (calcite and dolomite). Confined groundwater is significantly influenced by forward cation exchange, where Ca²⁺ or Mg²⁺ in groundwater replaces Na⁺ in aquifer minerals, with exchange intensity increasing along the flow path. (3) Hydrogeochemical modeling confirms that halite and gypsum are in a dissolved state, while calcite and dolomite are in dissolution-equilibrium. Mineral dissolution capacity is higher in unconfined groundwater than in confined groundwater, with saturation indices increasing downstream. Along the flow path, halite, dolomite, and gypsum dissolve, while calcite precipitates, and forward cation exchange occurs in confined groundwater. This study enhances the understanding of hydrogeochemical processes in arid oasis systems and provides a scientific basis for sustainable groundwater management. The findings highlight the need to address the risks associated with high Na⁺ and SO₄²⁻ concentrations in confined groundwater, particularly for irrigation and drinking water supplies. Future research should focus on the impacts of climate change and human activities on groundwater quality, as well as the development of adaptive management strategies to ensure the long-term sustainability of groundwater resources in arid regions. Declarations Acknowledgments The authors would like to thank the anonymous reviewers and editors for their valuable comments, which were crucial in improving the quality of this paper. Funding Thisresearch was funded by the Science and Technology Research Program of Chongqing Municipal Education Commission (KJQN202301209), the Science Technology Planning Project of WanZhou District, Chongqing (wzstc20230313, wzstc20230301) and Chongqing Water Conservancy Science and Technology Project (CQSLK-2024023). Data availability Not applicable. All the data used in this paper are provided herein Conflict of interests There are no competing interests regarding this work. Ethical approval Not applicable. Consent to participate Not applicable. Consent for publication Not applicable. Author contributions Author Contributions: Yulin Zhou as the corresponding author, curated the data and prepared the original draft. Xing Wei was responsible for the conceptualization and methodology of the study. Qingmei Zhang contributed to the visualization and investigation of the study's findings. Libo Ran and Delun Chen provided overall supervision and project administration. Xueting Dou, Yanan Fu and Gang Wu conducted validation and contributed to writing, reviewing, and editing of the manuscript. All authors have read and agreed to the published version of the manuscript. References Calvi C, Dapeña C, Quiroz Londoño OM, et al. (2022) Assessing recharge process in plain catchments using isotopic and hydrochemical techniques. Groundw Sustain Dev 19:100828. https://doi.org/10.1016/j.gsd.2022.100828 Gobashy MM, Metwally AM, Abdelazeem M, et al. (2021) Geophysical exploration of shallow groundwater aquifers in arid regions: a case study of Siwa Oasis, Egypt. Nat Resour Res 30:—. https://doi.org/10.1007/s11053-021-09897-3 Guo X, Feng Q, Si J, et al. (2019) Partitioning groundwater recharge sources in multiple aquifers system within a desert oasis environment: implications for water resources management in endorheic basins. J Hydrol 579:124212. https://doi.org/10.1016/j.jhydrol.2019.124212 Ju X, He J, Zhang Q, et al. (2023) Evolution pattern and driving mechanism of eco-environmental quality in arid oasis belt: a case study of oasis core area in Kashgar Delta. Ecol Indic 154:110866. https://doi.org/10.1016/j.ecolind.2023.110866 Katz BG, Eberts SM, Kauffman LJ (2011) Using Cl/Br ratios and other indicators to assess potential impacts on groundwater quality from septic systems: a review and examples from principal aquifers in the United States. J Hydrol 397(3–4):151–166. https://doi.org/10.1016/j.jhydrol.2010.11.017 Kim SS, Baik MH, Kang KC, et al. (2008) Solubilities of actinides in a domestic groundwater and a bentonite porewater calculated by using PHREEQC. J Ind Eng Chem 14(6):746. https://doi.org/10.1016/j.jiec.2008.07.005 Koncsos L, Murányi G (2024) A multi-scenario multi-model analysis of regional climate projections in a Central–Eastern European agricultural region: assessing shallow groundwater table responses using an aggregated vertical hydrological model. Appl Water Sci 14(3):—. https://doi.org/10.1007/s13201-023-02097-9 Kumar M, Ramanatahn AL, Tripathi R, et al. (2017) A study of trace element contamination using multivariate statistical techniques and health risk assessment in groundwater of Chhaprola Industrial Area, Gautam Buddha Nagar, Uttar Pradesh, India. Chemosphere 166:135–145. https://doi.org/10.1016/j.chemosphere.2016.09.086 Li C, Gao X, Xiang X, et al. (2024) Intense human activities induce the dynamic changes of interaction pattern between karst water–Quaternary groundwater in the basin–mountain coupling belt over the past 60 years. Water Resour Res 60(2):e2023WR035211. https://doi.org/10.1029/2023WR035211 Liu J, Pei X, Zhu W, et al. (2023) Simulation of the ecological service value and ecological compensation in arid area: a case study of ecologically vulnerable oasis. Remote Sens 15(16):3927. https://doi.org/10.3390/rs15163927 Liu J, Wang H, Jin D, et al. (2020) Hydrochemical characteristics and evolution processes of karst groundwater in Carboniferous Taiyuan Formation in the Pingdingshan coalfield. Environ Earth Sci 79(6):—. https://doi.org/10.1007/s12665-020-8898-4 Liu P, Wang G, Shang M, et al. (2021) Groundwater nitrate bioremediation simulation of in situ horizontal well by microbial denitrification using PHREEQC. Water Air Soil Pollut 232(9):1–11. https://doi.org/10.1007/s11270-021-05313-x Liu R, Xie X, Qian Y, et al. (2023) Groundwater sulfate in the Pearl River Delta driven by urbanization: spatial distribution, sources and factors. Appl Geochem 156:105766. https://doi.org/10.1016/j.apgeochem.2023.105766 Ma Q, Ge W, Tian F (2022) Geochemical characteristics and controlling factors of chemical composition of groundwater in a part of the Nanchang section of Ganfu Plain. Sustainability 14(13):7976. https://doi.org/10.3390/su14137976 Mahamuda A, Awinbire AB, Egbueri JC (2024) Understanding groundwater mineralization controls and the implications on its quality (Southwestern Ghana): insights from hydrochemistry, multivariate statistics, and multi-linear regression models. Acta Geophys 72(5):3563–3580. https://doi.org/10.1007/s11600-023-01271-6 Mao W, Zhu Y, Wu J, et al. (2020) Modelling the salt accumulation and leaching processes in arid agricultural areas with a new mass balance model. J Hydrol 591:125329. https://doi.org/10.1016/j.jhydrol.2020.125329 Marandi A, Shand P (2018) Groundwater chemistry and the Gibbs diagram. Appl Geochem 97:—. https://doi.org/10.1016/j.apgeochem.2018.07.009 Mostafa R, Abdel Moneim AA (2016) Factors controlling groundwater hydrogeochemistry in the area west of Tahta, Sohag, Upper Egypt. J Afr Earth Sci 118:328–338. https://doi.org/10.1016/j.jafrearsci.2015.10.002 Nematollahi MJ, Clark MJR, Ebrahimi P, et al. (2018) Preliminary assessment of groundwater hydrogeochemistry within Gilan, a northern province of Iran. Environ Monit Assess 190(4):—. https://doi.org/10.1007/s10661-018-6543-4 Palma M, Maggio S, Cappello C, et al. (2023) Spatio-temporal modeling of groundwater quality deterioration and resource depletion. Hydrogeol J 31(6):1443–1461. https://doi.org/10.1007/s10040-023-02692-9 Preethi B, Subramani T, Saravanan R, et al. (2025) Health risks due to geogenic and anthropogenic influences on groundwater quality in Southern India’s hard rock terrain. J Geochem Explor 274:107762. https://doi.org/10.1016/j.gexplo.2025.107762 Rouabhia A, Baali F, Fehdi C, et al. (2011) Hydrogeochemistry of groundwaters in a semi-arid region: El Ma El Abiod aquifer, Eastern Algeria. Arab J Geosci 4(5–6):973–982. https://doi.org/10.1007/s12517-010-0169-3 Sheng D, Meng X, Wen X, Wu J, Yu H, Wu M (2022) Contamination characteristics, source identification, and source-specific health risks of heavy metal(loid)s in groundwater of an arid oasis region in Northwest China. Sci Total Environ 841:156733. https://doi.org/10.1016/j.scitotenv.2022.156733 Singh N, Singh RP, Kamal V, et al. (2015) Assessment of hydrogeochemistry and the quality of groundwater in 24-Parganas districts, West Bengal. Environ Earth Sci 73(1):375–386. https://doi.org/10.1007/s12665-014-3431-2 Tang X, Huang Y, Pan X, et al. (2024) Managing the water–agriculture–environment–energy nexus: trade-offs and synergies in an arid area of Northwest China. Agric Water Manag 295:108776. https://doi.org/10.1016/j.agwat.2024.108776 Ullah A, Hussain S, Wang Y, et al. (2024) Integrated assessment of groundwater quality dynamics and land use/land cover changes in a rapidly urbanizing semi-arid region. Environ Res 260:119622. https://doi.org/10.1016/j.envres.2024.119622 Wang D, Zhang L, Pei L, et al. (2023) Chemical characteristics and controlling factors of shallow groundwater in the lower reaches of Changhua River Basin, Hainan Island, China. Water 15(19):3508. https://doi.org/10.3390/w15193508 Wang H, Jiang XW, Wan L, et al. (2015) Hydrogeochemical characterization of groundwater flow systems in the discharge area of a river basin. J Hydrol 527:433–441. https://doi.org/10.1016/j.jhydrol.2015.04.063 Wang P, Zhang W, Zhu Y, et al. (2024) Evolution of groundwater hydrochemical characteristics and formation mechanism during groundwater recharge: a case study in the Hutuo River alluvial–pluvial fan, North China Plain. Sci Total Environ 915:170159. https://doi.org/10.1016/j.scitotenv.2024.170159 Wang Z, Wang Y, Shi M, et al. (2024) Coordinated analysis of groundwater spatiotemporal chemical characteristics, water quality, and potential human health risks with sustainable development in semi-arid regions. Environ Geochem Health 46(10):—. https://doi.org/10.1007/s10653-024-02155-4 Xiao J, Jin ZD, Wang J, Zhang F (2015) Hydrochemical characteristics, controlling factors and solute sources of groundwater within the Tarim River Basin in the extreme arid region, NW Tibetan Plateau. Quat Int 380–381:237–246. https://doi.org/10.1016/j.quaint.2015.01.021 Yan Y, Shi H, Miao Q, et al. (2025) Evolution of chemical characteristics and irrigation suitability of groundwater in arid and semi-arid regions. Agric Water Manag 311:109361. https://doi.org/10.1016/j.agwat.2025.109361 Yang Q, Wang L, Ma H, et al. (2016) Hydrochemical characterization and pollution sources identification of groundwater in Salawusu aquifer system of Ordos Basin, China. Environ Pollut 216:340–349. https://doi.org/10.1016/j.envpol.2016.05.076 Yao C, Li Z, Wang Y, et al. (2024) Redefining the modified water benefit-based ecological index to evaluate the impact of cropland expansion on the ecological environment in an arid area. J Clean Prod 477:143730. https://doi.org/10.1016/j.jclepro.2024.143730 You J, Qi Y, Shao G, et al. (2024) Geochemical characteristics and controlling factors of groundwater chemical composition in the Zihe River source area, Shandong, China. Water 16(2):298. https://doi.org/10.3390/w16020298 Cite Share Download PDF Status: Published Journal Publication published 21 Feb, 2026 Read the published version in Acta Geophysica → Version 1 posted Editorial decision: Major revisions 14 Jan, 2026 Reviewers agreed at journal 23 Dec, 2025 Reviewers invited by journal 30 Nov, 2025 First submitted to journal 24 Nov, 2025 Editor assigned by journal 22 Nov, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8100581","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":553004581,"identity":"60fca9d3-d4a5-49a5-9ec5-781d87ceba81","order_by":0,"name":"Xing WEI","email":"","orcid":"","institution":"Chongqing Three Gorges University","correspondingAuthor":false,"prefix":"","firstName":"Xing","middleName":"","lastName":"WEI","suffix":""},{"id":553004582,"identity":"9ed184c4-ea69-41b3-a728-693d0bac7a62","order_by":1,"name":"Qingmei ZHANG","email":"","orcid":"","institution":"Chongqing Three Gorges University","correspondingAuthor":false,"prefix":"","firstName":"Qingmei","middleName":"","lastName":"ZHANG","suffix":""},{"id":553004583,"identity":"7351d047-442c-4325-9255-fcc26034d47d","order_by":2,"name":"yulin zhou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYDACCTBpwcPA3oDgShChRYKHgecAiVqAKAFdEAeQn918TJq3TULGXPL5w8+FbRbyBgeYD97mYbDLw6WFcc6xNJAWHsvZOcbSM85IGG44wJZszcOQXIxLC7NEjhlYi8HtHAZpngoJxg0HeMykeRgOJDbg0MIG13Lz+OPfPAYS9hsO8H/Dq4UHruUGgxnIlkSgLWx4tUhIpCVbzjkH1HImx8ya54xE8szDbMaWcwyScWqRn5F88MabMht7g+PHH9/mbauz7Tve/PDGmwo7nFpAgIkHNURAhAEe9UDA+AO//CgYBaNgFIx0AADtJElPiGsn8AAAAABJRU5ErkJggg==","orcid":"","institution":"Chongqing Three Gorges University","correspondingAuthor":true,"prefix":"","firstName":"yulin","middleName":"","lastName":"zhou","suffix":""},{"id":553004584,"identity":"b2b91e72-19fb-445f-87bf-56596f4d781c","order_by":3,"name":"Libo RAN","email":"","orcid":"","institution":"Chongqing Three Gorges University","correspondingAuthor":false,"prefix":"","firstName":"Libo","middleName":"","lastName":"RAN","suffix":""},{"id":553004585,"identity":"55b0863e-5034-48f8-b6cc-db3de7869b21","order_by":4,"name":"Delun CHEN","email":"","orcid":"","institution":"Chongqing Three Gorges University","correspondingAuthor":false,"prefix":"","firstName":"Delun","middleName":"","lastName":"CHEN","suffix":""},{"id":553004586,"identity":"041beb11-57a4-4386-84ee-7cd85a5f8475","order_by":5,"name":"Xueting DOU","email":"","orcid":"","institution":"Chongqing Three Gorges University","correspondingAuthor":false,"prefix":"","firstName":"Xueting","middleName":"","lastName":"DOU","suffix":""},{"id":553004587,"identity":"0ca040f4-1162-4401-ba87-a155ce3713b3","order_by":6,"name":"Yanan FU","email":"","orcid":"","institution":"Chongqing Three Gorges University","correspondingAuthor":false,"prefix":"","firstName":"Yanan","middleName":"","lastName":"FU","suffix":""},{"id":553004588,"identity":"839e5d17-d0cc-43f4-9d6c-7a4081fabe7b","order_by":7,"name":"Gang WU","email":"","orcid":"","institution":"Changjiang Water Resources Commission","correspondingAuthor":false,"prefix":"","firstName":"Gang","middleName":"","lastName":"WU","suffix":""}],"badges":[],"createdAt":"2025-11-13 02:17:42","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8100581/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8100581/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11600-026-01828-1","type":"published","date":"2026-02-21T15:59:22+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":97344373,"identity":"23667709-2a18-4650-9397-001aef17c1c8","added_by":"auto","created_at":"2025-12-03 11:40:04","extension":"xml","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":11888,"visible":true,"origin":"","legend":"","description":"","filename":"agphAGPHD2500971.xml","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/cad51bad4e1298a3b31e08cf.xml"},{"id":97344304,"identity":"70ba1f91-a015-4846-bc3d-24d9a89c5ac6","added_by":"auto","created_at":"2025-12-03 11:39:59","extension":"xml","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":926,"visible":true,"origin":"","legend":"","description":"","filename":"AGPHD250097125543.go.xml","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/9581954e7fe4c12378a733e0.xml"},{"id":97344310,"identity":"7999a706-40a5-45a8-b805-e0665fe74a23","added_by":"auto","created_at":"2025-12-03 11:40:01","extension":"xml","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":894,"visible":true,"origin":"","legend":"","description":"","filename":"AGPHD2500971Import.xml","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/5c80f93884d897548a0c339f.xml"},{"id":97344376,"identity":"897df815-15ea-480a-8f9b-a9050bd369d1","added_by":"auto","created_at":"2025-12-03 11:40:04","extension":"xml","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":119551,"visible":true,"origin":"","legend":"","description":"","filename":"AGPHD25009710enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/fa1c9cbc05b9f3658e74bcb9.xml"},{"id":97344301,"identity":"9ec285ec-3528-4147-9056-43e9ab7a8072","added_by":"auto","created_at":"2025-12-03 11:39:53","extension":"jpeg","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":168015,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/f6062e8e2677aa63fd4471f5.jpeg"},{"id":97344297,"identity":"b55838f0-eec6-42ac-b1e4-9f87131e7836","added_by":"auto","created_at":"2025-12-03 11:39:51","extension":"jpeg","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":191504,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/56c5ef43e538457a4fa796ac.jpeg"},{"id":97344311,"identity":"2900b0cd-44d6-4f5c-b78c-f18673b97ef1","added_by":"auto","created_at":"2025-12-03 11:40:01","extension":"jpeg","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":358210,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/af08feea543467b156fb0fb8.jpeg"},{"id":97371334,"identity":"a94d5d53-3b94-471c-8084-7ec27bcfb0b1","added_by":"auto","created_at":"2025-12-03 16:28:44","extension":"jpeg","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":272009,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/f79283fbdb27c91fbc7a38d8.jpeg"},{"id":97344374,"identity":"b07f04bd-2bc5-4b4c-9f12-7142bdba78c0","added_by":"auto","created_at":"2025-12-03 11:40:04","extension":"jpeg","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":815868,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/587ba6baec84b5f1684ee00e.jpeg"},{"id":97344384,"identity":"3fde76e2-8fdc-4397-9260-1e9b1d8ae872","added_by":"auto","created_at":"2025-12-03 11:40:07","extension":"jpeg","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":110644,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/221a05579c55557196c6e99a.jpeg"},{"id":97344377,"identity":"e65b7f62-4594-48b7-b54a-6e9d16fde2b3","added_by":"auto","created_at":"2025-12-03 11:40:04","extension":"png","order_by":11,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":62893,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/7a0c2639741a207e0f5b77ae.png"},{"id":97344298,"identity":"9216e700-5ead-4c8d-b07d-59b121088063","added_by":"auto","created_at":"2025-12-03 11:39:51","extension":"png","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":50541,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/3a75f17eaacd47c2a8934417.png"},{"id":97344306,"identity":"ed75433a-0822-40f4-b132-750c5c6ec548","added_by":"auto","created_at":"2025-12-03 11:39:59","extension":"png","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":77750,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/7cc36e015fde79a6d5590858.png"},{"id":97344300,"identity":"fd4a35e8-6103-4205-b1a0-ac6273d75a4c","added_by":"auto","created_at":"2025-12-03 11:39:52","extension":"png","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":58859,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/75ff9267f60000b88eca6c1b.png"},{"id":97344395,"identity":"8b238948-21af-4422-a078-0823ed5f723b","added_by":"auto","created_at":"2025-12-03 11:40:08","extension":"png","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":184794,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/9b002ae76b3a32016c28867b.png"},{"id":97344299,"identity":"f65031ce-ad2d-4022-a594-426efef1145f","added_by":"auto","created_at":"2025-12-03 11:39:52","extension":"png","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":25424,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/705fc84752a4abf462f46efe.png"},{"id":97344314,"identity":"0579f8f0-5690-4558-80eb-342dc481a966","added_by":"auto","created_at":"2025-12-03 11:40:02","extension":"xml","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":118289,"visible":true,"origin":"","legend":"","description":"","filename":"AGPHD25009710structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/c43c88d0ff7bd154c778ed54.xml"},{"id":97344387,"identity":"6cc8c460-1245-4492-b397-773615ca33b7","added_by":"auto","created_at":"2025-12-03 11:40:07","extension":"html","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":122652,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/0c43f8f7fae1794e04af62f0.html"},{"id":97371294,"identity":"6d10f97a-cd7f-477c-9405-2929a52ac142","added_by":"auto","created_at":"2025-12-03 16:28:41","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":176687,"visible":true,"origin":"","legend":"\u003cp\u003eLocation and sampling site map of the study area\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/b1fb26fc9b913ba4cfcf5669.png"},{"id":97344380,"identity":"bc5bcee6-afed-4de1-9bc7-70e78461f6dd","added_by":"auto","created_at":"2025-12-03 11:40:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":198378,"visible":true,"origin":"","legend":"\u003cp\u003ePiper diagram of groundwater\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/d74e383acb0de5a79e9ff8ae.png"},{"id":97344393,"identity":"2fb60bae-4d7a-42d9-9fc0-f78f75255410","added_by":"auto","created_at":"2025-12-03 11:40:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":160601,"visible":true,"origin":"","legend":"\u003cp\u003eGibbs diagram of groundwater: (a) TDS vs. Na\u003csup\u003e+\u003c/sup\u003e/(Na\u003csup\u003e+\u003c/sup\u003e+Ca\u003csup\u003e2+\u003c/sup\u003e); (b) TDS vs. Cl\u003csup\u003e-\u003c/sup\u003e/(Cl\u003csup\u003e-\u003c/sup\u003e+HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/7dbfcc058128041f5b76e155.png"},{"id":97344307,"identity":"aa0763bf-cfc2-4a7d-a670-01f233bd7d84","added_by":"auto","created_at":"2025-12-03 11:39:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":121533,"visible":true,"origin":"","legend":"\u003cp\u003eRelations between γ (Mg\u003csup\u003e2+\u003c/sup\u003e+Ca\u003csup\u003e2+\u003c/sup\u003e−SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e−HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) vs. γ (Na\u003csup\u003e+\u003c/sup\u003e−Cl\u003csup\u003e-\u003c/sup\u003e) and Choro-Alkaline indices vs. TDS\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/f700f5f18c9ad3e0b71fdc35.png"},{"id":97344308,"identity":"51e17664-8603-4faa-b24a-d37f31ce25cf","added_by":"auto","created_at":"2025-12-03 11:40:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":230258,"visible":true,"origin":"","legend":"\u003cp\u003eProportional relationship of main ions: (a) (Na\u003csup\u003e+\u003c/sup\u003e+K\u003csup\u003e+\u003c/sup\u003e) vs. Cl\u003csup\u003e-\u003c/sup\u003e; (b) (Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e) vs. HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e; (c) (Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e) vs. (HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e); (d) (SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e+ Cl\u003csup\u003e-\u003c/sup\u003e) vs. HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e; (e) C\u003csup\u003ea2+\u003c/sup\u003e vs. SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e; (f) (Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e- HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) vs. [SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e(Na\u003csup\u003e+\u003c/sup\u003e-Cl\u003csup\u003e-\u003c/sup\u003e)]\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/374051f1912d19a5e2d9eff6.png"},{"id":97344305,"identity":"117845cc-3932-4ccb-b41b-b9981b7b6cc8","added_by":"auto","created_at":"2025-12-03 11:39:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":56712,"visible":true,"origin":"","legend":"\u003cp\u003eSaturation index relationships of minerals in groundwater\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/d8d60c7ed68c58e2f6d07564.png"},{"id":103251726,"identity":"760cb2dc-762f-4c42-80d4-5e67dd545913","added_by":"auto","created_at":"2026-02-23 16:11:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1702274,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8100581/v1/bbe3e04d-0df9-48dc-b8e7-959bd3d75904.pdf"}],"financialInterests":"","formattedTitle":"Hydrogeochemical Characteristics and Controlling Factors of Groundwater in a Typical Oasis in Arid Regions","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eArid regions cover a substantial portion of global land, and their unique climatic conditions and fragile ecosystems have attracted considerable interdisciplinary attention (Yao et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Tang et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Within these environments, oases function as relatively humid refugia that support human survival and development, playing an essential regional role (Liu et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ju et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Their existence relies on multiple natural resources, with groundwater being the most critical. Groundwater provides indispensable water for vegetation growth and agricultural irrigation and is central to maintaining ecological balance (Sheng et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Gobashy et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Ullah et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Yet groundwater in arid regions is particularly vulnerable to environmental change because of limited recharge and high evaporative losses, making its sustainable management a global challenge (Yan et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn recent years, climate change and intensifying human activities have caused groundwater degradation in more than 20% of oasis irrigated areas worldwide (Mao et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Problems such as persistent groundwater-level decline and progressive water-quality deterioration have emerged (Palma et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), placing unprecedented pressure on aquifer systems. For instance, excessive irrigation pumping has driven salinization and nitrate pollution in many arid oases, threatening ecosystem health and water security. As a crucial component of water resources in oasis systems, the hydrogeochemical characteristics of groundwater reveal its formation and evolution; however, the relative contributions of controlling factors to groundwater chemistry are often poorly quantified (Wang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Koncsos et al., 2024). Recent studies highlight the value of integrating hydrochemical and isotopic techniques to disentangle complex interactions between natural processes (e.g., rock weathering, evaporation) and anthropogenic influences (e.g., irrigation return flow, wastewater discharge) on groundwater quality (Preethi et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). A comprehensive understanding of groundwater hydrogeochemistry and its controlling factors in typical arid-region oases is therefore of great theoretical and practical significance for sustainable use and protection of groundwater resources, maintaining ecological balance, and ensuring safe water supplies.\u003c/p\u003e\u003cp\u003eDespite substantial progress, several knowledge gaps remain. First, the relative roles of natural processes (e.g., mineral dissolution, evaporation) and human activities (e.g., agricultural practices, urbanization) in shaping groundwater chemistry are still not well constrained (Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Second, the spatial and temporal variability of groundwater quality in oasis systems\u0026mdash;particularly under a changing climate\u0026mdash;remains insufficiently understood (Guo et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Third, there is a lack of integrated frameworks that couple traditional hydrochemical methods with advanced modeling to predict future groundwater evolution (Kumar et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn China, Xinjiang is a typical arid region with numerous oases, among which the Changji Hui Autonomous Prefecture stands out as a representative area. The unique geographical location and geological conditions of this region contribute to the complexity and distinctiveness of its oasis groundwater system. For example, the interaction between surface water and groundwater, coupled with the high evaporation rates, creates a dynamic hydrogeochemical environment that is highly sensitive to external perturbations. In recent years, the growing reliance on groundwater has resulted in excessive extraction, significantly altering its chemical composition. Therefore, this study focuses on a typical oasis in this arid region. Using field surveys, water sample collection, and analytical testing, a comprehensive approach was adopted, integrating statistical analysis, Piper diagrams, Gibbs diagrams, ion ratios, and hydrogeochemical modeling to reveal the groundwater\u0026rsquo;s chemical characteristics and controlling factors in the area. Insights into groundwater circulation processes from this study provide scientific evidence and references for the sustainable utilization of groundwater resources and environmental protection in arid-region oases.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e2.1.\u003c/em\u003e Study Area\u003c/h2\u003e\u003cp\u003eThe Changji Hui Autonomous Prefecture is situated on the northern slope of the Tianshan Mountains and the southeastern edge of the Junggar Basin, between latitudes 43\u0026deg;20\u0026prime;\u0026ndash;45\u0026deg;00\u0026prime; N and longitudes 85\u0026deg;17\u0026prime;\u0026ndash;91\u0026deg;32\u0026prime; E, covering a total area of 73,900 square kilometers (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The topography gradually descends from higher altitudes in the southern region to lower areas in the north, with a southeast-to-northwest gradient. The region's landforms can be divided into four types: the Tianshan Mountains, sloping plains, desert basins, and the Beita Mountains. The central plains lie between the southern mountains and northern desert, forming a flat, fertile oasis zone with favorable water and soil conditions created by alluvial and fluvial deposits. The study area has a typical continental arid climate, marked by low precipitation and high evaporation. Annual precipitation ranges from 160 to 190 mm, while evaporation reaches 1,900 to 2,700 mm. The average annual temperature is 6 to 7.5\u0026deg;C, indicating a typical arid oasis environment.\u003c/p\u003e\u003cp\u003eGeologically, the study area is divided from south to north into the Bogda Anticline, the Junggar Central Depression, the Qitai Uplift, and the Almant-Karamay Mountain Uplift. The exposed strata in this area consist primarily of the Quaternary, Carboniferous, and Devonian systems, with lithology becoming progressively finer from south to north, characterized by cobble, gravel, sand, and silty sand. The piedmont sloping plain serves as the main groundwater recharge zone, with replenishment primarily through river valley underflow, infiltration from storm runoff, and return flow from irrigation canals and fields. This process forms an unconfined aquifer with a single-layer structure, where groundwater depth exceeds 5 meters. The general groundwater flow direction is from south to north, with a hydraulic gradient of 3\u0026ndash;4\u0026permil;. In the alluvial and aeolian plains, the aquifer medium is composed of fine-grained or weakly permeable layers, resulting in poor groundwater flow conditions where vertical alternating movement predominates. This creates an upper unconfined-lower confined multilayered aquifer structure, with groundwater depths ranging from 5 to 200 meters. Discharge occurs mainly through spring outflow, evaporation, lateral runoff, and artificial extraction.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Sample Collection and Chemical Analysis of Groundwater\u003c/h2\u003e\u003cp\u003eIn September 2022, groundwater samples were methodically collected from boreholes across the study area, comprising a total of 198 samples\u0026mdash;133 from unconfined aquifers and 65 from confined aquifers (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Samples were collected in 500 mL polyethylene bottles, which were rinsed three times with deionized water before sampling and then rinsed three times with the water to be collected. All water samples were filtered using a 0.45 \u0026micro;m microporous membrane. For anion analysis, samples were sealed immediately after filtration, while for cation analysis, high-purity nitric acid was added to acidify the samples to a pH of \u0026le;\u0026thinsp;2. GPS was used to record the latitude, longitude, and elevation of each sampling location.\u003c/p\u003e\u003cp\u003eOn-site measurements of pH, temperature, conductivity, TDS, and redox potential were conducted using a pH meter (pH818), a portable conductivity/TDS meter (AR8011), and an oxidation-reduction potential meter (AZ8552), with accuracies of 0.01, 0.1\u0026deg;C, 1 \u0026micro;S\u0026bull;cm⁻\u0026sup1;, 1 mg\u0026bull;L⁻\u0026sup1;, and 1 mV, respectively. Ion analysis was performed by the Changji Prefecture Institute of Water Science and Technology, testing for pH, K⁺, Na⁺, Ca\u0026sup2;⁺, Mg\u0026sup2;⁺, Cl⁻, SO₄\u0026sup2;⁻, HCO₃⁻, total hardness (TH), and TDS, along with other indicators. Concentrations of K⁺, Na⁺, Ca\u0026sup2;⁺, and Mg\u0026sup2;⁺ were measured using an inductively coupled plasma optical emission spectrometer (iCAP6300); Cl⁻, SO₄\u0026sup2;⁻, and NO₃⁻ were determined using an ion chromatograph (ICS1100); and HCO₃⁻ was measured by acid-base titration. The detection limit for all ions was 0.01 mg\u0026bull;L⁻\u0026sup1;. The cation-anion charge balance error for all water samples was maintained within \u0026plusmn;\u0026thinsp;5%.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Analytical Method\u003c/h2\u003e\u003cp\u003eUsing the hydrogeological conditions and groundwater chemistry data from the study area, the chemical characteristics of groundwater and their controlling factors were analyzed through a combination of statistical analysis, Piper trilinear diagrams, Gibbs diagrams, ion ratios, and hydrogeochemical modeling. Excel was used for statistical analysis of hydrochemical parameters, while Grapher 10.0 was employed to generate Piper trilinear diagrams, Gibbs diagrams, and ion relationship plots. The saturation index and inverse hydrogeochemical modeling were conducted using PHREEQC 2.8, and other figures were created with Photoshop and ArcGIS 10.2.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e3.1.\u003c/em\u003e Statistical Results\u003c/h2\u003e\u003cp\u003eThe statistical results of groundwater hydrochemical parameters in the study area are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The pH of unconfined groundwater ranges from 7.08 to 8.52, with an average of 7.69, while the pH of confined groundwater ranges from 7.19 to 8.30, with an average of 7.81, indicating weak alkalinity in both cases. The TDS of unconfined groundwater varies from 182.45 to 3255.81 mg/L, with an average of 551.44 mg/L, whereas TDS in confined groundwater ranges from 241.20 to 3886.37 mg/L, with an average of 640.02 mg/L. The total hardness of unconfined groundwater ranges from 88.12 to 1261.76 mg/L, with an average of 273.64 mg/L, while in confined groundwater, it ranges from 79.11 to 1472.06 mg/L, with an average of 276.62 mg/L. Ion concentrations of both cations and anions are higher in confined groundwater than in unconfined groundwater.\u003c/p\u003e\u003cp\u003eThe average cation concentration in unconfined groundwater follows the trend Ca\u0026sup2;⁺ \u0026gt;Na⁺ + K⁺ \u0026gt;Mg\u0026sup2;⁺, while the average anion concentration follows HCO₃⁻ \u0026gt;SO₄\u0026sup2;⁻ \u0026gt;Cl⁻. In confined groundwater, the average cation concentration trend is Na⁺ + K⁺ \u0026gt;Ca\u0026sup2;⁺ \u0026gt;Mg\u0026sup2;⁺, and the anion concentration follows SO₄\u0026sup2;⁻ \u0026gt;HCO₃⁻ \u0026gt;Cl⁻.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eStatistical results of hydrochemical parameters of groundwater\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"11\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eParameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eUnconfined groundwater (n\u0026thinsp;=\u0026thinsp;133)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"5\" nameend=\"c11\" namest=\"c7\"\u003e\u003cp\u003eConfined groundwater (n\u0026thinsp;=\u0026thinsp;65)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMax\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMin\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMean\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSD\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eCV\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eMax\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eMin\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eMean\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eSD\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eCV\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003epH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e8.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e7.19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e7.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.03\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTDS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3255.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e182.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e551.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e378.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e3886.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e241.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e640.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e556.46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.87\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1261.76\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e88.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e273.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e182.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1472.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e79.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e276.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e231.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.84\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNa\u003csup\u003e+\u003c/sup\u003e+K\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e587.86\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e51.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e66.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e941.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e12.61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e84.89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e124.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e1.46\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCa\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e566.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e83.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e64.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e447.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e27.27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e73.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e59.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.81\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMg\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e125.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e17.61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e19.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e170.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e22.68\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e27.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e1.19\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCl\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e830.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e71.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e92.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e830.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e12.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e86.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e121.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e1.41\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHCO\u003csup\u003e3-\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e440.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e90.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e180.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e78.34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e510.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e100.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e184.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e76.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.41\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e989.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e30.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e149.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e142.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1545.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e28.53\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e188.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e231.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e1.23\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"11\"\u003eNote: In the table, SD represents standard deviation; VC represents coefficient of variation; pH represents a dimensionless quantity; the rest of the water chemical indicators are in mg/L, and the coefficient of variation is in %.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e3.2.\u003c/em\u003e Hydrochemical Types\u003c/h2\u003e\u003cp\u003eThe Piper diagram is a widely adopted tool for illustrating the composition and evolution of major ions in groundwater chemistry, offering the benefit of being independent of human-induced impacts. (Wang et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Yang et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). As shown in the Piper trilinear diagram for the study area (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), in the cation triangle (left triangle), most unconfined and confined groundwater samples are categorized as calcium-type with mixed sodium-type, with a higher proportion of sodium-type in confined groundwater, indicating the influence of ion accumulation in confined water. In the anion triangle (right triangle), both unconfined and confined groundwater are primarily bicarbonate-type and sulfate-type, with a small fraction of unconfined water showing chloride-type characteristics. The Piper diamond-shaped diagram further shows that the hydrochemical types of unconfined groundwater are predominantly HCO₃\u0026bull;SO₄-Ca and HCO₃\u0026bull;SO₄-Na\u0026bull;Ca, while confined groundwater is mainly of the HCO₃\u0026bull;SO₄-Na\u0026bull;Ca and HCO₃\u0026bull;SO₄\u0026bull;Cl-Na\u0026bull;Ca types.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e3.3.\u003c/em\u003e Mechanisms Controlling Groundwater Geochemistry\u003c/h2\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e\u003cem\u003e3.3.1.\u003c/em\u003e Dominant Factors\u003c/h2\u003e\u003cp\u003eThe Gibbs diagram provides a qualitative framework for evaluating hydrochemical evolution processes, which are influenced by atmospheric precipitation (Marandi\u0026amp;Shand, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), evaporative concentration, and rock weathering. Although initially developed for surface water, the Gibbs diagram requires contour adjustments for groundwater analysis, as groundwater has a much longer residence time in aquifers. This extended residence time leads to extensive water-rock interactions, which expand the \u0026ldquo;rock weathering control\u0026rdquo; range (Marandi \u0026amp; Shand, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The Gibbs diagram for groundwater in the study area shows that both unconfined and confined groundwater are predominantly located within the rock weathering zone (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), indicating that groundwater in this area is primarily influenced by rock dissolution, with minimal influence from evaporation concentration or atmospheric precipitation. Some confined groundwater samples show a distinct clustering in \u003cem\u003eγ\u003c/em\u003e(Na⁺)/\u003cem\u003eγ\u003c/em\u003e(Na⁺+Ca\u0026sup2;⁺), while \u003cem\u003eγ\u003c/em\u003e(Cl⁻)/\u003cem\u003eγ\u003c/em\u003e(Cl⁻+HCO₃⁻) displays no clear pattern.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e\u003cem\u003e3.3.2\u003c/em\u003e. Cation Exchange\u003c/h2\u003e\u003cp\u003eCation exchange is typically assessed by examining the relationship between \u003cem\u003eγ\u003c/em\u003e (Mg\u0026sup2;⁺ + Ca\u0026sup2;⁺ \u0026minus; SO₄\u0026sup2;⁻ \u0026minus; HCO₃⁻) and \u003cem\u003eγ\u003c/em\u003e (Na⁺ \u0026minus; Cl⁻). If cation exchange occurs, the ratio between these two values should be approximately \u0026minus;\u0026thinsp;1(Xiao et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, confined groundwater exhibits a strong negative correlation (\u003cem\u003eR\u003c/em\u003e\u0026sup2; = 0.91) between \u003cem\u003eγ\u003c/em\u003e (Mg\u0026sup2;⁺ + Ca\u0026sup2;⁺ \u0026minus; SO₄\u0026sup2;⁻ \u0026minus; HCO₃⁻) and \u003cem\u003eγ\u003c/em\u003e (Na⁺ \u0026minus; Cl⁻), with the ratio close to -1, indicating the occurrence of cation exchange in confined groundwater. In contrast, unconfined groundwater shows a ratio that deviates significantly from \u0026minus;\u0026thinsp;1, with a weaker correlation (\u003cem\u003eR\u003c/em\u003e\u0026sup2; = 0.29), suggesting that cation exchange is not prominent in unconfined groundwater. This observation is consistent with the findings of Ma et al., who reported cation exchange in confined groundwater within alluvial fan systems (Ma et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe chloro-alkaline indices (CAI-1 and CAI-2) are used to characterize the direction and intensity of ion exchange during groundwater chemical evolution (Singh et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Nematollahi et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). When CAI-1 and CAI-2 are less than 0, it indicates forward cation exchange, where Ca\u0026sup2;⁺ or Mg\u0026sup2;⁺ in groundwater displaces Na⁺ from aquifer minerals. Conversely, when CAI-1 and CAI-2 are greater than 0, it suggests reverse cation exchange, where Na⁺ in groundwater displaces Ca\u0026sup2;⁺ or Mg\u0026sup2;⁺ from aquifer minerals (Wang et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb shows the relationship between the chloro-alkaline indices and TDS for confined groundwater, where most CAI-1 and CAI-2 values are less than 0, indicating forward cation exchange. This suggests that Ca\u0026sup2;⁺ and Mg\u0026sup2;⁺ in confined groundwater have exchanged with Na⁺ and K⁺ from the surrounding rock, consistent with previous analyses. The larger absolute values of CAI-2 further indicate stronger ion exchange. Along the groundwater flow path, the particle size of confined aquifer media in the alluvial plain gradually becomes finer, with an increase in clay minerals. This enhances cation exchange, as surface-adsorbed Na⁺ is replaced by Ca\u0026sup2;⁺ and Mg\u0026sup2;⁺ in the water.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e\u003cem\u003e3.3.3.\u003c/em\u003e Dissolution Processes\u003c/h2\u003e\u003cp\u003eThe primary minerals in the study area\u0026rsquo;s strata include sulfates, carbonates, silicates, and halite. Sulfate minerals consist mainly of gypsum and mirabilite, carbonate minerals include calcite and dolomite, and silicate minerals are primarily quartz, mica, and feldspar. Through weathering and water-rock interactions, these minerals dissolve into the groundwater, contributing to its chemical composition (Mahamuda et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; You et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Ion ratio relationships are used to analyze these dissolution processes.\u003c/p\u003e\u003cp\u003eUnconfined groundwater sampling points are located near the line \u003cem\u003eγ\u003c/em\u003e (Na⁺ + K⁺)/\u003cem\u003eγ\u003c/em\u003e (Cl⁻)\u0026thinsp;=\u0026thinsp;1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), indicating that the hydrochemical composition of unconfined groundwater is primarily influenced by halite dissolution. In contrast, most confined groundwater sampling points are positioned above \u003cem\u003eγ\u003c/em\u003e (Na⁺ + K⁺)/\u003cem\u003eγ\u003c/em\u003e (Cl⁻)\u0026thinsp;=\u0026thinsp;1, suggesting that, in addition to halite dissolution, the hydrochemical composition of confined groundwater may also be affected by the dissolution of other sodium salts. In the confined groundwater of the river alluvial plain, Na⁺ + K⁺ concentrations deviate significantly from the 1:1 line, likely due to cation exchange, resulting in Na⁺ + K⁺ concentrations exceeding those of Cl⁻.\u003c/p\u003e\u003cp\u003eBoth unconfined and confined groundwater sampling points are positioned above the line \u003cem\u003eγ\u003c/em\u003e (Ca\u0026sup2;⁺ + Mg\u0026sup2;⁺)/\u003cem\u003eγ\u003c/em\u003e (HCO₃⁻)\u0026thinsp;=\u0026thinsp;1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), indicating that, in addition to the weathering and dissolution of calcite and dolomite, other Ca\u0026sup2;⁺-bearing minerals are also dissolving (Wang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). A significant linear relationship is observed between \u003cem\u003eγ\u003c/em\u003e (Ca\u0026sup2;⁺ + Mg\u0026sup2;⁺) and \u003cem\u003eγ\u003c/em\u003e (HCO₃⁻ + SO₄\u0026sup2;⁻) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec), with most groundwater sampling points falling below the line \u003cem\u003eγ\u003c/em\u003e (Ca\u0026sup2;⁺ + Mg\u0026sup2;⁺)/\u003cem\u003eγ\u003c/em\u003e (HCO₃⁻ + SO₄\u0026sup2;⁻)\u0026thinsp;=\u0026thinsp;1.\u003c/p\u003e\u003cp\u003eThe relationship between \u003cem\u003eγ\u003c/em\u003e (SO₄\u0026sup2;⁻ + Cl⁻) and \u003cem\u003eγ\u003c/em\u003e (HCO₃⁻) can be used to evaluate the contributions of sulfate and carbonate minerals to groundwater ions (Liu et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Most unconfined and confined groundwater sampling points are located above the line \u003cem\u003eγ\u003c/em\u003e (SO₄\u0026sup2;⁻ + Cl⁻)/\u003cem\u003eγ\u003c/em\u003e(HCO₃⁻)\u0026thinsp;=\u0026thinsp;1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed), indicating that sulfate dissolution is the dominant contributor to ions in the water, with Ca\u0026sup2;⁺ primarily sourced from the dissolution of gypsum and mirabilite. A linear relationship between \u003cem\u003eγ\u003c/em\u003e(Ca\u0026sup2;⁺) and \u003cem\u003eγ\u003c/em\u003e(SO₄\u0026sup2;⁻) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee) further suggests that gypsum dissolution is the main source of both Ca\u0026sup2;⁺ and SO₄\u0026sup2;⁻ in the groundwater.\u003c/p\u003e\u003cp\u003eIn addition to the increase in Na⁺ concentration in confined groundwater due to cation exchange, the primary sources of Na⁺ in groundwater are the weathering and dissolution of halite and mirabilite, while Ca\u0026sup2;⁺ mainly originates from gypsum dissolution and, to a lesser extent, the weathering of carbonates. The parameter \u003cem\u003eγ\u003c/em\u003e (Ca\u0026sup2;⁺ + Mg\u0026sup2;⁺ \u0026minus; HCO₃⁻) represents the Ca\u0026sup2;⁺ concentration derived from gypsum dissolution, and \u003cem\u003eγ\u003c/em\u003e [SO₄\u0026sup2;⁻ \u0026minus; (Na⁺ \u0026minus; Cl⁻)] represents the SO₄\u0026sup2;⁻ concentration from gypsum dissolution. If all SO₄\u0026sup2;⁻ in the water samples is derived from gypsum dissolution, the value of \u003cem\u003eγ\u003c/em\u003e (Ca\u0026sup2;⁺ + Mg\u0026sup2;⁺ \u0026minus; HCO₃⁻)/\u003cem\u003eγ\u003c/em\u003e [SO₄\u0026sup2;⁻ \u0026minus; (Na⁺ \u0026minus; Cl⁻)] should equal 1. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef, groundwater sampling points in the study area are located near or below the y\u0026thinsp;=\u0026thinsp;x line, further confirming that SO₄\u0026sup2;⁻ in groundwater primarily originates from gypsum dissolution.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003ePHREEQC software was used to calculate the saturation indices (SI) of various minerals to assess their dissolution and precipitation states (Liu et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kim et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Generally, when SI\u0026thinsp;\u0026lt;\u0026thinsp;\u0026minus;\u0026thinsp;0.5, the mineral is in a dissolution state; when SI is between \u0026minus;\u0026thinsp;0.5 and 0.5, the mineral is in a dissolution-precipitation equilibrium state; and when SI\u0026thinsp;\u0026gt;\u0026thinsp;0.5, the mineral is in a saturated state (Rouabhia et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn the groundwater environment of the study area, the saturation index (SI) of calcite ranges from \u0026minus;\u0026thinsp;0.69 to 1.43(Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), with an average of 0.25, indicating an overall state of equilibrium. The SI of dolomite ranges from \u0026minus;\u0026thinsp;2.13 to 2.52, averaging 0.09; most dolomite in unconfined groundwater is in equilibrium, with a small portion in a dissolution state, while dolomite in confined groundwater is generally in a saturated or equilibrium state. The SI of gypsum ranges from \u0026minus;\u0026thinsp;2.29 to \u0026minus;\u0026thinsp;0.49, with an average of \u0026minus;\u0026thinsp;1.60, indicating a general dissolution state. Halite has an SI range of \u0026minus;\u0026thinsp;8.54 to \u0026minus;\u0026thinsp;4.81, with an average of \u0026minus;\u0026thinsp;7.27, also indicating dissolution. Overall, these minerals show a higher dissolution capacity in unconfined groundwater than in confined groundwater. The saturation indices of minerals gradually increase from upstream to downstream, trending toward saturation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e3.4.\u003c/em\u003e Hydrogeochemical Modeling\u003c/h2\u003e\u003cp\u003ePHREEQC software enables quantitative simulation of water-rock interactions influenced by various natural processes and human activities (You et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Along the groundwater flow direction, the unconfined groundwater pathway Q45 \u0026rarr; Q49 \u0026rarr; Q50 and the confined groundwater pathway C49 \u0026rarr; C45 \u0026rarr; C40 were selected for hydrogeochemical modeling.\u003c/p\u003e\u003cp\u003eIn the model, primary minerals in the Quaternary aquifer of the study area\u0026mdash;quartz, halite, calcite, dolomite, and gypsum\u0026mdash;are designated as \u0026ldquo;potential mineral phases.\u0026rdquo; Since unconfined groundwater is in an open system, CO₂ is also included as a \u0026ldquo;potential mineral phase\u0026rdquo; along the unconfined groundwater pathway. In contrast, confined groundwater, being relatively deep and in a semi-closed system, does not involve CO₂ in hydrogeochemical processes. However, cation exchange occurs in confined groundwater, and this process is added as an additional \u0026ldquo;potential mineral phase\u0026rdquo; along the confined groundwater pathway. The model\u0026rsquo;s uncertainty factor is set at 0.05.\u003c/p\u003e\u003cp\u003eThe simulation results (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) indicate that along the unconfined groundwater pathway Q45 \u0026rarr; Q49 \u0026rarr; Q50, halite, dolomite, and gypsum undergo dissolution. As gypsum dissolves, the Ca\u0026sup2;⁺ concentration in unconfined groundwater increases, leading to calcite precipitation (with a precipitation amount of 5.280 \u0026times; 10⁻⁴ mmol/L). Along the confined groundwater pathway C49 \u0026rarr; C45 \u0026rarr; C40, calcite precipitates while halite, dolomite, and gypsum remain in a dissolved state. Forward cation exchange occurs in confined groundwater, with the intensity of this exchange increasing along the flow path (from 1.268 \u0026times; 10⁻\u0026sup3; mmol/L to 1.872 \u0026times; 10⁻\u0026sup3; mmol/L), maintaining a relatively low Ca\u0026sup2;⁺ concentration. Consequently, the hydrochemical type evolves from HCO₃\u0026bull;SO₄-Ca\u0026bull;Na to HCO₃\u0026bull;SO₄\u0026bull;Cl-Na\u0026bull;Ca.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eReverse simulation results of unconfined groundwater and confined groundwater flow paths\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eMolar Transfer Amount /mmol\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eUnconfined Groundwater Pathway\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eConfined Groundwater Pathway\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMineral Phase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eChemical Formula\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eQ45\u0026rarr;Q49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMineral Phase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eChemical Formula\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eQ45\u0026rarr;Q49\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHalite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNaCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.402\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eHalite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eNaCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2.402\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCalcite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCaCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.427\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCalcite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCaCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2.427\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDolomite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCaMg(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.001\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDolomite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCaMg(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.001\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGypsum\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCaSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.177\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eGypsum\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCaSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.177\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.355\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3.355\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCation Exchange\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCaX\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u0026mdash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCation Exchange\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCaX\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026mdash;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNaX\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u0026mdash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026mdash;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eNaX\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026mdash;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"6\"\u003eNote: In the table, a positive value indicates dissolution; a negative value indicates precipitation; and \u0026ldquo;\u0026mdash;\u0026rdquo; indicates that the mineral did not participate in the reaction.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e4.1.\u003c/em\u003e Hydrochemical Characteristics and Evolution\u003c/h2\u003e\u003cp\u003eThe weakly alkaline nature of groundwater in the study area is consistent with findings in other arid regions, such as the Tarim Basin and the Yinchuan Plain (Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The higher TDS and ion concentrations in confined groundwater compared to unconfined groundwater suggest longer residence times and more extensive water-rock interactions, as observed in similar alluvial systems (Marandi \u0026amp; Shand, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The dominance of Ca\u0026sup2;⁺ and HCO₃⁻ in unconfined groundwater reflects the influence of carbonate weathering, which is typical in recharge zones where fresh water interacts with carbonate-rich sediments (Katz et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In contrast, the shift to Na⁺ and SO₄\u0026sup2;⁻ dominance in confined groundwater indicates the increasing role of silicate weathering and cation exchange processes, as reported in the Hexi Corridor. This evolution of hydrochemical types along the flow path is a common feature in arid regions, where groundwater chemistry is strongly influenced by the mineralogy of aquifer materials and the intensity of water-rock interactions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e4.2.\u003c/em\u003e Mechanisms Controlling Groundwater Chemistry\u003c/h2\u003e\u003cp\u003eThe Gibbs diagram results confirm that rock weathering is the primary control on groundwater chemistry, consistent with findings in other arid regions (Gibbs, 1970; Marandi \u0026amp; Shand, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). However, the distinct clustering of confined groundwater samples in the \u003cem\u003eγ\u003c/em\u003e(Na⁺)/\u003cem\u003eγ\u003c/em\u003e(Na⁺+Ca\u0026sup2;⁺) plot suggests additional influences from cation exchange, as reported in the North China Plain (Xiao et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Cation exchange is particularly significant in confined aquifers due to the presence of clay minerals, which provide abundant exchange sites for Na⁺, Ca\u0026sup2;⁺, and Mg\u0026sup2;⁺. This process not only alters the ionic composition of groundwater but also affects its suitability for irrigation, as high Na⁺ concentrations can lead to soil sodicity and reduced agricultural productivity (Singh et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe strong negative correlation between \u003cem\u003eγ\u003c/em\u003e (Mg\u0026sup2;⁺ + Ca\u0026sup2;⁺ \u0026minus; SO₄\u0026sup2;⁻ \u0026minus; HCO₃⁻) and \u003cem\u003eγ\u003c/em\u003e (Na⁺ \u0026minus; Cl⁻) in confined groundwater (\u003cem\u003eR\u003c/em\u003e\u0026sup2; = 0.91) indicates significant cation exchange, a phenomenon also observed in the Nile Delta (Mostafa \u0026amp; Abdel, 2016). In contrast, the weaker correlation in unconfined groundwater (\u003cem\u003eR\u003c/em\u003e\u0026sup2; = 0.29) suggests limited cation exchange, likely due to shorter residence times and coarser aquifer materials (Ma et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This difference highlights the importance of aquifer lithology and groundwater flow dynamics in controlling hydrochemical processes. For example, the finer-grained sediments in confined aquifers promote more extensive cation exchange, while the coarser materials in unconfined aquifers favor rapid recharge and limited water-rock interactions (Liu et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e4.3.\u003c/em\u003e Mineral Dissolution and Precipitation\u003c/h2\u003e\u003cp\u003eThe dissolution of halite and gypsum, along with the equilibrium state of calcite and dolomite, is consistent with findings in the Loess Plateau (Liu et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) and the Arabian Peninsula (Rouabhia et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The higher dissolution capacity in unconfined groundwater compared to confined groundwater reflects the influence of recharge processes and open-system conditions, as observed in the Badain Jaran Desert. In unconfined aquifers, the continuous influx of fresh water enhances the dissolution of soluble minerals such as halite and gypsum, while the semi-closed nature of confined aquifers limits dissolution and promotes mineral saturation (Kim et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). This spatial variability in mineral dissolution has important implications for groundwater quality, as it influences the concentrations of major ions such as Na⁺, Ca\u0026sup2;⁺, and SO₄\u0026sup2;⁻, which are critical for assessing water suitability for drinking and irrigation.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e\u003cem\u003e4.4.\u003c/em\u003e Implications for Groundwater Management\u003c/h2\u003e\u003cp\u003eThe evolution of hydrochemical types from HCO₃\u0026bull;SO₄-Ca\u0026bull;Na to HCO₃\u0026bull;SO₄\u0026bull;Cl-Na\u0026bull;Ca along the flow path highlights the need for targeted management strategies. For example, the high Na⁺ and SO₄\u0026sup2;⁻ concentrations in confined groundwater may pose risks for irrigation and drinking water supplies, as reported in the Indus Basin (Singh et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Elevated Na⁺ levels can lead to soil degradation and reduced crop yields, while high SO₄\u0026sup2;⁻ concentrations may cause health issues such as gastrointestinal discomfort. To mitigate these risks, it is essential to implement measures such as controlled groundwater extraction, artificial recharge, and the use of alternative water sources for irrigation. Furthermore, the findings of this study have broader implications for sustainable groundwater management in arid regions. The integration of hydrochemical and isotopic techniques, as demonstrated here, provides a robust framework for understanding groundwater evolution and identifying contamination sources (Calvi et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Future studies should focus on quantifying the impacts of climate change and human activities on groundwater quality, particularly in vulnerable oasis systems. For example, the increasing intensity of agricultural practices and urbanization in arid regions is likely to exacerbate groundwater degradation, necessitating the development of adaptive management strategies.\u003c/p\u003e\u003c/div\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis study investigated the hydrochemical characteristics and controlling factors of groundwater in a typical oasis city in an arid region using statistical analysis, Piper diagrams, Gibbs diagrams, ion ratios, and hydrogeochemical modeling. The main findings are as follows:\u003c/p\u003e\u003cp\u003e(1) Groundwater in the study area is weakly alkaline, with higher TDS, total hardness, and ion concentrations in confined groundwater compared to unconfined groundwater. The hydrochemical types of unconfined groundwater are predominantly HCO₃\u0026bull;SO₄-Ca and HCO₃\u0026bull;SO₄-Na\u0026bull;Ca, while confined groundwater is mainly HCO₃\u0026bull;SO₄-Na\u0026bull;Ca and HCO₃\u0026bull;SO₄\u0026bull;Cl-Na\u0026bull;Ca.\u003c/p\u003e\u003cp\u003e(2) Rock dissolution is the primary control on groundwater chemistry, with minimal influence from evaporation and atmospheric precipitation. Major ions (Na⁺, Ca\u0026sup2;⁺, HCO₃⁻, Cl⁻, and SO₄\u0026sup2;⁻) are derived from the dissolution of evaporites (halite, gypsum, and mirabilite) and carbonates (calcite and dolomite). Confined groundwater is significantly influenced by forward cation exchange, where Ca\u0026sup2;⁺ or Mg\u0026sup2;⁺ in groundwater replaces Na⁺ in aquifer minerals, with exchange intensity increasing along the flow path.\u003c/p\u003e\u003cp\u003e(3) Hydrogeochemical modeling confirms that halite and gypsum are in a dissolved state, while calcite and dolomite are in dissolution-equilibrium. Mineral dissolution capacity is higher in unconfined groundwater than in confined groundwater, with saturation indices increasing downstream. Along the flow path, halite, dolomite, and gypsum dissolve, while calcite precipitates, and forward cation exchange occurs in confined groundwater.\u003c/p\u003e\u003cp\u003eThis study enhances the understanding of hydrogeochemical processes in arid oasis systems and provides a scientific basis for sustainable groundwater management. The findings highlight the need to address the risks associated with high Na⁺ and SO₄\u0026sup2;⁻ concentrations in confined groundwater, particularly for irrigation and drinking water supplies. Future research should focus on the impacts of climate change and human activities on groundwater quality, as well as the development of adaptive management strategies to ensure the long-term sustainability of groundwater resources in arid regions.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch3\u003eAcknowledgments\u003c/h3\u003e\n\u003cp\u003eThe authors would like to thank the anonymous reviewers and editors for their valuable comments, which were crucial in improving the quality of this paper.\u003c/p\u003e\n\u003ch3\u003eFunding\u003c/h3\u003e\n\u003cp\u003eThisresearch was funded by the Science and Technology Research Program of Chongqing Municipal Education Commission (KJQN202301209), the Science Technology Planning Project of WanZhou District, Chongqing (wzstc20230313, wzstc20230301) and Chongqing Water Conservancy Science and Technology Project (CQSLK-2024023).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e Not applicable. All the data used in this paper are provided herein\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interests\u003c/strong\u003e There are no competing interests regarding this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthor Contributions: \u003cstrong\u003eYulin Zhou\u003c/strong\u003e as the corresponding author, curated the data and prepared the original draft. \u003cstrong\u003eXing Wei\u003c/strong\u003e was responsible for the conceptualization and methodology of the study. \u003cstrong\u003eQingmei Zhang\u0026nbsp;\u003c/strong\u003econtributed to the visualization and investigation of the study\u0026apos;s findings. \u003cstrong\u003eLibo Ran\u003c/strong\u003e and \u003cstrong\u003eDelun Chen\u003c/strong\u003e provided overall supervision and project administration. \u003cstrong\u003eXueting Dou, Yanan Fu\u003c/strong\u003e and \u003cstrong\u003eGang Wu\u003c/strong\u003e conducted validation and contributed to writing, reviewing, and editing of the manuscript. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli dir=\"LTR\"\u003eCalvi C, Dape\u0026ntilde;a C, Quiroz Londo\u0026ntilde;o OM, et al. (2022) Assessing recharge process in plain catchments using isotopic and hydrochemical techniques. \u003cem\u003eGroundw Sustain Dev\u003c/em\u003e 19:100828. https://doi.org/10.1016/j.gsd.2022.100828\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eGobashy MM, Metwally AM, Abdelazeem M, et al. (2021) Geophysical exploration of shallow groundwater aquifers in arid regions: a case study of Siwa Oasis, Egypt. \u003cem\u003eNat Resour Res\u003c/em\u003e 30:\u0026mdash;. https://doi.org/10.1007/s11053-021-09897-3\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eGuo X, Feng Q, Si J, et al. (2019) Partitioning groundwater recharge sources in multiple aquifers system within a desert oasis environment: implications for water resources management in endorheic basins. \u003cem\u003eJ Hydrol\u003c/em\u003e 579:124212. https://doi.org/10.1016/j.jhydrol.2019.124212\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eJu X, He J, Zhang Q, et al. (2023) Evolution pattern and driving mechanism of eco-environmental quality in arid oasis belt: a case study of oasis core area in Kashgar Delta. \u003cem\u003eEcol Indic\u003c/em\u003e 154:110866. https://doi.org/10.1016/j.ecolind.2023.110866\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eKatz BG, Eberts SM, Kauffman LJ (2011) Using Cl/Br ratios and other indicators to assess potential impacts on groundwater quality from septic systems: a review and examples from principal aquifers in the United States. \u003cem\u003eJ Hydrol\u003c/em\u003e 397(3\u0026ndash;4):151\u0026ndash;166. https://doi.org/10.1016/j.jhydrol.2010.11.017\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eKim SS, Baik MH, Kang KC, et al. (2008) Solubilities of actinides in a domestic groundwater and a bentonite porewater calculated by using PHREEQC. \u003cem\u003eJ Ind Eng Chem\u003c/em\u003e 14(6):746. https://doi.org/10.1016/j.jiec.2008.07.005\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eKoncsos L, Mur\u0026aacute;nyi G (2024) A multi-scenario multi-model analysis of regional climate projections in a Central\u0026ndash;Eastern European agricultural region: assessing shallow groundwater table responses using an aggregated vertical hydrological model. \u003cem\u003eAppl Water Sci\u003c/em\u003e 14(3):\u0026mdash;. https://doi.org/10.1007/s13201-023-02097-9\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eKumar M, Ramanatahn AL, Tripathi R, et al. (2017) A study of trace element contamination using multivariate statistical techniques and health risk assessment in groundwater of Chhaprola Industrial Area, Gautam Buddha Nagar, Uttar Pradesh, India. \u003cem\u003eChemosphere\u003c/em\u003e 166:135\u0026ndash;145. https://doi.org/10.1016/j.chemosphere.2016.09.086\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eLi C, Gao X, Xiang X, et al. (2024) Intense human activities induce the dynamic changes of interaction pattern between karst water\u0026ndash;Quaternary groundwater in the basin\u0026ndash;mountain coupling belt over the past 60 years. \u003cem\u003eWater Resour Res\u003c/em\u003e 60(2):e2023WR035211. https://doi.org/10.1029/2023WR035211\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eLiu J, Pei X, Zhu W, et al. (2023) Simulation of the ecological service value and ecological compensation in arid area: a case study of ecologically vulnerable oasis. \u003cem\u003eRemote Sens\u003c/em\u003e 15(16):3927. https://doi.org/10.3390/rs15163927\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eLiu J, Wang H, Jin D, et al. (2020) Hydrochemical characteristics and evolution processes of karst groundwater in Carboniferous Taiyuan Formation in the Pingdingshan coalfield. \u003cem\u003eEnviron Earth Sci\u003c/em\u003e 79(6):\u0026mdash;. https://doi.org/10.1007/s12665-020-8898-4\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eLiu P, Wang G, Shang M, et al. (2021) Groundwater nitrate bioremediation simulation of in situ horizontal well by microbial denitrification using PHREEQC. \u003cem\u003eWater Air Soil Pollut\u003c/em\u003e 232(9):1\u0026ndash;11. https://doi.org/10.1007/s11270-021-05313-x\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eLiu R, Xie X, Qian Y, et al. (2023) Groundwater sulfate in the Pearl River Delta driven by urbanization: spatial distribution, sources and factors. \u003cem\u003eAppl Geochem\u003c/em\u003e 156:105766. https://doi.org/10.1016/j.apgeochem.2023.105766\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eMa Q, Ge W, Tian F (2022) Geochemical characteristics and controlling factors of chemical composition of groundwater in a part of the Nanchang section of Ganfu Plain. \u003cem\u003eSustainability\u003c/em\u003e 14(13):7976. https://doi.org/10.3390/su14137976\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eMahamuda A, Awinbire AB, Egbueri JC (2024) Understanding groundwater mineralization controls and the implications on its quality (Southwestern Ghana): insights from hydrochemistry, multivariate statistics, and multi-linear regression models. \u003cem\u003eActa Geophys\u003c/em\u003e 72(5):3563\u0026ndash;3580. https://doi.org/10.1007/s11600-023-01271-6\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eMao W, Zhu Y, Wu J, et al. (2020) Modelling the salt accumulation and leaching processes in arid agricultural areas with a new mass balance model. \u003cem\u003eJ Hydrol\u003c/em\u003e 591:125329. https://doi.org/10.1016/j.jhydrol.2020.125329\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eMarandi A, Shand P (2018) Groundwater chemistry and the Gibbs diagram. \u003cem\u003eAppl Geochem\u003c/em\u003e 97:\u0026mdash;. https://doi.org/10.1016/j.apgeochem.2018.07.009\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eMostafa R, Abdel Moneim AA (2016) Factors controlling groundwater hydrogeochemistry in the area west of Tahta, Sohag, Upper Egypt. \u003cem\u003eJ Afr Earth Sci\u003c/em\u003e 118:328\u0026ndash;338. https://doi.org/10.1016/j.jafrearsci.2015.10.002\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eNematollahi MJ, Clark MJR, Ebrahimi P, et al. (2018) Preliminary assessment of groundwater hydrogeochemistry within Gilan, a northern province of Iran. \u003cem\u003eEnviron Monit Assess\u003c/em\u003e 190(4):\u0026mdash;. https://doi.org/10.1007/s10661-018-6543-4\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003ePalma M, Maggio S, Cappello C, et al. (2023) Spatio-temporal modeling of groundwater quality deterioration and resource depletion. \u003cem\u003eHydrogeol J\u003c/em\u003e 31(6):1443\u0026ndash;1461. https://doi.org/10.1007/s10040-023-02692-9\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003ePreethi B, Subramani T, Saravanan R, et al. (2025) Health risks due to geogenic and anthropogenic influences on groundwater quality in Southern India\u0026rsquo;s hard rock terrain. \u003cem\u003eJ Geochem Explor\u003c/em\u003e 274:107762. https://doi.org/10.1016/j.gexplo.2025.107762\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eRouabhia A, Baali F, Fehdi C, et al. (2011) Hydrogeochemistry of groundwaters in a semi-arid region: El Ma El Abiod aquifer, Eastern Algeria. \u003cem\u003eArab J Geosci\u003c/em\u003e 4(5\u0026ndash;6):973\u0026ndash;982. https://doi.org/10.1007/s12517-010-0169-3\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eSheng D, Meng X, Wen X, Wu J, Yu H, Wu M (2022) Contamination characteristics, source identification, and source-specific health risks of heavy metal(loid)s in groundwater of an arid oasis region in Northwest China. \u003cem\u003eSci Total Environ\u003c/em\u003e 841:156733. https://doi.org/10.1016/j.scitotenv.2022.156733\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eSingh N, Singh RP, Kamal V, et al. (2015) Assessment of hydrogeochemistry and the quality of groundwater in 24-Parganas districts, West Bengal. \u003cem\u003eEnviron Earth Sci\u003c/em\u003e 73(1):375\u0026ndash;386. https://doi.org/10.1007/s12665-014-3431-2\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eTang X, Huang Y, Pan X, et al. (2024) Managing the water\u0026ndash;agriculture\u0026ndash;environment\u0026ndash;energy nexus: trade-offs and synergies in an arid area of Northwest China. \u003cem\u003eAgric Water Manag\u003c/em\u003e 295:108776. https://doi.org/10.1016/j.agwat.2024.108776\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eUllah A, Hussain S, Wang Y, et al. (2024) Integrated assessment of groundwater quality dynamics and land use/land cover changes in a rapidly urbanizing semi-arid region. \u003cem\u003eEnviron Res\u003c/em\u003e 260:119622. https://doi.org/10.1016/j.envres.2024.119622\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eWang D, Zhang L, Pei L, et al. (2023) Chemical characteristics and controlling factors of shallow groundwater in the lower reaches of Changhua River Basin, Hainan Island, China. \u003cem\u003eWater\u003c/em\u003e 15(19):3508. https://doi.org/10.3390/w15193508\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eWang H, Jiang XW, Wan L, et al. (2015) Hydrogeochemical characterization of groundwater flow systems in the discharge area of a river basin. \u003cem\u003eJ Hydrol\u003c/em\u003e 527:433\u0026ndash;441. https://doi.org/10.1016/j.jhydrol.2015.04.063\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eWang P, Zhang W, Zhu Y, et al. (2024) Evolution of groundwater hydrochemical characteristics and formation mechanism during groundwater recharge: a case study in the Hutuo River alluvial\u0026ndash;pluvial fan, North China Plain. \u003cem\u003eSci Total Environ\u003c/em\u003e 915:170159. https://doi.org/10.1016/j.scitotenv.2024.170159\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eWang Z, Wang Y, Shi M, et al. (2024) Coordinated analysis of groundwater spatiotemporal chemical characteristics, water quality, and potential human health risks with sustainable development in semi-arid regions. \u003cem\u003eEnviron Geochem Health\u003c/em\u003e 46(10):\u0026mdash;. https://doi.org/10.1007/s10653-024-02155-4\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eXiao J, Jin ZD, Wang J, Zhang F (2015) Hydrochemical characteristics, controlling factors and solute sources of groundwater within the Tarim River Basin in the extreme arid region, NW Tibetan Plateau. \u003cem\u003eQuat Int\u003c/em\u003e 380\u0026ndash;381:237\u0026ndash;246. https://doi.org/10.1016/j.quaint.2015.01.021\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eYan Y, Shi H, Miao Q, et al. (2025) Evolution of chemical characteristics and irrigation suitability of groundwater in arid and semi-arid regions. \u003cem\u003eAgric Water Manag\u003c/em\u003e 311:109361. https://doi.org/10.1016/j.agwat.2025.109361\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eYang Q, Wang L, Ma H, et al. (2016) Hydrochemical characterization and pollution sources identification of groundwater in Salawusu aquifer system of Ordos Basin, China. \u003cem\u003eEnviron Pollut\u003c/em\u003e 216:340\u0026ndash;349. https://doi.org/10.1016/j.envpol.2016.05.076\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eYao C, Li Z, Wang Y, et al. (2024) Redefining the modified water benefit-based ecological index to evaluate the impact of cropland expansion on the ecological environment in an arid area. \u003cem\u003eJ Clean Prod\u003c/em\u003e 477:143730. https://doi.org/10.1016/j.jclepro.2024.143730\u003c/li\u003e\n \u003cli dir=\"LTR\"\u003eYou J, Qi Y, Shao G, et al. (2024) Geochemical characteristics and controlling factors of groundwater chemical composition in the Zihe River source area, Shandong, China. \u003cem\u003eWater\u003c/em\u003e 16(2):298. https://doi.org/10.3390/w16020298\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"acta-geophysica","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"agph","sideBox":"Learn more about [Acta Geophysica](http://link.springer.com/journal/11600)","snPcode":"11600","submissionUrl":"https://www.editorialmanager.com/agph/default2.aspx","title":"Acta Geophysica","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Arid Region Oasis, Groundwater, Hydrogeochemistry, Hydrogeochemical Modeling, Controlling Factors","lastPublishedDoi":"10.21203/rs.3.rs-8100581/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8100581/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn arid regions, oases are critical to human survival and development, relying heavily on groundwater to sustain ecological balance and support socio-economic growth. This study focuses on a representative oasis city, where 198 groundwater samples were systematically collected in September 2022. A suite of analytical methods\u0026mdash;including statistical analysis, Piper and Gibbs diagrams, ion-ratio analysis, and hydrogeochemical modeling\u0026mdash;was used to characterize groundwater chemistry and identify its controlling factors. The results indicate that groundwater in the area is slightly alkaline. Unconfined groundwater is dominated by HCO₃\u0026middot;SO₄\u0026ndash;Ca and HCO₃\u0026middot;SO₄\u0026ndash;Na\u0026middot;Ca types, whereas confined groundwater is mainly HCO₃\u0026middot;SO₄\u0026ndash;Na\u0026middot;Ca and HCO₃\u0026middot;SO₄\u0026middot;Cl\u0026ndash;Na\u0026middot;Ca. Groundwater ion composition is influenced by water\u0026ndash;rock interaction, with major ions primarily derived from the dissolution of halite, evaporites, and carbonates; cation exchange processes further affect confined groundwater. Halite and gypsum dissolve, while calcite and dolomite are near dissolution\u0026ndash;precipitation equilibrium; overall dissolution propensity is higher in unconfined than in confined groundwater. Hydrogeochemical modeling quantitatively corroborates the primary water\u0026ndash;rock interactions inferred from qualitative analyses of groundwater flow. These findings improve understanding of hydrogeochemical evolution in oasis groundwater within arid regions.\u003c/p\u003e","manuscriptTitle":"Hydrogeochemical Characteristics and Controlling Factors of Groundwater in a Typical Oasis in Arid Regions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-03 11:39:16","doi":"10.21203/rs.3.rs-8100581/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revisions","date":"2026-01-14T09:58:32+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-12-23T11:56:19+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-11-30T20:08:24+00:00","index":"","fulltext":""},{"type":"submitted","content":"Acta Geophysica","date":"2025-11-24T20:45:49+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-22T10:57:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"acta-geophysica","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"agph","sideBox":"Learn more about [Acta Geophysica](http://link.springer.com/journal/11600)","snPcode":"11600","submissionUrl":"https://www.editorialmanager.com/agph/default2.aspx","title":"Acta Geophysica","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f5c6f9d1-9c5b-4f85-becb-ddc2b7ba1231","owner":[],"postedDate":"December 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-02-23T16:08:08+00:00","versionOfRecord":{"articleIdentity":"rs-8100581","link":"https://doi.org/10.1007/s11600-026-01828-1","journal":{"identity":"acta-geophysica","isVorOnly":false,"title":"Acta Geophysica"},"publishedOn":"2026-02-21 15:59:22","publishedOnDateReadable":"February 21st, 2026"},"versionCreatedAt":"2025-12-03 11:39:16","video":"","vorDoi":"10.1007/s11600-026-01828-1","vorDoiUrl":"https://doi.org/10.1007/s11600-026-01828-1","workflowStages":[]},"version":"v1","identity":"rs-8100581","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8100581","identity":"rs-8100581","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}