Study on the characteristics of water chemistry evolution in typical alpine karst basins

Study on the characteristics of water chemistry evolution in typical alpine karst basins | 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 Study on the characteristics of water chemistry evolution in typical alpine karst basins Hongwei Liao, Li He, Yu Wang, Yan Wang, Haiyong Liu, Xiaodong Pan, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5888289/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 03 Jul, 2025 Read the published version in Carbonates and Evaporites → Version 1 posted 10 You are reading this latest preprint version Abstract High-altitude karst basins, as vital components of the "Asian Water Tower," are critical for water resource conservation on the Qinghai-Tibet Plateau. To investigate the hydrochemical evolution characteristics of the Yepuqu River Basin, we analyzed 23 water samples (snowmelt, groundwater, and surface water) using hydrochemistry, hydrogen-oxygen isotopes, mass balance principles, and principal component analysis (PCA). Results showed that the hydrochemical types are predominantly HCO 3 —Ca and HCO 3 ·SO 4 —Ca. Ion balance diagrams indicated that water mineralization was primarily controlled by rock weathering and dissolution, with additional contributions from cation exchange. PCA further reveals that hydrochemical evolution is influenced by carbonate mineral dissolution, evaporite dissolution, and anthropogenic activities. Isotopic analysis demonstrated that surface water was originated from atmospheric precipitation (8%), snowmelt (74%), and groundwater (18%), with dynamic mutual transformation between groundwater and surface water, accompanied by intense water-rock interactions and evaporation. Through comparison of the results of water chemical evolution of similar alpine karst basins, it was found that the strength of human activities directly affects the differences in water chemical evolution. The study provides the first comprehensive analysis of hydrochemical evolution in the high-altitude karst basin of the Yepuqu River, enhancing the theoretical foundation for water resource protection in the Lhasa River Basin and offering crucial data to advance research on surface water-groundwater cycling in alpine karst systems. Yepuqu Alpine karst Karst water Hydrochemical characteristics Hydrochemical evolution Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1 Introduction The Lhasa River Basin is located in the south-central Qinghai-Tibet Plateau, known as the "Water Tower of Asia", and is an important water source gathering area in the Tibet Autonomous Region (Zhang et al., 2021 ). The water quality in the Lhasa River directly affects the water quality in the “Asian Water Tower”. Karst basins contribute to the stable base flow recharge of the Lhasa River through their unique groundwater regulation capacity, mitigating seasonal droughts (Ford, D et al., 2007). The fractures and conduits in karst landscapes form natural storage reservoirs, enhancing regional water resource resilience and supporting agricultural irrigation and ecological water demands within the basin (Hartmann et al., 2014 ). Additionally, groundwater circulation processes in karst systems filter contaminants, improving water quality and ensuring drinking water safety for Lhasa City and downstream areas (Khadka et al., 2020 ). Furthermore, the dynamic interactions between karst aquifers and surface water regulate hydrological regimes, reducing the impacts of extreme hydrological events on sustainable basin development (Yang et al., 2021 ). Some researchers have conducted hydrochemical characteristics (Li et al., 2023 ; Ming et al., 2024), heavy metal pollution assessments (Li et al., 2023 ), hydrological model studies (Zhang et al., 2021 ), and sediment health assessments on the Lhasa River (Chen et al., 2022 ). These studies provided a good theoretical basis for the protection and utilization of water resources in the Lhasa River Basin. Karst water is an important source of drinking water worldwide (Liao et al., 2022 ; Liu et al., 2023 ). The alpine karst basin is an important source of supply for the Lhasa River basin and is a major component of water resources on the Qinghai-Tibet Plateau. However, there were few studies on the high-altitude karst water in the Lhasa River Basin. The research reports on karst water focused more on low-altitude areas (Wang et al., 2022 ; Li et al., 2023 ; Luo et al., 2022 ; Liu et al., 2022 ). There were few reports on the research on the hydrochemical evolution mechanism of alpine karst basins. Therefore, studying the hydrochemical evolution characteristics of alpine karst basins is of great significance to protecting water resources in the Qinghai-Tibet Plateau. Elements in water were participants and recorders of water chemical reaction processes (Jeong et al., 2001). The analysis of water chemical characteristics helped us understand the formation and evolution of water bodies and played a vital role in revealing the hydrogeochemical processes and laws of water bodies in the basin (Pu et al., 2017 ; Scanlon et al., 2023 ). Water isotopes (D and 18 O) as tracers in the water cycle can effectively reveal the evolutionary relationship between different water bodies in a basin (Li et al., 2021 ). Therefore, this study focuses on the high-altitude karst basin of the Yepu Qu River. Through systematic sampling of snowmelt water, surface river water, and groundwater across the basin, we employ an integrated approach combining hydrochemistry, hydrogen-oxygen isotopes, mass balance principles, and principal component analysis (PCA) to address three key research questions: ① Identify the water chemical characteristics in the basin; ② Reveal the sources of different water bodies and quantify the contribution ratio of each source; ③ Explore the hydrogeochemical processes and influencing factors of water bodies. The study pioneers the investigation of hydrochemical evolution characteristics in the high-altitude karst basin of the Yepuqu River, ‌enhancing the theoretical foundation‌ for water resource conservation in the Lhasa River Basin. It establishes ‌a critical data-driven framework‌ to advance future research on surface water-groundwater interactions in alpine karst systems globally. 2 Materials and methods 2.1 Study area The Yepuqu karst basin is located in Yangda Township, Doilungdeqen District, Lhasa, with a basin area of about 21.3 km 2 . The overall terrain of the basin is high in the north and low in the south, with an altitude ranging from 3650 to 5500m, belonging to the medium-high mountain valley landform. The climate type belongs to the plateau temperate semi-arid climate, with an average annual rainfall of 400 ~ 500mm, and rainfall mainly occurs from June to September (Li et al., 2023 ; Ming et al., 2023). The exposed strata in the Yepuqu Basin include the Quaternary (Q), Cretaceous (K), Jurassic (J), and Paleogene (E), including sediments, sandstone, limestone, granite and Granodiorite‌‌. The Yepuqu River flows from north to south. The northern part of the basin (S01-R02) is the recharge area, where snow water and groundwater mix along the streams and flow into the Yepuqu River. In the middle part of the basin (P02-R07), there is frequent exchange of surface water and groundwater, strong water-rock interaction, and complex hydrochemical evolution. The southern part of the basin (R08 ~ R12) is the discharge area, where the Yepuqu River flows southward to the Tuilongqu River and finally flows from west to east into the Lhasa River(Fig. 1 ). 2.2 Sample collection and testing In this study, 23 groups of water samples were collected from November 3 to 6, 2023, including 2 groups of melt-water samples, 9 groups of groundwater samples, and 12 groups of surface water samples. The sampling locations are shown in Fig. 1 . The pH value, total dissolved solids (TDS), dissolved oxygen, and water temperature of the water samples were measured in the field using a portable multi-parameter measuring instrument (WTWMulti3430, Germany), with errors of 0.01, 0.01 mg·L − 1 , 0.01 mg·L-1 and 0.1°C, respectively. The concentrations of HCO 3 − and Ca 2+ were measured by on-site titration using an alkalinity test kit (Merck, Germany), with an error of 0.1 mmol·L-1 and 2 mg·L-1, respectively. Before sampling, rinse the pre-cleaned polyethylene plastic bottle 2 to 3 times with the original water sample. All water samples were first filtered using a 0.45 µm microporous filter membrane, and then quickly filled into a 550 mL bottle, capped and labeled, and then stored at low temperature, and sent for inspection within 24 hours. The water samples used to test cations were acidified by adding HNO 3 (1:1) to a pH value less than 2. The sample testing was completed by the Karst Geological Resources and Environmental Supervision and Inspection Center of the Chinese Academy of Geological Sciences. The cations were measured using a full spectrum direct reading plasma spectrometer (IRIS Intrepid Ⅱ XSP, Thermo Electron, USA) with a test accuracy of 0.01 mg·L − 1 . Anions were tested using a chromatograph (ICS-2100, Dionex, USA) with a test accuracy of 0.001 mg·L − 1 . The δD and δ 18 O-H 2 O were measured by GasBench II connected to MAT-253, with an accuracy better than 0.1‰ and 0.1‰ respectively (Ren et al., 2022 ). 2.3 Data analysis The hydrochemical data of the Puqu karst watershed were analyzed using ‌descriptive statistics‌ in SPSS 22.0. Principal Component Analysis (PCA) was employed to identify factors with eigenvalues ‌>1‌ and extract characteristic principal components (PCs) (Azzeddine R et al., 2024 ; Drouiche A et al., 2022 ). Hydrogeological maps and sampling site distributions were generated using ‌MapGIS 6.7‌, while Piper trilinear diagrams and scatter plots illustrating relationships between hydrochemical parameters for different karst groundwater types were created in ‌Origin 2018‌. 3 Results and discussion 3.1 Water chemistry and isotopic characteristics The test results of melt-water, groundwater, and surface water are shown in Table 1. The pH value of melt-water was 8.0. The average pH value of groundwater was 8.1, ranging from 7.4 to 8.3, and the average pH value of surface water was 8.1, refocused from 7.8 to 8.3. The pH value of groundwater and surface water was almost the same. The average groundwater temperature was 7.9℃, ranging from 2.1℃ to 12.5℃; and the average surface water temperature was 6.5℃. The average TDS values of groundwater, surface water, and melt-water were 263.3, 201.3, and 44.1 mg·L -1 , respectively. The Ca 2+ ions were the absolute dominant cations in all samples, with Ca2+ accounting for 59~90% of the total cation equivalents in groundwater (average 80%) and 56~87% in surface water (average 79%). The cation equivalent ratio of Mg 2+ was less than 20% at all sampling points. (K + +Na + ) accounted for 29% and 37% of the cation equivalents in granite spring water (P08) and Doilungqu River (R12). The average anion equivalent ratio of HCO 3 − in groundwater and surface water were greater than 81%, followed by SO 4 2− .The SO 4 2− in groundwater P01 and P07 and surface water R04 and R07 exceeded 20% of the total anion equivalent. As shown in Figure 2, the melt-water was of Ca-HCO3 type, and the groundwater and surface water were mainly Ca-HCO 3 type (accounting for 81%), followed by Ca-HCO 3 ·SO 4 (accounting for 19%). The values of dD and d 18 O-H 2 O of melt-water were −135.2~−134.1‰ and −18.1~−17.9‰. The average values of dD and d 18 O-H 2 O for groundwater were −137.0‰ and −18.0‰, and those for surface water were −135.4‰ and −17.9‰, respectively. Surface water was richer in heavy D and d 18 O-H 2 O than groundwater, and the average dD value of groundwater was lighter than that of melt-water, while the average dD value of surface water was close to that of melt-water. Table 1 Chemical and isotope test results of sampling water in the study area Type ID pH T TDS K + Na + Ca 2+ Mg 2+ Cl - SO 4 2- HCO 3 - NO 3 - δD δ18O-H 2 O /℃ /(mg·L -1 ) /‰ Melt-water S01 8.0 8.3 51.9 0.25 1.33 13.1 1.09 2.02 14.99 38.7 2.15 -134.1 -17.90 S02 8.0 10.6 36.3 0.29 1.49 7.5 1.38 1.98 11.28 31.6 2.62 -135.2 -18.10 Groundwater P01 8.0 2.1 197.8 0.35 3.04 40.8 2.79 2.12 67.64 73.4 4.00 -138.9 -18.90 P02 7.4 6.7 384.1 0.47 3.24 80.4 3.06 2.89 41.26 152.9 3.51 -138.8 -18.60 P03 8.3 5.9 193.3 0.36 2.26 38.2 1.17 2.08 43.44 109.2 3.05 -138.8 -18.30 P04 8.2 7.2 286.2 0.36 2.75 56.8 2.13 2.44 38.98 122.5 3.25 -139.7 -18.50 P05 8.0 7.1 439.4 0.39 3.96 106.3 2.93 2.84 48.12 231.5 2.76 -141.6 -18.8 P06 8.2 6.5 401.5 0.38 3.74 80.4 2.67 2.68 41.92 225.1 2.76 -140.9 -18.6 P07 8.3 12.4 222.8 1.17 6.25 48.7 4.16 4.59 48.5 109.9 10.98 -134.6 -17.3 P08 7.9 12.5 105.4 0.47 2.56 22.1 1.69 2.59 6.89 85.0 5.10 -134.2 -17.7 P09 8.3 10.4 139.4 2.77 4.68 22.2 2.53 2.51 5.4 91.6 2.50 -125.4 -15.2 Surface water R01 8.0 11.6 177.0 0.52 1.66 18.5 1.67 2.07 15.05 42.6 2.43 -131.4 -16.9 R02 8.1 7.8 57.6 0.28 1.04 16.5 1.17 2.01 12.18 42.4 3.17 -135.7 -18.2 R03 8.0 6.2 367.3 0.43 3.12 68.8 2.89 2.83 39.5 219.5 3.27 -138.4 -18.5 R04 8.2 4.5 58.6 0.27 1.26 14.5 1.06 2.13 11.88 24.4 3.78 -135 -18.2 R05 8.1 4.8 230.3 0.35 2.36 46.7 2.14 2.53 26.9 115.3 3.02 -137.2 -18.3 R06 7.8 5.1 229.3 0.35 2.36 44.5 2.15 2.54 26.92 122.1 2.58 -136.6 -18.3 R07 8.0 5.1 224.5 0.4 2.56 50.5 2.32 2.51 29.68 73.0 3.40 -136.5 -18.2 R08 8.1 6.1 223.2 0.42 2.57 43.6 2.32 2.54 29.32 115.0 2.92 -136.8 -18.2 R09 8.0 7.9 220.2 0.46 2.64 42.7 2.29 2.52 29.5 116.0 2.87 -136.6 -18.2 R10 8.1 8.7 219.3 0.49 2.67 43.3 2.3 2.52 29.7 115.8 0.05 -136.6 -18.2 R11 8.3 3.2 179.8 2.05 2.74 36.0 5.52 2.26 6.05 134.3 0.05 -128.5 -16.1 R12 8.1 6.8 228.7 1.83 12.9 36.2 2.77 8.44 29.57 91.9 3.36 -135.5 -17.9 3.2 Hydrochemical characteristics indications of hydrochemical evolution During the water cycle in the karst basin, different water bodies interacted physically, chemically, and biologically with the surrounding environment, causing water chemical evolution (Kortatsi et al., 2007; Wen et al., 2008), and changing in water substances (Belousova et al., 1999). Analysis of the relationship between the main ions in the water of the study area can reveal the main geochemical effects that control the chemical evolution in the karst basin. Gibbs diagrams were widely used to analyze the controlling factors in the formation and chemical evolution of water bodies (Gibbs, 1970; Ranjan et al., 2013; Gao, et al., 2010). According to Gibbs’s analysis (Fig. 3), the TDS content in the water was moderate, and the Na + /(Na + +Ca 2+ ) values were all less than 0.4, far below 0.5. All samples were full in the area of rock weathering, indicating that rock weathering was the main source of water chemistry in the study area (Ming et al., 1982). In summary, the Ca 2+ concentration in water bodies may come from the dissolution of calcite, dolomite, or gypsum, as well as the dissolution of calcite and dolomite. The equations were as follows: CaCO 3 +CO 2 +H 2 O=Ca 2+ +2HCO 3 － （1） CaMg(CO 3 ) 2 +2CO 2 +2H 2 O= Ca 2+ + Mg 2+ +4HCO 3 － （2） CaSO 4 ·2H 2 O= Ca 2+ +SO 4 2 － +2H 2 O （3） According to equations (1) to (3), the molar ratios of Ca 2+ / HCO 3 － produced by the dissolution of calcite, dolomite, and calcite and dolomite were 1/2, 1/4, and 1/3, respectively. The molar ratios of Mg 2+ / HCO 3 － produced by the dissolution of dolomite and calcite and dolomite are 1/4 and 1/6, respectively. Therefore, the non-gypsum source of calcium is obtained (Fig. 4(a)). Most of the sampling points in the basin full within the range of the 1:4 to 1:2 relationship line in Figure 4(a), indicating that different water bodies in the study area had undergone water-rock interactions with calcite and dolomite after receiving atmospheric precipitation. The proportion of surface water dissolving in calcite (greater than 1:2) and in calcite and dolomite (1:3~1:2) was 15% and 85% respectively. The proportion of groundwater dissolving in calcite and in calcite and dolomite was 33% and 67% respectively. The melting water (less than 1:4) showed no water-rock interaction (Figure. 4(a)). If gypsum dissolution would produce equal molar masses of Ca 2+ and SO 4 2 － , however, the [Ca 2+ ]/[SO 4 2 － of the study area samples ranged from 1.45 to 14.30, with an average value of 4.29. If the Ca 2+ , Mg 2+ , HCO 3 － and SO 4 2 － in the water body were mainly derived from the dissolution of calcite, dolomite and gypsum, then the milligram equivalent concentrations of (Ca 2+ +Mg 2+ )/(HCO 3 － +SO 4 2 － ) were equal (Kumar et al., 2006; Barzegar et al., 2016), while the values of (Ca 2+ +Mg 2+ )/(HCO 3 － +SO 4 2 － ) in the study area ranged from 0.39 to 0.90, with an average value of 0.56. At the same time, the fitting curve of the sampling points is near the 1:2 relationship line and does not completely correspond to Fig. 4(b). The above analysis showed that the surface water and groundwater mainly underwent calcite dissolution and the combined dissolution of calcite and dolomite, while the gypsum dissolution was not obvious. At the same time, other hydrogeochemical reactions may have occurred. Assuming that the dissolution of rock salt would result in equal amounts of Na+ and Cl － entering the water body. Except for the melt-water points, the [Na + ]/[Cl － ] at most of the sample points in the study area was greater than 1 (Fig. 5(a)), indicating that there were other sources of Na + in the water body besides the dissolution of rock salt, such as cation exchange and/or sodium sulfate dissolution. The Na + dissolved in non-carbonate rocks was the total Na + minus the Cl － dissolved in rock salt, which was [Na + ]-[Cl － ] (meq·L -1 ). From equation (4), we can see that the Ca 2+ from non-carbonate rock salt dissolution was [Ca 2+ ]-0.33[HCO 3 － ] (meq·L -1 ). Comparing the sum of Na + dissolved from non-carbonate rocks and Ca 2+ dissolved from non-carbonate rock salt with the SO 4 2 － equivalent concentration (Fig 5(b)), it could be seen that very few sampling points were located near the gypsum-salt stone line (1:1), indicating that very little Na + and SO 4 2 － in the water body of the study area came from the dissolution of saltstone, and there were other geochemical effects. If de-dolomite bloom occurs in the water, the dissolution of calcite will be weakened due to the common ion effect, causing calcite supersaturation and precipitation, thereby reducing the Ca 2+ concentration and increasing the Mg 2+ and SO 4 2 － (Bischoff et al., 1994; Back et al., 1983). The relationship diagram between [Mg 2+ /Ca 2+ ] and SO 4 2 － in the water body of the study area did not show an overall increase (Fig. 6(a)), indicating that there was no obvious de-dolomite blooming effect. As mentioned above, the sources of some Na+ in the study area need to be further discussed. [Na + ]/[Cl － ] can be used to characterize the degree of cation exchange (Xing et al., 2013). Na + in the soil can enter the water body by replacing Mg 2+ and Ca 2+ in the water body (Stimson et al., 2001), thereby increasing the Na + concentration in the water body and reducing the Mg 2+ and Ca 2+ concentration in the water (Hidalgo et al., 2001). The clay minerals contained in the carbonate salt in the study area provided the material basis for cation exchange. When cation exchange exists, (Ca 2+ +Mg 2+ )/( HCO 3 － +SO 4 2 － ) in water is less than 1 (Cerling et al., 1991; Li et al., 2016). At most sampling points in the water bodies of the study area, (Ca 2+ +Mg 2+ )/( HCO 3 － +SO 4 2 － ) was less than 1 (Fig 4(b)), and [Na + ]/[Cl － ] was greater than 1 (Fig 5(a)), which was consistent with the Ca 2+ - Na + or Mg 2+ - Na + cation exchange process (Stimson et al., 2001; Marghade et al., 2011), indicating that cation exchange had a certain contribution to the Na + in the study water. In addition, there was an equivalent 1:1 linear relationship between Na + and the replaced Mg 2+ or Ca 2+ during the cation exchange process (Li et al., 2016; Fisher et al., 1997), and the water points in the study area showed a linear relationship near and above 1:1 (Fig 6(b)), indicating that there were other sources of HCO 3 － +SO 4 2 － in the water body of the study area. Considering that the gypsum dissolution in the study area was not strong, the remaining SO 4 2 － may come from the oxidation of pyrite in the strata of the study area (Alderton et al., 2005; Kumari et al., 2010). The generated SO 4 2 － would react with the surrounding carbonate rock salt when it entered the water body, and the concentration of HCO 3 － and SO 4 2 − in the water body will increase (Equations (4)-(6)): FeS 2 +7/2O 2 +H 2 O→Fe 2+ +2SO 4 2- +2H + (4) 2Ca x Mg (1-x) CO 3 +H 2 SO 4 =2xCa 2+ +2(1-x)Mg 2+ +SO 4 2- +2HCO 3 － (5) Ca x Mg (1-x) CO 3 +H 2 CO 3 =xCa 2+ +(1-x)Mg 2+ +2HCO 3 － (6) From equations (4) to (6), it can be seen that if only carbonic acid dissolved carbonate rock, [Ca 2+ +Mg 2+ ]/[HCO 3 - ] was equal to 1, the concentration of SO 4 2- was low and [SO 4 2- ]/[ HCO 3 - ] was equal to 0; when sulfuric acid participated in the water-rock reaction, [Ca 2+ +Mg 2+ ]/[HCO 3 - ] was 2, and the value of [SO 4 2- ]/[HCO 3 - ] was 1; when carbonic acid and sulfuric acid simultaneously dissolved carbonate rock minerals to reach equilibrium, [Ca 2+ +Mg 2+ ]/ [HCO 3 - ]=3/2, [SO 4 2- ]/[HCO 3 - ]=1/2 (Alderton et al., 2005; Kumari et al., 2010), and the reaction equation was as follows: 3CaxMg (1-x) CO 3 + H 2 SO 4 +H 2 CO 3 =3xCa 2+ +3(1-x)Mg 2+ +SO 4 2- +4HCO 3 - (7) From the relationship between [(Ca 2+ +Mg 2+ )/ HCO 3 - ] and [SO 4 2- /HCO 3 - ] in water (Fig 7), it can be concluded that part of groundwater and surface water were mainly weathered by carbonate rocks with the participation of H 2 CO 3 (accounting for 13%); and the vast majority of groundwater, surface water and melt-water were located around the "cross" in the figure, at which time [Ca 2+ +Mg 2+ ]/[HCO 3 - ]=3/2, [SO 4 2- ]/[HCO 3 - ]=1/2, indicating that H 2 SO 4 and H 2 CO 3 jointly participated in the water-rock reaction in the water (accounting for 74%).In addition, a small number of surface water and groundwater points showed [Ca 2+ +Mg 2+ ]/[HCO 3 - ]＞3/2, [SO 4 2- ]/[HCO 3 - ]＞1/2 (accounting for 13%), which was mainly due to the increase in SO 4 2- concentration caused by the oxidation of pyrite in the formation. 3.3 Isotope indications of water chemical evolution Based on the marking characteristics of stable hydrogen and oxygen isotopes in the water cycle, the recharge sources, recharge patterns, and hydraulic connections between water bodies in the regional water bodies can be revealed, thereby clearly understanding the hydrochemical processes of different water bodies in the study area (Bedaso et al., 2021). The local precipitation line in Lhasa (LMWL: dD=7.90d 18 O+6.29) was selected as the reference data (Tian et al., 2001), and combined with the global atmospheric precipitation line (GMWL: dD=8d 18 O+10) (Craig, 2023), the relationship diagram of dD and d 18 O-H 2 O of the water body in the study area was drawn (Fig 8). As shown in Figure 8, the groundwater and surface water sampling points were located on and near the Lhasa Local Weathering Line (LMWL) and the Global Weathering Line (GMWL), indicating that the surface water and groundwater in the Yepuqu Basin were mainly atmospheric precipitation. Both groundwater and surface water were distributed within a certain range. Compared with surface water, groundwater was more dispersed in the figure and was more concentrated in ice and snow meltwater. Among them, groundwater P07 and P09 and surface water R01 and R11 showed enrichment of heavy water isotopes and appeared at the lower right of the local atmospheric precipitation line (LMWL) and the global atmospheric precipitation line (GMWL), indicating that these water bodies underwent water-rock interaction or evaporation during runoff (Ren et al., 2023), and the natural geographical conditions of the study area promoted the occurrence of this phenomenon (Ge et al., 2020). The δD and δ 18 O of surface water, groundwater, and melt-water showed a gradual dispersion in Fig 8, and there were an intersection between different water bodies, indicating that different degrees of mutual transformation have occurred between different types of water bodies (Ren et al., 2023). It also showed that the three types of water bodies may have mutually transformed or been mixedly replenished by water sources carrying different deuterium and oxygen information. The values of δD and δ 18 O in water depended on the respective compositions in the recharge source and are affected by fractionation due to evaporation processes (Ma et al., 2015). The variation characteristics of hydrogen and oxygen isotopes in different water bodies are different (Yang et al., 2018). Most of the surface water, groundwater, and melt-water in the study area were distributed between the LMWL and GMWL. The intersection of the fitting lines of groundwater and surface water with the local precipitation line was close to the average isotopic composition of water bodies in the region, indicating that surface water and groundwater were mainly recharged by atmospheric precipitation (Sun et al., 2017). The slopes of the fitting lines for groundwater and surface water (4.18, 3.82) were similar and smaller than those of LMWL) and GMWL (7.90, 8.0), indicating that the hydraulic connection between groundwater and surface water was strong and that they had experienced strong evaporation. This was consistent with the local natural geographical conditions of dry climate, low precipitation, high evaporation, and being located inland far away from steam sources (Ge et al., 2020). The high altitude of the study area makes secondary evaporation easy to occur during rainfall, and d 18 O in water vapor is more easily enriched, which also caused the slope of the precipitation line to be low (Yang et al., 2018; Song et al., 2017). In addition, the results of the water chemical characteristic analysis showed that there was obvious carbonate salt dissolution in the surface water and groundwater in the study area, which also explained the reason for the low slope of the fitting line of groundwater and surface water. 3.4 Impact of human activities Principal Component Analysis (PCA), a widely adopted method for identifying hydrochemical element sources (Abdelmalek D et al., 2024; Zahi F et al., 2024), was applied to 11 hydrochemical parameters. The Kaiser-Meyer-Olkin (KMO) value (0.613) and Bartlett’s test significance (p < 0.001) confirmed the ‌suitability of the dataset‌ for PCA-based factor loading analysis. Three principal components (PCs, Table 2) were extracted, collectively accounting for ‌73.88% of the cumulative variance‌, effectively capturing the dominant hydrochemical patterns in the study area. Table 2 Pearson correlation matrix of hydrochemical parameters in the Yepuqu River karst basin Parameter PC1 PC2 PC3 Communalities pH -0.15 0.50 -0.34 0.61 T -0.29 0.35 0.50 0.75 TDS 0.94 -0.25 -0.01 0.94 K + 0.10 0.81 -0.45 0.87 Na + 0.51 0.77 0.15 0.87 Ca 2+ 0.92 -0.32 0.01 0.94 Mg 2+ 0.63 0.36 -0.39 0.93 Cl - 0.43 0.73 0.26 0.88 SO 4 2- 0.73 -0.25 0.32 0.81 HCO 3 - 0.87 -0.21 -0.18 0.92 NO 3 - 0.17 0.32 0.75 0.83 Eigenvalues (%) 3.98 2.65 1.5 Variance (%) 36.19 24.09 13.6 Cumulative (%) 36.19 60.28 73.88 Notes: Extraction method: principal component analysis. Factor loadings beyond-0.6 to 0.6 are marked by bold font. bold font. Based on the characteristic loadings of variables within each factor, the influencing mechanisms can be categorized into three groups: The ‌PC1‌ (Ca²⁺, Mg²⁺, SO₄²⁻, and HCO₃⁻) predominantly originates from ‌carbonate mineral dissolution‌, as evidenced by hydrogeochemical modeling in Section 3.2 and dissolution processes detailed in Equations (4)–(7). The ‌PC2‌ (K⁺, Na⁺, and Cl⁻) is attributed to ‌evaporite dissolution‌, supported by the median (K⁺+Na⁺)/Cl⁻ ratio of 0.93 (<1), which rules out significant marine aerosol contributions (given the inland location) and aligns with widespread evaporite-bearing granite formations in the study area (Figure 1). The ‌PC3‌ (NO₃⁻) reflects ‌anthropogenic inputs‌, as the maximum NO₃⁻ concentration (10.98 mg·L⁻¹) substantially exceeds both the local minimum (0.05 mg·L⁻¹) and the reported maximum in the Lhasa River Basin (0.84 mg·L⁻¹) (Lin et al., 2021). Spatial analysis confirms elevated NO₃⁻ levels in agricultural zones, where excessive fertilizer application exceeds crop uptake capacity, leading to nitrate leaching into groundwater systems. The Yulong Snow Mountain-Lijiang alpine karst basin, as a representative of high-altitude karst regions, has been previously studied regarding hydrochemical variation patterns and driving mechanisms (Ren K et al., 2024). Existing findings indicate that its water recharge originates predominantly from ‌atmospheric precipitation‌, with significant anthropogenic impacts from tourism activities altering hydrochemical signatures—particularly elevated concentrations of K⁺, Na⁺, Cl⁻, and SO₄²⁻. ‌In contrast‌, our study reveals that hydrochemical variations in the target basin are primarily governed by ‌mineral dissolution processes‌, with human activities exerting influence solely on NO₃⁻ concentrations (ρ(NO₃⁻)). However, the current research is constrained by ‌single-season sampling‌, limiting insights to preliminary hydrochemical evolution characteristics. To advance understanding, future studies will employ ‌integrated hydrochemical-isotopic approaches‌ with ‌hydrological-year sampling campaigns‌ across groundwater and surface water systems. Concurrent real-time monitoring of critical hydrogeological parameters will be implemented to unravel water-rock interaction dynamics during the surface water-groundwater cycling processes in alpine karst basins, thereby generating foundational data for watershed water resource conservation strategies. 3.5 Sources of surface water in the basin The chemical properties of hydrogen and oxygen isotopes are stable, and there are certain differences in the hydrogen and oxygen isotope values in different water bodies (Zhang et al., 2014), which can better identify the supply end members (Gao et al., 2019; Huang et al., 2018). Therefore, based on the mass conservation principle of hydrogen and oxygen isotopes, a two-component mixing model was used to calculate the mixing ratio of different water bodies (Lei et al., 2020). Assuming that the concentrations of the two end members before mixing conform to the linear law, since the test precision and accuracy of δD were lower than those of δ 18 O, δ 18 O was selected to calculate the mixing ratio of surface water. The δ 18 O of melt-water and groundwater were similar, and they are regarded as a mixing unit. Atmospheric precipitation was regarded as a mixing end member. The calculation equation is as follows (Ogunkoya et al., 1991): δ 18 O R =δ 18 O S ·X+δ 18 O P (1-X) （9） Where: X was the recharge ratio, %; δ 18 O R , δ 18 O S, and δ 18 O P were the average δ 18 O test values of surface water, atmospheric precipitation, and groundwater (including melt-water) in the study area, respectively. According to the test data (Table 1) and the rainfall data in Lhasa in November(Yang et al., 2009), the values of δ 18 O R , δ 18 O S, and δ 18 O P were 17.93, 14.1, and 18.3 respectively. The mixing ratio of the above surface water was calculated. The results showed that atmospheric precipitation accounted for 8% of surface water, while groundwater (including melt-water from ice and snow) accounted for 92%. The groundwater recharge rate in the basin can be estimated by using the chloride ion mass balance method in the water body. The calculation formula was as follows (Leaney et al., 1995): R (%)=100·( C Cl S / C Cl P ) （10） In the formula, R was the proportion of groundwater; C Cl S was the average concentration of chloride ions in ice and snow meltwater; C Cl P was the average concentration of chloride ions in groundwater. The results showed that melt-water accounted for 81% of groundwater. By combining equations (9) and (10), the study concluded that 8% of surface water came from atmospheric precipitation, 74% from ice and snow meltwater, and 18% from groundwater. The reasons for the low proportion of atmospheric precipitation in surface water may be that the sampling time was the period of relatively small rainfall in the study area, and the main rainfall period was concentrated from June to September; or the sampling time was the main time for ice and snow to melt, and a large amount of ice and snow melt water flowed into the surface water. 4 Conclusion The Yepuqu River karst basin’s snowmelt water exhibited a Ca-HCO 3 type, while 81% of surface and groundwater shared this type, with 19% classified as Ca-HCO 3 ·SO 4 . Water chemistry primarily originated from rock weathering, dominated by carbonate dissolution alongside minor mirabilite dissolution and cation exchange. A small portion (13%) involvesd H 2 CO 3 -driven carbonate weathering, while pyrite oxidation elevated SO 4 2− levels. Most water (74%) showed combined H 2 SO 4 and H 2 CO 3 water-rock interactions. Hydrochemical evolution was driven by carbonate and evaporite dissolution, as well as human activities. Comparisons with similar alpine karst basins highlight human activity intensity as a key factor in hydrochemical variation. The surface water and groundwater in the study area were mainly derived from atmospheric precipitation. Eight percent of surface water came from atmospheric precipitation, 74% from ice and snow meltwater, and 18% from groundwater. Affected by natural geographical conditions, the slopes of the groundwater and surface water fitting lines (4.18, 3.82) were similar and smaller than the slopes of LMWL and GMWL (7.90, 8.0). The hydraulic connection between groundwater and surface water was strong and had experienced strong water-rock interaction and evaporation. This study presented the first investigation into the hydrochemical evolution characteristics of the alpine karst basin in the Yepuqu River through systematic sampling. The next phase will involve sampling across the entire hydrological year in the study area, along with real-time monitoring of hydrological parameters in key groundwater and surface water zones. The research aims to explore the hydrochemical evolution characteristics during the surface water- groundwater cycle in alpine karst basins, providing foundational data for water resource protection in the basin. Declarations Author Contribution Hongwei Liao: Conceptualization, Methodology, Software, Investigation, Writing - original draft. Huaying Wu and Li He: Validation, Supervision. Yan Wang and Yu Wang: Validation, Supervision. Tengfang Li: Resources, Writing - review & editing, Supervision. Xiaodong Pan and Qibo Huang: Formal analysis, Visualization, funding acquisition. Changpei Zou and Kun Ren: Software. Haiyong Liu and Junfei Ma: Investigation. Acknowledgement Data availabilityNo data was used for the research described in the article.Declaration of competing interestThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.AcknowledgmentThe authors would like to appreciate anonymous reviewers and the editor for their constructive comments. We acknowledge Dr. Xiong, and Jianguo Yu for writing assistance.FundingThis research was supported by Central government-guided local special projects (XZ202301YD0005C), Basic scientific research operating expenses project of the Institute of Karst Geology, Special Fund for Basic Scientific Research of Institute of Karst Geology, CAGS (2023007), National General Fund Project (42372294), Guangxi Fund projects (2025GXNSFAA069189)， National Youth Fund Project (41702281), the China Geological Survey’s Project（DD20251205）; and Special Fund for Basic Scientific Research of Institute of Karst Geology, CAGS（2023018）. References Abdelmalek D, Azzeddine R, Mohamed A, et al. Groundwater quality assessment using revised classical diagrams and compositional data analysis (CoDa): Case study of Wadi Ranyah, Saudi Arabia [J]. Journal of King Saud University-Science, 2024, 36(10): 103463. Alderton D, Serafimovski T, Mullen B, et al. 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12:23:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5888289/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5888289/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s13146-025-01131-y","type":"published","date":"2025-07-03T15:57:37+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81530391,"identity":"0fd737a6-6e99-4e98-82cc-f8bfdc56d69b","added_by":"auto","created_at":"2025-04-28 09:25:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":184788,"visible":true,"origin":"","legend":"\u003cp\u003eHydrogeological sketch and sampling sites distribution of the study area\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/2a9a565a8684d8de1d7f05e5.png"},{"id":81530390,"identity":"741fb880-c9ef-4c44-8a8d-330ab60a6c92","added_by":"auto","created_at":"2025-04-28 09:25:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":228693,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePiper diagram of Hydrochemistry in the study area\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/bd4bdd15b8073b566dbfa967.png"},{"id":81532573,"identity":"90f9e4bf-8896-4ed6-a11c-6db1a0c1b1c4","added_by":"auto","created_at":"2025-04-28 09:41:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":193643,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGibbs diagram of water chemistry in the study area\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/039ebff0f6796035263e31f7.png"},{"id":81531406,"identity":"938528b6-a101-4a23-8dbb-4b74215b501e","added_by":"auto","created_at":"2025-04-28 09:33:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":193519,"visible":true,"origin":"","legend":"\u003cp\u003eCarbonate salt dissolution relationship in the study area\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/fdbb42fddfd8b92a5b273db4.png"},{"id":81531407,"identity":"ca97ceae-d6bb-416a-b6de-b96ad8811fb9","added_by":"auto","created_at":"2025-04-28 09:33:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":230539,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship of dissolved ions of non-carbonate rock salt in the study area\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/4e2e9676520e912714fb7019.png"},{"id":81532575,"identity":"5f3e9dff-4844-4455-b917-58be56579add","added_by":"auto","created_at":"2025-04-28 09:41:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":243684,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between [Mg\u003csup\u003e2+\u003c/sup\u003e/Ca\u003csup\u003e2+\u003c/sup\u003e] and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2－\u003c/sup\u003e and cation exchange in the study area\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/7442f1df5ac84e5170020308.png"},{"id":81530403,"identity":"630c8018-bb21-4d9a-84e8-5e39e0454268","added_by":"auto","created_at":"2025-04-28 09:25:59","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":282085,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between [(Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e)/HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] and [SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e/HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] in different types of water\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/a81d5bf7ef7c828e6f9cbfcf.png"},{"id":81530409,"identity":"640dcf84-3d20-499c-99e4-928c17a59098","added_by":"auto","created_at":"2025-04-28 09:25:59","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":157038,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDual isotopic plot of dD and d\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e18\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003eO-H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO of sampled waters in the study area\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/4819c7c16cc6387bcfba253c.png"},{"id":86179718,"identity":"8e632271-73e9-4ebc-b7da-2a944568dad8","added_by":"auto","created_at":"2025-07-07 16:18:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2766931,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5888289/v1/9199a13b-a050-4161-aa99-062ad1494468.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Study on the characteristics of water chemistry evolution in typical alpine karst basins","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe Lhasa River Basin is located in the south-central Qinghai-Tibet Plateau, known as the \"Water Tower of Asia\", and is an important water source gathering area in the Tibet Autonomous Region (Zhang et al., \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The water quality in the Lhasa River directly affects the water quality in the \u0026ldquo;Asian Water Tower\u0026rdquo;. Karst basins contribute to the stable base flow recharge of the Lhasa River through their unique groundwater regulation capacity, mitigating seasonal droughts (Ford, D et al., 2007). The fractures and conduits in karst landscapes form natural storage reservoirs, enhancing regional water resource resilience and supporting agricultural irrigation and ecological water demands within the basin (Hartmann et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Additionally, groundwater circulation processes in karst systems filter contaminants, improving water quality and ensuring drinking water safety for Lhasa City and downstream areas (Khadka et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Furthermore, the dynamic interactions between karst aquifers and surface water regulate hydrological regimes, reducing the impacts of extreme hydrological events on sustainable basin development (Yang et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSome researchers have conducted hydrochemical characteristics (Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ming et al., 2024), heavy metal pollution assessments (Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), hydrological model studies (Zhang et al., \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and sediment health assessments on the Lhasa River (Chen et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These studies provided a good theoretical basis for the protection and utilization of water resources in the Lhasa River Basin. Karst water is an important source of drinking water worldwide (Liao et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The alpine karst basin is an important source of supply for the Lhasa River basin and is a major component of water resources on the Qinghai-Tibet Plateau. However, there were few studies on the high-altitude karst water in the Lhasa River Basin. The research reports on karst water focused more on low-altitude areas (Wang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Luo et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). There were few reports on the research on the hydrochemical evolution mechanism of alpine karst basins. Therefore, studying the hydrochemical evolution characteristics of alpine karst basins is of great significance to protecting water resources in the Qinghai-Tibet Plateau.\u003c/p\u003e \u003cp\u003eElements in water were participants and recorders of water chemical reaction processes (Jeong et al., 2001). The analysis of water chemical characteristics helped us understand the formation and evolution of water bodies and played a vital role in revealing the hydrogeochemical processes and laws of water bodies in the basin (Pu et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Scanlon et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Water isotopes (D and \u003csup\u003e18\u003c/sup\u003eO) as tracers in the water cycle can effectively reveal the evolutionary relationship between different water bodies in a basin (Li et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, this study focuses on the high-altitude karst basin of the Yepu Qu River. Through systematic sampling of snowmelt water, surface river water, and groundwater across the basin, we employ an integrated approach combining hydrochemistry, hydrogen-oxygen isotopes, mass balance principles, and principal component analysis (PCA) to address three key research questions: ① Identify the water chemical characteristics in the basin; ② Reveal the sources of different water bodies and quantify the contribution ratio of each source; ③ Explore the hydrogeochemical processes and influencing factors of water bodies. The study pioneers the investigation of hydrochemical evolution characteristics in the high-altitude karst basin of the Yepuqu River, \u0026zwnj;enhancing the theoretical foundation\u0026zwnj; for water resource conservation in the Lhasa River Basin. It establishes \u0026zwnj;a critical data-driven framework\u0026zwnj; to advance future research on surface water-groundwater interactions in alpine karst systems globally.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study area\u003c/h2\u003e \u003cp\u003eThe Yepuqu karst basin is located in Yangda Township, Doilungdeqen District, Lhasa, with a basin area of about 21.3 km\u003csup\u003e2\u003c/sup\u003e. The overall terrain of the basin is high in the north and low in the south, with an altitude ranging from 3650 to 5500m, belonging to the medium-high mountain valley landform. The climate type belongs to the plateau temperate semi-arid climate, with an average annual rainfall of 400\u0026thinsp;~\u0026thinsp;500mm, and rainfall mainly occurs from June to September (Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ming et al., 2023). The exposed strata in the Yepuqu Basin include the Quaternary (Q), Cretaceous (K), Jurassic (J), and Paleogene (E), including sediments, sandstone, limestone, granite and Granodiorite\u0026zwnj;\u0026zwnj;. The Yepuqu River flows from north to south. The northern part of the basin (S01-R02) is the recharge area, where snow water and groundwater mix along the streams and flow into the Yepuqu River. In the middle part of the basin (P02-R07), there is frequent exchange of surface water and groundwater, strong water-rock interaction, and complex hydrochemical evolution. The southern part of the basin (R08\u0026thinsp;~\u0026thinsp;R12) is the discharge area, where the Yepuqu River flows southward to the Tuilongqu River and finally flows from west to east into the Lhasa River(Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Sample collection and testing\u003c/h2\u003e \u003cp\u003eIn this study, 23 groups of water samples were collected from November 3 to 6, 2023, including 2 groups of melt-water samples, 9 groups of groundwater samples, and 12 groups of surface water samples. The sampling locations are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The pH value, total dissolved solids (TDS), dissolved oxygen, and water temperature of the water samples were measured in the field using a portable multi-parameter measuring instrument (WTWMulti3430, Germany), with errors of 0.01, 0.01 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 0.01 mg\u0026middot;L-1 and 0.1\u0026deg;C, respectively. The concentrations of HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e and Ca\u003csup\u003e2+\u003c/sup\u003e were measured by on-site titration using an alkalinity test kit (Merck, Germany), with an error of 0.1 mmol\u0026middot;L-1 and 2 mg\u0026middot;L-1, respectively.\u003c/p\u003e \u003cp\u003eBefore sampling, rinse the pre-cleaned polyethylene plastic bottle 2 to 3 times with the original water sample. All water samples were first filtered using a 0.45 \u0026micro;m microporous filter membrane, and then quickly filled into a 550 mL bottle, capped and labeled, and then stored at low temperature, and sent for inspection within 24 hours. The water samples used to test cations were acidified by adding HNO\u003csub\u003e3\u003c/sub\u003e (1:1) to a pH value less than 2. The sample testing was completed by the Karst Geological Resources and Environmental Supervision and Inspection Center of the Chinese Academy of Geological Sciences. The cations were measured using a full spectrum direct reading plasma spectrometer (IRIS Intrepid Ⅱ XSP, Thermo Electron, USA) with a test accuracy of 0.01 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Anions were tested using a chromatograph (ICS-2100, Dionex, USA) with a test accuracy of 0.001 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The δD and δ\u003csup\u003e18\u003c/sup\u003eO-H\u003csub\u003e2\u003c/sub\u003eO were measured by GasBench II connected to MAT-253, with an accuracy better than 0.1\u0026permil; and 0.1\u0026permil; respectively (Ren et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Data analysis\u003c/h2\u003e \u003cp\u003eThe hydrochemical data of the Puqu karst watershed were analyzed using \u0026zwnj;descriptive statistics\u0026zwnj; in SPSS 22.0. Principal Component Analysis (PCA) was employed to identify factors with eigenvalues \u0026zwnj;\u0026gt;1\u0026zwnj; and extract characteristic principal components (PCs) (Azzeddine R et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Drouiche A et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Hydrogeological maps and sampling site distributions were generated using \u0026zwnj;MapGIS 6.7\u0026zwnj;, while Piper trilinear diagrams and scatter plots illustrating relationships between hydrochemical parameters for different karst groundwater types were created in \u0026zwnj;Origin 2018\u0026zwnj;.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1 Water chemistry and isotopic characteristics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe test results of melt-water, groundwater, and surface water are shown in Table 1. The pH value of melt-water was 8.0. The average pH value of groundwater was 8.1, ranging from 7.4 to 8.3, and the average pH value of surface water was 8.1, refocused from 7.8 to 8.3. The pH value of groundwater and surface water was almost the same. The average groundwater temperature was 7.9℃, ranging from 2.1℃\u0026nbsp;to 12.5℃; and the average surface water temperature was 6.5℃. The average TDS values of groundwater, surface water, and melt-water were 263.3, 201.3, and 44.1 mg\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e, respectively. The Ca\u003csup\u003e2+\u003c/sup\u003e ions were the absolute dominant cations in all samples, with Ca2+ accounting for 59~90% of the total cation equivalents in groundwater (average 80%) and 56~87% in surface water (average 79%). The cation equivalent ratio of Mg\u003csup\u003e2+\u003c/sup\u003e was less than 20% at all sampling points. (K\u003csup\u003e+\u003c/sup\u003e+Na\u003csup\u003e+\u003c/sup\u003e) accounted for 29% and 37% of the cation equivalents in granite spring water (P08) and Doilungqu River (R12). The average anion equivalent ratio of HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in groundwater and surface water were greater than 81%, followed by SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e.The SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e in groundwater P01 and P07 and surface water R04 and R07 exceeded 20% of the total anion equivalent. As shown in Figure 2, the melt-water was of Ca-HCO3 type, and the groundwater and surface water were mainly Ca-HCO\u003csub\u003e3\u003c/sub\u003e type (accounting for 81%), followed by Ca-HCO\u003csub\u003e3\u003c/sub\u003e\u0026middot;SO\u003csub\u003e4\u003c/sub\u003e (accounting for 19%).\u003c/p\u003e\n\u003cp\u003eThe values of\u0026nbsp;dD and\u0026nbsp;d\u003csup\u003e18\u003c/sup\u003eO-H\u003csub\u003e2\u003c/sub\u003eO of melt-water were \u0026minus;135.2~\u0026minus;134.1\u0026permil; and \u0026minus;18.1~\u0026minus;17.9\u0026permil;. The average values of\u0026nbsp;dD and\u0026nbsp;d\u003csup\u003e18\u003c/sup\u003eO-H\u003csub\u003e2\u003c/sub\u003eO for groundwater were \u0026minus;137.0\u0026permil; and \u0026minus;18.0\u0026permil;, and those for surface water were \u0026minus;135.4\u0026permil; and \u0026minus;17.9\u0026permil;, respectively. Surface water was richer in heavy D and\u0026nbsp;d\u003csup\u003e18\u003c/sup\u003eO-H\u003csub\u003e2\u003c/sub\u003eO than groundwater, and the average\u0026nbsp;dD value of groundwater was lighter than that of melt-water, while the average\u0026nbsp;dD value of surface water was close to that of melt-water.\u003c/p\u003e\n\u003cp\u003eTable 1 Chemical and isotope test results of sampling water in the study area\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 7px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eID\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eTDS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eK\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eNa\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eCa\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eMg\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eCl\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eHCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e\u0026delta;D\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e\u0026delta;18O-H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 7px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e/℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"8\" style=\"width: 52px;\"\u003e\n \u003cp\u003e/(mg\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 13px;\"\u003e\n \u003cp\u003e/\u0026permil;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 7px;\"\u003e\n \u003cp\u003eMelt-water\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eS01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e51.9\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e13.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e14.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e38.7\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.15\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-134.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-17.90\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eS02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e10.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e36.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e7.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e11.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e31.6\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.62\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-135.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.10\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"9\" style=\"width: 7px;\"\u003e\n \u003cp\u003eGroundwater\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eP01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e197.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e40.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e67.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e73.4\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e4.00\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-138.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.90\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eP02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e7.4\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e6.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e384.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e80.4\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e41.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e152.9\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.51\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-138.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.60\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eP03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e5.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e193.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e38.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e43.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e109.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.05\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-138.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.30\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eP04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e7.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e286.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e56.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e38.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e122.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.25\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-139.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.50\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eP05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e7.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e439.4\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e106.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e48.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e231.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.76\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-141.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eP06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e401.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e80.4\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n 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6px;\"\u003e\n \u003cp\u003e6.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e48.7\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e4.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e4.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e48.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e109.9\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e10.98\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-134.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-17.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eP08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e7.9\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e12.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e105.4\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e22.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e6.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e85.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n 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6px;\"\u003e\n \u003cp\u003e2.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e5.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e91.6\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.50\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-125.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-15.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"12\" style=\"width: 7px;\"\u003e\n \u003cp\u003eSurface water\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e11.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e177.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e18.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e15.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e42.6\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.43\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n 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6px;\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e68.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e39.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e219.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.27\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-138.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e4.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e58.6\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e14.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e11.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e24.4\u0026nbsp;\u003c/p\u003e\n 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\u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e26.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e115.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.02\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-137.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e7.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e5.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e229.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e44.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e26.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e122.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.58\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-136.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e5.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e224.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e50.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e29.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e73.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.40\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-136.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e6.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e223.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e43.6\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e29.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e115.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.92\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-136.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e7.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e220.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e42.7\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e29.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e116.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.87\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-136.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e219.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e43.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e29.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e115.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.05\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-136.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-18.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e179.8\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e36.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e5.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e6.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e134.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e0.05\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-128.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-16.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003eR12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e6.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e228.7\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e12.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e36.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e8.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e29.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e91.9\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3.36\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-135.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e-17.9\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Hydrochemical characteristics indications of hydrochemical evolution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDuring the water cycle in the karst basin, different water bodies interacted physically, chemically, and biologically with the surrounding environment, causing water chemical evolution\u0026nbsp;(Kortatsi et al., 2007; Wen et al., 2008),\u0026nbsp;and changing in water substances\u0026nbsp;(Belousova et al., 1999). Analysis of the relationship between the main ions in the water of the study area can reveal the main geochemical effects that control the chemical evolution in the karst basin. Gibbs diagrams were widely used to analyze the controlling factors in the formation and chemical evolution of water bodies\u0026nbsp;(Gibbs, 1970; Ranjan et al., 2013; Gao, et al., 2010). According to Gibbs\u0026rsquo;s analysis (Fig. 3), the TDS content in the water was moderate, and the Na\u003csup\u003e+\u003c/sup\u003e/(Na\u003csup\u003e+\u003c/sup\u003e+Ca\u003csup\u003e2+\u003c/sup\u003e) values were all less than 0.4, far below 0.5. All samples were full in the area of rock weathering, indicating that rock weathering was the main source of water chemistry in the study area (Ming et al., 1982).\u003c/p\u003e\n\u003cp\u003eIn summary, the Ca\u003csup\u003e2+\u003c/sup\u003e concentration in water bodies may come from the dissolution of calcite, dolomite, or gypsum, as well as the dissolution of calcite and dolomite. The equations were as follows:\u003c/p\u003e\n\u003cp\u003eCaCO\u003csub\u003e3\u003c/sub\u003e+CO\u003csub\u003e2\u003c/sub\u003e+H\u003csub\u003e2\u003c/sub\u003eO=Ca\u003csup\u003e2+\u003c/sup\u003e+2HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;（1）\u003c/p\u003e\n\u003cp\u003eCaMg(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e+2CO\u003csub\u003e2\u003c/sub\u003e+2H\u003csub\u003e2\u003c/sub\u003eO= Ca\u003csup\u003e2+\u003c/sup\u003e+ Mg\u003csup\u003e2+\u003c/sup\u003e+4HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;（2）\u003c/p\u003e\n\u003cp\u003eCaSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO= Ca\u003csup\u003e2+\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e+2H\u003csub\u003e2\u003c/sub\u003eO \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;（3）\u003c/p\u003e\n\u003cp\u003eAccording to equations (1) to (3), the molar ratios of Ca\u003csup\u003e2+\u003c/sup\u003e/ HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e produced by the dissolution of calcite, dolomite, and calcite and dolomite were 1/2, 1/4, and 1/3, respectively. The molar ratios of Mg\u003csup\u003e2+\u003c/sup\u003e/ HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e produced by the dissolution of dolomite and calcite and dolomite are 1/4 and 1/6, respectively. Therefore, the non-gypsum source of calcium is obtained (Fig. 4(a)).\u003c/p\u003e\n\u003cp\u003eMost of the sampling points in the basin full within the range of the 1:4 to 1:2 relationship line in Figure 4(a), indicating that different water bodies in the study area had undergone water-rock interactions with calcite and dolomite after receiving atmospheric precipitation. The proportion of surface water dissolving in calcite (greater than 1:2) and in calcite and dolomite (1:3~1:2) was 15% and 85% respectively. The proportion of groundwater dissolving in calcite and in calcite and dolomite was 33% and 67% respectively. The melting water (less than 1:4) showed no water-rock interaction (Figure. 4(a)). If gypsum dissolution would produce equal molar masses of Ca\u003csup\u003e2+\u003c/sup\u003e and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e, however, the [Ca\u003csup\u003e2+\u003c/sup\u003e]/[SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e of the study area samples ranged from 1.45 to 14.30, with an average value of 4.29. If the Ca\u003csup\u003e2+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e in the water body were mainly derived from the dissolution of calcite, dolomite and gypsum, then the milligram equivalent concentrations of (Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e)/(HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e) were equal\u0026nbsp;(Kumar et al., 2006; Barzegar et al., 2016), while the values of (Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e)/(HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e) in the study area ranged from 0.39 to 0.90, with an average value of 0.56. At the same time, the fitting curve of the sampling points is near the 1:2 relationship line and does not completely correspond to Fig. 4(b). The above analysis showed that the surface water and groundwater mainly underwent calcite dissolution and the combined dissolution of calcite and dolomite, while the gypsum dissolution was not obvious. At the same time, other hydrogeochemical reactions may have occurred.\u003c/p\u003e\n\u003cp\u003eAssuming that the dissolution of rock salt would result in equal amounts of Na+ and Cl\u003csup\u003e－\u003c/sup\u003e entering the water body. Except for the melt-water points, the [Na\u003csup\u003e+\u003c/sup\u003e]/[Cl\u003csup\u003e－\u003c/sup\u003e] at most of the sample points in the study area was greater than 1 (Fig. 5(a)), indicating that there were other sources of Na\u003csup\u003e+\u003c/sup\u003e in the water body besides the dissolution of rock salt, such as cation exchange and/or sodium sulfate dissolution. The Na\u003csup\u003e+\u003c/sup\u003e dissolved in non-carbonate rocks was the total Na\u003csup\u003e+\u003c/sup\u003e minus the Cl\u003csup\u003e－\u003c/sup\u003e dissolved in rock salt, which was [Na\u003csup\u003e+\u003c/sup\u003e]-[Cl\u003csup\u003e－\u003c/sup\u003e] (meq\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e). From equation (4), we can see that the Ca\u003csup\u003e2+\u003c/sup\u003e from non-carbonate rock salt dissolution was [Ca\u003csup\u003e2+\u003c/sup\u003e]-0.33[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e] (meq\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e). Comparing the sum of Na\u003csup\u003e+\u003c/sup\u003e dissolved from non-carbonate rocks and Ca\u003csup\u003e2+\u003c/sup\u003e dissolved from non-carbonate rock salt with the SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e equivalent concentration (Fig 5(b)), it could be seen that very few sampling points were located near the gypsum-salt stone line (1:1), indicating that very little Na\u003csup\u003e+\u003c/sup\u003e and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e in the water body of the study area came from the dissolution of saltstone, and there were other geochemical effects.\u003c/p\u003e\n\u003cp\u003eIf de-dolomite bloom occurs in the water, the dissolution of calcite will be weakened due to the common ion effect, causing calcite supersaturation and precipitation, thereby reducing the Ca\u003csup\u003e2+\u003c/sup\u003e concentration and increasing the Mg\u003csup\u003e2+\u003c/sup\u003e and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e (Bischoff et al., 1994; Back et al., 1983). The relationship diagram between [Mg\u003csup\u003e2+\u003c/sup\u003e/Ca\u003csup\u003e2+\u003c/sup\u003e] and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e in the water body of the study area did not show an overall increase (Fig. 6(a)), indicating that there was no obvious de-dolomite blooming effect.\u003c/p\u003e\n\u003cp\u003eAs mentioned above, the sources of some Na+ in the study area need to be further discussed. [Na\u003csup\u003e+\u003c/sup\u003e]/[Cl\u003csup\u003e－\u003c/sup\u003e] can be used to characterize the degree of cation exchange\u0026nbsp;(Xing et al., 2013).\u0026nbsp;Na\u003csup\u003e+\u003c/sup\u003e in the soil can enter the water body by replacing Mg\u003csup\u003e2+\u003c/sup\u003e and Ca\u003csup\u003e2+\u003c/sup\u003e in the water body (Stimson et al., 2001), thereby increasing the Na\u003csup\u003e+\u003c/sup\u003e concentration in the water body and reducing the Mg\u003csup\u003e2+\u003c/sup\u003e and Ca\u003csup\u003e2+\u003c/sup\u003e concentration in the water (Hidalgo et al., 2001). The clay minerals contained in the carbonate salt in the study area provided the material basis for cation exchange. When cation exchange exists, (Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e)/( HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e) in water is less than 1 (Cerling et al., 1991; Li et al., 2016). At most sampling points in the water bodies of the study area, (Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e)/( HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e) was less than 1 (Fig 4(b)), and [Na\u003csup\u003e+\u003c/sup\u003e]/[Cl\u003csup\u003e－\u003c/sup\u003e] was greater than 1 (Fig 5(a)), which was consistent with the Ca\u003csup\u003e2+\u003c/sup\u003e- Na\u003csup\u003e+\u003c/sup\u003e or Mg\u003csup\u003e2+\u003c/sup\u003e- Na\u003csup\u003e+\u003c/sup\u003e cation exchange process (Stimson et al., 2001; Marghade et al., 2011), indicating that cation exchange had a certain contribution to the Na\u003csup\u003e+\u003c/sup\u003e in the study water. In addition, there was an equivalent 1:1 linear relationship between Na\u003csup\u003e+\u003c/sup\u003e and the replaced Mg\u003csup\u003e2+\u003c/sup\u003e or Ca\u003csup\u003e2+\u003c/sup\u003e during the cation exchange process (Li et al., 2016; Fisher et al., 1997), and the water points in the study area showed a linear relationship near and above 1:1 (Fig 6(b)), indicating that there were other sources of HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e in the water body of the study area.\u003c/p\u003e\n\u003cp\u003eConsidering that the gypsum dissolution in the study area was not strong, the remaining SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e may come from the oxidation of pyrite in the strata of the study area (Alderton et al., 2005; Kumari et al., 2010). The generated SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e－\u003c/sup\u003e would react with the surrounding carbonate rock salt when it entered the water body, and the concentration of HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in the water body will increase (Equations (4)-(6)):\u003c/p\u003e\n\u003cp\u003eFeS\u003csub\u003e2\u003c/sub\u003e+7/2O\u003csub\u003e2\u003c/sub\u003e+H\u003csub\u003e2\u003c/sub\u003eO\u0026rarr;Fe\u003csup\u003e2+\u003c/sup\u003e+2SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e+2H\u003csup\u003e+\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; (4)\u003c/p\u003e\n\u003cp\u003e2Ca\u003csub\u003ex\u003c/sub\u003eMg\u003csub\u003e(1-x)\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e=2xCa\u003csup\u003e2+\u003c/sup\u003e+2(1-x)Mg\u003csup\u003e2+\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e+2HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; (5)\u003c/p\u003e\n\u003cp\u003eCa\u003csub\u003ex\u003c/sub\u003eMg\u003csub\u003e(1-x)\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+H\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e=xCa\u003csup\u003e2+\u003c/sup\u003e+(1-x)Mg\u003csup\u003e2+\u003c/sup\u003e+2HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e－\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(6)\u003c/p\u003e\n\u003cp\u003eFrom equations (4) to (6), it can be seen that if only carbonic acid dissolved carbonate rock, [Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] was equal to 1, the concentration of SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e was low and [SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e]/[ HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] was equal to 0; when sulfuric acid participated in the water-rock reaction, [Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] was 2, and the value of [SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] was 1; when carbonic acid and sulfuric acid simultaneously dissolved carbonate rock minerals to reach equilibrium, [Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e]/ [HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e]=3/2, [SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e]=1/2 (Alderton et al., 2005; Kumari et al., 2010), and the reaction equation was as follows:\u003c/p\u003e\n\u003cp\u003e3CaxMg\u003csub\u003e(1-x)\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+ H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e+H\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e=3xCa\u003csup\u003e2+\u003c/sup\u003e+3(1-x)Mg\u003csup\u003e2+\u003c/sup\u003e+SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e+4HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(7)\u003c/p\u003e\n\u003cp\u003eFrom the relationship between [(Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e)/ HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] and [SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e/HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] in water (Fig 7), it can be concluded that part of groundwater and surface water were mainly weathered by carbonate rocks with the participation of H\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (accounting for 13%); and the vast majority of groundwater, surface water and melt-water were located around the \u0026quot;cross\u0026quot; in the figure, at which time [Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e]=3/2, [SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e]=1/2, indicating that H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e jointly participated in the water-rock reaction in the water (accounting for 74%).In addition, a small number of surface water and groundwater points showed [Ca\u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e]＞3/2,\u0026nbsp;[SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e]/[HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e]＞1/2\u0026nbsp;(accounting for 13%), which was mainly due to the increase in SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e concentration caused by the oxidation of pyrite in the formation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Isotope indications of water chemical evolution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBased on the marking characteristics of stable hydrogen and oxygen isotopes in the water cycle, the recharge sources, recharge patterns, and hydraulic connections between water bodies in the regional water bodies can be revealed, thereby clearly understanding the hydrochemical processes of different water bodies in the study area (Bedaso et al., 2021). The local precipitation line in Lhasa (LMWL:\u0026nbsp;dD=7.90d\u003csup\u003e18\u003c/sup\u003eO+6.29)\u0026nbsp;was selected as the reference data\u0026nbsp;(Tian et al., 2001),\u0026nbsp;and combined with the global atmospheric precipitation line (GMWL:\u0026nbsp;dD=8d\u003csup\u003e18\u003c/sup\u003eO+10)\u0026nbsp;(Craig, 2023),\u0026nbsp;the relationship diagram of\u0026nbsp;dD and\u0026nbsp;d\u003csup\u003e18\u003c/sup\u003eO-H\u003csub\u003e2\u003c/sub\u003eO of the water body in the study area was drawn (Fig 8).\u003c/p\u003e\n\u003cp\u003eAs shown in Figure 8, the groundwater and surface water sampling points were located on and near the Lhasa Local Weathering Line (LMWL) and the Global Weathering Line (GMWL), indicating that the surface water and groundwater in the Yepuqu Basin were mainly atmospheric precipitation. Both groundwater and surface water were distributed within a certain range. Compared with surface water, groundwater was more dispersed in the figure and was more concentrated in ice and snow meltwater. Among them, groundwater P07 and P09 and surface water R01 and R11 showed enrichment of heavy water isotopes and appeared at the lower right of the local atmospheric precipitation line (LMWL) and the global atmospheric precipitation line (GMWL), indicating that these water bodies underwent water-rock interaction or evaporation during runoff (Ren et al., 2023), and the natural geographical conditions of the study area promoted the occurrence of this phenomenon (Ge et al., 2020). The \u0026delta;D and \u0026delta;\u003csup\u003e18\u003c/sup\u003eO of surface water, groundwater, and melt-water showed a gradual dispersion in Fig 8, and there were an intersection between different water bodies, indicating that different degrees of mutual transformation have occurred between different types of water bodies (Ren et al., 2023). It also showed that the three types of water bodies may have mutually transformed or been mixedly replenished by water sources carrying different deuterium and oxygen information.\u003c/p\u003e\n\u003cp\u003eThe values of \u0026delta;D and \u0026delta;\u003csup\u003e18\u003c/sup\u003eO in water depended on the respective compositions in the recharge source and are affected by fractionation due to evaporation processes (Ma et al., 2015).\u0026nbsp;The variation characteristics of hydrogen and oxygen isotopes in different water bodies are different (Yang et al., 2018). Most of the surface water, groundwater, and melt-water in the study area were distributed between the LMWL and GMWL. The intersection of the fitting lines of groundwater and surface water with the local precipitation line was close to the average isotopic composition of water bodies in the region, indicating that surface water and groundwater were mainly recharged by atmospheric precipitation (Sun et al., 2017). The slopes of the fitting lines for groundwater and surface water (4.18, 3.82) were similar and smaller than those of LMWL) and GMWL (7.90, 8.0), indicating that the hydraulic connection between groundwater and surface water was strong and that they had experienced strong evaporation. This was consistent with the local natural geographical conditions of dry climate, low precipitation, high evaporation, and being located inland far away from steam sources (Ge et al., 2020). The high altitude of the study area makes secondary evaporation easy to occur during rainfall, and\u0026nbsp;d\u003csup\u003e18\u003c/sup\u003eO in water vapor is more easily enriched, which also caused the slope of the precipitation line to be low (Yang et al., 2018; Song et al., 2017). In addition, the results of the water chemical characteristic analysis showed that there was obvious carbonate salt dissolution in the surface water and groundwater in the study area, which also explained the reason for the low slope of the fitting line of groundwater and surface water.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4 \u0026nbsp;Impact of human activities\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePrincipal Component Analysis (PCA), a widely adopted method for identifying hydrochemical element sources (Abdelmalek D et al., 2024; Zahi F et al., 2024), was applied to 11 hydrochemical parameters. The Kaiser-Meyer-Olkin (KMO) value (0.613) and Bartlett\u0026rsquo;s test significance (p \u0026lt; 0.001) confirmed the \u0026zwnj;suitability of the dataset\u0026zwnj; for PCA-based factor loading analysis. Three principal components (PCs, Table 2) were extracted, collectively accounting for \u0026zwnj;73.88% of the cumulative variance\u0026zwnj;, effectively capturing the dominant hydrochemical patterns in the study area.\u003c/p\u003e\n\u003cp\u003eTable 2 Pearson correlation matrix of hydrochemical parameters in the Yepuqu River karst basin\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003ePC1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003ePC2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003ePC3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003eCommunalities\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eTDS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.94\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.94\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eK\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.81\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eNa\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.77\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eCa\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.92\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.94\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eMg\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.63\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eCl\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.73\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.73\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eHCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.87\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e-0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.92\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.75\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eEigenvalues (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e3.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eVariance (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e36.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e24.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e13.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eCumulative (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e36.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e60.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e73.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 122px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" style=\"width: 463px;\"\u003e\n \u003cp\u003eNotes: Extraction method: principal component analysis. Factor loadings beyond-0.6 to 0.6 are marked by bold font.\u003c/p\u003e\n \u003cp\u003ebold font.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eBased on the characteristic loadings of variables within each factor, the influencing mechanisms can be categorized into three groups: The \u0026zwnj;PC1\u0026zwnj; (Ca\u0026sup2;⁺, Mg\u0026sup2;⁺, SO₄\u0026sup2;⁻, and HCO₃⁻) predominantly originates from \u0026zwnj;carbonate mineral dissolution\u0026zwnj;, as evidenced by hydrogeochemical modeling in Section 3.2 and dissolution processes detailed in Equations (4)\u0026ndash;(7). The \u0026zwnj;PC2\u0026zwnj; (K⁺, Na⁺, and Cl⁻) is attributed to \u0026zwnj;evaporite dissolution\u0026zwnj;, supported by the median (K⁺+Na⁺)/Cl⁻ ratio of 0.93 (\u0026lt;1), which rules out significant marine aerosol contributions (given the inland location) and aligns with widespread evaporite-bearing granite formations in the study area (Figure 1). The \u0026zwnj;PC3\u0026zwnj; (NO₃⁻) reflects \u0026zwnj;anthropogenic inputs\u0026zwnj;, as the maximum NO₃⁻ concentration (10.98 mg\u0026middot;L⁻\u0026sup1;) substantially exceeds both the local minimum (0.05 mg\u0026middot;L⁻\u0026sup1;) and the reported maximum in the Lhasa River Basin (0.84 mg\u0026middot;L⁻\u0026sup1;) (Lin et al., 2021). Spatial analysis confirms elevated NO₃⁻ levels in agricultural zones, where excessive fertilizer application exceeds crop uptake capacity, leading to nitrate leaching into groundwater systems.\u003c/p\u003e\n\u003cp\u003eThe Yulong Snow Mountain-Lijiang alpine karst basin, as a representative of high-altitude karst regions, has been previously studied regarding hydrochemical variation patterns and driving mechanisms (Ren K et al., 2024). Existing findings indicate that its water recharge originates predominantly from \u0026zwnj;atmospheric precipitation\u0026zwnj;, with significant anthropogenic impacts from tourism activities altering hydrochemical signatures\u0026mdash;particularly elevated concentrations of K⁺, Na⁺, Cl⁻, and SO₄\u0026sup2;⁻. \u0026zwnj;In contrast\u0026zwnj;, our study reveals that hydrochemical variations in the target basin are primarily governed by \u0026zwnj;mineral dissolution processes\u0026zwnj;, with human activities exerting influence solely on NO₃⁻ concentrations (\u0026rho;(NO₃⁻)). However, the current research is constrained by \u0026zwnj;single-season sampling\u0026zwnj;, limiting insights to preliminary hydrochemical evolution characteristics. To advance understanding, future studies will employ \u0026zwnj;integrated hydrochemical-isotopic approaches\u0026zwnj; with \u0026zwnj;hydrological-year sampling campaigns\u0026zwnj; across groundwater and surface water systems. Concurrent real-time monitoring of critical hydrogeological parameters will be implemented to unravel water-rock interaction dynamics during the surface water-groundwater cycling processes in alpine karst basins, thereby generating foundational data for watershed water resource conservation strategies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.5 \u0026nbsp;Sources of surface water in the basin\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe chemical properties of hydrogen and oxygen isotopes are stable, and there are certain differences in the hydrogen and oxygen isotope values in different water bodies (Zhang et al., 2014), which can better identify the supply end members (Gao et al., 2019; Huang et al., 2018). Therefore, based on the mass conservation principle of hydrogen and oxygen isotopes, a two-component mixing model was used to calculate the mixing ratio of different water bodies\u0026nbsp;(Lei et al., 2020). Assuming that the concentrations of the two end members before mixing conform to the linear law, since the test precision and accuracy of \u0026delta;D were lower than those of \u0026delta;\u003csup\u003e18\u003c/sup\u003eO, \u0026delta;\u003csup\u003e18\u003c/sup\u003eO was selected to calculate the mixing ratio of surface water. The \u0026delta;\u003csup\u003e18\u003c/sup\u003eO of melt-water and groundwater were similar, and they are regarded as a mixing unit. Atmospheric precipitation was regarded as a mixing end member. The calculation equation is as follows (Ogunkoya et al., 1991):\u003c/p\u003e\n\u003cp\u003e\u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eR\u003c/sub\u003e=\u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eS\u003c/sub\u003e\u0026middot;X+\u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eP\u003c/sub\u003e(1-X) \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;（9）\u003c/p\u003e\n\u003cp\u003eWhere: X was the recharge ratio, %; \u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eR\u003c/sub\u003e, \u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eS,\u003c/sub\u003e and \u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eP\u003c/sub\u003e were the average \u0026delta;\u003csup\u003e18\u003c/sup\u003eO test values of surface water, atmospheric precipitation, and groundwater (including melt-water) in the study area, respectively. According to the test data (Table 1) and the rainfall data in Lhasa in November(Yang et al., 2009), the values of\u0026nbsp;\u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eR\u003c/sub\u003e,\u0026nbsp;\u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eS,\u003c/sub\u003e and \u0026delta;\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003eP\u003c/sub\u003e were 17.93, 14.1, and 18.3 respectively. The mixing ratio of the above surface water was calculated. The results showed that atmospheric precipitation accounted for 8% of surface water, while groundwater (including melt-water from ice and snow) accounted for 92%.\u003c/p\u003e\n\u003cp\u003eThe groundwater recharge rate in the basin can be estimated by using the chloride ion mass balance method in the water body. The calculation formula was as follows (Leaney et al., 1995):\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eR\u003c/em\u003e(%)=100\u0026middot;(\u003cem\u003eC\u003c/em\u003e\u003csub\u003eCl S\u003c/sub\u003e/\u003cem\u003eC\u003c/em\u003e\u003csub\u003eCl P\u003c/sub\u003e) \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;（10）\u003c/p\u003e\n\u003cp\u003eIn the formula, \u003cem\u003eR\u003c/em\u003e was the proportion of groundwater; \u003cem\u003eC\u003c/em\u003e\u003csub\u003eCl S\u003c/sub\u003e was the average concentration of chloride ions in ice and snow meltwater;\u003cem\u003e\u0026nbsp;C\u003c/em\u003e\u003csub\u003eCl P\u003c/sub\u003e was the average concentration of chloride ions in groundwater. The results showed that melt-water accounted for 81% of groundwater. By combining equations (9) and (10), the study concluded that 8% of surface water came from atmospheric precipitation, 74% from ice and snow meltwater, and 18% from groundwater. The reasons for the low proportion of atmospheric precipitation in surface water may be that the sampling time was the period of relatively small rainfall in the study area, and the main rainfall period was concentrated from June to September; or the sampling time was the main time for ice and snow to melt, and a large amount of ice and snow melt water flowed into the surface water.\u003c/p\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThe Yepuqu River karst basin\u0026rsquo;s snowmelt water exhibited a Ca-HCO\u003csub\u003e3\u003c/sub\u003e type, while 81% of surface and groundwater shared this type, with 19% classified as Ca-HCO\u003csub\u003e3\u003c/sub\u003e\u0026middot;SO\u003csub\u003e4\u003c/sub\u003e. Water chemistry primarily originated from rock weathering, dominated by carbonate dissolution alongside minor mirabilite dissolution and cation exchange. A small portion (13%) involvesd H\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e-driven carbonate weathering, while pyrite oxidation elevated SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e levels. Most water (74%) showed combined H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e water-rock interactions. Hydrochemical evolution was driven by carbonate and evaporite dissolution, as well as human activities. Comparisons with similar alpine karst basins highlight human activity intensity as a key factor in hydrochemical variation.\u003c/p\u003e \u003cp\u003eThe surface water and groundwater in the study area were mainly derived from atmospheric precipitation. Eight percent of surface water came from atmospheric precipitation, 74% from ice and snow meltwater, and 18% from groundwater. Affected by natural geographical conditions, the slopes of the groundwater and surface water fitting lines (4.18, 3.82) were similar and smaller than the slopes of LMWL and GMWL (7.90, 8.0). The hydraulic connection between groundwater and surface water was strong and had experienced strong water-rock interaction and evaporation.\u003c/p\u003e \u003cp\u003eThis study presented the first investigation into the hydrochemical evolution characteristics of the alpine karst basin in the Yepuqu River through systematic sampling. The next phase will involve sampling across the entire hydrological year in the study area, along with real-time monitoring of hydrological parameters in key groundwater and surface water zones. The research aims to explore the hydrochemical evolution characteristics during the surface water- groundwater cycle in alpine karst basins, providing foundational data for water resource protection in the basin.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eHongwei Liao: Conceptualization, Methodology, Software, Investigation, Writing - original draft. Huaying Wu and Li He: Validation, Supervision. Yan Wang and Yu Wang: Validation, Supervision. Tengfang Li: Resources, Writing - review \u0026amp; editing, Supervision. Xiaodong Pan and Qibo Huang: Formal analysis, Visualization, funding acquisition. Changpei Zou and Kun Ren: Software. Haiyong Liu and Junfei Ma: Investigation.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eData availabilityNo data was used for the research described in the article.Declaration of competing interestThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.AcknowledgmentThe authors would like to appreciate anonymous reviewers and the editor for their constructive comments. We acknowledge Dr. Xiong, and Jianguo Yu for writing assistance.FundingThis research was supported by Central government-guided local special projects (XZ202301YD0005C), Basic scientific research operating expenses project of the Institute of Karst Geology, Special Fund for Basic Scientific Research of Institute of Karst Geology, CAGS (2023007), National General Fund Project (42372294), Guangxi Fund projects (2025GXNSFAA069189)， National Youth Fund Project (41702281), the China Geological Survey\u0026rsquo;s Project（DD20251205）; and Special Fund for Basic Scientific Research of Institute of Karst Geology, CAGS（2023018）.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbdelmalek D, Azzeddine R, Mohamed A, et al. Groundwater quality assessment using revised classical diagrams and compositional data analysis (CoDa): Case study of Wadi Ranyah, Saudi Arabia [J]. 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Journal of Hydrology, 2021, 603: 127100.\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":"carbonates-and-evaporites","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"caev","sideBox":"Learn more about [Carbonates and Evaporites](http://link.springer.com/journal/13146)","snPcode":"13146","submissionUrl":"https://submission.nature.com/new-submission/13146/3","title":"Carbonates and Evaporites","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Yepuqu, Alpine karst, Karst water, Hydrochemical characteristics, Hydrochemical evolution","lastPublishedDoi":"10.21203/rs.3.rs-5888289/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5888289/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHigh-altitude karst basins, as vital components of the \"Asian Water Tower,\" are critical for water resource conservation on the Qinghai-Tibet Plateau. To investigate the hydrochemical evolution characteristics of the Yepuqu River Basin, we analyzed 23 water samples (snowmelt, groundwater, and surface water) using hydrochemistry, hydrogen-oxygen isotopes, mass balance principles, and principal component analysis (PCA). Results showed that the hydrochemical types are predominantly HCO\u003csub\u003e3\u003c/sub\u003e\u0026mdash;Ca and HCO\u003csub\u003e3\u003c/sub\u003e\u0026middot;SO\u003csub\u003e4\u003c/sub\u003e\u0026mdash;Ca. Ion balance diagrams indicated that water mineralization was primarily controlled by rock weathering and dissolution, with additional contributions from cation exchange. PCA further reveals that hydrochemical evolution is influenced by carbonate mineral dissolution, evaporite dissolution, and anthropogenic activities. Isotopic analysis demonstrated that surface water was originated from atmospheric precipitation (8%), snowmelt (74%), and groundwater (18%), with dynamic mutual transformation between groundwater and surface water, accompanied by intense water-rock interactions and evaporation. Through comparison of the results of water chemical evolution of similar alpine karst basins, it was found that the strength of human activities directly affects the differences in water chemical evolution. The study provides the first comprehensive analysis of hydrochemical evolution in the high-altitude karst basin of the Yepuqu River, enhancing the theoretical foundation for water resource protection in the Lhasa River Basin and offering crucial data to advance research on surface water-groundwater cycling in alpine karst systems.\u003c/p\u003e","manuscriptTitle":"Study on the characteristics of water chemistry evolution in typical alpine karst basins","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-28 09:25:54","doi":"10.21203/rs.3.rs-5888289/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-13T16:35:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-12T03:17:57+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-30T11:55:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"340179365220668104166847994730194104868","date":"2025-04-28T00:35:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"179657681016636062741778718024286809276","date":"2025-04-22T10:50:51+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-17T13:26:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"146697696203154559518981531665652310799","date":"2025-04-16T17:39:06+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-16T13:22:41+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-15T10:38:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Carbonates and Evaporites","date":"2025-04-15T09:13:51+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"carbonates-and-evaporites","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"caev","sideBox":"Learn more about [Carbonates and Evaporites](http://link.springer.com/journal/13146)","snPcode":"13146","submissionUrl":"https://submission.nature.com/new-submission/13146/3","title":"Carbonates and Evaporites","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d750b146-90b4-46a3-b6ba-3ed0e6f6cdb3","owner":[],"postedDate":"April 28th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-07T16:10:20+00:00","versionOfRecord":{"articleIdentity":"rs-5888289","link":"https://doi.org/10.1007/s13146-025-01131-y","journal":{"identity":"carbonates-and-evaporites","isVorOnly":false,"title":"Carbonates and Evaporites"},"publishedOn":"2025-07-03 15:57:37","publishedOnDateReadable":"July 3rd, 2025"},"versionCreatedAt":"2025-04-28 09:25:54","video":"","vorDoi":"10.1007/s13146-025-01131-y","vorDoiUrl":"https://doi.org/10.1007/s13146-025-01131-y","workflowStages":[]},"version":"v1","identity":"rs-5888289","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5888289","identity":"rs-5888289","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}