Hydrochemical and Isotopic Characteristics of the Yepu River Basin in Southern Tibet: A Preliminary Investigation
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摘要: 研究典型流域水化学和同位素组成对青藏高原水资源保护具有重要意义。本研究以青藏高原南部叶普曲为例，系统采集了泉水、河流、雨水和冰雪融水，分析其水化学和同位素组成，剖析流域水循环和岩石风化机制。结果表明：（1）泉水和河流水化学类型以Ca-HCO3型为主（占88%），其次为Ca-HCO3·SO4（占12%）。（2）利用氢氧同位素分割径流，得到冰雪融水和雨水对泉水的贡献分别为84%和16%；河流水补给来源中冰雪融水和地下水占68%，雨水占32%。（3）大气降水、碳酸盐岩和硅酸盐岩风化是流域水体溶质主要来源；硫酸和碳酸共同参与流域岩石风化，其中硫酸分别贡献泉水和河流阳离子总量的53%和52%。（4）泉水氘过量参数d值分布分散，揭示流域多数泉水属于独立的水文地质单元；河流分布集中，表明河流补给来源较泉水稳定。研究明确了叶普曲地下水和地表水水化学特征及成因机制，指出了硫化物氧化产酸对岩石风化的贡献，丰富了青藏高原流域水和物质循环理论研究，有利于地表水和地下水资源的保护和合理开发。Abstract: The Tibetan Plateau, known as the "Asian Water Tower," plays a critical role in regional water resource sustainability. This study focuses on the water cycle processes and hydrogeochemical mechanisms in the Yepuqu Basin, southern Tibet, through systematic sampling of spring water, river water, snowmelt, and rainwater (21 samples collected in June2023). By integrating hydrochemical analysis, hydrogen-oxygen isotope tracers (δD, δ18O), and deuterium excess (d-excess) parameters, the research investigates water cycle pathways, solute sources, and rock weathering dynamics. Key findings include: (1) Water chemistry predominantly follows the Ca-HCO3 type (88%), with Ca-HCO3·SO4 as a secondary classification (12%). Isotopic runoff separation reveals distinct recharge patterns: spring water derives 84% from snowmelt and 16% from rainfall, while river water combines 68% from snowmelt/groundwater and 32% from rainfall. Downstream analysis shows a gradual decrease in snowmelt and groundwater contributions along the river course. (2) Solutes originate primarily from atmospheric deposition, carbonate weathering, and silicate dissolution. Rainwater contributes 7.6% of total cations and 4.2% of ${\rm{SO}}_4^{2-}$ in springs, compared to 6.7% and 2.5% in rivers. Notably, sulfuric acid weathering dominates cationic contributions, accounting for 53% in springs and 52% in rivers—surpassing carbonate weathering inputs. This phenomenon is attributed to sulfide oxidation in coal-bearing strata, which generates substantial acidity within the basin. (3) Springs exhibit highly variable d-excess values (7.5‰−22.4‰) indicating isolated hydrogeological units with diverse recharge pathways. In contrast, river waters display clustered d-excess signatures (11.2‰−12.7‰), reflecting stable recharge sources. The downstream decline in river d-excess values suggests increasing groundwater contributions along the flow path. This study pioneers the quantification of sulfide oxidation as the dominant driver of rock weathering in Tibetan Plateau basins. The d-excess parameter is demonstrated to be a robust indicator for identifying aquifer structures and water-rock interactions. These findings advance the understanding of cryospheric hydrogeochemical processes and provide a scientific foundation for sustainable water resource management in high-altitude regions. The integration of multi-isotope tracers with hydrochemical proxies establishes a replicable framework for diagnosing water cycle dynamics in complex alpine environments. The methodology resolves critical uncertainties in distinguishing atmospheric, cryospheric, and lithospheric contributions to riverine systems. By elucidating the coupling mechanisms between sulfide-rich strata weathering and water quality evolution, this work highlights the vulnerability of Tibetan water resources to geological and climatic perturbations. The dominance of sulfuric acid weathering underscores the need to reassess carbon sink calculations in high-altitude basins, traditionally attributed to carbonate dissolution. This research enhances predictive models of water resource responses to glacier retreat and permafrost degradation, offering actionable insights for policymakers engaged in transboundary water governance across the Third Pole region.
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Key words:
- hydrochemistry /
- water isotopes /
- d-excess /
- water cycle /
- rock weathering /
- karst groundwater /
- Yepu River
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图 1 叶普曲流域位置和采样点分布
Figure 1. Geographical Location and Spatial Pattern of Sampling Sites in the Yepu River Basin
图 3 叶普曲流域水体δD与δ18O-H2O的关系
Figure 3. Dual isotopic plot of δD and δ18O-H2O of sampled waters in the Yepu River Basin
图 4 叶普曲流域地下水和地表水同位素径流分割结果
Figure 4. Results of isotopic hydrograph separation groundwater and surface water in the Yepu River Basin
图 5 叶普曲流域地下水和地表水不同离子浓度关系
Figure 5. Plots of relationships between different ions in the ground and surface waters in the Yepu River Basin
图 6 叶普曲流域硫酸和碳酸参与岩石风化贡献
Figure 6. Proportion of rock weathering involving carbonic and sulfuric acid in the Yepu River Basin
图 7 叶普曲流域d值变化范围及沿河流流程变化
Figure 7. Characteristics of d value and its variation along river flow in the Yepu River Basin
表 1 叶普曲流域地下水和地表水同位素径流分割结果
Table 1. Results of isotopic hydrograph separation groundwater and surface water in the Yepu River Basin
采样点类型 ID pH T K+ Na+ Ca2+ Mg2+ ${\rm{HCO}}_3^{-}$ Cl− ${\rm{SO}}_4^{2-}$ ${\rm{NO}}_3^{-}$ TDS δD δ18O-H2O d-excess 离子平衡 / ℃ /mg·L−1 /‰ /% 泉水 S1 8.2 3.9 0.44 3.20 31.5 3.73 23 0.50 76.97 3.59 128 −125.2 −17.4 13.7 −0.71 S2 7.8 6.2 0.53 3.34 72.7 3.61 191 1.74 45.31 2.52 223 −125.6 −17.1 11.4 −0.86 S3 8.3 16.4 0.13 1.95 37.6 1.10 72 0.18 40.58 0.37 118 −138.4 −18.2 7.5 0.49 S4 8.5 11.5 0.66 2.90 59.0 2.60 149 1.08 39.86 2.11 180 −133.4 −17.8 9.1 −0.50 S5 8.2 8,1 0.44 3.60 82.1 3.14 218 1.34 49.47 1.12 249 −140.5 −18.6 8.6 −1.47 S6 8.5 10.8 0.45 2.12 16.1 1.77 51 0.74 7.82 2.78 54 −123.5 −16.5 8.8 −0.28 S7 8.3 22 3.12 5.22 22.7 3.21 99 0.67 2.67 <0.05* 87 −114.4 −17.1 22.4 0.16 S8 7.9 17.8 2.07 5.21 21.9 1.88 58 3.44 19.51 2.09 83 −101.5 −14.1 11.4 1.09 冰雪融水 R1 8.0 13.2 0.39 1.78 13.0 2.31 37 <0.1 15.10 0.12 51 −134.2 −17.8 8.0 0.09 R2 8.0 12.6 0.32 0.99 7.3 1.18 25 0.25 7.84 2.36 31 −123.7 −17.0 12.6 −9.65 河流 R3 8.2 20.6 0.41 1.48 8.7 1.25 25 0.52 12.46 1.88 37 −120.7 −16.5 11.5 −8.12 R4 8.1 13.4 0.37 1.45 19.4 1.56 45 0.57 16.42 2.49 62 −115.7 −16.1 12.7 1.59 R5 8.4 15.1 0.41 1.59 22.1 1.61 54 0.62 17.25 2.21 71 −116.8 −16.1 12.2 0.43 R6 8.4 14.9 0.42 1.64 23.4 1.64 58 0.64 17.50 2.23 74 −117.1 −16.2 12.3 0.43 R7 8.4 22.9 0.51 1.82 23.7 1.72 62 0.70 18.51 <0.05 78 −116.8 −16.1 12.2 −0.38 R8 8.2 19.7 0.58 1.82 24.5 1.72 66 0.72 18.35 <0.05 81 −116.8 −16.1 12.2 −1.06 R9 8.7 16.6 1.87 4.87 19.0 1.90 52 3.28 19.70 <0.05 77 −102.1 −14.2 11.7 −0.08 R10 8.1 17.9 2.05 4.96 21.4 1.85 60 3.29 19.22 0.06 83 −101.0 −14.0 11.2 0.13 R11 8.1 15,7 1.88 4.21 18.0 1.86 49 2.75 17.76 1.17 71 −104.6 −14.6 12.4 0.76 雨水 P1 −82.5 −11.3 7.8 P2 0.16 0.35 2.9 0.14 16 0.38 1.07 0.43 13 −95.8 −12.8 6.8 −25.23 注：a 表示离子浓度低于检测限 
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