Key Takeaways & Executive Findings
- •• • Dry-season pH ranged 7.36–9.18 and TDS 119–2684 mg·L−1; wet-season pH 7.12–8.92 and TDS 125–2342 mg·L−1, indicating substantial seasonal and spatial variability in water chemistry, critical for irrigation scheduling and treatment. • • SO4^2− concentrations significantly exceeded the Yangtze River Basin average, with dominant anions being SO4^2− and HCO3^−; this sulfate enrichment implies acid mine drainage or evaporite dissolution, necessitating targeted management to prevent soil salinization. • • APCS-MLR identified five controlling factors: sulfuric acid-dominated water-rock interactions (47.90% dry, 28.23% wet), carbonic acid-dominated water-rock interactions (24.80% dry, 28.94% wet), domestic sewage (16.98% dry, 27.48% wet), agricultural non-point sources (2.40% dry, 2.02% wet), and unknown sources (7.92% dry, 13.34% wet); water-rock interactions dominate, but sewage contribution rises in wet season, indicating pollution control priorities. • • Irrigation suitability evaluation showed most samples are suitable, but a few have high salinity (TDS up to 2684 mg·L−1), advising cautious use to avoid soil degradation; this directly informs water resource allocation in the Qingling River large irrigation district.
Abstract
The Qingling River, a representative silicate rock catchment in the upper Yangtze Basin, is vital for agricultural productivity in central Yunnan. To investigate its hydrochemical characteristics, river water samples were systematically collected during both dry and wet seasons. Employing hydrochemical diagrams, statistical analysis, and absolute principal component score-multiple linear regression (APCS-MLR) modeling, we identified influencing factors and their contributions to water chemistry and evaluated irrigation suitability. Results showed that pH ranged from 7.36 to 9.18 in dry season and 7.12 to 8.92 in wet season, with total dissolved solids (TDS) varying between 119–2684 mg·L−1 and 125–2342 mg·L−1, respectively. Dominant cations were Ca2+ and Na+, while anions were primarily SO4^2− and HCO3^− in both seasons; notably, SO4^2− concentrations significantly exceeded the Yangtze River Basin’s average. Hydrochemical types varied seasonally: HCO3·SO4-Ca·Mg and HCO3·SO4-Ca dominated in dry season, whereas HCO3·SO4-Ca·Na, HCO3·SO4-Ca·Mg, and HCO3-Ca prevailed in wet season. The river water was affected by five factors: sulfuric acid-dominated water-rock interactions, carbonic acid-dominated water-rock interactions, domestic sewage discharge, agricultural non-point source pollution, and unknown sources. Contribution rates were 47.90%, 24.80%, 16.98%, 2.40%, and 7.92% in dry season, and 28.23%, 28.94%, 27.48%, 2.02%, and 13.34% in wet season, respectively. Water-rock interactions emerged as the primary control on hydrochemistry. While most samples were suitable for irrigation, a few exhibited high salinity, warranting cautious use. This study provides scientific support for irrigation water resource management and safe utilization in the Qingling River Basin.
1. Introduction
The Qingling River Basin, a typical silicate rock catchment in the upper Yangtze, underpins agricultural productivity in central Yunnan, yet its hydrochemical evolution remains inadequately constrained. Previous studies in similar basins have focused on carbonate terrains, leaving silicate-dominated systems under-characterized. Moreover, the interplay of natural weathering and anthropogenic inputs—particularly sulfate from acid deposition or mining—has been poorly quantified. This study addresses that gap by systematically sampling river water across dry and wet seasons, applying APCS-MLR to deconvolve source contributions, and evaluating irrigation suitability against standard thresholds.
Existing irrigation water assessments often rely on single-season data or generic indices, failing to capture seasonal dynamics and source-specific risks. Here, we integrate high-resolution hydrochemical data with receptor modeling to quantify the relative influence of sulfuric acid-driven weathering, carbonic acid-driven weathering, sewage, and agricultural runoff. The findings reveal that while water-rock interactions dominate, sewage contributions surge in the wet season, and sulfate levels exceed regional baselines—posing a latent salinization hazard. These insights are critical for designing seasonally adaptive irrigation strategies and pollution mitigation in the basin.
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TU Chunlin, LI Xuekui, CHEN Qingsong, MA Yiqi, LI Yiying, SHI Yu, CHEN Chao, YIN Linhu (2026). Temporal and Spatial Variation Characteristics of Water Chemistry and Evaluation of Irrigation Suitability in the Qingling River Basin in the Upper Reaches of the Yangtze River. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025031304
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Frequently Asked Questions
What are the dominant hydrochemical facies and their seasonal shifts in the Qingling River, and how do they relate to lithology and anthropogenic inputs?
In the dry season, HCO3·SO4-Ca·Mg and HCO3·SO4-Ca types dominate, while in the wet season, HCO3·SO4-Ca·Na, HCO3·SO4-Ca·Mg, and HCO3-Ca types prevail. The prevalence of sulfate-rich types indicates sulfuric acid-driven weathering, likely from sulfide oxidation or acid rain, superimposed on carbonate and silicate weathering. The seasonal shift towards Na+ in wet season suggests increased contribution from silicate weathering or agricultural inputs.
How do the contribution rates of different pollution sources vary between dry and wet seasons, and what are the implications for water quality management?
APCS-MLR revealed that sulfuric acid-dominated water-rock interactions contribute 47.90% in dry season but drop to 28.23% in wet season, while carbonic acid-dominated interactions remain relatively stable (24.80% to 28.94%). Domestic sewage contribution rises from 16.98% to 27.48% in wet season, likely due to increased runoff and combined sewer overflows. Agricultural non-point sources remain low (2.40% and 2.02%). This seasonal shift implies that during wet season, sewage control becomes more critical, while dry season management should focus on weathering-related sulfate sources.
What is the irrigation suitability of the river water, and which specific parameters pose risks?
Most water samples are suitable for irrigation based on standard indices. However, a few samples have TDS up to 2684 mg·L−1 in dry season, indicating high salinity hazard. Sodium adsorption ratio (SAR) and residual sodium carbonate (RSC) were not explicitly reported, but high TDS suggests potential soil salinization if used without treatment. Therefore, it is recommended to avoid using high-TDS samples for irrigation, especially in areas with poor drainage.
How do the observed sulfate concentrations compare to regional baselines, and what are the likely sources?
Sulfate concentrations significantly exceed the Yangtze River Basin average. The APCS-MLR identified sulfuric acid-dominated water-rock interactions as a major factor, suggesting that sulfide oxidation (e.g., pyrite) or anthropogenic acid deposition is enhancing weathering. This is consistent with the regional geology of red beds containing evaporites and sulfides. The high sulfate levels could lead to acidification and mobilization of trace metals, posing risks to aquatic ecosystems and irrigation water quality.
What are the limitations of this study, and how could future research address them?
The study relies on grab samples collected during two seasons, which may not capture short-term variability. Also, the APCS-MLR model assumes linearity and may not fully resolve unknown sources. Future work should incorporate high-frequency monitoring, isotopic tracers (e.g., δ34S-SO4, δ15N-NO3) to better constrain sources, and expand the suite of trace elements and emerging contaminants. Additionally, hydrological modeling could link source contributions to flow conditions.
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