Hydrochemical characteristics and effect of human activity of surface water in the Shuoduogang River Basin on the southeastern margin of Qinghai–Xizang Plateau

This paper is the result of geological survey engineering.

Objective The Shuoduogang River Basin, situated on the southeastern margin of Qinghai−Xizang Plateau, features a fragile ecological environment, abundant hydropower and tourism resources, and an underdeveloped local economy. To support the Rural Revitalization Strategy and the rational development and utilization of water resources, a study on surface water hydrochemistry was conducted.

Methods Based on a systematic investigation of the basin’s hydrogeological conditions, water samples were collected from the main stream and tributaries of the Shuoduogang River. The hydrochemical composition, spatial distribution, recharge sources, and main controlling factors of the surface water were analyzed using ion ratio analysis, Positive Matrix Factorization (PMF) source analysis, and geographical detectors.

Results The surface water in the Shuoduogang River Basin exhibits pH range of 7.52 to 8.66 and TDS values between 65.00 mg/L and 744.00 mg/L. Cation composition is dominated by Ca²⁺ and Mg²⁺, following the order Ca²⁺>Mg²⁺>Na⁺>K⁺, while anions are primarily HCO₃⁻ and SO₄²⁻, with concentrations decreasing as HCO₃⁻>SO₄²⁻>Cl⁻>NO₃⁻. The saturation indices of calcite and dolomite minerals increase progressively from first- to fourth-order streams, reaching saturation in all fourth-order waterways. Na⁺, K⁺, Cl⁻, and SO₄²⁻ show high coefficients of variation, indicating significant spatial variability. Hydrochemically, the water is predominantly of the HCO₃–Ca type, though influence from hydropower operations results in some samples exhibiting Cl–Na characteristics. Stable isotope values (δD: −120‰ to −103‰; δ¹⁸O: −15.9‰ to −14.1‰) suggest that atmospheric precipitation of oceanic origin is the main water source. In terms of influencing factors, NO₃⁻ is primarily affected by agricultural/pastoral activities and carbonate weathering; Ca²⁺, Mg²⁺, Na⁺, HCO₃⁻, SO₄²⁻, and TH mainly derive from the weathering of limestone, dolomite, and silicate rocks; Cl⁻, PO₄³⁻, and pH are chiefly influenced by livestock farming; while K⁺, NH₄⁺, and TDS are predominantly associated with agricultural practices.

Conclusions In the Shuoduogang River Basin, rock weathering, animal husbandry, agriculture, and the interaction between agricultural and animal husbandry activities contribute 33.8%, 24.6%, 22.1%, and 19.5%, respectively, to the water solute load. Notably, the presence of a hydropower station amplifies the impact of agricultural and animal husbandry activities, underscoring the significant influence of human activities on solute dynamics in the basin.