Tracing controlling factors of riverine chemistry in a headwater tributary of the Yangtze River, China, inferred from geochemical and stable isotopic signatures

The Jialing River is the second largest headwater tributary of the Yangtze River in China, therefore, the river water has been contaminated and water quality is deteriorated. Hence, this study aims to find the main controling factors of riverine chemistry. 52 water samples were collected for the determination of major ions and environmental isotopes of δ¹⁸O and δ²H. Stoichiometry of geochemical data with mixing end members and multivariate statistical analysis were employed with integrated GIS approach for data interpretations. The δ¹⁸O and δ²H of the Jialing River Basin (JRB) were used to define the origin of river water from meteoric water and water in the spring season is affected by high evaporation and evaporates dissolution. The average TDS 301 mg/L that is higher than the Yangtze River. In the JRB, 80% of the anion in water samples represented HCO₃⁻ (207 mg/L) and SO₄²⁻ (80 mg/L) while 80% of the cations were accounted by Ca²⁺ (59.8 mg/L) and Mg²⁺ (17.9 mg/L). The water chemistry mainly derived from the water rock interaction. Piper plot indicated that Ca-Mg-HCO₃⁻ was the most dominant water type and most ions derived from carbonate weathering by H₂SO₄ and H₂CO₃. The stoichiometry results further confirmed carbonate weathering is dominant than silicate weathering. Evaporate ions were modified by anthropogenic sources. Agricultural inputs are higher than the industry and atmospheric inputs. Redundancy analysis showed that most contributive land-use type in explaining riverine chemistry was the cultivate land (62.6, 66.4, and 67.9%) at all buffer scales of 30, 20, and 10 km, respectively. Forest and grasslands mostly correlate with Ca²⁺, Mg²⁺, Cl⁻, SO₄²⁻, EC, pH, and HCO₃⁻ while anthropogenic land-use types such as cultivated and construction lands correlate with Na⁺, K⁺, Cl⁻, and NO₃⁻. These results revealed that the lithology of the basin mainly controlled the upstream water chemistry while downstream riverine chemistry was controlled by both lithology and anthropogenic inputs. Nevertheless, this study suggested that explicitly determining the controlling factors of riverine chemistry involves a complex process and combination of different chemical constituents and factors on river water. However, this study managed to provide useful information to further understanding of the geochemical process in JRB.