Samples of hydrogen and oxygen stable isotopes in precipitation collected and analyzed during the summer monsoon in 2017 and 2018 in Chengdu are reported in this paper. Increasing (decreasing) trends of isotope values (δD and δ18O) occur from May to June (September to October), and the valleys occur from July to August. The correlation between δD and δ18O for both precipitation events and monthly average precipitation is significant, with high R2 values (≥0.98). The differences in regression lines may be due to the comprehensive influence of moisture sources, transport path and sub-cloud processes. Combining the d-excess values of precipitation and air mass trajectories generated by the HYSPLIT model, precipitation with a low (high) d-excess value and a more (less) negative δ18O corresponds to moisture from ocean (inland) sources. The δ18O–temperature (T) and δ18O–precipitation (P) correlations are not significant and vary greatly among different periods, which may be attributed to the mutual masking of different effects and the influence of atmospheric circulation processes. The results imply that the negative values in biological and geological proxies may be related to warmer climate, higher precipitation and a larger contribution of oceanic monsoon precipitation, but cannot indicate the changes in temperature and precipitation quantifiably.

The water-level fluctuation zone of the lower Jinsha River Basin is a fragile ecosystem with limited water resources in the southwest of China. Soil water is critical for maintaining ecological balance and promoting the healthy development of animals and plants in this region. In this study, eight typical soil profiles were monitored for hydrochemistry in soil-soluble salt from upstream to downstream of the lower Jinsha River Basin. The results show that the soil water content was low and had a negative correlation coefficient with major ions in the soil-soluble phase. The soil-soluble salt is slightly alkaline, and Ca²⁺, Na⁺, SO₄²⁻, and HCO₃⁻ are important components for ions in a soluble phase. Major ions in soluble salt originate from various sources, including precipitation, anthropogenic input, silicate weathering, and carbonate weathering, and the contribution rates from each end member were 0.7%, 45.1%, 25.2%, and 29%, respectively. The ion composition in surface soil soluble salt is mainly influenced by precipitation and human activities, while the ions in the 0–50 cm soil layer originate from the precipitation input and water-rock interaction. In addition, rock weathering is a vital process for releasing ions into soil-soluble salt from 50 to 100 cm soil layer. Our findings provide important references for ion sources and the eco-hydrological process in limited water resources in the water-level fluctuation zone of the lower Jinsha River Basin.

Riverine dissolved matter reflects geochemical genesis information, which is vital to understand and manage the water environment in a basin. The Ganjing River located in the hinterland of the Three Gorges Reservoir was systematically investigated to analyze the composition and spatial variation of riverine ions, probe the source and influencing factors, and assess the chemical weathering rates and CO₂ consumption. The results showed that the total dissolved solid value (473.31 ± 154.87 mg/L) with the type of “HCO₃⁻–Ca²⁺” was higher than that of the global rivers’ average. The hydrochemical parameters were relatively stable in the lower reservoir area of the Ganjing River, which was largely influenced by the backwater of Three Gorges Reservoir. The carbonate weathering source contributed 69.63% of TDS (Total dissolved solids), which generally dominated the hydrochemical characteristics. The contribution rates of atmospheric rainfall were relatively low and stable in the basin, with an average of 4.01 ± 1.28%. The average contribution rate of anthropogenic activities was 12.05% in the basin and even up to 27.80% in the lower reservoir area of the Ganjing River, which illustrated that the impoundment of Three Gorges Reservoir had brought great challenges to the water environment in the reservoir bay. The empirical power functions were tentatively proposed to eliminate the dilution effect caused by runoff discharge on the basis of previous studies. Accordingly, the rock weathering rate was calculated as 23.54 t/km² in the Ganjing River Basin, which consumed atmospheric CO₂ with a flux of 6.88 × 10⁵ mol/y/km². These results highlight the geochemical information of tributaries in the hinterland of the Three Gorges Reservoir, have significant implications for understanding the impact of impoundment, and provide data support for the integrated management of water resources in the Ganjing River Basin.