Effects of high dams and large reservoirs with cascade development on stable water isotopes

Cascade development alters the natural continuity of rivers in the watershed, thereby altering hydrologic characteristics. Based on the water sampling conducted in September 2020 and June 2021 in the Dadu River basin, Southwestern China, this study reports the influence of cascade development on the stable isotope compositional characteristics of the Dadu River basin and identifies the primary influencing environmental factors. The mean values of δD and δ¹⁸O in the waters of the Dadu River basin are −108.41‰, −15.34‰ and −95.88‰, −13.91‰ in September and June, respectively, and the isotopes are more enriched in June. From upstream to downstream, the stable isotopes exhibit an enrichment trend due to evaporation and tributary inflow. Overall, gradual increase in stream water temperature along the Dadu River, and the stable isotopes present a positive correlation with the water temperature. The water body of Dadu River show elevation, latitude, and longitude effect, but changes in latitude and longitude have a smaller effect on stable isotopes. To determine the weight of influences on stable isotopes in reservoir water, we used principal component analysis and found that water temperature was the main influence, while the retention time of the water body in the reservoir area has the smallest influence among the five influencing factors as 12.29%. The study reveals that the cascade development of high dams and large reservoirs affects the hydrological situation of the basin, which in turn causes changes in the ecological environment.