Variations of Stable Oxygen and Deuterium Isotopes in River and Lake Waters During Flooding Season Along the Middle and Lower Reaches of the Yangtze River Regions

Abstract

Stable isotope tracers have been widely applied to water sources and evolution, transforming relations, and pollution sources of various water bodies. This study analyzed the spatial variations of δ2H and δ18O in river and lake waters during flooding season, and revealed the factors underlying their variations along the middle and lower reaches of the Yangtze River based on a field sampling campaign in July 2018. Our results showed that δ2H and δ18O in the Yangtze River water were enriched from the Three Gorges reservoir region to the lower reaches of the Yangtze River, which was closely linked to isotopic variations in precipitation. There was no significant difference in δ2H and δ18O values in the mainstream river waters between the Three Gorges Reservoir Region and Yichang-Chenglingji. However, d-excess values in river water displayed a small variation range. In contrast, δ2H and δ18O values in the lake group from Dongting to Jianghan and Huayang to Poyang Lake were lower than in the lake group from Taihu to the Yangtze Delta. Negative d-excess values were observed in lake water from Taihu to the Yangtze Delta, suggesting the combined influence of enriched isotopic compositions in precipitation and strong evaporative enrichment. Of the lakes, the highest isotopic values were found in Dianshan Lake and Datong Lake, whereas the lowest isotopic values were recorded in Dongting Lake and Poyang Lake because of their direct connection with the Yangtze River. The water regimes of Dongting Lake and Poyang Lake were influenced by the Yangtze River, especially when a high water level of the Yangtze River occurred, and thus altered the isotopic compositions of Dongting Lake and Poyang Lake water. Hence, these findings will provide scientific data revealing the precipitation-river-lake interactions and investigating the rational utilization and management of water resources in the middle and lower reaches of the Yangtze River regions.