Stable isotope signatures of river and lake water from Poyang Lake, China: Implications for river-lake interactions

Interactions between the Yangtze River and Poyang Lake are undergoing rapid changes due to intensive human activities and ongoing climate change. This study investigates the spatiotemporal variations of isotopic compositions (delta H-2 and delta O-18) in river and lake water to explore the river-lake interactions in combination with water level and discharge in Poyang Lake watershed. The results showed that river and lake water isotopes (delta H-2 and delta O-18) exhibited highly temporal heterogeneity across seasons but their spatial differences were not remarkable, which is closely related with water sources from local precipitation and groundwater, and lake hydrology. The homogeneous patterns of lake water delta H-2 and delta O-18 indicated that Poyang Lake is a well-mixed lake in spatial scales. By contrast, the river (10.7 parts per thousand) and lake (10.8 parts per thousand) water d-excess and lc-excess (0.6 parts per thousand) were close to precipitation d-excess and lc-excess suggesting that precipitation is the main source for the lake and river. The slope and intercept of the river water line were slightly lower than those of the local meteoric water line and lake water line, which could be attributed to a greater evaporative enrichment in river water impacted by water flow regulation in the watershed. Interactions between Poyang Lake and Yangtze River vary seasonally, as evidently shown by the variations of water discharge and isotope compositions in river and lake water. The delta H-2 and delta O-18 of the Yangtze River water become more positive in the downstream zone than those in the upstream zone, indicating that the water from Poyang Lake has a great impact on downstream river water. This result can also be demonstrated by the efflux rate from the Poyang Lake to the Yangtze River, ranging from 17.9 parts per thousand to 67.9 parts per thousand across seasons except for the outlier rate in October resulted from the backflow of water from Yangtze River to the Poyang Lake. The complex lake-river interactions between Poyang Lake and Yangtze River mainly resulted from the regulation of Three Gorges Dam and water discharge from Poyang Lake watershed. These findings of the complex lake-river interactions will help to improve understanding of the hydrological processes and transport of pollutants and solutes around the confluence zone of the Yangtze River and Poyang Lake