In order to better understand the water cycle processes in Baiyangdian Lake, samples for precipitation, river water, lake water, and groundwater were collected in 2020 via the analysis of oxygen and hydrogen isotopes and the total dissolved solids. A combined approach including correlation analysis, end-member modeling, and evaporation modeling was used to identify hydrogen and oxygen isotopic characteristics of different water types and their indicative significance to evaporation, hydrodynamics, and lake-groundwater interactions. The results showed that the compositions of hydrogen and oxygen isotopes in surface water and groundwater differed from each other. The average values of δD and δ18O were the highest in samples from lake water in June, secondary for lake water in October, and the lightest in groundwater. The slope of the lake water line was lower than that of the local meteoric water line, which could be attributed to a greater evaporative enrichment in lake water. The water loss ratio was estimated to be 18.8%-42.3% in June and 2.7%-30.3% in October by applying an evaporation model using deuterium excess. Lake water isotopes exhibited highly spatial heterogeneity, which indicated that Baiyangdian Lake was a poor-mixed lake controlled by the complex hydrodynamic conditions. The values of δD and δ18O were lighter around the estuary area and higher in the district far from the estuary. Although the main water isotopes in areas such as channels had a short residence time, the spatial differences in lake water isotopes were not remarkable, which suggested that the well-mixed conditions of the lake water contributed to reducing the heterogeneity of the lake water isotopic compositions on a spatial scale. The contribution ratios of lake leakage to groundwater were 0-91.7% and varied spatially. It had a negative relationship with the buried depth of groundwater and the distance to the lakeshore. No obvious relationship was found between lake leakage magnitude and groundwater level gradient. This study could provide a theoretical basis and technical support for the sustainable development of water resources and ecological environment protection in Baiyangdian Lake.
Keywords: Baiyangdian Lake; evaporation; hydrodynamics; hydrogen and oxygen isotopes; lake-groundwater interactions.