Assessment of Water Stable Isotope Characteristics and Mean Transit Time in Huaihe River Basin, China

The Huaihe River Basin (HRB), as an important river in China and a climatic boundary between the subtropical and temperate zones within the East Asian monsoon region, plays a vital role in regional agricultural production and human activities. This study systematically analyzed the water stable isotope characteristics and mean transit time (MTT) in the HRB, based on 940 water samples collected across the basin. Results indicated that the spatial variability of precipitation and runoff among stations along the main stream was relatively weak, whereas groundwater exhibited greater spatial variability. Precipitation in the basin was subject to slight subcloud evaporation, and both groundwater and runoff were influenced to varying degrees by evaporation. Using stable isotopes and the sine-wave approach, MTTs at various stations across the basin were estimated to range from 2.49 to 10.11 mon, with the fraction of young water ranging from 0% to 69.93%. Analysis of the transit-time distribution for each station, corresponding to its MTT, revealed spatial differences in hydrological response among stations. This study also explored the influence of dams and other hydraulic infrastructure on MTT variations across the basin. The findings enhance the understanding of runoff generation processes and hydrological dynamics within the East Asian monsoon region and provide valuable insights for improved water resource management in the HRB.