Spatiotemporal characteristics, influencing factors and evolution laws of water exchange capacity of Poyang Lake

As an important indicator of pollutant transport and dispersion conditions in lakes, the water exchange capacity of large shallow lakes has always been a focus in research on lake hydrodynamic and water environment. Poyang Lake is a large shallow lake and also the largest freshwater lake in China, which is being given prominent environmental and ecological status. Poyang Lake’s hydrological situation fluctuates dramatically and the spatial and temporal characteristics and influencing factors of its water exchange capacity are complicated. In this paper, water age was selected to describe the water exchange capacity of Poyang Lake, and a water age model of Poyang Lake was established. With the water age model, the spatial and temporal characteristics and influencing factors of water age of Poyang Lake were studied and the law of response of the water age to the evolution of River-Lake relationship between Yangtze River and Poyang Lake and the proposed Poyang Lake Water Conservancy Hub was analyzed. The results showed that: (1) The water age of Poyang Lake demonstrates significant spatial and temporal heterogeneity, that is, the water age in summer and autumn is obviously higher than that in winter and spring and the water age in the disc-shaped lake and lake bay area is obviously higher than that in the main river channel and beach; (2) The water stage at Hukou and catchment inflow are the main factors affecting the water age of Poyang Lake and the influence of the water stage at Hukou on the water age of Poyang Lake is greater than that of the catchment inflow, and the higher water stage at Hukou, the higher the water age of Poyang Lake, while the higher the catchment inflow, the lower the water age of Poyang Lake; (3) After 2003, the water age of Poyang Lake decreases with the evolution of River-Lake relationship and the most significant decrease happens in autumn; (4) The proposed Poyang Lake Water Conservancy Hub may increase the water age of Poyang Lake to some extent while it alleviates the problem of low water in Poyang Lake. This study can provide a scientific base for the water environment management of Poyang Lake and provide a reference for research on water exchange capacity of other large shallow lakes.