Effects of Periodic Fluctuation of Water Level on Solute Transport in Seasonal Lakes in Poyang Floodplain System

Seasonal lakes appear in floodplain systems due to the seasonal variation of water level of rivers or main lakes and play an important ecological function. Previous studies have focused on exchange flux between the surface water and groundwater in seasonal lakes, but the process of solute transport at the sediment-water interface under the effect of seasonal water level fluctuations remains unclear. In this study, laboratory flume experiments and numerical simulations were conducted to investigate non-reactive solute transport and exchange in a seasonal lake under effects of hydrological connectivity, water level amplitude, sediment permeability and solute source. The results show that the recharge pattern between seasonal lakes and rivers or main lakes is determined by the seasonal water level. The solute transports from the groundwater of seasonal lakes to the main lake during the dry season, while the reverse applies during the wet season. The perennial hydrological isolation increases the concentration in the overlying water and pore water of the seasonal lake by 20.5% and 28.7%, respectively. The solute concentration in the overlying water and pore water of the seasonal lake decreases by 55.2% and 51.5%, respectively, when solute source occurs in the main lake compared with that occurs in the seasonal lake. The amplification of water level amplitudes leads to an increase of 6.46% and 10.55% in the solute concentration drop from the overlying water, respectively. These findings contribute to improving water resource utilization and protecting aquatic ecological environment in floodplain systems. Floodplains are usually populated and economically developed. Rivers such as Amazon River or main lakes such as Poyang Lake in floodplain systems are surrounded by many seasonal lakes that are subjected to floodplain process. Seasonal lakes serve an important ecological function by providing habitat for water birds and fish. The transport of solute in the surface water and groundwater is an important factor affecting the ecology and environment of seasonal lakes. To investigate solute transport in seasonal lakes, laboratory experiments and numerical simulations were conducted to describe the entire process. We find that water from high-water lakes flows toward low-water lakes. The decreasing water level of rivers or main lakes in recent years may lead to more serious pollution in seasonal lakes. The solute source occurring in the seasonal lake is more serious than that in the main lake. A stronger flooding process causes solutes in seasonal lakes to transport more easily to groundwater. These findings provide theoretical basis for better management of floodplain systems. Seasonality changes the water level difference between seasonal lakes and rivers or main lakes and affects the recharge patternThe disconnection of the overlying water causes the solute to be more concentrated in permanently isolated seasonal lakesSolute retention is higher in seasonal lakes when solute source occurs in seasonal lakes compared with that occurs in rivers or main lakes

Automated summary

Seasonal lakes are affected by the seasonal water level fluctuations and play an important ecological function. The exchange of solutes between seasonal lakes and main lakes is determined by the water level, and permanent hydrological isolation increases the solute concentration in seasonal lakes. The solute source in main lakes leads to a decrease in solute concentration in seasonal lakes. Higher water level amplitudes result in a greater decrease in solute concentration.