Unravelling groundwater budget in the Poyang floodplain system under intensifying seasonal lake inundation

Study region: Poyang Lake Plain at the south bank of the middle Yangtze River Study focus: The dynamics of the groundwater budget, prominently driven by the surface water-groundwater interaction, present significant challenges for water resources and the eco-environment in extensive river-lake-floodplain systems. This research utilizes a groundwater flow model through the application of the MODFLOW-NWT numerical simulator, aiming to explore the patterns of exchange between surface water and groundwater due to intensive seasonal lake inundation, and its consequential impact on the annual and seasonal groundwater storage within the vast Poyang Lake floodplain, China. New hydrological insights for the region: Simulation results indicate that the change in groundwater storage during the dry year (i.e., –24.96×107 m3/yr in 2022) has decreased by 186.35×107 m3 compared to the wet year (i.e., 161.38×107 m3/yr in 2020). The contribution of surface water infiltration is approximately 45 % of the regional groundwater budget during wet seasons, and groundwater discharge into surface waterbodies accounts for over 60 % of the groundwater budget during dry seasons. The lake infiltration during wet years is approximately 3 times that in dry years, and the flow of infiltrated lake water into plain aquifers is approximately 5 times that in dry years. The present study contributes significant knowledge regarding the impact of intensifying seasonal inundation on variations in regional groundwater budget in large lake-aquifer system.