Lake–aquifer connectivity controls groundwater dynamics in a multi-aquifer system within a typical floodplain

Study regionThe study was conducted in the Poyang Lake floodplain, China, where a vertically stratified multi-aquifer system interacts with Poyang Lake, a seasonal lake (Candou Lake), regional lateral flow, rainfall infiltration, and artificial ponds. Study focus: This study investigates the drivers of groundwater level dynamics in a vertically stratified aquifer system at small spatial scale (<30 m). High-frequency groundwater monitoring, cross-correlation analysis, wavelet analysis, and numerical groundwater flow modeling were integrated to identify aquifer-specific responses to hydrological and anthropogenic controls. New hydrological insights for the region: Groundwater dynamics presented pronounced vertical heterogeneity within < 30 m. The shallow aquifer was mainly controlled by rainfall infiltration and Candou Lake recharge. The intermediate aquifer was connected to both Candou Lake and Poyang Lake, but Candou Lake exerted stronger control during the flood period. The deep aquifer was alternately influenced by Poyang Lake recharge and regional lateral flow: the lake recharge initiates groundwater rise, whereas lateral recharge controlled peak groundwater levels. Model simulations confirmed that Candou Lake provides greater recharge to the shallow and intermediate aquifers than rainfall and Poyang Lake, respectively, while Poyang Lake initially dominated recharge to the deep aquifer. Artificial ponds elevated groundwater levels in shallow and intermediate aquifers, maintained high levels during the dry season, and enhanced local recharge. These findings highlight the necessity of high-resolution, multi-aquifer characterization to support groundwater management in floodplains.