Abstract: Abstract:【Objective】The essence of biogeochemical reactions in groundwater environments is electron transfer. Sediments serve as important electron reservoirs, potentially undergoing cyclical electron storage and release driven by water level fluctuations, profoundly affecting substance transformations and elemental cycles in the subterranean environment. However, current understanding of the patterns and mechanisms of sediment charging and discharging driven by groundwater level fluctuations remains limited.【Methods】This study developed a one-dimensional column system to simulate the groundwater fluctuation zone, combining chemical analysis, fine structural characterization, and molecular biology techniques to explore the patterns and mechanisms of sediment charging and discharging driven by water level fluctuations.【Results】The results indicate that under short-period fluctuation patterns, sediments can complete two charging-discharging cycles, with maximum charge and discharge capacities of 2.3 and 8 μmol e-·g-1 respectively, and maximum charge and discharge rates of 0.577 and 2.012 μmol e-·g-1·d-1. The electron sources in the sediments are primarily from adsorbed states, ion exchange states, and highly active structural states of Fe(II).Water level fluctuations facilitate the storage and release of electrons in sediments through the bioreduction of Fe(III) to Fe(II) and its subsequent chemical oxidation. With the cycle of reduction-oxidation reactions, the bioavailability of iron oxides decreases, leading to the inability of the sediments to sustain continuous charging and discharging. The input of the electron shuttle anthraquinone-2,6-disulfonate (AQDS) initially significantly increases the charging and discharging rates but accelerates the reduction in the bioavailability of ferric iron, ultimately causing a gradual decline in charge and discharge rates, and stopping the cycle at the third period. The addition