The spatial and temporal evolution of the seepage water chemistry below an artificial recharge pond was investigated to identify the impact of dynamic changes in water saturation and seasonal temperature variations. Geochemical analysis of the pond water, suction cup water and groundwater showed that during summer, nitrate and manganese reducing conditions dominate as long as saturated conditions prevail. Iron and sulphate reduction occur only locally. When the sediment below the pond becomes unsaturated, atmospheric oxygen penetrates from the pond margins leading to re-oxidation of previously formed sulphide minerals and enhanced mineralisation of sedimentary particulate organic carbon. The latter promotes the dissolution of calcite. During winter, both the saturated and the unsaturated stage were characterised by aerobic conditions. Thereby, nitrification of sedimentary bound nitrogen could now be observed because nitrate is not immediately consumed, as is the case during summer. This suggests that nitrification below the pond might be less affected by seasonal temperature changes than nitrate reduction.