The exchange of benthic dissolved organic carbon (DOC) was investigated in three pre-dams of drinking water reservoirs, focusing on fluxes, processes and drivers. The benthic systems were studied through sediment core incubation, resuspension, microbiological and DOC quality methods. Seasonal and multi-solute data enabled elucidation of major drivers and mechanism regulating DOC flux. Sediments were a source of DOC under anoxic conditions (0.5 to 5.3 mmol m-2 d-1). In contrast, they were both a sink and source of DOC under oxic conditions (-9.3 to 2.4 mmol m-2 d-1). Redox conditions and temperature were identified as the major drivers. DOC and Fe fluxes correlated positively under anoxic conditions, underlining immobilization/mobilization of DOC by Fe minerals as an important mechanism. DOC quality analysis supported this observation: under anoxic conditions oxygen rich organic compounds dominated, but disappeared when redox conditions were manipulated to oxic.