I assessed key drivers for processes in the soil carbon (C) balance of hardwood floodplain forests at the lower middle Elbe River. Floodplains play a significant role in the global C cycle, particularly due to their soil organic carbon (SOC) storage potential in hardwood floodplain forests. In floodplains, C input occurs from deposition of dead plant debris and fluviatile sediments. C losses are mainly driven by flood-induced soil erosion and SOC mineralization. These processes vary by relief position and vegetation type. However, anthropogenic landscape modifications have affected the natural flooding regime and the vegetation composition. The interaction between natural conditions and anthropogenic modifications complicate the understanding of processes in the C balance of hardwood floodplain forests. To determine the driving mechanisms for these processes, I selected 50 floodplain study sites along the lower middle Elbe River and categorized them into hydrologic situation (low and high relief position; active and former flooding zone) and vegetation type (forest and grassland; old and young forest). The aim of my dissertation is to understand the processes controlling the soil C balance of hardwood floodplain forests. To characterize the processes controlling the soil C balance of hardwood floodplain forests, I related SOC stocks, SOC stability, and soil CO2 efflux (through autotrophic and heterotrophic soil respiration) to vegetation (e.g., forest age, basal area) and soil characteristics, particularly pedological traits (e.g., hydromorphic features, soil texture, pH, C/N ratio). SOC stocks were determined up to a depth of 1 m and compared to topsoil SOC stocks. SOC density fractions, SOC mineralizability and microbial biomass in top- and subsoils were analyzed to identify drivers for SOC stability. Soil CO2 effluxes were measured over a full year using the closed-chamber method. Based on the response of soil CO2 efflux to soil moisture and temperature, annual rates were determined. Additionally, the ...