Lack of clarity regarding the relationship between hydroperiod and decomposition dynamics has long been a barrier to the development of a clear understanding of floodplain biogeochemistry. Relationships between hydroperiod and decomposition processes were investigated using a controlled, field approach on the Ogeechee River floodplain on south Georgia. The study intent was to develop cause-effect relationships between specific flooding regimes and decomposition parameters. Microcosms designed to manipulate flooding regimes were installed and used in combination with litterbags containing abscised foliage. Treatments were designed to mimic realistic hydroperiod-nutrient inflow scenarios and included: a nonflooded control, flooded for 6 mo, flooded for 3 mo, flooded intermittently for 4 mo, flooded for 3 mo with elevated P inflow, and flooded for 3 mo with elevated N inflow. Mass, C, N, and P dynamics were studied for a 106-wk period. Flooding stimulated mass, C, N, and P loss. The data suggest that single, brief flooding regimes may stimulate mass and C loss to the greatest extent. The proportion of N and P remaining after 106 wk was only marginally different among flooding regimes. However, temporal patterns of immobilization-mineralization were strongly influenced by the nature of the flooding regime.