Ecological and hydrological processes on floodplains combine to determine the biogeochemical fluxes of nitrogen and carbon.  These fluxes occur across several interfaces with differing horizontal and vertical gradients.  The fringing floodplain along the 2600 km reach of the Amazon River in Brazil contains about 6500 lakes and inundates up to about 80,000 km squared of flooded forests, open water and floating macrophytes.  These habitats fix atmospheric nitrogen and outgas significant amount of carbon dioxide and methane as a result of the complex autochthonous and allochthonous fixation and exchanges on the floodplain and in the neighboring uplands. Based on our measurements and those of others, we have assembled sufficient data to characterize the most of the fluxes and transformations of carbon and nitrogen in a representative central Amazon floodplain lake.  When combined with remotely sensed data that permit calculation of region patterns of inundation and vegetative phenology, we provide estimates of regional biogeochemical fluxes