Geochemical processes in organic-rich lagoon sediments are dominated by the influence of microbially mediated degradation of recently deposited organic matter. A detailed study of chemical distributions and transport processes in a small coastal lagoon, Cape Lookout Bight, North Carolina (USA), reveals that degradation of the metabolizable fraction of the total organic matter not only controls interstitial water chemical composition, but drives the recycling of mobile degradation and products to overlying waters and the troposphere.