『Abstract
　Organic carbon degradation experiments were carried out using flow-through reactors with sediments collected from an intertidal freshwater marsh of an eutrophic estuary (The Scheldt, Belgium). Concentrations of nitrate, nitrite, dissolved inorganic carbon (DIC), dissolved organic carbon, methane, dissolved cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺), total dissolved Fe, phosphate and alkalinity were measured in the outflow solutions from reactors that were supplied with or without the terminal electron acceptor nitrate. Organic carbon mineralization rates were computed from the release rates of DIC after correcting for the contribution of carbonate mineral dissolution. The experiments ran for several months until nitrate reducing activity could no longer be detected. In the reactors supplied with nitrate, 10-13％ of the bulk sedimentary organic carbon (SOC) was mineralized by the end of the experiments. In reactors receiving no nitrate, only 3-9％ of the initial SOC was mineralized. Organic matter utilization by nitrate reducers could be described as the simultaneous degradation of two carbon pools with different maximum oxidation rates and half-saturation constants. Even when nitrate was supplied in non-limiting concentrations about half of the carbon mineralization in the reactors was due to fermentative processes, rather than being coupled to nitrate respiration. Fermentation may thus be responsible for a large fraction of the DIC efflux from organic-rich, nearshore sediments.

Keywords: Organic carbon; Sediment; Bioavailability; Degradation; Nitrate reduction; Denitrification; Fermentation; Scheldt estuary』

Introduction
Materials and methods
　Site description and sampling
　Flow-through reactor experiments
　Analytical methods
Results
　Nitrate reduction
　Dissolved inorganic and organic carbon release
　Phosphate release
　Methane release
Discussion
　Nitrate reduction rates
　DIC release by CaCO3 dissolution, iron reduction and methanogenesis
　Carbon mineralization rate: determination
　Carbon mineralization rates: denitrification versus fermentation
　Dissolved organic carbon release: unamended reactors
　Dissolved organic carbon release: amended reactors
　Organic carbon bioavailability
　Kinetics of denitrification
　Carbon budgets
Conclusions
Acknowledgments
References