Natural colloids are part of the carbon cycle arising from sediment diagenesis. Natural colloids can be quantified as the dissolved organic carbon (DOC) present in the pore-water of sediment beds. In this paper we demonstrate that DOC is mobile in a system in which the dominant transport mechanism is Brownian diffusion. A simple model which assumes constant physico-chemical properties for the DOC adequately predicts the DOC release rate from a sediment bed in a microcosm. A single adjustable parameter, the water diffusivity, is used to fit the model to the experimental data. The experimental diffusivities obtained from the fitted data agree well with previously presented values.

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