Abstract

Many of the abundant burrows formed by animals in marine sediments are lined with thin layers of organic material. The permeability of these linings to solute diffusion can be an important determinant of the chemical composition of surrounding sediment and the burrow habitat. Measurement of the diffusive permeability of burrow linings from 8 species of marine invertebrates indicates that the diffusion coefficients of small inorganic solutes within linings are ∼ 10-40% that in free solution. The diffusion of anions, represented by Br−, is hindered somewhat relative to cations, represented by NH4+, indicating that linings have negatively charged regions at the pH of natural waters. The time dependence of diffusion through linings is affected by simple ion exchange within the lining material. Adsorption constants for solutes like NH4+ and Si(OH)4, are in the range of K ∼ 2-8 (relative to pore water volume). Silica shows evidence of interaction other than reversible ion exchange in some cases. The permeability of linings can affect sedimentary solute distributions differently depending on the types of reactions controlling a particular solute in surrounding sediment. The concentrations of solutes subject to zeroth-order reactions are greatly influenced by lining permeability but net fluxes (at steady state) across the lining are not. The opposite is true for solutes subject to first or higher order concentration-dependent reactions. Assuming burrow linings can act as molecular sieves, then some classes of solutes will be strongly influenced by the presence of irrigated burrows while others will be distributed in a deposit as though burrows were completely absent. This may greatly complicate sedimentary solute distributions.

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