A schematic presentation of the volumetric model used for quantification of carbon reaction rates in sandy coastal sediment with a depth of L cm: A, with irrigated burrows of the polychaetes Nereis diversicolor. The grey zones indicate oxic surface sediment (thickness Lox cm) and oxic burrow walls (thickness Box cm). All burrows have a radius of r cm and a length of Lb cm. B; with reworking by the headdown conveyor-belt feeding polychaetes Arenicola marina. The lightly hatched zone (Lox) indicates the oxic surface sediment. The darkly hatched zone (L1) indicates surface related labile material displaced into anoxic sediment. In both cases, the carbon oxidation rate (R1) of the labile detritus under both oxic and anoxic conditions is A1 times faster than the carbon oxidation rate (R2an) of the partly degraded detritus in the anoxic black sediment (R1 = A1 R2an), When deep subsurface sediment is exposed to oxygen in irrigated burrows or by reworking the reaction rate is enhanced A2 fold (R2ox = A2 R2an) (modified from Kristensen and Holmer).