The diffusion coefficients of sulfate, ammonium, and phosphate ions in anoxic marine sediments1

The diffusion coefficients of sulfate, ammonium, and phosphate ions were determined directly in the laboratory by placing two samples of homogenized, anoxic mud from Long Island Sound in contact with one another across a planar interface. After 141 h concentration profiles were determined and from them, values of effective diffusion coefficients (which incorporate the effects of adsorption) were calculated. Correction of these values for adsorption, using independently determined linear adsorption constants for the same sediments, gave the following values (× 10 −6 cm 2 · s −1 , 20°C, errors ±2σ): D s (SO 4 ), 5.0±1.2; D s (NH 4 ), 9.8±2.0; D s (PO 4 ), 3.6±1.1. These values agree well with values calculated for the same sediments from estimates of formation factors plus data for diffusion coefficients at infinite dilution.