laboratory measurement of soluble phosphorus diffusion coefficients in kaolinite and bentonite clay sediments

The specific effects of sediment resuspension on the rate and amount of phosphorus diffusion by commercially available kaolinite and bentonite soils were examined in a laboratory setting by amending the soils with phosphorus fertilizer (46% P2O5), reacting them in a plexiglass container (by removing a partition) and allowing the soils to mix with the overlying water column as they spread along the container bottom. The concentration of total phosphorus was measured at 1, 3, 6, 12, 24 and 36 hours after reaction occurred. A computer program was written to calculate the diffusion coefficients (D) for the different soil and fertilizer treatments. Correcting the D values for adsorption resulted in effective diffusion coefficients (De) values, averaged across all retardation factors, of 0.010; 0.0017 and 0.0124 cm^2/day for the 13,944; 9,295 and 4,648 mu g/1 phosphorus fertilizer kaolinite treatments and 0.0002; 0.0006 and 0.0013 cm^2/day for the 13,654; 9,103 and 4,552 mu g/1 phosphorus fertilizer bentonite treatments. The diffusion coefficients for the kaolinite soil treatments were consistently greater than those for the bentonite treatments.