Diffusion processes in water saturated spherical soil aggregates

Abstract

Abstract The release curves of D2O, K+, and Cl¯ from saturated spherical aggregates of four soils, presaturated with a 10 mol m−3 KCL and 10 kg m−3 D2O mixed solution, to a 10 mol m−3 NH4NO3 solution were analyzed to examine the diffusion processes in soil aggregates. Aggregates were taken from the weathering crust of a mudstone (MDR), the AB horizon of a Brown Lowland soil (BLS), the B horizon of a Brown Andosol (ADO), and the C horizon of a Vol-canogenous Regosol (PUM). The apparent diffusion coefficients of the solutes for each sample were obtained by fitting the spherical diffusion model to the release curves. Although the release rates of solutes from the 2-4 mm aggregates were higher than those from the 6-8 mm aggregates, almost the same diffusion coefficients (D) were obtained for both aggregate sizes. The values of the tortuosity factor (f) which was estimated as D/D 0 for D 2O(D 0 is the diffusion coefficient in free water) ranged from 0.25 to 0.51. Higher values were found in samples with a larg...