ORGANIC-CARBON SORPTION IN ARCTIC AND SUB-ALPINE SPODOSOL-B HORIZONS

The sorption of dissolved organic carbon (DOC) on B horizons from arctic and subalpine Spodosols was investigated at low temperatures typical of these soils. The arctic Spodosol, from northern Alaska, had an inverted horizon sequence (Bs overlying Bhs) and other properties inconsistent with the metal-fulvate theory of podzolization. The subalpine Spodosol, from the Cascade Range of Washington state, developed in a mixture of volcanic and glacial materials and had classic Spodosol morphology. Batch studies were conducted under the following conditions: 3-degrees-C, pH of 4.5, C/metal ratio of 59, a 10:1 solution/soil ratio, and an ionic strength of 10(-3) M. Final pH, DOC, Fe, Al, and Si concentrations were determined. Between 30 and 50% of the adsorption/desorption occurred within the first 0.25 h and steady-state DOC concentrations occurred within the first 0.25 h and steady-state DOC concentrations occurred between 4 and 12 h. Only the subalpine Bs horizon adsorbed DOC, while both Bhs horizons and the arctic Bs horizon desorbed DOC. Dispersion of fine colloids (< 0.2-mu-m) affected desorption in arctic soils at reaction times > 4 h. The results suggest that the main mechanism of DOC immobilization involved initial solubilization of metals, which lowered C/metal ratios in solution, followed by adsorption of the organo-metal complexes. The ability of the subalpine Bs horizon to effectively adsorb DOC may be due to the large concentration of uncoated short-range-order materials (imogolite and ferrihydrite) present in this horizon.