Soils of the northern boreal forest have undergone significant pedogenic losses of P. This study was undertaken to examine the hypothesis that the leaching of dissolved organic carbon (DOC) is a mechanism for P removal from forested soils. The sorption of DOC and DOC fractions by soil horizons from the shoulder, backslope, and footslope soils of a catenary sequence was examined. Variation in DOC sorption among the soil horizons, and between positions in the catena, was related to differences in the clay content ( r = 0.71) and citrate‐dithionate‐extractable Fe, Al, and Mn ( r = 0.66). The hydrophobic acid and the hydrophilic acid fractions were the most abundant in the soil solution (72% of the total DOC) and accounted for most of the sorption of DOC in the Bt and C horizons (isotherm distribution coefficient K d = 27.1 × 10 −4 to 337 × 10 −4 m 3 kg −1 ). The hydrophobic neutral fraction (14% of the DOC) was not sorbed by any of the soil horizons (average K d = 20.0 × 10 −4 m 3 kg −1 ). The hydrophobic neutral fraction (14% of the DOC) was not sorbed by any of the soil horizons (average K d = 20.0 × 10 −4 m 3 kg −1 ). The hydrophobic neutral fraction had a molar C/P ratio of 2800, compared with 21 000 and 35 600 for the hydrophobic acid and hydrophilic acid fractions, respectively. Phosphorus in the hydrophobic neutral fraction constituted 64% of the P measured in these three fractions. The high P content and low sorption of the hydrophobic neutral fraction suggests that the leaching of the hydrophobic neutral fraction may be a possible mechanism for the redistribution and loss of P in these soils.
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Donald et al. (1993) studied this question.