Adsorption of Dissolved Organic and Inorganic Phosphorus in Soils of a Weathering Chronosequence

Abstract

Leaching of dissolved organic matter (DOM) and associated nutrients can be a significant loss from developing ecosystems. We studied how the adsorption of dissolved organic P (DOP) and PO4 changes during the development of young andesitic soils and determined which soil characteristics are responsible for these changes. We sampled 77, 255, 616, and about 1200+ yr-old andesitic soils at the 0- to 10-, 30- to 40-, and 140- to 150-cm soil depths and performed adsorption isotherm analyses that were described using a modified Langmuir (for DOP) or linear equation (for PO4). We also sampled soil solution at the 10- to 20-, 40-, and 150-cm soil depths during the main snow melt period in 2001 and 2002 and analyzed it for DOP and PO4 The ability of the soils to adsorb DOP and PO4 increased with soil age. Stepwise multiple regression analyses between the adsorption capacity for DOP, or the slope of the adsorption isotherm for PO4, and several soil parameters showed that allophane concentrations control the adsorption of DOP and PO4 in these soils. Tests of preferential adsorption of DOP vs. PO4 and DOC vs. DOP showed that the adsorption strength increased in the following order: DOC < DOP < PO4 The preferential adsorption of PO4 vs. DOP and DOP vs. DOC increased significantly with increasing soil development, whereas the soil depth did not have a consistent and significant effect. Significant correlations between the null-point adsorption of DOP or PO4 and field soil solution concentrations indicated that the results obtained in laboratory experiments were applicable to field conditions. Consequently, the tendency of DOP and PO4 to leach from these andesitic soils decreases as soils and ecosystem develop.