Potential adsorption of dissolved organic matter in poorly podzolised, high-latitude soils

Abstract

Dissolved organic matter (DOM) plays an essential role in many biogeochemical processes in soil and water, and the retention of DOM in soils influences the amount and composition of DOM exported from terrestrial to aquatic ecosystems. Adsorption in soil mineral horizons is considered a main mechanism by which DOM is retained and stabilised in soils, and podzol soils have received attention due to their capacity to retain DOM in the mineral B horizon. With the projected increase in temperature and precipitation at higher latitudes, the transport of organic matter is expected to increase, but few studies have investigated the adsorption of DOM in poorly podzolised soils at higher latitudes. In this study, we used batch equilibrium experiments to investigate the potential for DOM adsorption in the B horizon of poorly podzolised soils from a confined area in Neiden, northern Norway. We used the Initial Mass (IM) isotherm to describe the amount of dissolved organic carbon (DOC) removed from or released to solution by the soil as a linear function of the amount of DOC added to the soil–water suspension.Our results suggest that the affinity for DOC of B horizons in poorly podzolised high-latitude soils is largely determined by the content of amorphous Fe and Al oxides, where adsorption is limited by the saturation of amorphous Fe and Al with organic matter. The B horizons show a relatively large variation in DOC sorption characteristics, with an overall low potential to adsorb added DOC at field relevant DOC concentrations. Six out of twelve B horizons show a net DOC desorption over the whole range of added DOC (0–480mgCkg−1 soil). These findings indicate a limited potential for retention and stabilisation of DOM in poorly podzolised soils at higher latitudes in a warmer and wetter climate.