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SOIL CHEMISTRY

Soil Properties Controlling the Adsorption of Dissolved Organic Carbon to Mineral Soils

^a Dep. of Geography and Global Environmental & Climate Change Center (GEC³), McGill Univ., 805 Sherbrooke St. West, Montréal, QC, H3A 2K6 Canada
^b Dep. of Natural Resource Sciences, Macdonald Campus, McGill Univ., 21, 111 Lakeshore Rd., Ste-Anne-de-Bellevue, Montréal, QC, Canada

^* Corresponding author (dollykothawala{at}trentu.ca).

Dissolved organic C (DOC) is the most reactive and mobile component of soil C and can be retained within mineral soils by adsorption. We determined the adsorption characteristics for 52 mineral soil samples from 17 temperate and boreal soil profiles, using a modified Langmuir equation. The DOC solution used for batch experiments was derived from the organic horizons of a Spodosol. We analyzed the extent to which soil properties, such as the sum of poorly crystalline Fe and Al (Fe_pc + Al_pc), texture, and soil C, are related to DOC adsorption to mineral soils. Sorption characteristics including the maximum adsorption capacity (Q_max), and the null point (np), where adsorption equals desorption, were best explained by Fe_pc + Al_pc (R² = 0.55 and 0.28, respectively). The Al_pc exerted a stronger influence than Fe_pc on Q_max. A simple method for estimating Q_max was developed whereby the change in pOH after treatment with NaF is well correlated to Fe_pc + Al_pc (R² = 0.71, P < 0.0001) and Q_max (R² = 0.50, P < 0.0001). The influence of clay content on Q_max was of secondary importance and was largely masked by the dominant influence of Fe_pc + Al_pc. Soil C did not have any influence on Q_max, but a slight negative influence on np. The B horizons of Spodosols and volcanic soils had the greatest Q_max, while large levels of soil C in Spodosols produced a high desorption potential. Results from this study emphasize the importance of considering the adsorption potential in conjunction with the desorption potential for better prediction of changes to the size of mineral soil C pools and DOC export to aquatic systems.

Abbreviations: Al_o, oxalate-extractable aluminum • Al_p, pyrophosphate-extractable aluminum • Al_pc, poorly crystalline aluminum • C_p, pyrophosphate-extractable carbon • DOC, dissolved organic carbon • ECEC, effective cation exchange capacity • Fe_cry, crystalline iron • Fe_d, dithionite-extractable iron • Fe_o, oxalate-extractable iron • Fe_p, pyrophosphate-extractable iron • Fe_pc, poorly crystalline iron • IM, initial mass • SMR, stepwise multiple regression