Successive sorption–desorption cycles of dissolved organic matter in mineral soil matrices

Sorptive and desorptive behaviors of dissolved organic matter (DOM) were explored in three organic matter-poor, alkaline soils with different mineral compositions. Batch sorption data revealed a positive effect of soil metal oxide content on sorption affinity and capacity for DOM. In contrast, the role of soil texture in DOM sorption could not be substantiated. The alkalinity of the investigated soils did not seem to reduce their DOM sorption capabilities relative to less alkaline soils having comparable Fe-oxide contents. Our data obtained from sequential cycles of sorption showed similar behaviors suggesting that DOM sorption capacity was not affected by the sorbed DOM. Desorption isotherms revealed highly hysteretic behavior of DOM, with up to 83% of the sorbed DOM retained in the soil after four sequential desorption steps. Both soil surface area and metal oxide content related positively to the level of sorption–desorption hysteresis.