Dissolved organic matter retention in volcanic soils with contrasting mineralogy: a column sorption experiment

There is an increasing recognition that sorption and precipitation reactions between the dissolved phase of organic matter and reactive minerals and metals found in soils are an important carbon stabilization mechanism. We explored the relative importance of this sorption mechanism with pedological shifts in soil properties by conducting a dissolved organic matter leaching/sorption experiment using intact soil cores from a substrate/age gradient in Hawai’i. In the subsurface horizons, sorption of dissolved organic carbon was often positively correlated short-range ordered (SRO) mineral content, with sorption rates approaching 100% when SRO minerals dominated. Dissolved organic matter sorption in the presence of SRO minerals was highly selective towards aromatic compounds, consistent with prior nuclear magnetic resonance spectroscopy conducted on carbon found in SRO rich mineral soil. In subsurface horizons where SRO content was low (youngest and oldest sites in the chronosequence), sorption was also found to be high but much less selective, more reversible and more degradable indicating that different stabilization mechanisms are operative. These experimental results provide further evidence for a direct mechanism by which volcanic soils are able to store disproportionately high amount of soil organic matter via retention of aromatic acids.