Climate warming is expected to have significant impact on the rate and extent of permafrost soil organic matter (SOM) degradation, but what remains elusive is to what extent the molecular-scale interactions between SOM and minerals such as SOM-iron complexation control the partitioning, stabilization, and respiration of SOM and its overall rates of mineralization. SOM is a complex mixture of polyfunctional organic compounds with varying pKa values, redox potenitals, aromaticities, and functional groups. Laboratory studies indicate that these organic compounds exhibit varying reactivities with iron and iron oxide minerals, resulting in sorption-desorption hysteresis, preferential transport and preservation over time and depth. These findings have important implications to the availability and functionality of different carbon pools influencing microbial metabolic rates. Field studies at Barrow Envroionmental Observatory, Alaska, show that dissolved organic matter (DOM) and iron are dominant ionic species in both surface waters and soil pore fluids in permafrost, and high ferrous iron concentrations up to 1 mM are observed in the pore water. Furthermore, ferrous iron increases with depth in the soil, suggesting that DOM-complexed ferric iron likely serves as an electron acceptor, driving organic matter respiration in oxygen-limited subsurface. These findings are important for developing a computational modeling framework in predicting feedbacks to warming climate.

Effects of iron and iron-oxides on the adsorption, transport, and degradation of soil organic matter

247th National Meeting (2014)

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