Association with solid-phase iron plays an important role in accumulation and stabilization of soil organic matter (SOM). Ferric minerals are subject to redox reactions, which can compromise the stability of iron-bound SOM. To date, limited information is available concerning the fate of iron-bound SOM during redox reactions. Herein, we investigated the release kinetics of hematite-bound organic carbon (OC) during abiotic reduction of hematite-humic acid (HA) complexes by dithionite, as an analog for the fate of iron-bound SOM in natural redox reactions. Our results indicate that the iron reduction release obeyed first-order kinetics. Initially, iron-bound OC was rapidly released and then became stable with residual fractions of 4.6% to 58.2% between 120 and 240 min. Aromatic carbon was released rapidly than overall OC. For all samples, 90% of aromatic carbon was released in first hour. Rapid release of aromatic OC was attributed to its potential distribution on the outer layer because of steric effects and possible reduction of quinoids. Our findings show that iron-bound OC and iron were asynchronously mobilized and aromatic carbon was released more readily than other organic components during iron reduction. This study illustrates the importance of evaluating the stability of iron-bound SOM, especially under aerobic-anaerobic transition conditions.<br/><br/>Note: Recipient of the Student Travel Award

Asynchronous mobilization of iron and organic carbon from hematite-humic acid complexes during abiotic iron reduction

251st National Meeting (2016)

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