Dissolution of Fe-Organic Associations by Peatland-Derived Phenolic Acids and Its Environmental Significance

Peatland is a type of wetland with global significance, and the study of the dissolution of phenolic-iron complexes by peat derived phenolic acids helps us to understand better the iron-carbon coupled geochemical cycle. In this study, humic substances were extracted from Jingchuan peatland soils and hematite, goethite, ferrihydrite and Fe-organic associations were synthesized. After that, a series of dissolution experiments were performed with three representative peatland-derived phenolic acids, including gallic acid, caffeic acid and protocatechuic acid. Results show that the amorphous ferrihydrite and the newly synthesized humic-Fe have weaker dissolution capacities, but the well-crystallized goethite, hematite and the humic-Fe after aging have better dissolution capacities, meanwhile the humic-Fe could be more stable in the phenolic acids solution than the pure iron oxides. It is confirmed that the organic iron makes up higher proportion in peatland soil, while the crystallized iron oxides make up higher proportion in mineral soils. The interaction between iron and carbon in peatland is complicated, where iron could be exported to aquatic ecosystem such as the ocean by complexing with iron, and organic carbon could also be preserved by forming Fe-organic complexes, thus affecting the global iron-carbon coupled geochemical cycle.