Geochemical interactions between iron and phenolics originated from peatland in Hani, China: implications for effective transport of iron from terrestrial systems to marine

Iron is a restrictive element for primary productivity in the oceans. The influence of dissolved organic matters as metal chelators on the bio-available iron input to the ocean has been widely reported. However, natural dissolved organic matters, especially the phenolics originated from peatlands and geochemical interactions with iron remains poorly understood. In this study, solid phase extraction-high performance liquid chromatography experiments were conducted to determine the vertical distributions of phenolic acids in different peat layers in Hani Peatland, China. Ten phenolic acids, including protocatechuic acid, p-hydroxybenzoic acid, gentisic acid, caffeic acid, etc. were detected. Simulation experiments of phenolics-Fe interactions under alkaline conditions (pH = 8.0 ± 0.1) indicated phenolic acids bearing either catechol or galloyl groups (such as protocatechuic acid, caffeic acid and gallic acid) could chelate iron to produce relatively stable phenolics-Fe complexes and therefore help to weaken its precipitation in the oxidative condition. In addition, the simulation experiments with artificial coastal waters demonstrated that this complexation could ensure that at least 25 % of the initial Fe load dissolve in coastal water, implying large part of dissolved iron in rivers draining from peatlands could be transported through the estuarine zones. Considering the wide distribution of peatlands globally, the higher concentration of Fe in peatlands, and the enhancement of marine organisms by Fe, the geochemical interactions between iron and phenolics originated from peatlands are of important significance to transport bio-available iron from terrestrial system to oceans.