Microbial Fe(III) reduction in a minerotrophic wetland – geochemical controls and involvement in organic matter decomposition

Todorova, S., Siegel, D., and A.M. Costello. 2005.

Applied Geochemistry 20:1120-1130.

Abstract

 This paper presents the results of a study on the geochemistry of Fe in a minerotrophic wetland in Central New York. Fine-scale geochemical trends in the peat and peat porewater were investigated to evaluate detailed vertical profiles of Fe in solution. Two sites within the wetland were examined: one site adjacent to an agricultural field receiving nutrient inputs and another (pristine) site in the middle of the wetland. Results revealed that Fe(II) was produced in situ in the wetland, most probably as a result of microbial Fe(III) reduction. Iron(II) concentration profiles suggested the existence of Fe(III) reduction in the zone adjacent to the agricultural field, whereas no significant evidence for Fe(III) reduction occurred in the pristine zone. Theoretical equilibrium modeling predicted that the difference in soluble Fe concentrations between the two zones was probably caused by abiotic reactions, such as pyrite precipitation. Geochemically, a correlation between Fe(II) and bulk density showed the importance of Fe reduction in the decomposition of organic matter in the organic rich peat and demonstrated the importance of the mineralogical composition for the reduction of Fe(III). Finally, a unique reversal of Fe and SO(2-/4) reduction was discovered in the zone adjacent to the agricultural field.