Dissimilatory reduction and transformation of ferrihydrite-humic acid coprecipitates.
Organic matter (OM) is present in most terrestrial environments and is often found coprecipitated with ferrihydrite (Fh). Sorption or coprecipitation of OM with Fe oxides has been proposed to be an important mechanism for long-term C preservation. However, little is known about the impact of coprecipitated OM on reductive dissolution and transformation of Fe(III) (oxyhydr)oxides. Thus, we study the effect of humic acid (HA) coprecipitation on Fh reduction and secondary mineral formation by the dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens strain CN32. Despite similar crystal structure for all coprecipitates investigated, resembling 2-line Fh, the presence of coprecipitated HA resulted in lower specific surface areas. In terms of reactivity, coprecipitated HA resulted in slower Fh bioreduction rates at low C/Fe ratios (i.e., C/Fe ≤ 0.8), while high C/Fe ratios (i.e., C/Fe ≥ 1.8) enhanced the extent of bioreduction compared to pure Fh. The coprecipitated HA also altered the secondary Fe mineralization pathway by inhibiting goethite formation, reducing the amount of magnetite formation, and increasing the formation of a green rust-like phase. This study indicates that coprecipitated OM may influence the rates, pathway, and mineralogy of biogeochemical Fe cycling and anaerobic Fe respiration within soils.
Department of Soil and Crop Sciences, Colorado State University , Fort Collins, Colorado 80523, United States.
Masayuki
M
Shimizu
Jihai
J
Zhou
Christian
C
Schröder
Martin
M
Obst
Andreas
A
Kappler
Thomas
T
Borch
D011232:Chemical Precipitation; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism*; D052203:Ferrosoferric Oxide / Q000737:chemistry / Q000378:metabolism; D006812:Humic Substances; D058085:Iron Compounds / Q000737:chemistry / Q000378:metabolism; D008903:Minerals / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D020614:Shewanella putrefaciens / Q000378:metabolism
D005290:Ferric Compounds; D006812:Humic Substances; D058085:Iron Compounds; D008903:Minerals; C094886:goethite; C092844:ferric oxyhydroxide; D052203:Ferrosoferric Oxide