Iron Isotope Fractionation during Bio- and Photodegradation of Organoferric Colloids in Boreal Humic Waters

Abstract

Adsorption of heavy Fe isotopes on heterotrophic bacteria cell surface Assimilation of light Fe isotopes by live P. aureofaciens cells Removal of heavy Fe isotopes from solution during sunlight oxidation of organo-ferric colloids Generation of isotopically light Fe(II) in LMW< 1 kDa during photolysis Bio-and photodegradation of organo-ferric colloids can produce very large, from-2.5 to +3.2‰

Large Fractionation in Iron Isotopes Implicates Metabolic Pathways for Iron Cycling in Boreal Shield Lakes

“…Photolysis of dissolved Fe complexed to DOC could enrich the dissolved phase in light Fe isotopes . In contrast, microbial decomposition of DOM followed by intracellular Fe uptake could make dissolved δ 56 Fe more positive . Our observed dissolved δ 56 Fe in the epilimnion and metalimnion of L227 is consistent with the isotopic values of microbial decomposition followed by intracellular uptake, but in contrast to the values of photolysis.…”

“…Other in-lake processes may also affect δ 56 Fe but probably to a lesser and largely unknown degree. Photolysis of dissolved Fe complexed to DOC could enrich the dissolved phase in light Fe isotopes . In contrast, microbial decomposition of DOM followed by intracellular Fe uptake could make dissolved δ 56 Fe more positive .…”

Seasonal Changes in Hydrology and Permafrost Degradation Control Mineral Element‐Bound DOC Transport From Permafrost Soils to Streams

“…During the peak flow to baseflow transition, the increase in Fe/Al ratio and Fe/DOC ratios show that more Fe is progressively transported as larger inorganic Fe oxyhydroxide colloids (rather than smaller Fe‐OC colloids). The change in the composition of Fe‐bearing colloids can be attributed to the degradation of Fe‐OC by abiotic (Neubauer, Köhler, et al., 2013; Neubauer, Schenkeveld, et al., 2013), microbial (Oleinikova et al., 2019; Oleinikova, Drozdova, et al., 2017; Oleinikova, Shirokova, et al., 2017) and light (Page et al., 2013) driven processes resulting in the formation of Fe oxyhydroxides and low molecular weight DOC (e.g., Oleinikova, Drozdova, et al., 2017; Oleinikova, Shirokova, et al., 2017; Porcal et al., 2009), likewise changes in colloidal Ca‐OC complexes during transport, result from the breakdown of Ca‐OC complexes and the formation of inorganic colloidal (Ingri & Widerlund, 1994) and dissolved phases. During the peak flow—baseflow transition, any pool of mineral element‐bound DOC transported unaltered from soils facing permafrost degradation must be disentangled from additional sources and/or the alteration of colloids during transport (beyond the scope of our study).…”

Contrasted redox-dependent structural control on Fe isotope fractionation during its adsorption onto and assimilation by heterotrophic soil bacteria

“…The remaining 10% are not detectable by spectroscopy but it is not excluded that they can be responsible for observed isotope fractionation, provided that the isotopic offsets of reactions with these minor compounds strongly exceed those of the major binding constituents of Fe. Recently, Oleinikova et al 69 studied the adsorption of organo-ferric colloids onto P. aureofaciens and demonstrated an enrichment in d 57 Fe (+0.4&) of cell surfaces compared to the remaining solution. Consistent with the results of Gonzalez et al 40 and of the present study, this could be explained by the dominance of Fe(III)-complexes with phosphoryl groups on cell surfaces.…”