Transformation of organo-ferric peat colloids by a heterotrophic bacterium

Olga V. Oleinikova (1) , Liudmila S. Shirokova (1) , Emmanuele Gérard (2) , Olga Yu. Drozdova , Sergey A. Lapitskiy , Andrey Yu. Bychkov , Oleg S. Pokrovsky (1)

1 GET - Géosciences Environnement Toulouse
2 IPGP - Institut de Physique du Globe de Paris

Bacterial mineralization of allochthonous (soil) dissolved organic matter (DOM) in boreal waters governs the CO₂ flux from the lakes and rivers to the atmosphere, which is one of the main factor of carbon balance in high latitudes. However, the fate of colloidal trace element (TE) during bacterial processing of DOM remains poorly constrained. We separated monoculture of Pseudomonas saponiphila from a boreal creek and allowed it to react with boreal Fe-rich peat leachate of approximate colloidal (3 kDa-0.45 μm) composition C₁₀₀₀Fe₁₂Al_3.3Mg₂Ca_3.7P_1.2Mn_0.1Ba_0.5 in nutrient-free media. The total net decrease of Dissolved Organic Carbon (DOC) concentration over 4 day of exposure was within 5% of the initial value, whereas the low molecular weight fraction of C_org (LMW_{<3 kDa}) yielded a 16%-decrease due to long-term bio-uptake or coagulation. There was a relative depletion in Fe over C_org of 0.45 μm, colloidal and LMW fraction in the course of peat leachate interaction with P. saponiphila. Al, Mn, Ni, Cu, Ga, REEs, Y, U were mostly affected by bacterial presence and exhibited essentially the adsorption at the cell surface over first hours of reaction, in contrast to Fe, Ti, Zr, and Nb that showed both short-term adsorption and long-term removal by physical coagulation/coprecipitation with Fe hydroxide. The low molecular weight fraction (LMW_{<3 kDa}) of most TE was a factor of 2-5 less affected by microbial presence via adsorption or removal than the high molecular weight (HMW) colloidal fractions (<0.45 μm and <50 kDa). The climate change-induced acceleration of heterotrophic bacterial activity in boreal and subarctic waters may lead to preferential removal of Fe over DOC from conventionally dissolved fraction and the decrease of the proportion of LMW < 3 kDa fraction and the increase of HMW colloids. Enhanced heterotrophic mineralization of organo-ferric colloids under climate warming scenario may compensate for on-going "browning" of surface waters.

Mots clés: Organic carbon; DOC; Fe; Al; Trace element; Biodegradation; Adsorption; Coagulation; Precipitation; Boreal; Water

Domaines: Planète et Univers [physics]

Olga V. Oleinikova, Liudmila S. Shirokova, Emmanuele Gérard, Olga Yu. Drozdova, Sergey A. Lapitskiy, et al.. Transformation of organo-ferric peat colloids by a heterotrophic bacterium. Geochimica et Cosmochimica Acta, 2017, 205, pp.313-330. ⟨10.1016/j.gca.2017.02.029⟩. ⟨insu-03661376⟩