Preprints
https://doi.org/10.5194/bg-2021-253
https://doi.org/10.5194/bg-2021-253

  15 Nov 2021

15 Nov 2021

Review status: this preprint is currently under review for the journal BG.

Aqueous system-level processes and prokaryote assemblages in the ferruginous and sulfate-rich bottom waters of a post-mining lake

Daniel A. Petrash1,2, Ingrid M. Steenbergen1,3, Astolfo Valero1,3, Travis B. Meador1,3, Tomáš Pačes2, and Christophe Thomazo4,5 Daniel A. Petrash et al.
  • 1Biology Centre of the Czech Academy of Sciences, České Budějovice, 370 05, Czechia
  • 2Czech Geological Survey, Prague, 152 00, Czechia
  • 3University of South Bohemia, České Budějovice, 370 05, Czechia
  • 4University of Burgundy, Dijon, 21000, France
  • 5Institut Universitaire de France, Paris, 75000, France

Abstract. In the aqueous oligotrophic ecosystem of a post-mining lake (Lake Medard, Czechia), reductive Fe(II) dissolution outpaces sulfide generation from microbial sulfate reduction (MSR), and ferruginous conditions occur without quantitative sulfate depletion. An isotopically constrained estimate of the rates of sulfate reduction (SRR) suggests that despite a high genetic potential, this respiration pathway is limited by the rather low amounts of metabolizable organic carbon. This points to substrate competition exerted by iron and nitrogen respiring prokaryotes. Yet, the microbial succession across the nitrogenous and ferruginous zones of the bottom water column also indicates sustained genetic potential for chemolithotrophic sulfur oxidation. Therefore, our isotopic SRR estimates could be rather portraying high rates of anoxic sulfide oxidation to sulfate, probably accompanied by microbially induced disproportionation of S intermediates. Near and at the anoxic sediment-water interface, vigorous sulfur cycling can be fuelled by ferric and manganic particulate matter and redeposited siderite stocks. Sulfur oxidation and disproportionation then appear to prevent substantial stabilization of iron monosulfides as pyrite but can enable the interstitial precipitation of small proportions of equant microcrystalline gypsum. This latter mineral isotopically fingerprints sulfur oxidation proceeding at near equilibrium with the ambient anoxic waters, whilst authigenic pyrite-sulfur displays a 38 to 27 ‰ isotopic offset from ambient sulfate, suggestive of incomplete MSR and likely reflective also of an open sulfur cycling system. Pyrite-sulfur fractionation decreases with increased reducible reactive iron in the sediment. In the absence of ferruginous coastal zones today, the current water column redox stratification in the post-mining Lake Medard has scientific value for (i) testing emerging hypotheses on how a few interlinked biogeochemical cycles operated in nearshore paleoenvironments during redox transitional states; and (ii) to acquire insight on how similar early diagenetic redox proxy signals developed in sediments affected by analogue transitional states in ancient water columns.

Daniel A. Petrash et al.

Status: open (until 27 Dec 2021)

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  • RC1: 'Comment on bg-2021-253', Anonymous Referee #1, 30 Nov 2021 reply

Daniel A. Petrash et al.

Data sets

Planktonic prokaryote microbiome: bottom ferruginous/sulfate-rich water column of a lignite post-mining lake, NW Czechia Ingrid M. Steenbergen & Daniel A. Petrash https://www.ebi.ac.uk/

Daniel A. Petrash et al.

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Short summary
We spectroscopically evaluated the gradients of dissolved C, N, S, Fe and Mn in a newly formed redox stratified lake. The lake features an intermediate redox state between nitrogenous and euxinic conditions that encompass vigorous open sulfur cycling, fuelled by the reducible Fe and Mn stocks of the anoxic sediments. This results in substantial bottom water loads of dissolved Fe and sulfate. Observations made in this ecosystem have relevance for deep time paleoceanographic reconstructions.
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