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Microbially mediated kinetic sulfur isotope fractionation: reactive transport modeling benchmark


Microbially mediated sulfate reduction is a ubiquitous process in many subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate-reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S32O42−) over the heavier isotopologue (S34O42−). Detection of isotopic shifts has been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing heavy metal and radionuclide bioremediation. Reactive transport modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies. We developed a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction. The benchmark problem set is comprised of three problem levels and is based on a large-scale laboratory column experimental study of organic carbon amended sulfate reduction in soils from a uranium-contaminated aquifer. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and iron-sulfide reactions are included in the problem set. This benchmark also explores the different mathematical formulations in the representation of kinetic sulfur isotope fractionation as employed in the different RTMs. Participating RTM codes are the following: CrunchTope, TOUGHREACT, PHREEQC, and PHT3D. Across all problem levels, simulation results from all RTMs demonstrate reasonable agreement.

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This work was supported as part of the Watershed Function Science Focus Area at Lawrence Berkeley National Laboratory funded by the U.S. Department of Energy, Office of Science, Biological and Environmental Research under Contract No. DE-AC02-05CH11231. This work was also supported in part by the Energy Biosciences Institute. The authors would like to thank the reviewers for their constructive comments.This material is based upon work supported as part of the Energy Biosciences Institute and the Watershed Function Science Focus Area (SFA). The Watershed Function SFA at Lawrence Berkeley National Laboratory is funded by the U.S. Department of Energy, Office of Science, Biological and Environmental Research under Contract No. DE-AC02-05CH11231.


This material is based upon work supported as part of the Energy Biosciences Institute and the Watershed Function Science Focus Area (SFA).

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Correspondence to Yiwei Cheng.

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Cheng, Y., Arora, B., Şengör, S.S. et al. Microbially mediated kinetic sulfur isotope fractionation: reactive transport modeling benchmark. Comput Geosci 25, 1379–1391 (2021).

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  • Reactive transport modeling
  • Benchmark
  • Microbial sulfate reduction
  • S isotopes
  • Kinetic isotope fractionation