Simple Sulfate Reduction Model Example

[Isaac Prud'homme]

Hi all,

I'm attempting to model microbial sulfate reduction and pyrite mineral kinetics within a coastal wetland. All examples I have found of sulfate reduction within PFLOTRAN have been tied to land surface models (like ELM) which is more complex than my expertise.

Seeing a simpler example of these reactions or any tips on adapting the aerobic_respiration shortcourse for sulfate reduction would be much appreciated!

Thanks!

Isaac

[Hammond, Glenn E]

Isaac,

Thank you for reaching out with your question. From your mention of ELM, I gather you may have seen Ben Sulman’s paper (https://doi.org/10.1029/2023MS004002). To keep things simple, I recommend narrowing the reaction network in Table 1 to just the sulfate reduction and pyrite mineral precipitation-dissolution processes. As a starting point, you can refer to this regression test:

https://bitbucket.org/pflotran/pflotran/src/master/regression_tests/default/column/pyrite_dissolution.in 

To incorporate microbially mediated sulfate reduction, follow the aerobic respiration example from the short course, but use the inhibited version of the reaction for better performance once acceptor or donor is depleted:

https://bitbucket.org/pflotran/pflotran/src/master/shortcourse/exercises/0D_aerobic_respiration/inhibited_aerobic_respiration.in 

Make sure to designate SO4-- and HS- as primary species in your input deck to include them within the kinetic microbial reaction:

CH3COO- + SO4-- + 2 H+ → 2 CO2 + HS-

It’s necessary to replace SO4-- with HSO4- and O2(aq) with HS- in your configuration. Essentially, this adjustment means that HSO4- and O2(aq) will now be treated as secondary species within your model.

If you encounter any challenges, please share your input deck with us and we can work through it together. Working through these details will help you grow and refine your approach.

Regards,

Glenn

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Date: Saturday, April 4, 2026 at 10:16 AM
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[Isaac Prud'homme]

Glenn,

Thank you very much for your insight! I believe I've correctly set up the pyrite and sulfate reduction reactions based on Table 1 (Sulman) and included an immobile biomass from the inhibited aerobic respiration exercise.

Currently I'm hung up on where to replace SO4--  with HSO4- and O2(aq) with HS- within my configuration as well as how to begin setting up my constraints.

A secondary thing I noticed is that CH3COO- isn't present within my hanford.dat, is there a newer version that I should be utilizing?

Happy Easter!

Isaac

[Hammond, Glenn E]

Isaac,

I've swapped the species as discussed; however, I suggest revising the reaction expressions to use O2(aq) instead of HS-. Doing so allows inhibition when O2(aq) is present, since the code currently requires the inhibition species to be a primary species.

Additionally, I've added CH3COO- to the attached database.

I've commented out the FeS2 microbial reaction because the pyrite precipitation-dissolution reaction already manages pyrite dissolution. Should you want to incorporate microbially mediated pyrite dissolution, that would need to be set up in a reaction sandbox.

The attached input deck runs, but it will likely need further refinement.

Glenn

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