Redox gradient

For broader coverage of this topic, see Redox and Reduction potential.
Depiction of common redox reactions in the environment. Adapted from figures by Zhang[1] and Gorny.[2] Redox pairs are listed with the oxidizer (electron acceptor) in red and the reducer (electron donator) in black.
Relative favorability of redox reactions in marine sediments based on energy. Start points of arrows indicate energy associated with half-cell reaction. Lengths of arrows indicate an estimate of Gibb's free energy (ΔG) for the reaction where a higher ΔG is more energetically favorable (Adapted from Libes, 2011).[3]

A redox gradient is a series of reduction-oxidation (redox) reactions sorted according to redox potential.[4][5] The redox ladder displays the order in which redox reactions occur based on the free energy gained from redox pairs.[4][5][6] These redox gradients form both spatially and temporally as a result of differences in microbial processes, chemical composition of the environment, and oxidative potential.[5][4] Common environments where redox gradients exist are coastal marshes, lakes, contaminant plumes, and soils.[1][4][5][6]

The Earth has a global redox gradient with an oxidizing environment at the surface and increasingly reducing conditions below the surface.[4] Redox gradients are generally understood at the macro level, but characterization of redox reactions in heterogeneous environments at the micro-scale require further research and more sophisticated measurement techniques.[5][1][7][6]

  1. ^ a b c Zhang, Zengyu; Furman, Alex (2021). "Soil redox dynamics under dynamic hydrologic regimes - A review". Science of the Total Environment. 763: 143026. Bibcode:2021ScTEn.76343026Z. doi:10.1016/j.scitotenv.2020.143026. ISSN 0048-9697. PMID 33143917. S2CID 226249448.
  2. ^ Gorny, J.; Billon, G.; Lesven, L.; Dumoulin, D.; Madé, B.; Noiriel, C. (2015). "Arsenic behavior in river sediments under redox gradient: a review". The Science of the Total Environment. 505: 423–434. doi:10.1016/j.scitotenv.2014.10.011. PMID 25461044. S2CID 24877798.
  3. ^ Libes, Susan (2009). Introduction to marine biogeochemistry. Amsterdam Boston: Elsevier/Academic Press. ISBN 978-0-08-091664-4. OCLC 643573176.
  4. ^ a b c d e Borch, Thomas; Kretzschmar, Ruben; Kappler, Andreas; Cappellen, Philippe Van; Ginder-Vogel, Matthew; Voegelin, Andreas; Campbell, Kate (2009). "Biogeochemical Redox Processes and their Impact on Contaminant Dynamics". Environmental Science & Technology. 44 (1). American Chemical Society (ACS): 15–23. doi:10.1021/es9026248. ISSN 0013-936X. PMID 20000681. S2CID 206997593.
  5. ^ a b c d e Lau, Maximilian Peter; Niederdorfer, Robert; Sepulveda-Jauregui, Armando; Hupfer, Michael (2018). "Synthesizing redox biogeochemistry at aquatic interfaces". Limnologica. 68: 59–70. Bibcode:2018Limng..68...59L. doi:10.1016/j.limno.2017.08.001.
  6. ^ a b c Peiffer, S.; Kappler, A.; Haderlein, S. B.; Schmidt, C.; Byrne, J. M.; Kleindienst, S.; Vogt, C.; Richnow, H. H.; Obst, M.; Angenent, L. T.; Bryce, C. (2021). "A biogeochemical–hydrological framework for the role of redox-active compounds in aquatic systems". Nature Geoscience. 14 (5): 264–272. Bibcode:2021NatGe..14..264P. doi:10.1038/s41561-021-00742-z. ISSN 1752-0894. S2CID 233876038.
  7. ^ Zakem, Emily J.; Polz, Martin F.; Follows, Michael J. (2020). "Redox-informed models of global biogeochemical cycles". Nature Communications. 11 (1): 5680. Bibcode:2020NatCo..11.5680Z. doi:10.1038/s41467-020-19454-w. ISSN 2041-1723. PMC 7656242. PMID 33173062.