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]
^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. PMID25461044. S2CID24877798.
^Libes, Susan (2009). Introduction to marine biogeochemistry. Amsterdam Boston: Elsevier/Academic Press. ISBN978-0-08-091664-4. OCLC643573176.