[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.
[6][5][1] Typical environments to measure redox potential are in bodies of water, soils, and sediments, all of which can exhibit high levels of heterogeneity.
[8][6] Gradients are caused by varying physiochemical properties including availability of oxygen, soil hydrology, chemical species present, and microbial processes.
[1][4][9][8] Specific environments that are commonly characterized by redox gradients include waterlogged soils, wetlands,[8] contaminant plumes,[9][4] and marine pelagic and hemipelagic sediments.
Benthic sediments exhibit redox gradients produced by variations in mineral composition, organic matter availability, structure, and sorption dynamics.
[1][8][6] In the event of a flood, saturated soils can shift from oxic to anoxic, creating a reducing environment as anaerobic microbial processes dominate.
[8] Redox gradients form based on resource availability and physiochemical conditions (pH, salinity, temperature) and support stratified communities of microbes.
[5] Due to this heterogeneity, gradients of reducing and oxidizing chemical species do not always overlap enough to support electron transport needs of niche microbial communities.
[5] Biofilms, found in tidal flats, glaciers, hydrothermal vents, and at the bottoms of aquatic environments, also exhibit redox gradients.