Redox gradients are commonly found in the environment as functions of both space and time, particularly in soils and aquatic environments. Gradients are caused by varying physiochemical properties including availability of oxygen, soil hydrology, chemical species present, and microbial processes. Specific environments that are commonly characterized by redox gradients include waterlogged soils, wetlands, contaminant plumes, and marine pelagic and hemipelagic sediments.
The following is a list of common reactions that occur in the environment in order from oxidizing to reducing (organisms performing the reaction in parentheses):
# Aerobic respiration (aerobes: aerobic organisms)
# Denitrification (denitrifiers: denitrifying bacteria)
# Manganese reduction (Manganese reducers)
# Iron reduction (iron reducers: iron-reducing bacteria)
# Sulfate reduction (sulfate reducers: Sulfur-reducing bacteria)
# Methanogenesis (methanogens)