Sequence of chemical compounds being reduced in soil after submergence Oxidized Slightly Reduced Moderately Reduced Severely Reduced NO3- H2O MnO2 N2 Mn2+ Fe3+ Fe2+ SO4-2 CO2 H2S CH4 Reaction sequence following submergence Reaction sequence after draining

Chemical Compounds in Aerated Soil Nitrate Manganese (IV) dioxide Iron (III) Hydroxide Sulfate Carbon dioxide Submerging soil causes a change from aerobic to anaerobic organisms Anaerobic bacteria cause a sequence of chemical reductions during respiration Nitrogen gas Manganese (II) ion Iron (II) ion Hydrogen Sulfide Methane Chemical Compounds in Submerged Soil

Oxygen (O2) in the soil is reduced to water (H2O) Oxygen (O2) in the soil is reduced to water (H2O). It is the first to undergo reduction and O2 levels are undetectable within a day. Manganese oxide (MnO2) is reduced to Manganese ion (Mn2+) Redox Potential (mV) Nitrate (NO3) is the next to be reduced after O2 concentrations are already low. Nitrate reduces to nitrogen gas (N2) in a process called denitrification. O2 Carbon dioxide (CO2) is reduced to methane (CH4) CO2 NO2 Iron hydroxide (Fe(OH)3 is reduced to iron ions (Fe2+). Mn2+ NH4 Fe2+ Sulphate (SO42-) is reduced to (H2S) SO42- Reaction Sequence in Anaerobic Soils Reaction Sequence in Reaerated Soils