Nitrogen related processes in Wetlands
Wetland soils are mostly anerobic, with a small aerobic layer at the top. As a result, nitrogen cycling involves both anerobic and aerobic processes, and many plants utilize nitrogen when oxygen is unavailiable. Excepting oxygenated areas surrounding roots (rhizosphere), nitrogen is an essential wetland nutrient. The nitrogen cycle in a wetland is only somewhat different than the terrestrial cycle. This difference is mainly because the anerobic soils affect where certain processes can occur.
The change of organic nitrogen to ammonium nitrogen (NH4+) is ammonification, possible in both aerobic and anerobic conditions. Ammonium nitrogen, as the product, can be absorbed and utilized by anaerobic microorganisms and plants. Plants generally utilize this nitrogen through symbiotic relationships with bacteria in their roots which are able to uptake and process the nitrogen. Ammonium nitrogen can also be secured onto soil particles (negatively charged). This process is responsible for some of the nitrogen unavailability in wetlands. Ammonification is more common in anerobic soils, and as the concentration of ammonium nitrogen increases it diffuses up into the oxidized soil layer, where nitrification occurs.
Nitrification is the conversion of ammonium nitrogen to nitrate (NO3-), an aerobic process (requiring oxygen), resulting in a more moveable form of nitrogen than ammonium nitrogen. In this process, ammonium is oxidized to form nitrate. Nitrates are generally either quickly utilized by plants or just as quickly lost through groundwater outflows. Otherwise, they are quickly reduced to ammonium nitrogen or proceed through denitrification. Denitrification occurs when high concentrations of nitrates force a diffusion back into the anerobic soil.
Denitrification converts nitrate to the nitrous oxide gas (N20) and nitrogen (N2). This is generally done by anerobic bacteria, such as genera members Bacillus and Pseudomonas. Nitrous gas escapes into the atmosphere, while nitrogen remains in the system to undergo nitrogen cycling. This is the most common way for nitrogen to escape from wetland soils.