One is the interaction of the soil with the watertable. There can also be vertical exchange of water between the groundwater and saturated soil. For example, capillary effects pull water upward into the soil from the water table. Besides the vertical and horizontal flow of water, the area of the soil taken up by water is important. Wetland soils are either saturated or nearly saturated so that much of the pore space is taken up by water.
Air plays a much more minor role in saturated soils than in unsaturated soil.
The high water content of these soils causes the chemistry to be primarily reducing rather than oxidizing as it is in most other soils. Most of the reactions are mediated by biological activities. Such a chemical environment means that the rate of decomposition of organic matter is relatively slow. Saturated soils tend to decompose organic matter slowly, transform nitrates, and reduce the solubility of metals such as iron. The species that inhabit saturated soils are adapted to the high water content and low oxygen content that characterize these soils.