Characteristics of Wetlands
From just these definitions, it is clear that a wetland has soil that becomes saturated from precipitation, bodies of water such as rivers and oceans, or from ground water. The saturation must be predictable to some extent. The saturation may be relatively constant at the edge of a river or other permanent body of water like a lake. It may happen daily, where tides flood the area and recede. It may become saturated seasonally for extended periods by rain or snow raising the water table.
This saturation impacts the soil and what lives in it. Dry soil has pockets of air in it providing oxygen to plants, bacteria, and animals for respiration. When air in the soil is replaced by water, as in gleyed soil, it changes the types of bacteria that live in the soil. The type of bacteria will impact the acidity of the soil and decomposition. Hydric soil can be anaerobic with anaerobic bacteria or functional anaerobic bacteria living in wetland soil. These anaerobic bacteria give wetlands the methane and sulfur smell often associated with them. Some are responsible for maintaining the nitrogen cycle. Others maintain the sulfur cycle. The reducing of inorganic molecules by bacteria in wetlands give rise to the hydric soil.
Any mix of interdependent plants and animals are shaped by their physical environment of air, land, and water. In wetlands, ignoring latitude, water - how much there is, how often and long it saturates the soil - with the salinity and pH shapes everything else. Abiotic conditions shape plant species mix. Plants, as the basis for the food web, with hydrology and latitude shape what animals live in a wetland.