A wetland is any biome where an expanse of water (generally stagnant) dominates the landscape. While smaller wetlands may occur naturally in Tropical biomes, larger stable wetlands form from major Rivers flooding an area of land. Wetlands can be both freshwater and saltwater.
Categories of Wetland
Different wetlands are groups by what types of wildlife they can support, and how they are formed.
Swamp: Swamps contain high amount of well-mixed decayed nutrients, and can easily support denser populations of large flora (above 2 m)
Marsh: These floodplains are constantly recycling their water, and so are better suited for smaller, more flexible flora. Marshes are generally freshwater, filtering salts from neighboring saltwater regions.
Bog: Bogs form over longer periods of time as decaying floral matter forms a thick layer of peat on the ground. This peat layer restricts nutrient flow, preventing large populations of flora from growing.
Fen: Fens are similar to bogs, with the exception that they form close to a Water Table. The water table provides a constant slow flow of water, which allows nutrients to mix. Thus fens can support slightly greater populations than bogs.