Soil Taxonomy as defined by the USDA does not delineate between wetland, desert or any other type of above-surface terrain as it relates to moisture content. While terrain according to vegetation can have some bearing, soil orders and suborders are defined according to the layout and content of the stratified layers, called horizons, which make up soil. Wetlands are made up any combination of three possible soil suborders: Aquert, Fibrist and Saprist.
Aquerts are members of the Vertisol order and are found only in Louisiana, Mississippi, Alabama and the Great Lakes. They contain loam and high amounts of clay called montmorillonite, resulting in very low water permeability. Regardless of water table, the presence of Aquerts in high amounts results in a pond or standing water, contributing to the creation of many wetland environments. This suborder is the most fertile of the Vertisols, invariably possessing high iron and manganese deposits, which account for its dark brown to black coloring.
Saprists are a suborder of Histosol which are found in Florida, Michigan, Wisconsin, Alaska, and Minnesota. They spend the majority if not the entirety of the year submerged, and because of that have had much of their major plant nutrients such as nitrogen, potassium, and phosphorous washed away. To be a Saprist, the top 80 centimeters of soil must contain 50 percent decayed organic plant matter. Because of this, Saprists contain high amounts of muck, which can be dried and used for fuel because of its high carbon content.
Fibrists are another suborder of Histosol, and somewhat rarer. The only place they appear in North America is the lowlands of Alaska. Like Saprists, Fibrists must contain a minimum of 50 percent decaying plant matter or 12 percent organic carbon by weight to qualify. But unlike Saprists, Fibrists spend at least half of every year above water. This results in a lower density of decaying plant matter, which is classified as peat rather than muck for this reason.