Types of wetlands
Wetlands come in all kinds of shapes and sizes and each one is different.
Two wetland classification methods are commonly used in Minnesota. The mapping method used for the initial wetland protection program and the DNR-regulated waters inventory (public waters inventory) legislation of 1976 and 1979 was identified in "Wetlands of the United States," published as U.S. Fish and Wildlife Service Circular 39 Document by Shaw and Fredine in 1956 (reprinted 1971).
Eight wetland types are recognized in Minnesota, but none are assigned to rivers and lakes.
In 1979, the U.S. Fish and Wildlife Service published the Cowardin et al. method, "Classification of Wetlands and Deepwater Habitats in the United States." This comprehensive representation of all wetland habitats is used on the National Wetlands Inventory (NWI) Maps .
For more information on associated plant types, see Wetland Plants and Plant Communities of Minnesota and Wisconsin .
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Bogs, or peatlands, are wetlands whose soils are made up of peat (the partially decomposed remains of plants and animals). Northcentral Minnesota has extensive peatlands. Some good places to see these wetlands are at Lake Bemidji and Hayes Lake State Parks.
- Soil: Usually waterlogged
- Hydrology: Water table at or near the surface
- Vegetation: Woody, herbaceous, or both supporting a spongy covering of mosses; typical plants are heath shrubs, sphagnum mosses, sedges, leatherleaf, Labrador tea, cranberry, and cottongrass; may include stunted black spruce and tamarack
- Common sites: Mostly on shallow glacial lake basins and depressions, flat terrains, and along sluggish streams
- NWI Symbols: PFO2, 4, and 7B; PSS2, 3, 4, and 7B
Shallow and Deep marshes are the most familiar to us. These open areas provide food and resting areas for migratory birds and wildlife. In southern and western Minnesota these types of wetlands may be called prairie potholes. You can see this wetland type at many state parks including Lake Shetek, Sakatah Lake and William O'Brien.
- Soil: Usually waterlogged early during growing season
- Hydrology: Often covered with 6 inches or more of water
- Vegetation: Grasses; bulrush; spikerush; and various other marsh plants, such as cattail, arrowhead, pickerelweed, and smartweed
- Common sites: May nearly fill shallow lake basins or sloughs; may border deep marshes on landward side, commonly as seep areas near irrigated lands
- NWI Symbols: PEMC and F, PSSH, PUBA and C
- Soil: Inundated
- Hydrology: Usually covered with 6 inches to 3 feet or more of water during growing season
- Vegetation: Cattail, reed, bulrush, spikerush, and wild rice; open areas may have pondweed, naiad, coontail, watermilfoil, waterweed, duckweed, waterlily, and spatterdock
- Common sites: May completely fill shallow lake basins, potholes, limestone sinks, and sloughs; may border open water in such depressions
- NWI Symbols: L2ABF, L2EMF and G, L2US, PABF and G, PEMG and H, PUBB and F
Shallow open water
Shallow ponds and reservoirs are included in this wetland type.
Shallow open water
- Soil: Inundated
- Hydrology: Usually covered with less than 10-foot-deep water; includes shallow ponds and reservoirs
- Vegetation: Fringe of emergent vegetation similar to open areas of Type 4
- Common sites: Shallow lake basins and may border large open water basins
- NWI Symbols: L1; L2ABG and H; L2EMA, B, and H; L2RS; L2UB; PABH; PUBG and H
Prairie potholes are shallow depressions formed by retreating glaciers. They provide excellent habitat and breeding grounds for migratory birds. Sibley, Crow Wing, and Maplewood State Parks provide good examples of these wetlands.
Shrub and Wooded swamps are shrubby or forested wetlands found along the edges of lakes, rivers, and streams. Common wooded swamps are the black ash and black spruce forests found in Scenic, Wild River and Lac Qui Parle State Parks.
- Soil: Usually waterlogged during growing season
- Hydrology: Often covered with as much as 6 inches of water; water table is at or near the surface
- Vegetation: Includes alder, willow, buttonbrush, dogwood, and swamp privet
- Common sites: Along sluggish streams, drainage depressions, and occasionally on floodplains
- NWI Symbols: PSSA, C, F, and G; PSS1, 5, and 6B
- Soil: Waterlogged within a few inches of the surface during the growing season
- Hydrology: Often covered with as much as 1 foot of water; water table is at or near the surface
- Vegetation: Hardwood and coniferous swamps with tamarack, northern white cedar, black spruce, balsam fir, balsam poplar, red maple, and black ash; deciduous sites frequently support beds of duckweed and smartweed
- Common sites: Mostly in shallow ancient lake basins, old riverine oxbows, flat terrains, and along sluggish streams
- NWI Symbols: PFO1, 5, and 6B; PFOC and F
Seasonal basins or flats are small, isolated wetlands that contain water only seasonally. Once the water recedes they can be cropped in agricultural areas or logged in floodplain forests. These wetlands are important places for amphibians to reproduce and provide habitat for rare plant species. Seasonal basins or flats are found throughout Minnesota including Fort Snelling State Park.
- Soil: Usually well-drained during much of the growing season
- Hydrology: Covered with water or waterlogged during variable seasonal periods
- Vegetation: Varies greatly according to season and duration of flooding from bottomland hardwoods to herbaceous plants
- Common sites: Upland depressions, bottomland hardwoods (floodplain forests)
- NWI Symbols: PEMA, PFOA, PUS
Wet meadows are low-lying grassy areas with saturated soils often found near streams, lakes and marshes. They include low prairies, sedge meadows and rare calcareous fens.
- Soil: Saturated or nearly saturated during most of the growing season
- Hydrology: Usually without standing water during most of the growing season but waterlogged within at least a few inches of the surface
- Vegetation: Grasses, sedges, rushes, various broad-leaved plants
- Common sites: May fill shallow basins, sloughs, or farmland sags; may border shallow marshes on the landward side and include low prairies, sedge meadows, and calcareous fens
- NWI Symbols: PEMB
- Soil: Non-acidic, sedge-derived peat; saturated or nearly saturated during most of the growing season
- Hydrology: Constant, upwelling groundwater; waterlogged within at least a few inches of the surface with scattered small pools and rivulets
- Vegetation: Grasses, sedges, rushes, shrubs, various broad-leaved plants; many rare species
- Common sites: Calcareous fens are found throughout much of Minnesota, with the general exception of the northeast part of the state. They occur at the base of river terraces and glacial lake beach ridges and in other areas where confining layers force mineral-rich groundwater to the surface.
- NWI Symbols: PEMB, PSSB