Types of wetlands

There are many types of wetlands in Minnesota with widely varying characterists. Some are dry for much of the year; others are almost always covered by water several feet deep. Wetland vegetation may be grasses and sedges, shrubs, or trees. They may be very small confined basins or they may extend for hundreds of miles. Over the years, a variety of classification methods have been developed to categorize and describe the various wetland types.

Several wetland classification methods are commonly used in Minnesota:

  • Circular 39 - The "Circular 39" classification system, published as "U.S. Fish and Wildlife Service Circular 39" (Shaw and Fredine, 1956, reprinted 1971) is used for the DNR Public Waters Inventory, which identifies wetlands, as well as lakes and streams, regulated by the DNR. Under Circular 39, eight wetland types are recognized in Minnesota.
  • Cowardin - The National Wetlands Inventory, a comprehensive wetland mapping program, uses the Cowardin system of wetlands classification, described in the U.S. Fish and Wildlife Service report "Classification of Wetlands and Deepwater Habitats in the United States" (Cowardin et al., 1979 and FGDC, 2013). The DNR is currently in the process of updating the National Wetland Inventory Maps for Minnesota.
  • Egges and Reed - The Eggers and Reed classification system is a descriptive approach based on wetland plant communities, developed specifically for Minnesota and Wisconsin ("Wetland Plants and Plant Communities of Minnesota and Wisconin," 3rd Edition, 2011.)
  • Native Plant Community Classification - The Native Plant Community Classification, developed by the DNR, is not strictly a wetland classification system but it does include classifications and descriptions of the various types of wetlands found in Minnesota.

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Bogs

Bogs, or peatlands, are wetlands whose soils are made up of peat, which is the partially decomposed remains of plants. Northcentral Minnesota has among the most extensive peatlands in the lower 48 states. Some good places to see these wetlands are at Lake Bemidji and Hayes Lake State Parks and the Big Bog State Recreation Area, which has a mile-long boardwalk into the bog.

  • Soil/Hydrology: Peat (organic) soil, with the water table at or near the soil surface year-round
  • 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
  • Classifications:
    • Circular 39: Type 8
    • NWI (Cowardin) Symbols: PFO2, 4, and 7B; PSS2, 3, 4, and 7B
    • Eggers & Reed: Bogs
    • Native Plant Community Classification: APn, FPn, FPs, FPw, OPn

Marshes

Shallow and Deep marshes are prehaps the most familiar wetland types to most Minnesotans. These water-filled basins, with a mix of open water, emergent and submergent vegetation provide food and resting areas for a wide variety of 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.

Shallow Marsh

  • Soil/Hydrology: Organic or mineral soil, usually waterlogged early during growing season and often covered with six 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; lakes and river backwaters on landward side;
  • Classifications:
    • Circular 39: Type 3
    • NWI Symbols: PEMC and F, PSSH, PUBA and C
    • Eggers & Reed: Shallow Marsh
    • Native Plant Community Classification: MRn, Mru, MRs

Deep Marsh

  • Soil/Hydrology: Organic or mineral soil, inundated in most years with six inches to three 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
  • Classifications:
    • Circular 39: Type 4
    • NWI Symbols: L2ABF, L2EMF and G, L2US, PABF and G, PEMG and H, PUBB and F
    • Eggers & Reed: Deep Marsh
    • Native Plant Community Classification: MRn, Mru, MRs

Shallow Open Water

Shallow ponds and reservoirs are included in this wetland type, because of their value for wildlife. Many of these wetlands are specially designated and managed under the Shallow Lakes Program.

Shallow open water

  • Soil/Hydrology: Organic or mineral soil, usually inundated with three to 10-foot-deep water
  • Vegetation: Fringe of emergent and floating leaf vegetation similar to marshes; submergent vegetation such as pondweed, naiad, coontail, watermilfoil
  • Common sites: Shallow lake basins and may border large open water basins
  • Classifications:
    • Circular 39: Type 5
    • NWI Symbols: L1; L2ABG and H; L2EMA, B, and H; L2RS; L2UB; PABH; PUBG and H
    • Eggers & Reed: Shallow Open Water
    • Native Plant Community Classification: portions may be MRn, Mru, MRs; open water areas are not classified under this system

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.

Swamps

Shrub and Wooded swamps are shrubby or forested wetlands found along the edges of lakes, rivers, and streams and in glacial basins. Shrub swamps are common throughout the state. Some good examples of wooded swamps are the black ash and black spruce forests found in Scenic, Wild River and Lac qui Parle State Parks.

Shrub Swamp

  • Soil/Hydrology: Organic or mineral soil; water table is at or near the surface for most of the growing season and may be covered with as much as six inches of water
  • Vegetation: Includes alder, willow, dogwood, and buttonbush (southeast Minnesota)
  • Common sites: Along sluggish streams, drainage depressions, and occasionally on floodplains
  • Classifications:
    • Circular 39: Type 6
    • NWI Symbols: PSSA, C, F, and G; PSS1, 5, and 6B
    • Eggers & Reed: Shrub-Carr, Alder Thicket
    • Native Plant Community Classification: FPn73, WMn82, WMs83, WMp73

Wooded Swamp

  • Soil/Hydrology: Organic or mineral soil, water table is at or near the surface during much of the growing season; may be covered with as much as one foot of water for shorter periods
  • 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
  • Classifications:
    • Circular 39: Type 7
    • NWI Symbols: PFO1, 5, and 6B; PFOC and F
    • Eggers & Reed: Hardwood Swamps, Coniferous
    • Native Plant Community Classification: WFn, WFs, WFw, FPn, FPs, FPW

Wet meadows (including Calcareous Fens)

These wetlands are characterized by generally low-growing grass, sedge or rush communities with various broad-leaved plants. They include wet prairies and calcareous fens. They may be found along the borders of streams, lakes and marshes, in small depressions, and in extensive flats on glacial lake beds. Calcareous fens are a rare type of wet meadow supported by constant, upwelling groundwater rich in calcium carbonate. Because of their specialized hydrology and chemistry, they often support rare plant species. Calcareous fens receive special protection under the Minnesota Wetland Conservation Act and the DNR maintains a list of known calcareous fens. PDF

Wet Meadow/Wet Prairie

  • Soil/Hydrology: Organic or mineral soil, saturated or nearly saturated during most of the growing season; usually without standing water
  • 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
  • Classifications:
    • Circular 39: Type 2
    • NWI Symbols: PEMB
    • Eggers & Reed: Sedge Meadow, Fresh (Wet) Meadow, Wet to Wet-Mesic Prairie, Calcareous Fen
    • Native Plant Community Classification: WMn, WMs, WMp, OPp91

Calcareous Fens

  • Soil/Hydrology: Non-acidic, sedge-derived peat; saturated or nearly saturated during most of the growing season due to constant, upwelling groundwater; scattered small pools and rivulets present
  • Vegetation: Grasses, sedges, rushes, shrubs, various broad-leaved plants; many rare species
  • Common sites: Calcareous fens are found along the beach ridges of Glacial Lake Agassiz in northwest Minnesota, at the base of river terraces along the Minnesota River Valley, and in the karst region of southeast Minnesota
  • Classifications:
    • Circular 39: Type 2
    • NWI Symbols: PEMB, PSSB
    • Eggers & Reed: Calcareous Fen
    • Native Plant Community Classification: OPp93, OPn93

Seasonally flooded wetlands

These wetlands generally contain water for relatively short periods during the growing season, primarily in spring or after heavy precipitation events. They include small, shallow basins supporting mostly annual plant species as well as floodplain forests. Because they are dry for much of the year, seasonally flooded wetlands are often farmed. Even so, they are still valuable food sources in the spring for migrating waterfowl and shorebirds. When left intact, these wetlands provide essential breeding habitat for amphibians, especially in forested settings. Floodplain forests help protect and maintain the water quality of their associated rivers and streams. These wetland types are found throughout the state.

Seasonally Flooded Basins

  • Soil/Hydrology: Generally mineral soils, usually well-drained during much of the growing season but inundated or waterlogged during variable seasonal periods, especially in the spring
  • Vegetation: Grasses, sedges, strong component of annual plants such as smartweeds, beggarticks and wild millet
  • Common sites: Upland depressions
  • Classifications:
    • Circular 39: Type 1
    • NWI Symbols: PEMA, PUS
    • Eggers & Reed: Seasonally Flooded Basins
    • Native Plant Community Classification: WMs92, WMp73

Floodplain Forests

  • Soil/Hydrology: Generally mineral soils, usually well-drained during much of the growing season but inundated or waterlogged during variable seasonal periods, especially in the spring
  • Vegetation: Flood-tolerant tree species such as silver maple, cottonwood, American elm; often sparse understory but includes jewelweed, clearweed, nettles
  • Common sites: Along rivers and streams
  • Classifications:
    • Circular 39: Type 1
    • NWI Symbols: PFOA
    • Eggers & Reed: Floodplain Forest
    • Native Plant Community Classification: FFn, FFs