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Wetland Plants and Plant Communities of Minnesota and Wisconsin

VIII. SEASONALLY FLOODED BASINS


Seasonally flooded basins are poorly drained, shallow depressions that may have standing water for a few weeks each year, but are usually dry for much of the growing season. These basins may be kettles in glacial deposits, low spots in outwash plains, or depressions in floodplains. They are frequently cultivated. However, when these basins are not cultivated, wetland vegetation can become established. Typical species include smartweeds, beggarticks, nut-grasses, and wild millet. One unique aspect of seasonally flooded basins is that the alternating periods of flood and drought can eliminate perennial plants so that annual plant species typically dominate the community

Seasonally flooded basins are important for waterfowl and shorebirds. These temporary water holding basins frequently have an abundance of plant seeds and invertebrates, which makes them ideal feeding and resting areas for migrating waterfowl and shorebirds. In spring, seasonally flooded basins are used as pairing ponds by ducks, and the abundant invertebrate population provides a protein-rich diet for egg-laying hens.

A seasonally flooded basin in Kenosha County, Wisconsin

VEGETATION: The seasonally flooded basin shown by the photograph above is located in a corn (Zea mays) field and was photographed in May when little or no vegetation is visible. Annual species, and other species adept at colonizing mudflats, would become established later in the growing season.

SOILS: Ashkum silty clay loam (Typic Haplaquolls), a poorly-drained soil underlain by calcareous glacial till in drainageways and depressions. Landscape position of this example is a shallow, closed depression in the nearly level plain of Glacial Lake Chicago.

HYDROLOGY: Ponding following spring snowmelt and heavy summer rainfall events, as well as a high water table. Ashkum soils have a seasonal high water table with 12 inches of standing water to a water table 24 inches below the surface during April through June of most years.

LOCATION: Kenosha County, Wisconsin.

A seasonally flooded basin in Nicollet County, Minnesota

VEGETATION: The seasonally flooded basin shown above is within an alfalfa (Medicago sativa) field. When this photograph was taken in late August, the mudflats left by the ponded conditions of the early growing season had been colonized by nearly 100 percent vegetative cover dominated by nodding smartweed (Polygonum lapathifolium) and pinkweed (Polygonum pensylvanicum). Other species present include foxtail (Setaria viridis), wild millet (Echinochloa crusgalli), common ragweed (Ambrosia artemisiifolia) and goosefoot (Chenopodium album).

SOILS: Glencoe silty clay loam (Cumulic Haplaquolls), a very poorly-drained mineral soil formed in glacial till. Landscape position is a prairie pothole depression in gently rolling terrain. Under natural conditions, this was a closed basin (no defined outlet or inlet).

HYDROLOGY: Ponding following spring snowmelt and heavy summer rainfall events, as well as a high water table. In an undrained condition, Glencoe soils have a seasonal high water table with 12 inches of standing water to a water table 12 inches below the surface during October through July of most years. However, the above example has been partially drained by a surface ditch converting this hydrologic regime to that of a seasonally flooded basin -- ponded for only a few weeks during most growing seasons.

LOCATION: Nicollet County, Minnesota.

SPECIES ACCOUNTS:

Pinkweed (Polygonum pensylvanicum L.)
Wild Millet (Echinochloa crusgalli (L.) Beauv.)
Red-root Flatsedge (Cyperus erythrorhizos Muhl.)
Blunt Spike-rush (Eleocharis obtusa (Willd.) Schult.)
Beggartick (Bidens cernua L.)


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