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Under the Cowardin et al. (1979) wetland classification, the prairie wetlands referred to in this report are palustrine and lacustrine systems. There are no subsystems in the palustrine system. For the lacustrine system, only the littoral subsystem is dealt with in this report. This subsystem extends from the shoreward boundary to a depth of 2 m below low water or to the maximum extent of nonpersistent emergents, if these grow at depths >2 m. The latter conditions are rare or absent in the pothole region of the Dakotas. An outline of the Cowardin et al. (1979) classification system, as it applies to the Prairie Pothole Region of the Dakotas, is shown in Table 1. Only subclasses dominated by plants are included in Table 1 because these subclasses are by far the most common in the region. Little is known about the animals that dominate unvegetated substrates that are known to exist in several wetland classes found in the region.

Classes

Classes of the palustrine system found in the Prairie Pothole Region of the Dakotas are emergent, aquatic bed, unconsolidated shore, unconsolidated bottom, forested, and shrub-scrub. Classes of lacustrine system represented are aquatic bed, emergent wetland, unconsolidated shore, unconsolidated bottom, and rocky shore.

Emergent wetland. This class of wetland, containing erect rooted herbaceous hydrophytes, is by far the most common wetland class in the region. Emergent wetland supports vegetation that is largely perennial, and present during most of the growing season most years. Emergent wetland is often called marsh, meadow, fen, slough, or swamp in the region. Persistent emergents are by far the most common, although under disturbances such as heavy grazing or cultivation, nonpersistent emergents can dominate.

Aquatic bed. The class "aquatic bed" includes wetland dominated by plants that grow principally on or below the water surface for most of the growing season during most years. This is the second most common wetland class in the region.

Unconsolidated shore. This class is mostly associated with the erosional and depositional shoreline zones of wetlands not dealt with in this report, but the class commonly occurs in many shallow prairie wetlands as bottoms are exposed during drought.

Unconsolidated bottom. This class is mostly associated with the unstable bottoms of wetlands with more permanent water regimes than are dealt with in this report, but can occur in some deeper prairie wetlands as bottoms are exposed during extreme drought.

Scrub-shrub. The class "scrub-shrub" includes wetlands dominated by woody vegetation <6 m tall. In prairie wetlands, this class is mostly limited to temporarily flooded sites long protected from fire and grazing by domestic livestock.

Forested. The class "forested" includes wetlands dominated by woody vegetation 6 m or more tall. In prairie wetland, this class is mostly limited to temporarily flooded sites long protected from fire and grazing by domestic livestock. The class can sometimes develop where artificial disturbance creates sites favorable to germination and growth of seeds from trees with wind-disseminated propagules.

Rocky shore. This class is found only on a few large wetlands in the Prairie Pothole Region where glacial slumping and ice action have strewn boulders along high-energy shorelines. This class is seldom found in the wetlands dealt with in this report.

Water Regimes

The water regimes dealt with in this report are temporarily flooded, seasonally flooded, and semipermanently flooded. Basins where the central or deepest portion is subject to these water regimes compose nearly 90% of all basins in the Prairie Pothole Region. The concentric pattern of these regimes in lacustrine and palustrine wetland systems is shown in Figure 2.

Figure 2. Arrangement of Cowardin et al. (1979) water regimes around lacustrine and palustrine wetlands in the Prairie Pothole Region of the Dakotas (from Kantrud et al. 1989).

Subclasses

Emergent wetland contains vegetation of the subclasses persistent or nonpersistent. "Persistent" vegetation in prairie wetlands is normally perennial in habit and remains standing at least until the beginning of the next growing season. Persistent vegetation is the predominant subclass in nearly all prairie wetlands, often referred to as "wet grasslands. Nearly always annual in habit, "nonpersistent" vegetation increases with falling water levels and disturbance in prairie wetlands.

Aquatic bed can include the subclasses "algal," "aquatic moss," "rooted vascular," or floating. "Rooted vascular" is the predominant subclass because the highly mineralized and alkaline waters of the region are not conducive to the growth of most mosses, and the relatively windy conditions that prevail in the region usually move floating algae and vascular floating plants into emergent wetland, where they can appear below the canopy. The subclasses aquatic moss and floating vascular are found most often in small basins, small bays of larger basins, or openings in emergent wetland, whereas the subclass algal is most often seen in small, highly eutrophic wetlands.

Unconsolidated shore in the wetlands dealt with in this report is usually of the subclass "vegetated." Unconsolidated shore can quickly appear in seasonally flooded wetlands, normally of the class aquatic bed, if drought conditions prevail early in the growing season.

Unconsolidated bottom in the prairie region is usually of the subclasses "sand" or "mud. Areal cover of vegetation in this subclass usually does not exceed 30% (Cowardin et al. 1979). However, in semipermanently flooded wetlands of the Prairie Pothole Region, annuals can germinate and grow to cover values exceeding 30% during years of extreme drought (L.M. Cowardin, Northern Prairie Wildlife Research Center, pers. comm.).

Only the subclasses "broad-leaved deciduous" and "dead" are found in forested and scrub-shrub wetland in the Prairie Pothole Region of the Dakotas.

Relation to Other Wetland Classification

This report includes only information on basins with the temporarily, seasonally, and semipermanently flooded water regimes of Cowardin et al. (1979). These water regimes correspond to those found in the central zones of ponds and lakes classified as temporary (Class 2), seasonal (Class 3), and semipermanent (Class 4) by Stewart and Kantrud (1971). This system was developed specifically for the glaciated prairie region, and unlike the former system, was designed to classify entire basins, rather than the central or concentric peripheral zones or bands of vegetation around the basins that are wetland of differing water regime in the Cowardin et al. (1979) system. The terms "pond" and "lake" usually refer only to the water contained in the basins. Hereafter in this report the terms temporary, seasonal, and semipermanent wetlands will refer to entire basins, and the corresponding zones will be termed wet meadow, shallow marsh, and deep marsh, following Stewart and Kantrud (1971).

Wetland Inventory Maps

Use of the Cowardin et al. (1979) classification system results in large numbers of combinations of wetland system, subsystem, class, and water regime. These combinations are shown as legends (alphanumeric codes) on the National Wetland Inventory maps that are currently being prepared for the United States. Copies of the pamphlet Photointerpretive Conventions for the National Wetlands Inventory (1987), which contains an explanation of these legends, and the status of the wetland mapping effort for the region, is available from the U.S. Fish and Wildlife Service, Regional Wetlands Coordinator, National Wetlands Inventory, Federal Center, Denver, CO 80225. The legends can be used to locate temporary, seasonal, and semipermanent wetland basins by noting instances where these codes are shown for the deepest or central area of a basin. The maps are intended to show the potential natural vegetation. Thus, cultivated wetlands are designated as emergent even though emergent vegetation may be absent.

Wetland Soils

The soils underlying wetland basins in North Dakota have been classified, and classification is in progress for similar soils in South Dakota (Jimmie Richardson, North Dakota State University, pers. comm.). The development of wetland soils depends strongly on length of flooding, water quality, and the relative position of the basins with respect to the ground-water table, according to Bigler and Richardson(1984), Richardson and Bigler (1984), and Fulton et al. (1986). These sources and other material referenced by them show that temporary and seasonal wetlands are usually recharge areas that receive water from the surrounding uplands by runoff or direct precipitation. Clays are dispersed and carried downward by an abundance of fresh water. This results in highly developed soil profiles with argillic horizons. Soil series observed in these situations include Lindaas and Parnell (Typic Agriaquolls) and Tonka, an Argiaquic Agialboll.

Most semipermanent wetlands in North Dakota are flow-through wetlands that receive ground-water discharge and also recharge the ground water. Evapotranspiration, frost action, and a near-surface water table allow water to move from the wetland body to the soils in the wet meadow. Reducing conditions in the water column aid in mobilizing salts into the wet meadow. Several other little-understood factors result in higher soil salinity in the wet meadow than in the adjacent uplands or the interior zones of the wetland basin. These flow-through wetlands have a large range of salinity, and salinization of the whole wetland occurs in some cases. Soils in these wetlands range from Typic Haplaquolls and Calciaquolls in the wet meadow to dominantly Fluvaquentic Haplaquolls such as the Southham series in the shallow marsh and deep marsh zones (Bigler and Richardson 1984) . It is in these basins that drainage followed by tillage often results in crop failure because land salinization occurs as the ground-water system delivers low-quality water to the freshly broken soils (Richardson 1986) .

A small number of semipermanent wetlands in North Dakota can be considered discharge wetlands. These are underlain by saline soils such as the poorly developed Minnewaukon and Lallie series (Typic Fluvaquents ) . If drainage is attempted on these soils, salinization prevents the growth of crops other than hay.

Little is known about heavy metals in soils of prairie wetlands. Martin and Hartman (1984) examined arsenic, cadmium, lead, mercury, and selenium concentrations in sediments of riverine and palustrine wetlands of the North Central United States. Samples from three palustrine wetlands in the Cottonwood Lake area northwest of Jamestown, North Dakota, averaged 6.2 (4.5-9.3), 0.46 (0.42-0.50), 12 (7.4-17), 0.04 (0.02-0.07), and 0.99 (0.43-1.6) mg/kg dry weight of these metals, respectively. Sediments from palustrine wetlands have significantly higher concentrations of arsenic, cadmium, lead, and selenium than those from riverine wetlands, but, with one exception, concentrations were within normal or background ranges.