Classification of Natural Ponds and Lakes
in the Glaciated Prairie Region
Major Classes of Natural Ponds and Lakes
Seven major classes of wetlands in natural basins are recognized on the basis of ecological differentiation. Each class is distinguished by the vegetational zone occuring in the central or deeper part and occupying 5 percent or more of the total wetland area being classified. The plant species characteristic of these classes are listed in appendix A. The classes are designated as follows:
Class I-ephemeral ponds.
The wetland-low-prairie zone dominates the deepest part of the pond basin. A pond of this class is illustrated in plate 1.
Class II-temporary ponds.
The wet-meadow zone dominates the deepest part of the wetland area. A peripheral low-prairie zone is usually present. Ponds of this class are illustrated in plates 2 to 5.
Class III-seasonal ponds and lakes.
The shallow-marsh zone dominates the deepest part of the wetland area. Peripheral wet-meadow and low-prairie zones are usually present. Ponds of this class are illustrated in plates 6 to 12.
Class IV-semipermanent ponds and lakes.
The deep-marsh zone dominates the deepest part of the wetland area. Shallow-marsh, wet-meadow, and low-prairie zones are usually present, and isolated marginal pockets of fen zones occasionally occur. Ponds or lakes of this class are illustrated in plates 13 to 23.
Class V-permanent ponds and lakes.
The permanent-open-water zone dominates the deepest part of the wetland area. Peripheral deep-marsh, shallow-marsh, wet-meadow, and low-prairie zones are often present, and isolated marginal pockets of fen zone occasionally occur. Permanent lakes are illustrated in plates 24 to 26.
Class VI-alkali ponds and lakes.
The intermittent-alkali zone dominates the deepest part of the wetland area. Peripheral shallow-marsh, wet-meadow, and low-prairie zones are usually present. A deep-marsh zone is normally absent except occasionally for isolated patches near marginal seepage areas. A few isolated pockets of fen zone are normally present along the margins. Alkali lakes are illustrated in plates 27 and 28.
Class VII-fen (alkaline bog) ponds.
The fen zone dominates the deepest part of the wetland area. Peripheral wet-meadow and low-prairie zones are often present. The central part of a large fen is illustrated in plate 29.
Illustrations of the spatial relations of vegetational zones in the major classes of ponds and lakes are shown in figure 2. Normally, wetland classes are easily distinguished in the field. Occasionally, a pond or lake intermediate between two classes will be encountered in which the deepest part of the wetland area is occupied by a mixture of species characteristic of two different zones (plates 10 and 11). In such a case the class designation would depend on which characteristic species group represents more than 50 percent of the vegetational growth in the deeper central area.
Figure 2. Spatial relation of vegetational zones in major classes of natural ponds and lakes.
During extended periods of abnormal water conditions, certain ponds and lakes may shift from one class to another. For example, in Stutsman County, N. Dak., in 1966, many shallow-marsh species, responding to extremely high water levels, invaded typical wet- meadow zones. During this period, some wetlands were transformed from temporary (Class II) to seasonal (Class III) ponds. Conversely, extreme drought in 1961 allowed wet-meadow vegetation to become established in many zones formerly dominated by shallow-marsh species, converting these wetlands from seasonal (Class III) to temporary (Class II) ponds. Immediately after the transition from one class to another, there may be a temporary reversal in the usual spatial relations of vegetational zones. For instance, stands of shallow-marsh emergents may develop in the deeper parts of a pond formerly occupied by the deep-marsh open-water phase, while surrounding bands of deep-marsh emergents may persist for a time in shallower water (plate 12).
Seasonal (Class III) and semipermanent (Class IV) ponds and lakes are the predominant wetlands in terms of total acreage throughout the glaciated prairie region. Large numbers of ephemeral ponds (Class I) and temporary ponds (Class II) are present, but their total acreage is somewhat less. Permanent and alkali ponds and lakes (Classes V and VI), although often quite large individually, are few in number and therefore only of secondary significance. Fen ponds (Class VII) are usually small and quite local in occurrence.
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