Northern Prairie Wildlife Research Center
Figure 5. Water level changes during the ice-free season over a 6-year period in a seasonal (lower) and semipermanent (upper) basin wetland in North Dakota (from Kantrud et al. 1989).
Figure 6. Environmental factors influencing prairie wetland ecology.
Glacial topography and geologically governed permeability variations have a significant effect on surface and ground-water hydrology. Tills in moraines are generally silty and clayey materials that are not very permeable. Outwash deposits, on the other hand, generally consist of stratified sand and gravel, materials that are very permeable. The tills in the eastern Dakotas tend to be much higher in shale-derived material. These tills are more clayey and less permeable to water than those to the west and south, which have a larger proportion of limestone, sandstone, and siltstone derivatives (Winter 1989). Because prairie wetlands are characteristically nonintegrated, ground-water flow systems play a dominant role in their hydrologies. Lissey (1971) described the principles of depression-focused ground-water recharge and discharge in the glaciated prairie of southwestern Manitoba. LaBaugh et al. (1987) studied the hydrology of a wetland complex in the Cottonwood Lake area of Stutsman County, ND, that contained wetlands situated at different altitudes along a topographic slope and hydraulic gradient. This area has been described in detail by Winter and Carr (1980). LaBaugh et al. (1987) confirmed the concept of depression-focused ground-water recharge and discharge as proposed by Lissey (1971).
Wetland basins in the Cottonwood Lake area perform three basic functions with respect to ground water (Lissey 1971). These functions are reflected in the water chemistry of these wetlands (Swanson et al. 1988). Some basins function as ground-water recharge areas; such basins tend to be temporarily or seasonally flooded; they hold water for only a few months each year, and the water is generally low in dissolved solids. Some basins are through-flow systems with respect to ground water; that is, ground water flows in through parts of their bed while other parts recharge ground water. Through-flow basins hold water over longer periods and the water tends to have higher concentrations of dissolved solids. Some basins serve only as discharge areas for ground water. Lakes that receive discharge from both regional and local ground-water flow systems and do not lose water to seepage or surface outflow are highly saline, having specific conductance as high as 70 mS/cm.
Wetland hydrologic functions control the chemical characteristics of prairie lakes, and as a result, plant and invertebrate communities.