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Wetland Symposium

A Functional Assessment of Restored Prairie Wetlands and Implications for Restoration Programs


Iowa State University, Department of Botany, 353 Bessey, Ames, IA 50011

Between 1987 and 1991, 1,892 wetlands (2,714 ha) were restored by state and federal agencies, most as part of the Conservation Reserve Program, in northern Iowa, southern Minnesota, and southeastern South Dakota. Restored wetlands are assumed to provide wildlife habitat and improve water quality. These assumptions were evaluated by comparing features of restored wetlands to those of natural wetlands (historic or extant). A preliminary evaluation was made on all restorations; more detailed information was collected on 62 wetlands restored in 1988. The water-quality evaluation is based on watershed land use, basin morphometry, and development of emergent vegetation. The evaluation of restored wetlands as wildlife habitat is based on wetland type, water regime, and vegetation composition and zonation. Thirty-six of the 62 restorations do not have any part of their watershed in row-crop production and only 10 had more than 50% in row crops. Earthen dams were installed on most (73%) of all restorations in the region, increasing the full pool volume and consequently the potential water-residence time. However, nearly all wetlands restored by removing drainage tile (17% of all sites) had inlets positioned next to outlets, greatly diminishing water-residence time at full pool. Most restorations are less than 4 ha and 41% have soils indicating an ephemeral to seasonal pre-drainage water regime. Wetlands restored to be ephemeral/temporary are under-represented compared with their pre-agricultural extent. After three years, wet prairie and sedge meadow zones have not re-established in most restorations (0 and 9%, respectively). The number of wet prairie, sedge meadow, and shallow emergent species is less than in natural wetlands. Natural wetlands have 1-22 wet prairie species, whereas restored wetlands have 0-2 species. Sedge meadow species number 7-49 in natural wetlands and 0-9 in restored wetlands. Seven to 19 shallow emergent species are present in natural wetlands, compared with 1-8 species for restored wetlands. Deep emergent and submersed aquatic zones develop in restored wetlands and the species richness of these communities is comparable to that of natural wetlands. The lack of revegetation in shallow portions of prairie potholes may result in wetlands without suitable habitat for some wildlife species. Multiple-use planning of restorations at the scale of several counties may be an appropriate mechanism for ensuring that wetland restorations provide water quality and wildlife functions at a landscape scale.

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