Wetland mitigation in abandoned gravel pits.

632333876Final report.PDFTech ReportMN/RC 2010-11(c) 89261 (wo) 14Gravel pitsWetlandsMinnesotaMinnesota. Dept. of TransportationJohnson, Kurt W.University of Minnesota, Duluth. Center for Applied Research and Technology DevelopmentMinnesota. Dept. of Transportation. Research Services SectionNTL-ENERGY AND ENVIRONMENT-Environment ImpactsNTL-PLANNING AND POLICY-Land UseUS Transportation CollectionIt is becoming increasingly difficult to provide on-site mitigation for wetland impacts due to road construction innortheastern Minnesota counties that retain greater than 80 percent of their pre-settlement wetlands. Abandonedgravel pits are one of the few remaining areas that can serve as wetland mitigation sites. The overall goal of theproject is to develop cost-effective methods for creating functional mitigation wetlands on abandoned gravel pitsites to compensate for wetland impacts due to road construction. Two approximately 1-hectare wetland creationdemonstration sites were established in adjacent abandoned gravel pits within the U.S. Trunk Highway 53reconstruction corridor to evaluate techniques for wetland establishment. Wet meadow and shrub swamp wetlandswere attempted on one site, and wooded swamp and bog wetlands on the other. Wetland seed mixes provided bothpositive and negative effects on the developing plant communities on both sites initially but their effect was limitedto the first year. Alder thicket and bog donor soil applications had positive effects but not until the third year of thestudy. Hardwood willow cuttings were effective for establishing a shrub component. Conifer seedlings did notsurvive unless planted on soil mounds. Fertilizer proved ineffective for promoting wetland plant growth during thestudy period. The use of straw mulch is questionable on saturated wetland sites such as those in this study