An evaluation of the effectiveness of existing North Carolina Department of Transportation wetland mitigation sites, phase 1 report
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An evaluation of the effectiveness of existing North Carolina Department of Transportation wetland mitigation sites, phase 1 report

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  • Creators:
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    East Carolina University. Dept. of Biology
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  • Publication/ Report Number:
    FHWA/NC/00-002
  • Resource Type:
    Research Paper
  • Geographical Coverage:
    North Carolina
  • Abstract:
    In this study, 49 North Carolina Department of Transportation (NCDOT) wetland compensatory mitigation sites and 11 reference sites were evaluated on-site in 1999. Seventeen of the larger sites consisted of more than one type of mitigation (restoration, creation and/or preservation). In total, 71 mitigation parcels (approximately 3,000 acres) were evaluated to assess the likelihood that mitigation sites would achieve some level of structure and functioning similar to natural, self-sustaining wetland ecosystems and to provide recommendations for improvements. Ecological success was related to whether or not natural geomorphology had been successfully restored. Sites from which fill was removed were generally successful. Sites in which water impediment structures were constructed showed mixed results for vegetation survival, presumably because it was difficult to determine how wet to make a site. Wetland creations were generally unsuccessful because most all involved excavating soil to reach the underlying saturated zone, thus inhibiting growth of vegetation on sub-soils. Predictions of success were difficult due to the immaturity of sites, but it appeared that many created wetlands would not likely resemble historic, natural ecosystems. Of the 71 compensatory mitigations examined, 26 were judged to be ecologically successful, 19 were preservation sites (automatically judged to be successful), 9 were judged to be unsuccessful, 10 lacked sufficient data (mostly hydrologic data) for judging success, 4 sites were too young to predict the outcome for vegetation survival, and 3 were undergoing construction at the time of the site visit. Alteration of and failure to restore natural geomorphology in compensatory mitigation sites was the major factor associated with the lack of mitigation success, regardless of whether success was defined by permit success criteria or by ecological success. More use of information from reference sites could improve outcomes. Compensatory wetland mitigation involving restoration and creation appears to have gravitated toward relatively narrow sets of conditions for hydrology and vegetation, with little room for flexibility. In contrast, no standards are being used for soil condition. Current success criteria and standards should undergo critical examination to see if they are consistent with no-net-loss wetland policies, and if alternative measures should to be taken. Tables, refs, 2 appendices. 124 p.
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