United States Department of Transportation
i
An Evaluation of North Carolina Department of Transportation Wetland Mitigation Sites: Selected Case Studies – Phase II Report
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2002-03-01
[PDF-2.08 MB]
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Edition:Final report.
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Abstract:Phase 1 of this study evaluated 50 NCDOT wetland compensatory mitigation sites and 11 reference sites in 1999. The Phase 2 component (this report) examines five of the compensatory mitigation sites to provide a more in-depth analysis. The
objective of the two reports is to help NCDOT and wetland regulatory agencies develop a framework to improve NCDOT’s compensatory mitigation, to enhance communication between NCDOT and regulatory agencies, and to benefit wetland restoration overall. We encountered problems with various definitions (restoration, preservation, enhancement, etc.) that are not compatible with current scientific understanding of ecosystem functioning. This has led to avoiding the potential for improving the condition of severely altered wetlands because they meet the jurisdictional definition in spite of a highly degraded condition. Elsewhere, socioeconomic limitations may prevent complete restoration. In such cases, partial restorations may be better than none at all. For example, preservation through purchase or conservation easements of headwater streams and their buffers in a partially degraded condition would provide opportunities for improving water quality. Undue reliance on criteria for hydrology over criteria for soil, in extreme cases, has led to soil excavation that reduced survivorship of planted seedlings and lowered recruitment capacity. In general, reference sites have been little utilized to design restorations and to gauge success. Depending on initial conditions, the restoration of wetland structure and function may take many decades to achieve maturity. Presently, all monitoring stops once permit conditions have been met. Institutional memory then rests almost entirely with personnel in the NCDOT organization. To encourage long-term research, regulatory agencies must be willing to provide mitigation credit for establishing reference sites and to conduct long-term research in comparing them with a variety of restoration practices. To avoid unintentional shifting of distribution among one set of hydrogeomorphic classes to others, it will be necessary to track restoration at drainage basin scales according to hydrogeomorphic wetland classes. Many of these suggestions will require acceptance by regulatory agencies and implementation by all parties. Regulatory agencies would have to be willing to accept success criteria based on data from reference wetlands.
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