United States Department of Transportation
i
Ecological assessment of a wetlands mitigation bank (Phase I: baseline ecological conditions and initial restoration efforts)
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2001-08-01
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[PDF-3.18 MB]
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Abstract:The Tulula Wetlands Mitigation Bank, the first wetlands mitigation bank in the Blue Ridge Province of North Carolina, was created to compensate for losses resulting from highway projects in western North Carolina. The overall objective for the Tulula Wetlands Mitigation Bank has been to restore the functional and structural characteristics of the wetlands. Specific ecological restoration objectives of this Phase I study included: 1) reestablishing site hydrology by realigning the stream channel and filling drainage ditches; 2) recontouring the floodplain by removing spoil that resulted from creation of the golf ponds and dredging of the creek; 3) improving breeding habitat for amphibians by constructing vernal ponds; and 4) reestablishing floodplain and fen plant communities. Efforts to restore Tulula have focused on the altered hydrology of the site, particularly on the re-meandering of Tulula Creek, which had been previously been dredged into a gully-like channel. The footprint of the new meandering channel has been completed, and the contractor will join the separate segments of the new channel together in fall of 2001. Former golf course ponds were filled or partially filled to create shallow ponds, thus creating thirteen new breeding sites for amphibians. The site currently contains 23 constructed ponds and about 10 smaller amphibian breeding sites. Overall, constructed ponds contained a significantly greater number of breeding species than natural breeding habitats of Tulula. The majority of the floodplain has been mapped and classified as Nikwasi loam. Disturbance of the soil profiles was limited to the surface layer over most of the site, allowing the presence of a remnant seedbank in the soil to enhance development of the plant community. Thirteen vegetation communities are described in the report, including four disturbed and nine natural communities. Over 400 vascular and nonvascular plant species have been identified; many of these species are new records for Graham County. Red maple saplings and shrub saplings were planted in two disturbed fairways adjacent to the fen in 1996. At the end of this study, approximately one-half of the planted shrub saplings were alive. The red maple saplings survived reasonably well, but were outperformed by the extensive natural regeneration of red maple on the site, resulting in the conclusion that large-scale planting of canopy trees is unnecessary at Tulula. The database on hydrology, soils, flora, and fauna that has resulted from these efforts will provide the framework for documenting the long-term success of wetland restoration activities at Tulula. After the Tulula Wetlands Mitigation Bank is restored, the site is expected to support 40 ha of wetlands, 38 ha of upland buffers, and 11 ha of surrounding upland protection areas. The proposed mitigation credit for Tulula is based on restored surface water and groundwater flow gradients in wetland areas, coupled with spoil removal from the floodplain. The report offers several recommendations for approaching wetland restoration both general and specific to Tulula. A key recommendation is to maintain flexibility in the regulatory components of restoration; rather than trying to use a "cookbook" approach, federal and state agencies that work cooperatively on wetland restoration activities should use site-specific baseline ecological conditions to develop restoration strategies that are appropriate for each site. 117 p., 26 figures, 24 tables and 6 appendices.
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