Ecological Assessment of a Wetlands Mitigation Bank (Phase III : Restoration Efforts)

The overall objective for the Tulula Wetlands Mitigation Bank has been to restore the functional and structural characteristics of a mountain stream and the adjacent alluvial wetlands. Specific restoration objectives of this study included: 1) determining the success of stream realignment by evaluating the geomorphology of a new channel before and after water release, 2) evaluating changes in ecosystem structure and function associated with plant community succession in planted and unplanted portions of the floodplain in response to restored hydrology, and 3) evaluating wildlife use of the site in response to changing hydrologic conditions (amphibians) and plant community succession (birds). A meandering channel (8,500 linear feet in length) was constructed across the floodplain and water was released into the new channel in 2001 and 2002. Eight random channel segments were used for measurements of stream geomorphology and after two years of water flow few differences were noted for channel pattern, although changes were observed for cross-sectional areas of riffles and pools. Isolated areas of bank and bed erosion were noted. The hydrology of Tulula has been influenced by the stream restoration, with most notable differences occurring for water-table wells located near the channel. Although the hydrology of Tulula fen was not influenced by stream restoration, the composition of wetland plant communities in the fen was influenced by natural succession. Restoration did influence the composition of some plant communities. For example, restored wetland areas contained fewer species than unrestored areas or restored dry areas, and the species that dominated the restored wet areas were OBL and FACW plants. In addition, production of both vegetative and reproductive stems of a common rush was influenced by restoration and hydrologic change. Recently disturbed areas at Tulula had lower decomposition rates and fewer litter microarthropods compared to older plant communities. Data collected from 1996-2004 indicate that constructed ponds are of higher quality than reference ponds based on physiochemical characteristics, seasonal hydroperiod, and use by resident amphibians. Amphibians rapidly colonized constructed vernal ponds, and the number of species that utilize these as breeding sites averaged about 50% higher than that of reference ponds. The survivorship and output of wood frog and spotted salamander juveniles have declined since pond construction, in part due to the accumulation of predators in ponds, the outbreak of a virus pathogen, and premature pond drying associated with drought. In 2004, bird species richness and relative bird abundance decreased significantly from 2002 levels. Bird species richness decreased 15% and relative bird abundance decreased 52%. Generalist species, such as Song Sparrow and Rufous-Sided Towhee, continued to be the most abundant species, while many Neotropical migrants of conservation concern, including the Golden-winged Warbler, Chestnut-sided Warbler, Hooded Warbler, and Yellow-breasted Chat, declined substantially. The significant declines in bird species richness and relative bird abundance are attributed to habitat changes associated with the flooding of a large proportion of the floodplain as a result of beaver activity. Management intervention is recommended to control the flooding caused by beaver, and to maintain a variety of early-successional habitat types throughout the site.

Language

  • English

Media Info

  • Media Type: Web
  • Edition: Final Report
  • Features: Appendices; Figures; Maps; References; Tables;
  • Pagination: 88p

Subject/Index Terms

Filing Info

  • Accession Number: 01099515
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/NC/2004-09, Research Project 2003-18
  • Files: UTC, TRIS, USDOT
  • Created Date: May 6 2008 1:13PM