Mountain stream. Photo courtesy of the NC Department of Environment and Natural Resources

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From the N.C. Dept. of Environment and Natural Resources Office of Environmental Education and Public Affairs, shared April 5:

RALEIGH A report issued today by the Division of Water Quality shows an increase in the number of successful wetland mitigation projects in North Carolina in comparison to a decade ago and discusses ways to further improve that success rate.

Wetland and stream mitigation projects either create wetlands and/or improve streams and wetlands to balance the environmental impacts that come with development.

The study, “Compensatory Stream and Wetland Mitigation in North Carolina – An Evaluation of Regulatory Success,” evaluated components of 82 wetland mitigation sites and components of 79 stream mitigation sites. The research showed that 75 percent of wetland and stream mitigation projects were successful in meeting their regulatory requirements – a marked improvement from two studies done in 1995 that showed a 20 percent and 42 percent success rate for wetland projects. Since this is the first study of its kind for stream restoration, it was not possible to make comparisons between past and present success rates. The current research indicates that preserving and enhancing streams brings much more success than trying to repair streams that have already suffered damage.

Success criteria for stream restoration included evidence of stable stream banks and the reestablishment of plants and trees along the stream. For wetlands, success criteria included appropriate soil saturation and survival of wetland plant species. As a result of the study, some sites deemed unsuccessful at the time they were evaluated for the study are slated for improvements.

The study evaluated mitigation projects developed by the state’s Ecosystem Enhancement Program, the North Carolina Department of Transportation and private mitigation providers. The study found no statistically significant difference in the success rates achieved by the different mitigation providers.

Several observations made during the research may lead to greater success in future mitigation projects.

  • Mitigation takes time and the 5-7 year monitoring time frame required by regulation may be too short to fully evaluate project success and see functional improvements.
  • Mitigation projects in the mountains and coastal plain are more successful than projects in the Piedmont. The clay soils of the Piedmont area tend to be highly erodible once disturbed and make it more difficult to establish vegetation. Increased use of soil amendments during site construction, stockpiling and reuse of topsoil, project design that addresses the high variability of Piedmont hydrology and a phased planting approach may be needed to improve success in this region.
  • The presence and variety of aquatic insects has been a well-established indicator of stream health for streams with watersheds that are three square miles or larger. Most watersheds for stream mitigation sites are less than three square miles. Through an EPA grant, DWQ is evaluating a modified approach that uses the aquatic bug index for smaller watersheds, to assess whether stream mitigation success can be measured by biological change.

To view the entire report, visit the DWQ website at www.ncwaterquality.org and scroll down to the Hot Topics section.

Kathleen O'Nan

Kathleen O'Nan is a contributing reporter to Carolina Public Press.

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