NC
Department of Transportation Center for Transportation and the Environment:
The Effects of Highways on Wetlands.
A major objective of research at the Duke Wetland Center is to develop methods to assess and minimize human impacts on wetland systems. We are currently refining a functional assessment framework for wetlands using carefully chosen parameters as "key indicators" of ecosystem level functions. For wetland systems we have grouped these functions into five categories including hydrologic flux and storage, biological productivity, biogeochemical cycling and storage, decomposition and community/wildlife habitat. In our studies these key indicators are measured simultaneously in the impact wetland and several reference wetlands.
In the first phase of our study, we assessed the impacts of highway operation upon two Cypress/hardwood swamps located in the coastal plain region of North Carolina. Alterations of hydrology in these wetlands have resulted in reductions in woody plant cover and in changes in the aquatic invertebrate community. These changes in hydrology are largely related to the elevation of drainage culverts that pass through highway fill. The culvert bottoms are positioned at higher elevations than the sediment surface in the surrounding wetlands. As a result, ponding occurs upstream of the highway during periods of low flow and this has resulted in a shift from a forested wetland community to an open water or emergent plant community. Simple changes in highway design such as the number and placement of culverts could reduce the impact of highways upon similar wetland systems.
In our current phase we are assessing the impact of highway construction on brackish wetlands located adjacent to the New River Estuary near Jacksonville, N.C. The assessment framework developed in the previous phase is being refined and modified for brackish wetlands. We have collected baseline data for a full field season prior to the beginning of highway construction in both an impact wetland and two reference wetlands. We plan to monitor these wetlands through the construction phase and through any recovery phase. The objectives of our current research are to produce assessment criteria specific to coastal wetlands and to identify highway construction techniques and designs that minimize impacts.
Contributed by Neal Flanagan, Ph.D.
[Research]
