An assessment of highway impacts on ecological function in palustrine forested wetlands in the upper coastal plain of North Carolina

Population growth and transportation needs have resulted in highway construction in wetlands. The impact of highway construction on wetland ecological functions is not clearly understood, although the alteration of wetland ecological functions such as hydrologic flux and storage, biological productivity, and nutrient flux by highways has been observed. An assessment of the effects of fill and culvert-type highway crossings on ecological functions in palustrine forested wetlands in the Upper Coastal Plain of North Carolina was performed. A combination of functional indicators, which were used as surrogate measures of wetland function, were tested in the field and the most predictive ones were utilized in a response surface model. Using the functional indicator field data, a general functional assessment strategy/methodology was refined and functional response surface models were created to synthesize assessment results. Differences were detected between study areas upstream and downstream of the crossings and a reference area for five wetland functions--hydrologic flux and storage (180-245%), plant productivity (35-80%), biogeochemical cycling and storage (85-115%), decomposition (90-125%), and community/wildlife habitat (120-205%). Results from this exploratory study suggest that fill and culvert-type crossings disrupt or alter wetland ecological functions, mainly upstream. This study can be used in formulating a needed regional functional assessment protocol for this wetland type in the Southeast United States. Continued research is required to refine wetland response models, and to determine the effects of highway construction at increasing time intervals after highway completion.