STREAM INCISION IN THE SOUTHEASTERN PIEDMONT AS A DRIVER OF HABITAT CHANGE

Human impact on the environment causes stream incision throughout many parts of the world. Specifically, incision along the valley bottom drives deep vertical erosion of stream channels faster than is natural and without the accompanying horizontal erosion. At our specific site, a small 1st order stream within Fisher Farms Park in Davidson, NC, stream incision is actively occurring in the form of a knickpoint migrating headwardly through the valley bottom. Below the knickpoint, the stream is deeply incised while above the knickpoint the stream has an anastomosing morphology. To examine the impact of the incision on hydrologic and ecologic systems, we examined groundwater levels, plant communities, and macroinvertebrate communities. Our results indicate that the stark difference in incision is accompanied by differences in groundwater levels, plant assemblages, and macroinvertebrate assemblages, suggesting stream incision is a driver of these environmental differences. Specifically, groundwater levels upstream of the knickpoint rarely fell more than 0.4 meters below the surface while the depth below the knickpoint was regularly more than a meter below the surface. Plant communities above and below the knickpoint were different with more than two thirds of species only being found in one habitat. Species diversity was also higher upstream. The macroinvertebrates also had dissimilar assemblages above and below the knickpoint but had similar levels of diversity. In conclusion, our results suggest that the differences in groundwater level and flood frequency drive changes in the habitat, leading to differences observed in plant and macroinvertebrate assemblages. Our data suggests that widespread stream incision caused the loss of much of the natural riparian habitat found throughout the southeastern Piedmont and that valley bottom ecology was likely much different prior to Euroamerican settlement.