Channel head response to anthropogenic landscape modification: A case study from the North Carolina Piedmont, USA, with implications for water quality

European-American settlement of the south-eastern United States introduced agricultural practices that included extensive clearing of forested hillslopes to support food and cash-crop agriculture. This land disturbance has long-term effects on stream morphology by displacing channel heads down-valley, impacting downstream sediment and nutrient supply as channel heads migrate back up-valley towards their pre-disturbance locations. This study investigates 40 stream channels in William B. Umstead State Park in the Piedmont of North Carolina using relationships between local slope and contributing drainage areas to predict channel head locations and compare these to their observed positions. Further, expected eroded sediment and nutrient contributions are quantified using migration distances and sampled soils near channel heads. Of the 40 investigated channel heads, 23 are located down-valley from their predicted location by an average of 174.4 m +/- 109.6 (1 - sigma). Using this distance and average channel cross-sectional area, 1.6 +/- 1.4 m(2) (1 - sigma), the expected future erosion per channel is 282.6 +/- 177.6 m(3) (1 - sigma). Drainage density was used to extrapolate volumes to the 23 km(2) park using a conservative estimate that 50% of the first-order channel heads will migrate up-valley, implying an additional 90.4 +/- 56.8 x 10(3) m(3) (1 - sigma) of sediment is expected to erode from the study area. Finally, scaling these volume estimates to sampled soil nutrient values indicates that approximately 1053 +/- 662 t (68% confidence) of carbon, 51 +/- 32 t of total nitrogen, and 15 +/- 9 t of phosphorus are anticipated to enter the fluvial system in response to channel head migration from within the confines of this state park, representing only 1% of the land area in Wake County. These findings suggest that regional water quality challenges posed by suspended sediments and nutrients will persist for hundreds to perhaps thousands of years from non-point sources as first-order channels continue to erode headward towards their equilibrium landscape positions.