Nineteenth century land-use, watershed erosion, and sediment yield in Southern Appalachia.

摘要

The purpose of this research was to gain insight into the anthropogenic forcing of geomorphic systems, specifically how nineteenth century land-use changes impacted watershed hydrologic, upland erosional, and sediment delivery subsystems of Southern Appalachian headwater catchments. Identification and analysis of the timing and rate of change in these subsystems, and the reestablishment of presettlement conditions, were used to address landscape sensitivity and watershed inheritance issues in a region undergoing population expansion and development.;Archival research was used to reconstruct concurrent land-use changes in the catchments of two nineteenth century water-powered mills. Changes in the physical properties of mill pond sediments including, organic content, particle size distribution, and magnetic susceptibility, were used to interpret trends in sediment source during the span of mill operation. Interpolation of augering and coring data was used to determine mill pond sediment mass and pond capacity.;Hillslope hydrologic change occurred almost immediately following land conversion. Upland erosion began with the removal of A-horizon fines, and progressed with the removal of A-horizon coarse particulates, and then B-horizon particulates. Change from one source category to another was punctuated by high flow events signifying an integration of human activity and climate in the changing of system boundary conditions.;Late nineteenth century sediment yield in Southern Appalachia was almost as high as that reported for the adjoining Piedmont although only 25 percent of highland watersheds were converted to agriculture. However, sediment delivery ratios were relatively low indicating a more complicated relationship between hillslope-channel connectivity and soil erosion. In reforested watersheds, both the hydrological and erosional subsystems reverted to presettlement conditions within a few years but may have taken up to one hundred years for sediment yield rates to return to presettlement conditions. Finally, the sediment trapped behind nineteenth century dams has served as a significant source of ecologically damaging washload to highland streams during the twentieth century.