A comparison of glacial and land-use controls on erosion in the northeastern United States

Abstract

Global studies assert that anthropogenic activity now leads to disproportionately higher rates of landscape change compared with background geomorphic processes. This study explores the relative influence of anthropogenic, glacial, and geologic processes on erosion rates (E) in the northeastern United States (NEUS) by analyzing published erosion and sedimentation data across multiple methods and timescales. I compile erosion rates and sediment yields from records of stream gauging, reservoir sedimentation, lake sedimentation, cosmogenic nuclides in stream sediment, and thermochronology. These data serve as a comparison point for quantified volumes of sediment deposited in valley bottoms as a result of European settlement in the NEUS, where glacial history may influence the availability of erodible sediment and, as a result, the relative magnitude of deposited sediment. I hypothesize that E in the formerly glaciated region will be lower than unglaciated E over last century (stream gauging and reservoir sedimentation) timescales due to the erosive power of continental glaciation and resultant thin upland soils, and that there will be an increase in E evident over the last century as a result of human influence. 499 sites with location data were compiled across the NEUS, converted to erosion rate (mm/yr) and sediment yield (Ys; t km-2 yr-1), and analyzed using statistical z-tests to determine whether the population means are significantly different. Mean E from all record types across both the glaciated and unglaciated NEUS exhibits a range smaller than one order of magnitude (0.012-0.055 mm/yr), much less variable than order-of-magnitude differences reported by other researchers comparing modern and geologic erosion, both regionally and globally. Last century timescales exhibit higher E in the unglaciated region than the glaciated region, but only reservoir sedimentation shows a significant difference in E between regions (0.012 vs. 0.055 mm/yr; glaciated and unglaciated, respectively); stream gauging E did not exhibit a significant regional difference, likely due to the large basin sizes, short measurement timescales, and disproportionate spatial distribution of the measurements. E does not increase from geologic to last century timescales: late Quaternary (lake sedimentation and cosmogenic nuclide) records consistently yield lowest E, with geologic (thermochronology) records showing the highest E in both regions, perhaps indicating the relative importance of E over timescales during which major orogenies were occurring in the NEUS. The similarities in mean E and large range of the distributions of all timescales, however, point to the relative stability of E over time in the NEUS.