Collaborative research: Is Anthropocene sedimentation in valley bottoms a geologically significant event?

Franklin And Marshall College, Lancaster PA

Investigators

Abstract

Non-technical description of the project's broader significance and importance Recent research in geomorphology, the study of Earth's surface and the processes that shape it, has found that human modification of land in the northeastern U.S. over the past few centuries has resulted in large volumes of sediment being eroded from hillsides and deposited in valleys along rivers and streams. Prior research has suggested that this sediment transfer is the most important modification of Earth's landscape in tens of thousands of years. This project will evaluate the significance of these deposits on a regional scale by carefully measuring them in representative field locations and then using newly available high-resolution topographic data to extrapolate the findings to whole watersheds and regions. Knowledge of how human activities have contributed to landscape change is a prerequisite for informed land-management and restoration decisions. To ensure broad communication of project findings, the researchers will interact with policy makers, planners, government agencies, and non-profit organizations interested in stream and wetland conservation. This project also will include strong opportunities for student research, since the collaborating institutions are heavily invested in undergraduate education as a priority. Technical description of the project Recent global sedimentation studies demonstrate that rates of erosion due to human activities exceed the amount of sediment delivered to the oceans by rivers. At the same time, field-based studies at the channel to watershed scale have found large quantities of sediment stored in valley bottoms during the past few centuries. This project will bridge the gap between global and watershed-based approaches by quantifying the amount of Anthropocene (recent, human related) sediment stored in valley bottoms of the northeastern United States, and then comparing this amount to published volumes and timescales of (1) erosion from the landscape, and (2) deposition in reservoirs, lakes, and estuaries along the Atlantic margin. The research will use high-resolution topographic data to map the extent and thickness of this fill over large spatial areas (1,000-10,000 square km), and will test these methods using fieldwork (mapping, coring, geophysical data collection, sediment sampling and dating) in key watersheds. A central goal is to evaluate the extent to which sediment storage in the unglaciated mid-Atlantic region applies in the glaciated, less-studied New England region, where upland soils are thin, sediment sources are generally localized to glacial deposits, and large natural lakes and wetlands provide terrestrial accommodation space. The results of the project will help resolve the discrepancy between erosion and deposition rates at small spatial (watershed) and temporal (decadal to centennial) scales versus the rates that occur globally and over geological time.