PRELIMINARY EXAMINATION OF POST-GLACIAL SEDIMENTATION IN OSSIPEE LAKE, NEW HAMPSHIRE: LAND-USE VERSUS CLIMATE CHANGE

Land-cover and climate changes, attributed to natural and anthropogenic forcings, cause deviations in geomorphic processes that act to deliver sediment from watersheds to lakes. Results from a study in Vermont show that lake sedimentation appears to be sensitive to antecedent soil moisture conditions and flooding rather than the extensive land-use changes that have occurred in New England over the past few centuries (Cook et al., 2015, Geophysical Research Letters). Using lake sediment cores from Ossipee Lake (43.7°N, 71.1°W), Ossipee, New Hampshire, this project aims to quantify watershed erosion patterns over centennial to millennial timescales to understand how land-use and climate change affect this landscape. A 2.2 m core, in addition to two shorter cores, was recovered during the summer of 2017. A seismic survey was also conducted, which provides evidence for historic lake level changes and the formation of a large sandy shelf at the mouth of a river input. Down core measurements of magnetic susceptibility, loss on ignition, charcoal counts, and bulk chemistry, combined with age-depth modeling, are used to quantify changes in deposition rates through time. Preliminary lake-sediment data suggest that clastic deposition has varied widely with pre-settlement deposition matching or exceeding changes observed over the historic period. Changes in watershed erosion patterns inferred from the lake sediments will be compared with documented flooding, land-use, historical, and paleoclimate records to identify the sources and processes of erosion in the watershed.