POST-GLACIAL SEDIMENT DELIVERY CONTINUUM TO AN IMPOUNDED VALLEY REACH IN CENTRAL MAINE: A MULTI-DISCIPLINARY APPROACH

Freshwater lakes in the northern United States and Canada archive stratigraphy that can provide records of sediment supply since deglaciation. The records are unique due to the presence of glacial sediments, glacially-carved pools in the longitudinal profiles of stream and river valleys, and the influence of dams and human activities on surface water hydraulic conditions. We use ground-penetrating radar (GPR), sedimentary core analysis, acoustic bottom mapping, existing high-resolution topography, and empirical modeling to investigate dynamics from para- and post-glacial periods through the present. We map sediment sources and the stratigraphy and volume of deposits associated with a 175 ha freshwater lake system with a 33.1 km² watershed on the Kennebec-Penobscot watershed divide (Kingsbury Pond, central Maine, USA). A combination of core data and GPR analysis indicate that high inorganic sediment delivery (1,417–1,913 Mg yr^-1) dominated Kingsbury’s sedimentary environment until 8,550–8,410 cal yr BP—implying longer paraglacial conditions than assumed—after which sediment load decreased by more than an order of magnitude (to just 65–87 Mg yr^-1). We compare these calculations to empirical estimates of water erosion for the watershed and discuss the implications and limitations of such comparisons. We also examine topographic evidence that suggests that much of the inorganic sediment may have been excavated from large outwash channels during deglaciation, and potentially that an extended paraglacial watershed configuration delayed the transition from inorganic to organic-dominant sediment.