The sediment delivery continuum from deglaciation to the modern watershed based on lake sedimentary deposits in the Northeastern USA


Nesbitt, Ian M.; Campbell, Seth W.; Smith, Sean MC; Koffman, Bess G.; Arcone, Steven A.; Schild, Kristin M.

Quaternary Research (in review)

doi: None

PDF (preprint)


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, and existing high-resolution topography 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 (Kingsbury Pond, central Maine, USA). 14C and core data analysis indicate that high inorganic sediment load 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. 210Pb analysis shows a threefold sediment load increase since AD ~1960, coinciding with extensive disturbances from human activity, which exceeds empirical erosion estimates for this watershed by a factor of five. We suggest our methods could be used throughout New England because the generally low water conductivity allows effective use of GPR.

Plain-text abstract

Lakes in the northern United States and Canada contain sediment that can provide records of sediment delivery since the end of the last ice age. The records are unique (in comparison to lakes from unglaciated areas) due to the presence of glacial sediment, glacially-carved pools in the river valleys, and the influence of dams and human activities. We use ground-penetrating radar (GPR), sediment cores, sonar mapping, and existing high-resolution elevation data to investigate how the landscape has changed since the glacial period. We map sediment volume, structure, and distribution in Kingsbury Pond, a 175 hectare freshwater lake system with a 33.1 square kilometer watershed in central Maine, USA. While the ice sheet had retreated past this location by about 14,200 years ago, radiocarbon and core sediment data tell us that the sediment delivery rate was high and the sediment was very low in organic material until about 8,500 years ago, which is much longer than we expected. Normally, organic material replaces inorganic material as the dominant sediment type fairly quickly after a glaciation ends. After this transition period, the sediment load decreased by more than 90% and became primarily organic. The late transition could be due to changes in the watershed that occurred long after the ice sheet retreated. Analysis of the radioactivity of a naturally occurring type of lead in the top half-meter or so of sediment tells us that sediment delivery has increased by a factor of three since about 1960, which coincides roughly with modern post-colonial settlement. These methods could be used in other lakes in New England that have very low salinity, as that provides the ideal conditions for GPR surveys.