DEPOSITIONAL SIGNATURES OF HISTORICAL FLOOD AND HUMAN LANDSCAPE DISTURBANCES AND THE PERSISTENCE OF ELEVATED SUSPENDED SEDIMENT YIELDS FOLLOWING EXTREME EVENTS

Sedimentary archives in lakes and ponds are widely used to reconstruct past climatic and environmental conditions, as well as to quantify the environmental impacts of human activity. In this study, we summarize the characteristics of sedimentary deposits associated with different types of disturbances including floods, landslides, and human land use. We evaluated sediment cores from a network of lakes across the northeastern U.S. in combination with remotely sensed observations of suspended sediment concentration in major northeast rivers. Cores were analyzed to identify distinct event deposits and changes in clastic sediment input indicative of landscape disturbances. Lacustrine flood deposits are typically thin (mm to cm scale) layers characterized by sharp contacts between dominant gyttja and fine-grained clastic flood layers; the most extreme hydrologic events that are associated with widespread landslide activation (such occurred during tropical storm Irene in 2011) result in sharp basal contacts between gyttja and clastic sediment, and thick (10s of cm) deposits characterized by compositional grading from more clastic to more organic rich sediment, and have complex patterns of textural variability. Repeat coring over more than 10 years following tropical storm Irene, demonstrate that these depositional characteristics reflect the persistent legacy of elevated sediment delivery over multiple years as the landscape continues to stabilize following the original disturbance. Remotely sensed observations of suspended sediment further reveal the legacy of landscape disturbances that resulted from Irene, with more frequent occurrences of elevated suspended sediment after 2011 in numerous rivers across the northeast region.