EXPLORING THE DEGLACIAL, HOLOCENE, AND ANTHROPOGENIC HISTORY OF LONG POND, WILLSBORO NY, USING SEDIMENT CORES AND A GPR

Long Pond is a small naturally existing diamictic lake at the eastern edge of the Adirondack Mountains in Willsboro, New York. At an elevation of 179 m ASL it is perfectly positioned above Lake Champlain for studies of local deglaciation as well as subsequent changes through the Holocene. Previous cores in the main body of Long Pond have focused on the varve record from the earliest (Coveville) phase of glacial Lake Vermont, which was the only level high enough to reach Long Pond. Each of those cores bottomed in a gravely diamicton which may be glacial till, although the varve record suggests that there should have been at least 50 more varves below those observed. In February 2020 we began investigating the very south end of Long Pond, which we hypothesized to be a separate small sub-basin within the lake, with the goals of comparing the varve record and the depth to the diamicton, as well as focusing on the Holocene record and potential evidence of modern human impacts within the small lake basin.

The fieldwork for this study began with two Russian borings (February 2020 and March 2021) to collect material for pollen, LOI, and Pb concentration analysis and was completed with a vibracore in March 2023 and a GPR survey in June 2023. Depth of water at the core location was about 2.4 m and the GPR profile confirms that the location is in a sub-basin separated from the main body of the lake by a bedrock rise. The cores show about 6 m of organic material with a notable increase of carbonate from <1% in the top 2.2 m to as much as 9% below 3 m. There is also a sharp decline in organic carbon from >80% to <10% at 4.5 m depth. Below the shallow lacustrine sequence is a sharp contact with about 1.8 m of silt and clay glacial lacustrine varves that bottom out in the gravel diamicton. This overall sedimentary sequence is nearly identical to those found in cores from other locations in the lake, one of which has a calibrated age of 13,055 – 12,730 BP just above the varves. While we could not positively identify modern human impacts in the basin using concentrations of Pb or Ambrosia (Ragweed) pollen as we had hoped, we hypothesize that the change in carbonate concentration at 2.2 m sediment depth may be related to anthropogenic activity.