SEDIMENTOLOGICAL RECORD OF LARGE MAGNITUDE FLOODS RECORDED IN COLLINS POND, SCOTIA NEW YORK

Any attempt to attribute changes in the frequency and magnitude of floods to human induced climate change requires an understanding of the natural variability of the hydrologic system prior to instrumental records. Prehistoric records of flood events are preserved in the sediment of ox bow lakes and avulsed channels, and this study investigates lake cores as a paleoclimatic proxy of global changes due to anthropogenic impacts on the environment.

Collins Pond (42°50’N; 73°57’W; 64 m asl) is a small (0.25 km²), shallow (z_max=8.5 m), slightly oligotrophic pond on the floodplain of the Mohawk River near Scotia, New York. The small, closed drainage basin of Collin’s Pond is similar in size to the lake itself, yet Collin’s Pond has accumulated sediment at a high rate (~7 mm yr^-1 for the last 1000 years). A 144-cm long core spanning the past ~200-yr was extracted from the center of Collins Pond in the winter of 2014. The core contains numerous alternations of dark gray and light reddish/pink laminations. Flood waters in the Mohawk River in response to Hurricane Irene 29-30 August, 2011 deposited a 14-cm thick layer of allochthonous sediment with a slightly pink color throughout the lake basin. Towards the middle of the core, there is a thick layer of pink sediment occurring from 30 to 50 cm, followed by a consistent horizon of dark gray material that extends from ~50-90cm depth. Two distinct layers of pink sediment also occur from 90-110cm and from 140-144cm, and these correspond with sharp peaks in magnetic susceptibility. These latter characteristics suggest that clastic layers were deposited by overflow during flooding events of the Mohawk River. Laminae from flood events were sampled and treated to remove biogenic silica and analyzed with a Coulter LS 230 laser grain size analyzer, as well as analyzed for total carbon and total inorganic carbon. The fine silt laminae from flood layers are slightly finer-grained than clastic sediment deposited during non-flood events; the latter sediment is derived from erosion of the steep slopes to the north of the lake basin, which are underlain by sand and gravel. Flood laminae from Hurricane Irene are the thickest flood laminae of the last 700 yr of record.