A PALEOLIMNOLOGICAL STUDY OF HOLOCENE SEDIMENTS IN ST. ALBANS BAY, LAKE CHAMPLAIN (USA-CANADA)

Undisturbed lake sediments retain information on ecosystem changes within the lake and surrounding watershed. Therefore, a multi-proxy analysis of lacustrine sediment cores is a useful means of creating paleoenvironmental reconstructions. The chemical and physical characteristics of lake sediments can provide information about sources of organic matter, lake productivity, and a record of previous climatic fluctuations. Two sediment cores extracted from St. Albans Bay (SAB), Lake Champlain, Vermont, are being analyzed to record the lake’s response to climatic and environmental changes from ~500 to 9000 years ago, determine if the bay shows similar responses to natural climate variability versus cultural eutrophication, and to determine the rates of deposition and origins of organic matter in Holocene sediments in the bay. SAB occupies a drowned river valley in Lake Champlain’s northeast arm, and covers 7.2 km² with an estimated volume of .09 km³, with a mean water depth of 8 m. It has a catchment area of 130 km² that drains a watershed comprised of 24% forest, 56% agriculture, and 14% developed areas.

A previous study (Burgess, 2007) used a sediment core from SAB to investigate the last 4500 years of the bay’s history. Results showed that relatively high organic matter (OM) content in older sediments mimicked amounts recorded in the most recent sediments. Recent elevated amounts of OM are thought to be a consequence of human-induced eutrophication. Archaeological studies indicate that before about 1750 there was not a large enough population of humans in the Champlain Valley to significantly alter nutrient loading to the lake. This suggests that in the lower portion of the sediment record, elevated productivity levels in the lake were related to natural climate and environmental change rather than human disturbance. This study compares proxy results from long sediment cores, encompassing the last ~9000 years, to the results of the Burgess 2007 study. Proxies used include magnetic susceptibility, organic matter content (measured as %C_org), C/N ratios, biogenic silica (BSi), particle grain size, and stable carbon isotopes.