A 2500 year sediment record from Fayetteville Green Lake, New York: evidence for anthropogenic impacts and historic isotope shift

A series (N = 12) of short (< 1 m) sediment cores were collected from merom ictic Green Lake in Fayetteville, New York to investigate potential anthrop ogenic impacts on the watershed during historic time and environmental chan ge over the past similar to2,500 years. Stratigraphic data document an abru pt basinwide change during the early 1800's A.D. from brown laminated sedim ents to grey varved sediments separated by a transition zone rich in aquati c moss. Deforestation of the region by European settlers during the early 1 800's A.D. resulted in a flux of nutrients and increased biological product ivity followed by a 7-fold increase in sediment accumulation rates. Element al geochemical data document the anthropogenic loading of lead to the to th e lake basin via atmospheric fallout. Stable oxygen isotope (delta O-18 cal cite) data also provide evidence for an abrupt shift in the isotopic compos ition of lake water similar to 150-200 years ago. This isotopic shift could have been a local phenomenon related to an increased supply of summer enri ched precipitation following removal of forest vegetation, or it might have reflected broader scale climatic changes. We hypothesize that the delta (1 )8O calcite shift was the result of the polar front jet stream migrating fr om a more southerly prehistoric position to a contracted, northerly configu ration similar to 150-200 years ago. Such a shift could have been natural, associated with the end of the Little Ice Age or it may have been anthropog enically forced.