STABLE ISOTOPE CHEMISTRY OF BIOGENIC CARBONATE AND LAKE WATER; CENTRAL NEW YORK STATE

A study of water and mollusc (clam and snail) shell stable isotopes in Woodman Pond has been undertaken to develop a baseline for continued annual sampling to assess ongoing trends. Woodman Pond is a 92-acre hardwater kettle lake located near the geographic center of New York State on the northern Appalachian uplands. The lake has well developed marl benches and an abundant and diverse gastropod fauna. Isotopic analyses of surface waters show evaporative enrichment in the summer of 1999 (a relatively hot, dry summer) by up to 6 o/oo in d18O. Gastropod shell carbonate precipitated that summer averages –7.9 o/oo d18OPDB. In contrast, samples from the summer of 2000 (cool, wet summer)are characterized by water and gastropod carbonate that are, on average, lighter in terms of 18O by nearly 2.5 o/oo. Data from unionid bivalves are similar, but annual differences are subdued, perhaps because of the benthic habit of the clams. Carbon isotope data from bivalves suggest changes in either water depth or dietary preferences as the clams grow. The results of this study suggest that stable isotope data from gastropods may be a more sensitive indicator of climate change in lake systems than bivalve data.