POST-GLACIAL EVOLUTION OF NORTHERN NEW ENGLAND LAKES

Sedimentary records from northern New England lakes provide insight into the changes in surface and lacustrine processes that took place during the early Holocene. The timing and rate of aquatic and terrestrial ecosystem development can be investigated using the elemental and isotopic compositions of sedimentary organic matter. This study focuses on lakes formed in the barren, carbon and nutrient poor watersheds that resulted from deglaciation during the late Pleistocene/early Holocene.

Four to six meter long sediment cores were retrieved from six small (0.07 to 1.43 square km) post-glacial lakes in Maine, New Hampshire, and western New York. Each core displays a transition from organic-poor sands and silts to organic-rich gyttja-type sediments. The amount of organic matter present in the sediments is an indicator of the paleoproductivity within the lake. Stable carbon isotope and carbon/nitrogen (C/N) ratios were used to determine the origin of the organic matter (aquatic vs. terrestrial) in the sediments as well as track fluctuations in the types of vegetation growing in the surrounding watershed.

Negative carbon isotope shifts of up to 7 per mil were observed in the studied cores. These correspond to increases in organic matter content within the sedimentary record, and correlate with the transition from the older organic-poor sediments to the younger organic-rich sediments.

Detailed records of isotopic and elemental composition have been produced by previous studies for four post-glacial lakes in Vermont. Comparing the isotopic and elemental records of the lakes in Maine, New Hampshire, and New York with those in Vermont gives us the opportunity to investigate differences in ecosystem establishment in northern New England on both a local and a regional scale.