Organic Geochemical Analysis of Late-Glacial and Early-Holocene Ecosystem Changes: A Case Study from Northern New England Lakes

The lacustrine sedimentary archive of organic remains provides important evidence for the reconstruction of the environmental histories of lakes and their watersheds, recording the response of the Earth\u27s biota to changes on scales varying from the local to the global. The last Glacial-Interglacial transition presents an opportunity to investigate how, and at what rates, watershed and lake ecosystems were established on once glaciated, carbon and nutrient-poor landscapes. The small lakes of northern Vermont (USA) provide an appropriate setting in which to investigate such changes. As part of a multidisciplinary study of three Vermont lake sediment cores, samples ranging in age from approximately 5 to 11 ka were subjected to molecular organic geochemical analysis by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Diagnostic compounds in the pyrolyzates (e.g., indole and guaiacol) permit discrimination between the principal organic matter sources (e.g., microbial and higher plant) and their shifting proportions over time as a function of environmental change. While the nature of this shift is similar, it does not occur at the same rate in all three lakes, indicating the profound influence of local conditions