ANTHROPOGENIC ENVIRONMENTAL CHANGE RECORDED IN BALLSTON LAKE, NEW YORK

Ballston Lake occupies a portion of an avulsed channel of the Mohawk River between Schenectady and Saratoga Springs, New York. The lake is about 5 km long, generally less than 200 m wide, and is shallow (~8 m deep) and dimictic except for the southern end, which is meromictic and over 30-m deep. Long cores (>8 meters long) indicate that the lake formed ~13,000 cal yr BP. This study was undertaken to document the record of recent environmental change recorded in the upper portion of sediment in Ballston Lake. Three sediment cores ~40 cm long were acquired from ~8 m water depth at the north end of Ballston Lake (42°57.101’N, 73°51.066’W), and were analyzed for exchangeable metals, magnetic susceptibility, total organic carbon (TOC), total inorganic carbon (TIC), and stable isotopes of carbon and nitrogen. An age model of the cores was established by correlating the initiation of a prominent increase in Pb (from 25 to >100 ppm) to AD 1900 based on ²¹⁰Pb dating of cores from nearby lakes. Other metals also show significant increases at this time, including Cu (30-200 ppm), Mn (400-1700 ppm), and Zn (75-150 ppm). Other parameters reveal progressive change from 1900 to the present; these are a steady increase in the magnetic susceptibility of the sediment, a steady decline in the C:N ratio of organic matter (from 13-10), and a steady decline in the δ¹³C values of organic matter (from -29 to -30.5 ‰). Nitrogen isotope values are generally low and vary little (+3.4 ± 0.1 ‰), but exhibit an increase of 0.6 ‰ in the last 8 cm of the core (last ~30 years). Collectively, these trends reflect a lake that is increasingly eutrophic and subjected to the atmospheric delivery of heavy metals, and with organic matter that is increasingly autochthonous.