ENVIRONMENTAL DIATOM RECORD OF CONESUS LAKE (WESTERN NEW YORK)

This study aims to assess the geohistorical record of Conesus Lake, the westernmost Finger Lake in western New York (Livingston County, NY). Ecological shifts in diatom populations can be used to pinpoint times of changes in lake conditions, like temperature. The south basin of Conesus Lake was studied from a piston core collected at 17 meters in depth resulting in 127 cm of sediments. The core was split, imaged, and analyzed for both magnetic susceptibility and XRF using a multi-sensor core logger. Sediments were sub-sampled at strategic intervals and digested in nitric acid to remove all but siliceous material. After digestion, 6 dilutions were performed and ammonium chloride was added to aid in dispersion. The solution was mounted on Optical and Scanning electron microscope slides using Naphrax mounting medium. Diatom populations were gathered using an optical microscope at 40x magnification. 300 intact individual valves were counted per slide, while complete frustules were counted as two individuals. Over 18 genera of diatoms were identified, 5 planktic and 13 benthic resulting in 21,510 occurrences. Planktonic diatoms were the most abundant throughout the core, making up 78% of all occurrences. The dominance of planktonic diatoms in the core are likely caused by deep water depth at the site of collection since light availability is limited at the lake bottom. Two of the most abundant planktonic genera, Aulacoseira and Stephanodiscus both live in similar conditions, however, Aulacoseira prefers cooler temperatures (6-20°C) while Stephanodiscus prefers slightly warmer conditions (18-19°C). When compared stratigraphically, a clear change in lake temperature occurs where Aulacoseira abundance declines towards the present (62% to 41%) and Stephanodiscus occurrences increase towards the top of the core (11% to 28%). A similar trend is shown with Asterionella (thermal tolerance of 6-15°C) with an increase of 2 to 13% towards the present and Tabellaria (2.5-16°C) with a decline from 22 to 11% towards the top of the core. Since 1970, Conesus Lake has warmed by 1.5°C (NYDEC) and the changes in diatom populations mirror the instrumental record with an overall temperature increase. Diatom populations can be further used to evaluate other environmental changes based on genus-specific autecology and abundances.