CALIBRATING PALEO-BIOMONITORS IN LAKE GEORGE, NY SEDIMENTS WITH MODERN GEOCHEMICAL AND LIMNOLOGICAL MEASUREMENTS

Lake George (NY) is surrounded by Forever Wild forest in the Adirondack Park and has a Class AA Special water quality rating. Nonetheless, lake monitoring revealed increasing anthropogenic impact over the past 30 years (Boylen et al. 2014). To reconstruct anthropogenic influence on the lake (e.g., salt loading, eutrophication, pollution, climate warming), we characterize modern testate amoebae and diatom assemblages in surface sediments from 33 lake-wide sites and link their biotic variability to carbon and nitrogen sediment stable isotopes as well as 30 years of water quality data.

Diatom and testate amoebae assemblages categorize modern lakebed sites into four subgroups: 1) benthic macrophyte; 2) high nutrient/shallow transition; 3) deep transition/sulfate; and 4) oligotrophic planktonic. Linear regression analyses support testate amoebae as rapid responders and recorders of environmental change. Taxa are strongly correlated with percent change of important water quality parameters. Our assessment indicates that: 1) Cucurbitella tricuspis is a valuable aquatic macrophyte indicator, supported by the co-occurrence of Cocconeis spp.; 2) centropyxids may be useful in determining the presence of salt loading, although salt is not likely the driving parameter for their distribution in Lake George; 3) Difflugia protaeiformis “claviformis” and D. protaeiformis “acuminata” have both overlapping and unique correlations, suggesting the need for further investigation into the utility of these closely related strains; and 4) Difflugia oblonga “bryophila” shows intolerance to NO₃ and a strong correlation with sodium. Difflugia oblonga “bryophila” is not often cited in the literature as a useful proxy, but our study indicates that along with having a low tolerance for NH₄, it may be a cold-water, low-silicon, high salt content, and/or a low water clarity indicator. Our results show that testate amoebae are highly sensitive to small environmental change even in an oligotrophic lake with very good water quality. Correlation coefficients of water quality variables and strains within a species illustrate gradational relationships, suggesting that testate amoebae exhibit ecophenotypic plasticity. These surface sediment calibrations of microfossil assemblages will facilitate downcore interpretations in future work.