The Canary in the Coal Mine: Testate Amoebae Record Anthropogenic Impacts in Sediments of Oligotrophic Lake George, NY, USA

Abstract

Lake George (NY) is surrounded by Forever Wild Forest in the Adirondack Park and has a Class AA Special water quality rating, yet lake monitoring has revealed increasing anthropogenic impacts from salt and nutrient loading over the past 30 years. To reconstruct anthropogenic influence on the lake (e.g., salt loading, eutrophication, climate warming), we characterized modern stable isotopes and testate amoeba and diatom assemblages in surface sediments from 33 lake-wide sites and compared their variability to 36 years of water-quality data. Linear regression analyses support testate amoebae as rapid responders and recorders of environmental change because taxa are strongly correlated with percent change of important water quality parameters. Our assessment indicates that: 1) Netzelia gramen is associated with aquatic plants and filamentous algae, making them a valuable aquatic plant/alga indicator, which is supported by the co-occurrence of the diatom Cocconeis spp.; 2) difflugids are generally good indicators of eutrophication, except for Difflugia protaeiformis; and 3) seasonal differences in water quality trends are reflected in the fossil record on decadal time scales. We show that testate amoebae are highly sensitive to small environmental changes in an oligotrophic lake and exhibit established relationships from eutrophic and mesotrophic lakes as well as new, likely oligotrophic-specific correlations. Correlation coefficients of water quality variables and strains within a species also illustrate gradational relationships, suggesting testate amoebae exhibit ecophenotypic plasticity. Diatom and testate amoeba assemblages categorize modern lakebed sites into four subgroups: 1) benthic macrophyte; 2) high nutrient; 3) high alkalinity; and 4) salt loading assemblages.