Calibration, comparison, and experimentation of testate amoebae (arcellacea) as Holocene water quality proxies in lacustrine systems

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Kornecki, Krystyna
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Linear regression analyses support testate amoeba 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 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 a good indicator of eutrophication, except for Difflugia proaetiformis; 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; we also find 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.
Experiments yielded algal (diatom) blooms in some tanks. Testate amoebae were found within these blooms, mainly Centropyxis aculeata and Cucurbitella tricuspis. Amoebae also occurred in sediment and water samples, indicating living tests propagated in both areas. Though the species distributions did not correlate with nutrient enrichment treatments, this first attempt at observing testate amoebae in mesocosms shows promise for future studies. An assessment of methodology and future improvements are discussed.
A pilot study on testate amoebae was conducted utilizing mesocosms as a means to cross-check previous work by the author and to validate correlative water quality values from previous studies in the testate amoeba literature. Mesocosm experiments provided an intermediary approach between natural settings where many variables cannot be controlled and laboratory experiments that have shown to be problematic when culturing testate amoebae. Mesocosms were treated for no-, low-, and high-nutrient systems and testate amoebae and diatom communities were quantified.
Pollen zones, radiocarbon, Cs, and Pb profiles constrain sediment ages and mixing depth. Our modern testate amoebae and diatom assemblages (Kornecki et al. submitted), together with published records of testate amoebae, diatoms, pollen, and NPP, in the literature from proximal lakes provide the means to interpret downcore proxies and reconstruct past lake conditions. Increases in phosphorus-tolerant difflugid strains of testate amoebae, as well as high productivity diatoms and NPP, indicate modern eutrophication (post European-settlement). Proximity to well-developed and populated shorelines is not clearly related to amount or timing of increase in nutrients (eutrophication) based on microfossil evidence. Sediment sources and paleo-records are noticeably different at Paradise Bay and Huletts Landing, displaying different microfossil and stable isotope records than the rest of those described in the Lake George basin. Dome Island core (~30 m water depth) may have been impacted by strong bottom currents, indicated by sparse, low-diversity oxidation-resistant NPP and testate amoeba assemblages. Proxy data does not support a strong influence from road-salt contamination in Lake George.
We conducted a multi-proxy study using microfossil assemblages (testate amoebae, diatoms, pollen, and non-pollen palynomorphs-NPP) and bulk sediment stable isotopes (δ15N, δ13C) from 8 cores to reconstruct anthropogenic influence on the lake (e.g., salt loading, eutrophication, pollution, temperature).
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 reveals increasing anthropogenic impact over the past 30 years. To reconstruct anthropogenic influence on the lake (e.g., salt loading, eutrophication, climate warming), modern stable isotopes and testate amoeba and diatom assemblages were characterized in surface sediments from 33 lake-wide sites and link their variability to 36 years of water quality data.
August 2018
School of Science
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Rensselaer Polytechnic Institute, Troy, NY
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