LB 2-9 - CANCELLED - Who’s Left Out in the Cold? Shallow and Deep Winter Phytoplankton Assemblages (Finger Lakes, N.Y., USA)

Background/Question/Methods:

Historically, phytoplankton sampling was constrained to temperate zone lakes in the spring through fall seasons. Concerns about climate change reducing the time of ice cover have highlighted the lack of knowledge of plankton over winter in most lakes. Many key processes related to summer plankton assemblages and eutrophication may occur under the ice. As ice-on periods in northern temperate zones decrease, there is increasing urgency to characterize winter conditions in diverse lakes, to improve understanding and modeling efforts. Differences among winter phytoplankton assemblages in New York Finger Lakes with varying trophic states and ice covers (due to depth and fetch) may have implications for predicting and modeling the consequences of increasing loss of ice cover under global climate change scenarios. New York State DEC and SUNY ESF collaborated to examine the winter plankton of the Finger Lakes over four years (2018-2021), as part of a larger NYSDEC winter limnology project. At each sampling, phytoplankton were collected from both shallow (1.5 m) and deep water. Phytoplankton were preserved with Lugol’s iodine solution, settled using the Utermöhl technique, and counted on an inverted microscope. Phytoplankton assemblage data were analyzed for each sampled Finger Lake, from November through April for each study year.

Results/Conclusions:

Phytoplankton assemblages were less diverse and phytoplankton less abundant than reported from historical summer data, with a reduction in large colonial and filamentous taxa. Deep phytoplankton assemblages were less diverse and had lower cell densities than did the shallow assemblages.