IMPACT OF RUN-OFF VARIABILITY ON PHYTOPLANKTON COMMUNITY STRUCTURE AND FUNCTION - RESULTS FROM A LAKE MESOCOSM EXPERIMENT

Extreme rainfall can cause high loadings of coloured dissolved organic matter (cDOM) and nutrients from the catchment into lakes. While phytoplankton and bacteria compete for nutrients, the outcome depends on whether the phytoplankton is limited by light reduction caused by cDOM, and how much the bacteria are able to utilise DOM-carbon. In addition, we propose that the temporal variability in loading may strongly impact the plankton community, specifically phytoplankton community composition, biomass and function. We tested the run-off variability in a mesocosm experiment at SITES AquaNet in Lake Erken, Sweden, in summer 2022. The same amount of cDOM and nutrients were added, but at different frequency and intensity: Daily, Intermittent, Extreme, no addition (Control) over 20 days, followed by a 16-day recovery phase of no additions. Phytoplankton community composition was analysed using microscopy and FlowCam with a semi-automated machine-learning approach for classification. We show that the Daily and Intermittent cDOM and nutrient additions promoted opportunistic taxa such as cyanobacteria and small green algae, while light limitation resulted in lower phytoplankton growth and biomass, but appeared to promote competition with bacteria in the Extreme additions. Phytoplankton functional groups showed pronounced differences between treatments in terms of size, coloniality and trophic strategy. We conclude that run-off variability impacts the taxonomic and functional composition of the phytoplankton community, thus affecting energy transfer and food web processes in lakes.

Presentation Preference: Oral

Primary Presenter: Katerina Symiakaki, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) (katerina.symiakaki@igb-berlin.de)

Authors:

Katerina Symiakaki, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (katerina.symiakaki@igb-berlin.de)

Emma Gray, ATU Marine and Freshwater Research Centre  (Emma.Gray@atu.ie)

Bence Gergácz, Eötvös Loránd University  (bencegergacz@gmail.com)

Bence Buttyán, Eötvös Loránd University  (bence.buttyan@gmail.com)

Gabriela Ágreda-López, Uppsala University  (gagredal@gmail.com)

Antonija Kulaš, University of Zagreb  (antonija.kulas@biol.pmf.hr)

Yaqoob Majd Muwafaq, University of Debrecen  (majd.muwafaq@science.unideb.hu)

Ingrid Sassenhagen, Leibniz Institute of Baltic Sea Research Warnemünde  (ingrid.sassenhagen@io-warnemuende.de)

Jens Nejstgaard, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (Jens.Nejstgaard@igb-berlin.de)

Silke Langenheder, Uppsala University  (silke.langenheder@ebc.uu.se)

Stella Berger, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (Stella.Berger@igb-berlin.de)