PHYTOPLANKTON CONTROLS ON NUTRIENT INFLUXES: EVIDENCE FROM FRESHWATER MESOCOSM SYSTEMS

Interactions between nutrient availability and phytoplankton growth play a foundational role in shaping lake ecosystem function. However, climate change has disrupted the rate and timing of nutrient delivery to lakes via extreme storm events, drought, changing ice cover, and altered mixing regimes. Increased and variable nutrient loading can stimulate changes in phytoplankton biomass, community composition, and functional diversity. To investigate the impact of changing nutrient delivery timing on phytoplankton functional diversity and biomass, we deployed 16 pelagic (closed-bottom) mesocosms on Lake Champlain, Vermont, USA. We tested three nutrient addition treatment groups and a control over a 14 day period: all nutrients at once (pulse), daily additions (press) and sporadic (random pulse). Besides the control group, all treatments were increased by the same nutrient concentration by the end of the 14 days (84 µg NH4-N/L and NO3-N/L and 31 µg PO4/L), manipulating only the rate of delivery. The treatments were meant to simulate natural occurrences of nutrient pulses into lakes such as agricultural run-off, mild or extreme rain events, intermittent mixing, and snow melt. Preliminary results indicate variability in phytoplankton response between treatments, with ongoing analyses examining differences in metabolic carbon flux. These results provide insight into phytoplankton traits that are conserved across disturbance events and will facilitate prediction of community composition and functional diversity of phytoplankton communities with intensifying climate change.

Presentation Preference: Poster

Primary Presenter: Eva Hendrickson, Rubenstein Ecosystem Science Laboratory (eva.hendrickson@uvm.edu)

Authors:

Eva Hendrickson, University of Vermont  (eva.hendrickson@uvm.edu)

Breeana Barile, University of Vermont  (bbarile1@uvm.edu)

Carl Betz, University of Vermont  (Carl.Betz@uvm.edu)

Ana Morales, University of Vermont  (Ana.Morales@uvm.edu)