THE EFFECTS OF EXTREME HYDROLOGIC DISTURBANCE EVENTS ON PHYTOPLANKTON COMMUNITY DYNAMICS IN SHALLOW DYSTROPHIC LAKES

Phytoplankton act as ecosystem sentinels in lakes where community structure, biomass, and primary production are rapidly affected by disturbance events. Over July 10-11th during both 2023 and 2024 the Northeast U.S. experienced high intensity precipitation events leading to catastrophic flooding and extensive ecosystem change across the region. Here we assess the effects of precipitation rate and quantity on phytoplankton community dynamics in two dystrophic, shallow lakes over two years. We integrated discrete bi-weekly sampling with high frequency temperature and dissolved oxygen measurements in two Vermont climate-sentinel lakes. We characterized water chemistry and phytoplankton community structure during the ice-free periods of 2023 and 2024. Both lakes are shallow with minimal  watershed development and no artificial water-level fluctuations. They differ in annual mixing regimes (dimictic and polymictic, respectively) and amount of precipitation during the two flood events. In both lakes phytoplankton biomass decreased with increased volume of precipitation within 30 days. Biomass of mixotrophic taxa, however, either increased or remained stable following extreme hydrological events across both sites. Our results suggest that slow growing, complex, colonial mixotrophs may be more resistant or resilient to extreme hydrologic disturbance events than obligate autotrophs in small dystrophic lakes. These findings have important implications for biogeochemical processing in these systems as the frequency and intensity of extreme events increases with climate change.

Presentation Preference: Poster

Primary Presenter: Rachel Cray, University of Vermont (rcray@uvm.edu)

Authors:

Rachel Cray, University of Vermont  (rcray@uvm.edu)

Ana Morales-Williams, University of Vermont  (ana.morales@uvm.edu)