SEASONAL DYNAMICS OF PHYTOPLANKTON NUTRIENT LIMITATION IN A HYPEREUTROPHIC RESERVOIR

In some areas, rainfall events are increasing in frequency and intensity, particularly in winter and spring seasons. Rising air temperatures also reduce ice cover in northern lakes and may raise lake temperature during the winter These changes impact aquatic ecosystems, affecting internal dynamics like lake stratification and external factors such as watershed nutrient inputs. Although recent studies highlight that phytoplankton can be active during the ‘non-growing season’, we know little about how altered precipitation or temperature regimes influence these communities. For example, it is unclear whether these non-growing season phytoplankton are nutrient-limited and how they respond to nutrient pulses. We performed weekly nutrient limitation bioassays in a Midwestern US  hypereutrophic reservoir for one year with four treatment groups (control, +Nitrogen (N), +Phosphorus (P), and +NP). We found substantial differences between the control and treatment groups. Phytoplankton transited from P to NP/N limitation in late summer, potentially due to reduced precipitation and nutrient loading. Outside the growing season, algae remained nutrient-limited into the winter, demonstrating continued activity. Phytoplankton biomass remained high until factors, such as hydraulic flushing or extreme cold temperatures, decreased abundance/prevented growth. Results highlight that algae can be nutrient-limited during the non-growing season and show the influence of precipitation and temperature on algal dynamics in a lake transitioning from winters with seasonal ice cover to open waters.

Primary Presenter: Kloe Atwood, Miami University (atwoodk2@miamioh.edu)

Authors:

Kloe Atwood, Miami Universtiy  (atwoodk2@miamioh.edu)

Lesley Knoll, Miami Universtiy  (knolllb@miamioh.edu)