PHYTOPLANKTON RESPONSE TO SEASONAL PROGRESSIONS IN MILWAUKEE HARBOR: UNDERSTANDING PATTERNS AND INFLUENCES ON DIATOM BLOOMS

Phytoplankton abundance and community composition respond to changing environmental factors, including light, temperature, nutrients, and physical disturbances. In 2023, diatom biomass notably increased in Milwaukee Harbor, continuing into 2024. Water samples for nutrient analysis, phytoplankton biomass and counts, temperature, and light data were collected from north and south basins of Milwaukee Harbor. Important, but less immediate results, such as counting cells, are in progress. Chemical analysis revealed silicate concentrations oscillated throughout the observed period (February-August 2024), showing drawdowns of dissolved silicate (DSil) as particulate silicate (PSil) increased and vice versa. Between sampling expeditions taken in June and August, DSil decreased in the south from 65.4 µM to 33.4 µM; PSil increased from 4.6 µM to 28.2 µM. During this time, a new dominant phytoplankton species took over. No biomass nutrient was limiting in this harbor; therefore, other factors were controlling phytoplankton community composition. For example, we found that intrusions of Lake Michigan water during wind events were able to temporarily separate locations with respect to chemical composition and abundance of phytoplankton. Weather-driven variability in nutrient fluxes and changes in phytoplankton abundance and community composition have implications for climate-induced alteration of biogeochemical cycles. Observing these progressions helps us to understand phytoplankton dynamics in a freshwater harbor system, giving insight into factors driving diatom blooms.

Presentation Preference: Oral

Primary Presenter: Mary Larson, University of Wisconsin-Milwaukee (larso329@uwm.edu)

Authors:

Mary Larson, University of Wisconsin-Milwaukee  (larso329@uwm.edu)

Carmen Aguilar, University of Wisconsin-Milwaukee  (aguilar@uwm.edu)

Russell Cuhel, University of Wisconsin-Milwaukee  (rcuhel@uwm.edu)