Award: OCE-1830002

This project sought to understand the microbial life that supports water quality, large economically important organisms, and nutrient cycles in freshwater systems. We focused on large lakes, which as immense freshwater systems support the health and economies of billions of people worldwide. From these water bodies people recover food and obtain resources that support local to regional economies. Freshwater systems also provide unseen essential services to the Earth system as microbial life in the water transforms energy and nutrients into new materials that support biodiversity and balance nutrients and energy across the planet. Despite the importance of these aquatic systems, and the microbial life that thrives within them, there are still many unanswered questions that limit our ability to manage resources, support human health, and predict what will happen when the system changes. We focused on photosynthetic microorganisms in the Laurentian Great Lakes. Our work revealed at least eight distinct small phytoplankton populations across the Great Lakes using a new flow cytometry approach which distinguishes cells based on the photosynthetic pigments inside them. By carefully quantifying these coexisting and closely related picophytoplankton in their environmental context for the first time, we discovered differences in the picophytoplankton community between lakes and over different depths within each lake. These results suggest that picophytoplankton perform different ecosystem services in different areas of the Great Lakes, despite the hydrological connectivity of the lake system. This finding suggests that the contributions picophytoplankton make to the entire system could then be dynamic in space and time. This work also provided water quality monitors and researchers with a new tool to test microbial dynamics of freshwater systems. Our novel approach can be adopted for use in diverse aquatic systems, from freshwater to marine. We demonstrated this application by quantifying microbial communities in two large river systems in our urban region. In addition, this work will enable future work that examines the dynamics of primary production over large-scale environmental dynamics in space and time. Through this award, we produced one peer-reviewed publication, one undergraduate thesis, and trained 4 individuals in aquatic microbiology. Last Modified: 12/06/2023 Submitted by: AnneWThompson