Factors Regulating Phytoplankton Community Composition in a Large Lake

Aquatic environments have experienced long term anthropogenic stressors from habitat alteration, invasive species, and nutrient inputs which leads to increased eutrophication. Lake Erie is a large lake system that has historically seen highly eutrophic conditions. Nutrient loading targets were put in place in the 1970s and successfully reduced lake wide eutrophication by the 1980s. However, Lake Erie has recently seen an increase in eutrophication and harmful phytoplankton species, such as Microcystis. Therefore, studying community composition and factors regulating community composition is necessary. This increase in eutrophication and potential shifts to problematic species was studied on spatial and temporal scales, and through microscopic and genomic techniques. Microscopy was used to determine annual average biomass which ranged between 4-6 g/m3 in 2016 and 2017. Microscopy and next generation sequencing (NGS) were used to determine phytoplankton community composition which was very diverse. Presence of oligotrophic species, such as Dinobryon, and eutrophic species, such as Microcystis, were seen in Lake Erie often during the same periods. Diatoms were a very dominant phytoplankton class especially in 2016 whereas cyanobacteria were slightly more dominant in 2017. Microscopic and genomic techniques were also used to determine factors regulating this composition through CCA plots. It was concluded that chemical factors such as SRP and NO2-NO3-, and physical factors such as wind, water temperature, and euphotic depth were important for potential harmful phytoplankton growth and distribution. It also concluded that there was a large spatial and temporal distribution of phytoplankton communities in what has been considered a well-mixed western basin. Future research is needed throughout the western basin on both the Canadian and American side to determine if there are long term patterns and shifts in phytoplankton community composition