Exploring Phytoplankton community structure, primary and bacterial productivity in the urbanized Toronto Harbour.

Toronto Harbour is a highly urbanized embayment with a history of eutrophication due to municipal wastewater and stormwater runoff. Although nutrient levels have decreased since the 1970s and the harbour is considered mesotrophic, wet weather conditions flush high concentrations of nutrients from the watershed into the harbour. Starting in 2016 seasonal patterns in phytoplankton community structure and primary productivity were measured. In 2019 phytoplankton biomass averaged 0.7 g m^-3 at the centre station and 1.3 g m^-3 at the Don River station. Diatoms were often the highest contributors to biomass but Chrysophyceae and Cryptophyceae were also important. Seasonal productivity rates averaged 14 mg C m^-3 hr^-1 in the central harbour compared to 22 mg C m^-3 hr^-1 near the Don River. Bacterial productivity near the Don River averaged 3.3 mg C m^-3 hr^-1, more than twice the central harbour value. This indicates that a considerable amount of organic matter is being deposited into the harbour from the river. The presentation will discuss how the Don River impacts phytoplankton and bacterial dynamics in Toronto harbour. [ABSTRACT FROM AUTHOR]