This dataset supports the assessment of plankton community structure and water quality within Toronto Area of Concern (AOC). The data was collected to evaluate the Beneficial Use Impairment (BUI) 13 - Degradation of Phytoplankton and Zooplankton Populations, and to provide georeferenced habitat information relevant to BUI 14 - Loss of Fish and Wildlife Habitat.

The dataset provides a complete suite of water quality, microbial, phytoplankton and zooplankton observations collected from multiple georeferenced stations throughout the Toronto Harbor. Each datapoint includes latitude and longitude, sampling date, year and season, along with physiochemical measurements such as temperature, dissolved oxygen, total phosphorus, total nitrogen, nitrate + nitrite, chlorophyll-a and turbidity. Biological data includes phytoplankton, zooplankton and rotifer abundance and biomass across major taxonomic groups, as well as size structured zooplankton data distinguishing small and large taxa. The dataset also includes microbial community metrics and rate-based parameters such as bacterial growth rates, primary productivity and bacterial production. Sampling was conducted across multiple ecotypes identified by “Area” in the dataset (Inner Harbor, Islands, Habitat Cells and Embayments). The data structure allows for comparisons among sites, seasons, ecotypes and provides the basis for statistical analysis of plankton community composition, trophic relationships and ecological patterns within the AOC of Toronto Harbor.

Results indicate water quality, zooplankton abundance and biomass differed across habitat ecotypes, with Inner Harbor exhibiting very low biomass similar to the open waters of Lake Ontario and a higher proportion of small taxa like rotifers, in spite of elevated nutrients. This pattern suggests environmental stress from runoff and contamination from the surrounding urban area. Zooplankton prey reductions are likely due to multiple urban environmental impacts including runoff and contaminants. Ecotype impacted zooplankton productivity but not primary productivity, indicating that protected systems (Island channels, Habitat Cells and Embayments) can offer diverse physical habitats and forage for fishes. Though primary productivity rates were reduced in most habitats, productivity was shunted into bacterial growth which were highly elevated throughout the entire AOC.