Quantifying microcystin concentrations, their composition and drivers across over 400 north-temperate and boreal Canadian lakes

Microcystins (MCs) are the most commonly measured of the cyanotoxins. Roughly 250 MC congeners have been identified to date with noted differences in their toxicity and persistence. Regional and national scale models for different parts of the world have been instrumental in identifying the drivers of total MC concentrations including toxin-producing cyanobacteria biomass, nutrients (total nitrogen and phosphorus), agricultural development in the watershed, temperature and light. Most of the MC work in Canadian lakes has focused on total concentrations and congener-specific data are lacking. Using the first Canada-wide lake set, with standardized sampling generated through the NSERC LakePulse Network, we quantified the importance of biotic and abiotic predictors of total MCs as well as several congeners from up to 440 lakes. Overall, MCs were detected in 30% of lakes using ELISA, mostly in central Canada within the Prairies and Boreal Plains ecoregions. Total concentrations were generally low, with just 10% of lakes exceeding the WHO drinking water guideline. While considering a broad suite of variables – physiography, water quality, land use, zooplankton abundance, climate, and cyanobacteria enumerations - MCs were most associated with high nutrients, low hypolimnetic oxygen, high chlorophyll-a and the biomass of known MC producers, particularly Microcystis.