MULTISTRESSOR EFFECTS OF CHLORIDE AND CALCIUM ON CANADIAN LAKE ZOOPLANKTON COMMUNITY ASSEMBLAGES

Salt concentrations (NaCl) associated with road de-icing are increasing in freshwater bodies in Canada and other regions that experience cold winters, posing concern for the health of those ecosystems. Some zooplankton, which play an important role as primary consumers of algae in freshwater bodies, have a high sensitivity to chloride (Cl^-) resulting in changes in zooplankton community composition, reduced biomass, and lower richness. Additionally, there is some evidence that zooplankton may be more sensitive to Cl^- in soft water conditions (i.e., low [Ca²⁺] and [Mg²⁺]), especially in regions where [Ca²⁺] is declining. We conducted a six week mesocosm experiment to test the interactive effects of Ca²⁺ (1, 5, and 10 mg/L) and Cl^- (gradient from 0.22 to 1500 mg/L) on zooplankton species abundances and community metrics. We found that abundances decrease across all taxonomic groups as Cl^- increases. Ca²⁺ has an ameliorating effect on some taxa like copepods, rotifers, large Cladocera, Monostyla spp., and Chydorus sphaericus. The ameliorative effect of Ca²⁺ on Daphnia pulicaria is unclear, but we observed higher D. pulicaria abundances at higher Ca²⁺. We also observed lower small Cladocera (excluding C. sphaericus) abundances at higher Ca²⁺. These results suggest that zooplankton communities in low Ca²⁺ environments may be more susceptible to Cl^- toxicity, and community dynamics may be influenced by shifts in dominant taxa.

Primary Presenter: Caelan Johnson, Queen's University (20cj3@queensu.ca)

Authors:

Caelan Johnson, Queen's University  (20cj3@queensu.ca)

Shelley Arnott, Queen's University  (arnotts@queensu.ca)

James Rusak, Ontario Ministry of the Environment, Conservation and Parks  (jim.rusak@ontario.ca)