Over seven million tonnes of de-icing salt are dispersed on Canadian roads each winter leading to an increase in lake chloride concentrations that can be toxic to freshwater aquatic life. However, the current Canadian Water Quality Guideline limits for chloride may not sufficiently protect aquatic life against rising lake salinity.
Lake salinity guidelines were developed based on chloride sensitivities of individual species under lab conditions and may not reflect sensitivities under lake conditions. Former Queen’s Biology graduate student Danielle Greco, along with co-supervisors Drs. Shelley Arnott and Brandon Schamp (Algoma University) and collaborator Dr. Isabelle Fournier at Laval University, investigated the effects of salt and nutrient concentrations on the pillar of aquatic life, plankton. By mimicking a natural lake environment using mesocosms, including communities rich in species and from multiple trophic levels, this study provides insight previously not observed during development of guidelines.
Even under relatively low chloride concentrations, zooplankton biomass and abundance significantly decreased. Total community biomass decreased by up to 71% when chloride concentrations reached guideline “safe” limits. This decline included the highly sensitive yet near ubiquitous copepods which were not even included in assessments when guidelines were designed. Zooplankton response to chloride did not differ by nutrient level, despite increased food availability under elevated nutrients. Phytoplankton and protist responses to chloride varied depending on nutrients. Under low nutrients, they increased in abundance, biomass, and richness with chloride. However, under high nutrients, abundance and biomass did not respond to chloride, while their richness decreased.
These results prompt immediate reassessment of Canadian Water Quality Guidelines regarding lake chloride concentrations. Furthermore, this work underscores the need for innovation in road salting practices. Find their article to read more in Limnology and Oceanography Letters.
