title: Rapid changes in water hardness and alkalinity: Calcite formation is lethal to Daphnia magna.
abstract: There is growing concern that freshwater ecosystems may be negatively affected by ever-increasing anthropogenic inputs of extremely hard, highly alkaline effluent containing large quantities of Ca(2+), Mg(2+), CO3(2-), and HCO3(-) ions. In this study, the toxicity of rapid and extreme shifts in water hardness (38-600mg/L as CaCO3) and alkalinity (30-420mg/L as CaCO3) to Daphnia magna was tested, both independently and in combination. Within these ranges, where no precipitation event occurred, shifts in water hardness and/or alkalinity were not toxic to D. magna. In contrast, 98-100% of D. magna died within 96h after exposure to 600mg/L as CaCO3 water hardness and 420mg/L as CaCO3 alkalinity (LT50 of 60h with a 95% CI of 54.2-66.0h). In this treatment, a CaCO3 (calcite) precipitate formed in the water column which was ingested by and thoroughly coated the D. magna. Calcite collected from a mining impacted stream contained embedded organisms, suggesting field streams may also experience similar conditions and possibly increased mortality as observed in the lab tests. Although further investigation is required to determine the exact fate of aquatic organisms exposed to rapid calcite precipitation in the field, we caution that negative effects may occur more quickly or at lower concentrations of water hardness and alkalinity in which we observed effects in D. magna, because some species, such as aquatic insects, are more sensitive than cladocerans to changes in ionic strength. Our results provide evidence that both calcite precipitation and the major ion balance of waters should be managed in industrially affected ecosystems and we support the development of a hardness+alkalinity guideline for the protection of aquatic life.
authors.affiliation: Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1K 3M4, Canada. Electronic address: Sarah.Bogart@uleth.ca.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Bogart
authors.affiliation: Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1K 3M4, Canada.
authors.forename: Samuel
authors.initials: S
authors.lastname: Woodman
authors.affiliation: Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1K 3M4, Canada.
authors.forename: Dylan
authors.initials: D
authors.lastname: Steinkey
authors.affiliation: British Columbia Ministry of Environment, 3rd Floor, 2975 Jutland Road, Victoria, British Columbia V8T 5J9, Canada. Electronic address: Cindy.Meays@gov.bc.ca.
authors.forename: Cindy
authors.initials: C
authors.lastname: Meays
authors.affiliation: Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1K 3M4, Canada. Electronic address: Gregory.Pyle@uleth.ca.
authors.forename: Greg G
authors.initials: GG
authors.lastname: Pyle
mesh_terms: D000818:Animals; D002119:Calcium Carbonate; D003621:Daphnia / Q000502:physiology*; D004784:Environmental Monitoring; D005618:Fresh Water / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008903:Minerals / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D008903:Minerals; D014874:Water Pollutants, Chemical; D002119:Calcium Carbonate
keywords: Alkalinity; CaCO(3); Calcite precipitation; Daphnia magna; Ion toxicity; Water hardness