Affiliation:
1. Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, Canada T1K 3M4
2. British Columbia Ministry of Environment and Climate Change Strategy, 525 Superior Street, Victoria, British Columbia, Canada V8V 1T7
Abstract
Anthropogenic activities have the potential to increase water hardness (Ca + Mg) in receiving waters to toxic concentrations, and thus, water quality guidelines (WQG) for Ca and Mg are warranted. However, Ca can modify Mg toxicity in Ca-poor water and additional interactions with other major ions (Na
+
, K
+
, HCO
3
−
/CO
3
2−
, SO
4
2−
and Cl
−
) may occur, potentially obscuring the water hardness–effect relationship. In a meta-analysis of toxicological studies, we: (i) evaluate the performance of three WQG derivation methods, and (ii) determine the influence of several variables (acute/chronic data, anions, Ca:Mg ratios, non-geographically relevant species) on the models. We find that the most sensitive species- or species sensitivity distribution (SSD)-based WQG derivation methods greatly overestimate water hardness toxicity, particularly if non-resident species are included. Broad-scale implementation of most sensitive species- or SSD-based WQG is impractical because water hardness varies beyond and within the regional scale. Anion type does not affect water hardness toxicity across species, but the Ca : Mg ratio is toxicologically relevant, underscoring the importance of considering ion ratios when developing major ion WQG. Although data supporting formal water hardness WQG are unavailable, we suggest using a two-component background condition approach that supports simultaneous management of water hardness and Ca : Mg ratio, and WQG that are applicable beyond the regional scale.
This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.
Funder
British Columbia Ministry of Environment and Climate Change Strategy
Government of Alberta, Campus Alberta Innovation Program (CIAP) Chair
Subject
General Agricultural and Biological Sciences,General Biochemistry, Genetics and Molecular Biology
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