Warm season chloride concentrations in stream habitats of freshwater mussel species at risk

Warm season (May–October) chloride concentrations were assessed in stream habitats of freshwater mussel species at risk in southern Ontario, Canada. Significant increases in concentrations were observed at 96% of 24 long-term (1975–2009) monitoring sites. Concentrations were described as a function of road density indicating an anthropogenic source of chloride. Linear regression showed that 36% of the variation of concentrations was explained by road salt use by the provincial transportation ministry. Results suggest that long-term road salt use and retention is contributing to a gradual increase in baseline chloride concentrations in at risk mussel habitats. Exposure of sensitive mussel larvae (glochidia) to increasing chloride concentrations may affect recruitment to at risk mussel populations.

► Warm season chloride concentrations were assessed in habitats of mussel species at risk.
► Concentrations increased significantly at 96% of 24 long-term monitoring sites.
► Concentrations increased with increases in road density and road salt use.
► Retention of road salt likely contributed to elevated warm season concentrations.
► Glochidia exposure to increasing concentrations may affect mussel reproduction.