Chloride trends in Ontario's surface and groundwaters

The Ontario Ministry of the Environment, Conservation and Parks leads 11 long-term monitoring pro-grams at over 2,500 surface and groundwater sampling locations across the province that report chloride (Cl-) concentration, some dating back to the 1960s. This study integrates these disparate datasets to pro-vide comprehensive evidence relevant to spatial and temporal Cl- trends in the Laurentian Great Lakes, and Ontario's inland lakes, streams and groundwaters. While the vast majority of historical Cl- data indicate concentrations are well below the chronic exposure Canadian Water Quality Guideline (120 mg L-1), many lake, stream and groundwater sampling locations proximal to roadways or in urbanized areas meet or exceed this guideline, and concentrations in these regional areas are persistently increasing. The cur-rent evidence implicates road salting activities for winter safety as a primary contributor to elevated Cl- concentrations, and the trends may be exacerbated with urbanization and population expansion, partic-ularly in southern Ontario. (C) 2022 The Author(s). Published by Elsevier B.V. on behalf of International Association for Great Lakes Research.

Automated summary

This study integrates historical chloride concentration data from over 2,500 surface and groundwater sampling locations in Ontario. The findings show that while most historical data indicate concentrations below the Canadian Water Quality Guideline, sampling locations near roadways or in urbanized areas exceed this guideline and concentrations in these areas are continuously increasing. The study suggests that road salting activities contribute to elevated chloride concentrations.