Protecting Water Quality: Understanding Chloride in the Upper Thames  

Keeping an eye on water quality is crucial for understanding and safeguarding the health of the Upper Thames River watershed. One major concern is chloride, a naturally occurring ion that can become elevated in freshwater due to human activities. Chloride is most commonly used in the form of road salt (Sodium chloride), but it can also be found in stormwater runoff, wastewater, and agricultural fertilizer. In this region, road salt is one of the most significant sources of chloride entering aquatic systems, particularly in urban areas because it is used in large quantities as a deicer to keep roads, sidewalks, and parking lots safe during winter. It is widely available and relatively inexpensive, particularly in southern Ontario, which is home to a major salt-mining industry. However, once applied, that salt can be carried by snowmelt and runoff into nearby streams, rivers, and groundwater. Chloride can also come from other sources. In agricultural areas, some fertilizers, such as potassium chloride, can contribute chloride to soil and nearby water through runoff and leaching. While small amounts of chloride occur naturally, such as through natural weathering of rocks, elevated chloride concentrations can negatively affect aquatic ecosystems and the organisms that depend on them.

Chloride is measured by collecting grab samples from various locations in the Upper Thames River watershed. These samples are checked for their chemical concentrations and then to sent to a lab for further research. These field measurements and water samples are important for tracking changes in water quality and ensuring the long-term health of the watershed.  

Why Chloride Matters

Elevated levels of chloride can have an adverse impact on aquatic ecosystems. This creates concern as chloride tends to persist in the environment, accumulating in groundwater, surface water, and other aquatic habitats. The Canadian Water Quality Guidelines for chloride levels identify 120 mg/L as the chronic guideline for long-term exposure, and 640 mg/L as the acute guideline for short-term exposure. Understanding these levels can provide a better knowledge of the health of the Upper Thames River watershed.

The Provincial Water Quality Monitoring Network (PWQMN) program has water quality data going back more than 60 years, allowing for educated and consistent insight on subwatershed health. Field work involves going to monitoring sites, using a multi-parameter sonde (a water quality monitoring instrument that measures several environmental properties), collecting surface water samples, tracking observations, and accurately documenting the field data. The information is then analyzed to spot trends in chloride concentrations and determine which areas might need extra monitoring or management.

Protecting Watershed Health  

Limiting chloride use, especially during the winter months, is an important step that individuals and communities can take to help protect local waterways. Small changes, such as using only the amount of salt needed, shoveling snow before applying salt, and choosing alternatives such as calcium magnesium acetate (CMA) ice melt or even beet-juice, can reduce the amount of chloride entering nearby waterways. Gardeners can use environmentally friendly fertilizers such as manure, alfalfa meal, and bone meal. When alternatives are not available, using the recommended amount of salt, about 2–4 pounds per 1,000 square feet, can help prevent unnecessary chloride from entering waterways. While these are small actions, they can have a positive impact on aquatic ecosystems when adopted by many people.

By understanding the sources of chloride and the actions we can take to reduce it, we can all play a role in protecting the Upper Thames River watershed.