Beneath the Surface: How road salt affects waterways

Unfortunately, when salt mixes with snow and melts into the soil, it can damage our soil, gardens, water and lake.

Ice is slippery stuff. To avoid injuries due to falling, many of us put de-icing products down on sidewalks and parking lots. Most of the de-icers we use are simply salt—common, everyday table salt. Sound innocent? Unfortunately, when salt mixes with snow and melts into the soil, it can damage our soil, gardens, water and lake.

How it works:

Salt lowers the freezing and melting point of water. When dry salt is spread onto an ice surface, it will dissolve and form a solution called brine. It is the brine that melts the snow and ice by reducing the temperature at which water will freeze. For example, a 10 per cent salt solution won’t freeze until about –7 C, meaning walkways will remain ice-free down to that temperature. A 20 per cent salt-water mixture will stay melted until -17 C. In common use, that perfect brine solution won’t form uniformly across icy surfaces. Given factors such as wind, traffic and longer melt times needed in colder weather, salt is only reported as being effective down to about -9 C.

Unintended damages:

When the snow and ice melt in the spring, salt adversely affects soil and vegetation, contaminates groundwater as it leaches through the soil, and damages aquatic ecosystems.

In streams and lakes, sodium and chloride — the two components of common salt — can be toxic to aquatic life. In a lake, salt-laden water will sink to the bottom of a lake because of its higher density. This can reduce circulation in lower depths, which can lead to a loss of dissolved oxygen and mortality of fish and other aquatic life living at the lake bottom. Prolonged periods of reduced oxygen can result in increased nutrient loading, which feeds algal growth in the spring and summer.

Excess salt doesn’t just damage waterways; it adversely affects our gardens, too. Too much salt in the soil can lead to brown lawns, scorched brown-looking leaves, and spring bulbs that are undernourished and may not flower.

How to stay safe on sidewalks while protecting our lake:

What are your de-icing alternatives?

• Spreading sand or gravel for traction is the safest alternative for the environment. But remember to clean it up in the spring so it won’t clog storm drains.

• Shovel or snow-blow soon after it stops snowing and before the snowy slush freezes, so that little or no de-icer is needed. Note that de-icers cannot melt all the way through compacted snow or built-up ice, so if you salt without shovelling, you will just waste the salt and contaminate land and waterways.

• Check the current and predicted outdoor temperatures before you use salt to de-ice, in case it is too cold and it proves ineffective (e.g. –9 C).

Kirsten Harma is the program co-ordinator for the Lake Windermere Ambassadors and can be reached at .