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Going Off Road: What Happens to Wildlife When Salt Escapes Into the Environment?

Lionel Jimenez
Deer by snowy road

Road salt is commonly used to melt snow and ice on sidewalks and pavement during the winter season in northern climates. While it is quite effective at making roads safer for human travel, it can also have harmful effects on the environment, particularly on wildlife that live in and near fresh water.

Road salt can harm wildlife by contaminating waterways, reducing the populations of organisms, and impacting food sources. When salt is applied to roads and sidewalks, it can be carried by runoff into nearby streams, rivers, ponds and lakes. This can lead to elevated levels of salt in the water, which can be toxic to plants and animals that rely on these water sources.

Salt causes the drying out and eventual death of many plants. Reduced plant populations can have cascading effects on local ecosystems.

Runoff can also cause soil salinization, the accumulation of salt in soil that affects the health of the environment. Salt absorbs water, resulting in less water being available to plants. That in turn causes the drying out (or desiccation) and eventual death of many plants. Reduced plant populations can have cascading effects on local ecosystems. For example, if one tree species becomes less abundant due to road salt, the organisms that depend on that tree for food or shelter may also suffer.

Although excessive salt is very harmful to freshwater ecosystems, in low concentrations salt is normal and helps to sustain aquatic life. Fish have the process of osmoregulation, through which they maintain an internal balance of salt and water. Salt helps fish and many other organisms, such as zooplankton and macroinvertebrates, to maintain themselves by reducing the loss of electrolytes. If this process goes awry (e.g., if there is more salt than is necessary for basic bodily functions), many aquatic food chains can be disrupted. This leads to a domino effect, reducing the population of many aquatic species.

Dead zones, areas in bodies of water where organisms cannot live due to the absence of oxygen, can also be caused by road salt runoff. That’s because runoff that contains salt is denser than surface water due to its increased mass, and therefore it typically sinks to the bottom of freshwater water bodies, where it forms a barrier that inhibits nutrients and oxygen from mixing and moving between the upper layers of the water column and the substrate. The biodiversity and abundance of life in freshwater ecosystems can be impacted by these dead zones, as water mixing is crucial for these ecosystems and the various species that live there.

Amphibians exposed to more salinated water while in the egg have a high frequency of malformations when hatched.

Fish, crustaceans and plants cannot survive in dead zones. Amphibians, known to be sensitive to changes in their environment, are also affected by increased salt levels in water. Many amphibian species lay eggs in water; those eggs later grow into a larval stage and then into their fully-grown adult stage. Fluctuation in salt levels causes problems with egg development. A paper by Kelly Ann Krolik found that amphibian eggs are less abundant in areas with higher salt levels. That’s because water plays a role in oxygen uptake and increasing space between the eggs, but when exposed to road salt, eggs may experience water loss that interferes with development and poses a major threat to their survival. Krolik found that amphibians exposed to more salinated water while in the egg have a high frequency of malformations when hatched.

Road salt can also be harmful to wildlife when ingested. Birds and other animals are sometimes drawn to salt granules on roadways and may eat the granules. Ingesting too much road salt can cause poisoning – not only from the salt itself, but also from heavy metals and other additives used to prevent salt granules from caking together during application. This in turn can cause numerous health problems in these species. In addition to the harm that comes from consuming salt, the animals confront dangers such as fast-moving automobiles that might hit them while they are focused on eating the salt.

A common misconception about placing salt on your sidewalk or driveway is that more salt means snow and ice will melt faster. More salt does not mean more melting.

Mindful salt usage is a way to prevent all these negative impacts on the environment. A common misconception about placing salt on your sidewalk or driveway is that more salt means snow and ice will melt faster. More salt does not mean more melting. In fact, salt works best when there is space between granules or between lines in liquid application. Salt works by lowering the freezing temperature of water and is effective down to about 15 degrees Fahrenheit. About 12 ounces of salt (the same amount that can fit in a typical coffee mug) can cover a 20-foot-long driveway or 10 sidewalk squares. Using less salt will help prevent additional effects of freshwater and soil salinization.

Even though road salt is a crucial part in keeping roads safe during the winter season, it can have various negative consequences on wildlife. Negative consequences such as direct harm through ingestion (in the case of birds and mammals), or indirect consequences such as soil and freshwater salinization, may disrupt survival and abundance of many organisms. It is important to use road salt responsibly to minimize these (and other) negative effects on the environment.

Learn more about responsible salting


Citations

Lionel Jimenez is a 2022-2023 Clean Water Intern at the Izaak Walton League of America’s National Office.

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