Salt used to deice America's roads has a lasting impact on the environment. When ice melts salty runoff contaminates surrounding soil and bodies of freshwater. Salt spray can also reach nearby plant foliage. Fresh water plants react differently to salt based on the plant species, body of water and quantity of salt.
Road Salt in Soil
Sodium chloride, the main component in road salt, decreases soil's ability to drain. Healthy soil is the consistency of wet coffee grounds. It remains damp but drains fast. Soil that holds too much water rots plant roots and makes favorable conditions for fungus and disease. The soil's overall fertility diminishes so that it also won't support new plant life.
Plant Species Considerations
Plant species differ in salt tolerance. Cattails, for example, often thrive along roads because they thrive in brackish water. Many grasses withstand salt. Trees and shrubs are more fragile. Their salt-related symptoms are browning leaves, early leaf drop, decreased growth and dying branches.
Manner of Salt Exposure
If road salt is sprayed on plant leaves and not quickly washed away it will scorch them. While this stresses the plant, it is not as severe as when salt is absorbed through the roots. Once taken into the plant, salt dehydrates plant cells and eventually kills the plant. Roots come in contact with salt easier in areas with a high water table.
It is impossible to predict how weather will impact salt damage to freshwater plants. Temperature, humidity, light, and precipitation combine to produce either a negative or positive result. Rain, alone, decreases road salt's damage by washing it from plant surfaces and diluting it in the groundwater.
How Road Salt Damages Aquatic Plants
Road salt that reaches freshwater will have varying impacts between rivers, lakes, ponds and streams. Plants living in large bodies of water do not suffer as much, because the salt is diluted. Road salt damages plants more in creeks and streams close to roads, because it is in higher concentrations.
In lakes and ponds, road salt settles at the bottom and inhibits oxygen from getting to all water depths. This ripens conditions for cyanobacteria. Cyanobacteria doesn't mind salt and steals nutrients from freshwater plants and animals. Plants show signs of overall decline, such as poor growth and mineral deficiencies. If the salt and consequential bacteria are not contained, aquatic plants eventually die.