Road Salt Impacts to Algae Populations

Living in the Northeast we depend on clear roads during winter to maintain of way of life. Organizations, agencies and municipalities throughout the Northeast understand that there is an impact to the environment from road salt application practices. We must find the balance that protects the environment and still allows for safe roads. Algae and zooplankton populations are not immune to impacts from road salt application, in fact they are one of the first impacted within an aquatic ecosystem. As algae are the base of the aquatic food web, any alterations within their composition can have direct impacts on the rest of the food chain.

Road salt application within aquatic ecosystems is generally measured in levels of chloride. Every body of water will differ as to what the background level were historically and at what level the addition of chloride will have an impact. A low nutrient body of water can experience impacts to algal populations at as little as between 2-10 mg/L of chloride, while other bodies of water with higher nutrient levels may not have an impact until chloride levels reach 70+ mg/L. Scientific research has shown that at 100 mg/L chloride, negative impacts to algal populations are substantial enough to remove sensitive species in favor of forms that are salt tolerant.

An increase in chloride levels will shift algal dominance from chlorophyte (green algae) to cyanobacteria (blue-green algae). Cyanobacteria tolerate higher osmotic stress due to enhanced synthesis of zeaxanthin as a protective xanthophyll. The shift can lead to increased algal biomass responding to the presence of chloride and due to the decreased presence of large bodied zooplankton that would feed on algal species. This is further compounded by the allelopathic effect on zooplankton populations from the cyanobacteria. The shift in algal dominance and the removal of large bodied zooplankton can lead to toxin producing harmful algal blooms.