Friends of the Muskoka Watershed is still in the process of pursuing funding, via grants and private donations, to enable us to fully roll out our “Halt the Salt” program in Muskoka. New, soon to be published research offers further evidence emphasizing the importance of this program and the need to act quickly in reducing and, in some cases, eliminating the use of road salt on Muskoka’s roads and highways.
The research, detailed in the paper, “Road salt impacts freshwater zooplankton at concentrations below current water quality guidelines”**, has determined that widespread use of road salt (NaCl) for road de-icing has caused increased chloride concentrations in lakes near urban centers and areas of high road density. Chloride is recognized as a toxic substance. This has resulted in water quality guidelines being developed at the federal level to protect aquatic life. However, these guidelines may not adequately protect organisms in low nutrient, soft water lakes such as those underlain by Precambrian Shield.
The research proceeded by conducting laboratory experiments on 6 Daphnia species (water fleas, of the order Cladocera), using a soft water culture medium. It also examined temporal changes in Daphnia accumulation in the sediments of two small lakes on the Canadian Shield; one near a highway and the other more than 3 km from a winter-maintained highway. The results showed that Daphnia were sensitive to low chloride concentrations with decreased reproduction and increased mortality occurring between 5 and 40 mg Cl-/L. Analysis of cladoceran remains in lake sediments revealed changes in assemblage composition that coincided with the initial application of road salt in this region. In contrast, there were no changes detected in the remote lake. The researchers found that 19.5% of recreational lakes in Ontario have chloride concentrations between 5 and 40 mg/L suggesting that cladoceran zooplankton in these lakes may be vulnerable to further increases in chloride.
In Canada, the current chloride water quality guideline for the protection of aquatic life is set at 120 mg/L (miligrams per litre) for chronic exposure and 640 mg/L for acute exposure. This current round of research, however, is showing negative impacts to aquatic life for chloride concentrations of 5 and 40 mg/L, far below the federal guidelines, in lakes like we have in Muskoka. Since Daphnia are extremely important in maintaining the overall health of a lake and their diminished presence will not only affect water quality but will also impact the food chain within the lake itself, the long term consequences of continued road salt use, especially in close proximity to lakes and ground water flows, will negatively impact aquatic life and lake quality. This is especially a concern in Precambrian Shield lakes in Canada where widespread calcium decline is already impairing growth and reproduction of Daphnia and other zooplankton, also a problem we are addressing in Muskoka via the ASHMuskoka program.
** co-authors: Shelley E. Arnott, Martha P. Celis-Salgado Robin E. Valleau, Anna M. DeSellas, Andrew M. Paterson, Norman D. Yan, John P. Smol, James A. Rusak in Environmental Science & Technology