As yet another winter storm descends on the United StatesLocal governments are now ready to dig their citizens outApplying deicing salts to asphalt or sidewalks. But the result? salt pollution in freshwater ecosystemsIt may be more difficult to dig ourselves out of the hole than we thought. De-icing chemicals have become the norm to reduce traffic accidents by up to 80%.
For those of us living in colder climates, we begrudgingly accept certain oddities of winter — the rasp of snow plows in the early hours of the morning and a thick layer of brine over everything — for the sake of safer roads. Some municipalities, such as New York State, apply an average of 23 tons of salt every mile for each lane of traffic. Although we are not likely to question the wisdom of such precautions they can have long-lasting consequences. Deicing salts seep into waterways and wash into aquifers.
De-icing salts, along with agricultural fertilizers, mining operations and climate change, contribute to a growing problem of salinity in freshwater lakes. New research published in the Proceedings of the National Academy of SciencesWe found that the thresholds set by government regulations on ionized chloride from human pollutant are inadequate to adequately protect critical freshwater zooplankton varieties. These microscopic grazing organisms are essential for the survival of algae. Without them, the entire ecosystem becomes depleted of oxygen and the food chain is ruined.
“It’s becoming increasingly clear that we need to develop new chloride thresholds, new water quality guidelines that really do protect our freshwater ecosystems from changes due to elevated salinity,” Dr. Bill Hintz asserted.
Hintz stressed the need for governments to review thresholds for what is considered acceptable concentrations of chloride for freshwater lakes.
“The desalination process is really expensive,” he added. “We can’t do it on a massive scale, so once we pollute a lake ecosystem with salt, that salt will stay in concentration pretty much until the lake turns over.”
Dr. Hintz and other scientists from The University of Toledo collaborated with Queen’s University in Kingston, Ontario to lead an international study to determine the impacts of salinity on zooplankton across North America and Europe. While previous research has been limited to lab settings, this study is unique in its scope and approach. Dr. Hintz described 16 sites as semi-natural communities of Zooplankton. Their goal was assessing thresholds for the chloride ions relative to variability in the geology, water chemistry, and species composition of the sites.
Scientists observed significant reductions in all major zooplankton group sizes when exposed to salinity levels considered safe by water quality guidelines in the United States and Canada.
“We’re seeing such a decline in the abundance of the zooplankton community that these guidelines really aren’t protective of these communities,” Dr. Hintz suggested. “When you lose those zooplankton — those zooplankton eat a ton of algae — at 47% of the sites, we see a greater algal abundance, which would be suppressed if we had the zooplankton feeding on that algae.”
Smaller species and young fish require zooplankton as a food source. Although it is still to be seen, fish population are likely to decrease as multiple trophic levels in the food chain contract. This is known as the cascade effect by biologists, which is a chain reaction that results from the disruption of one level of the food chain.
The impact is more like ripples than a cascade. The impact does not affect just one linear chain. While high salinity does not necessarily create “harmful algal blooms” that are toxic, a reduction of zooplankton undoubtedly could cause an overabundance of algae and other phytoplankton, sometimes going so far to create inhospitable “dead zones” that lack oxygen and light.
“I would say this issue is like climate change,” he insisted. “We need to act now. When you act 10 years, 15, 20, 30, 50 years down the road, every year that passes by, if you’re still using the salts you’re still increasing the concentration. It’s hard to predict how long it will take before it stops. However, science is proving to be clear. We need to do something about salt pollution.”
