A Briny Challenge to Cleaning the River
By Jorge Bogantes Montero
Natural Resources Specialist
With the exceptional polar surges we had earlier on, and a few significant snowstorms, the road salting season is in full swing. And with it come gargantuan quantities of sand applied to the sidewalks and roadways, often over applied, causing negative impacts on the waterways and the biodiversity of the watershed. This is one of the biggest challenges we face to improving the water quality in the Anacostia River and its tributaries since Sodium Chloride NaCl (aka salt) can affect the soils, water (both surface and ground water), plants and animals. Contamination of sodium in drinking water has been an issue in other areas of the country which is a concerning public health issue.
Salt can be detrimental for birds when they ingest salt crystals thinking they are seeds, their system can’t deal with excess sodium ending up in fatal kidney problems. Birds are some of the most sensitive terrestrial animals to salt through the consumption of salt crystals. Aquatic organisms take the biggest toll, macroinvertebrates, fish, and amphibians being some of the most affected.
Studies have shown the impacts of road salt on populations of Spotted salamanders (Ambystoma maculatum) and Wood frogs (Rana sylvatica) by measuring water conductivity. The electrical conductivity of water is related to the total dissolved salts present in it, therefore, it is used as an indicator of salinity levels in the water. Demographic models employed by researchers suggested that the effects of salt on eggs and larvae of these amphibians may have important impacts on populations near roads to the point of even causing local extinctions of spotted salamanders. Populations of these amphibians were more affected the closer to the roadside (within 54 yards) their habitat was.
A study in Canada found that amphibian abundance and diversity were steadily low in all wetlands where chloride levels exceeded 200 mg/l. The study indicated that chlorides may accumulate in wetlands over time and that the seasonal rise in chloride concentrations in wetlands may adversely affect the distribution of amphibian species.
Populations of vernal pool-breeding amphibians like spotted salamanders and wood frogs are negatively impacted by road salt.
Levels of chloride in many U.S. streams in urban areas exceed the EPA’s chloride guideline of 230 parts per million. Constant levels of chloride concentration equivalent to one teaspoon of salt in five gallons of water have been shown to be detrimental to aquatic organisms. The presence of chloride in the water even lasts through the summer months creating a chronic exposure that affects the aquatic life in complex ways, from benthic macroinvertebrates to fish. No wonder why the benthic macroinvertebrate communities throughout the watershed have been ranked as “Poor” or “Fair” for most of the tributaries of the Anacostia River according to data by the Anacostia River Watershed Restoration Partnership –of course, there are also other factors affecting these results. Fish fair a little better, but still a pretty good portion of the watershed ranks as “Poor”. It is important to note that there is no natural process by which chlorides are broken down or taken up by vegetation, they remain in the ecosystem just as other pollutants.
Road salt affects vegetation including our beloved urban trees, however, the plant tolerance to salt varies depending on the species, some species being very sensitive to salt (e.g. Sugar maple or Pin Oak). Of course it all depends on the amounts of salt being applied, high amounts of salt can affect just about any plant used in urban landscapes. Low salt levels in the soil disturb nutrient availability and uptake and affect tree growth whereas higher levels cause dehydration and death.
There are other de-icing alternatives to salt but they are not as efficient, they can damage plants, they contain other pollutants and/or they are more expensive. Calcium magnesium acetate is said to be a good alternative but its main flaw is that it is very expensive and requires more product application to achieve the same de-icing results. Calcium magnesium acetate may also deplete oxygen in aquatic habitats. The Maryland and DC governments have been using a salt brine/beet juice solution to pretreat roads before a snowstorm which is a good alternative to reduce the amounts of salt applied. This preventive solution can reduce the amount of salt needed by 30% and is way less harmful than other products. The City of Milwaukee recently started using cheese brine, a byproduct of cheese production, as a de-icer; while it is a promising alternative that saves money, its environmental effects are still a question mark.
There are measures that can be taken to reduce/eliminate the use of road salt, however, there is still not a single “silver bullet” solution, a solution that makes sense both environmentally and economically. Until then, sustainable de-icing practices should be a key issue in any environmental or public planning agenda especially under our current scenario of climate change.
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