The snow was magical. Then it was covered in muck. Now, it’s starting to melt.
That slushy snowmelt isn’t just a nuisance, scientists say. In towns and cities, it can send a toxic flood of road salt, sand and car exhaust, as well as dog poop, into rivers and streams.
“It’s all been accumulating in that snow,” said Rebecca Hale, who runs the watershed science lab at the Smithsonian Environmental Research Center in Maryland. “And when the snow melts, everything moves downstream in a big pulse.”
Snow is super absorbent. It even absorbs noise, which is why a snowy morning feels so quiet. And like a giant chemical sponge, it can absorb or carry all manner of pollution including road salt like sodium chloride (which is good for de-icing roads but can contaminate drinking water and harm wildlife), car exhaust and soot that settles onto the snow, rubber particles from car tires and antifreeze or other automotive fuels that can contain heavy metals.
And pet waste.
In cities like New York, melting snow can trigger a major pulse of water that washes into rivers and streams, similar to what happens after a significant storm. What’s different with snow is that pollutants in the snowpack are released suddenly, when the snow melts, sending a concentration of contaminants downstream, Dr. Hale said.
That can overwhelm the streams, rivers, lakes, and wetlands that normally help clean water by removing pollutants.
The influx of road salt can also kill organisms and microbes that would ordinarily help clean the water. And salt can leach nutrients and metals from the soil, carrying even more pollutants downstream. “It’s a triple whammy,” she said.
Snowmelt runoff and other “non-point-source pollution” is the leading cause of water pollution in the country, according to the Environmental Protection Agency. And groundwater monitoring over the past decade has also shown dramatically rising salt levels in many streams, rivers, lakes and drinking water reservoirs, harming wildlife.
Yevgen Nazarenko, assistant professor of environmental and industrial hygiene at the University of Cincinnati, said research was shining a light on how pollution from all sorts of vehicles — planes, cars, trucks — can get trapped in the snow.
“Snow has a very large surface area that’s in contact with the air, and so it scrubs up all the pollution,” he said. “We also found that when sunlight shines it changes the chemical identities of many of those compounds.”
In a less snowy environment, the exhaust pollution is usually carried away by the wind, he said. “But snow traps a lot of that pollution within the snowpack, so it just completely changes the dynamics” of where it ends up.
There are some solutions. Snowmelt runoff can be minimized by increasing urban green spaces that can absorb more of the melting snow, reducing the runoff. Impervious surfaces like roads, sidewalks and parking lots, on the other hand, can cause faster and larger flows during which more pollution can be swept up. Scientists are researching alternatives to road salt that are less harmful to the environment.
There are also practical steps people can take to reduce the use of rock salt, New York State says. Shovel first and then avoid the temptation to over-salt (only need 12 ounces or so can effectively melt snow and ice on a 20-foot driveway.) And know the temperature, because rock salt will not melt snow or ice below 15 degrees Fahrenheit.
And of course, picking up dog poop helps.
Hiroko Tabuchi covers pollution and the environment for The Times. She has been a journalist for more than 20 years in Tokyo and New York.
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