#73 Snow, Salt, and Streams
This show originally aired on January 17, 2008 on “The Rivanna Rambler,” a weekly public affairs show airing every Thursday at 11:55 a.m. on WTJU 91.1 FM or wtju.net.
As I emerged earlier this morning to put the trash and recycling on the street, the robins roosting in bushes along side the house erupted in a worried flush. They were late to emerge, having slept in, still awaiting the trigger of daylight that was coming reluctantly on this gray and cold morning heavy with the moisture and a prediction snowfall. At the street, the road was a blotchy white where Public Works trucks had made their first pass spreading salt in anticipation of the accumulation.
Salt melts the bond between the road surface and the ice or snow, making it easier to remove by shovel or plow and has been in widespread use since the 1970’s. But sodium chloride is not good for plants that flank the roads and driveways, as New Englanders learned in the 1950’s. Damage to roadside sugar maples, which are do not tolerate salt, gave rise to concerns. Evidence of contaminated wells soon followed, as well as corrosion to automobile under parts, highway structures and concrete in bridges and other surfaces. Since then, highway departments and public utilities have used a variety of methods to reduce the use of salt, ranging from sophisticated road weather information systems to calibrated application procedures, training of personnel, and alternative deicing chemicals.
But for the most part, salt is still used, however sparingly and now there is evidence from the University of Maryland of the long term and seasonal effects: our streams are becoming more salty and, as one might expect, this is not good for the health of aquatic life. The chloride component of road salt is extremely soluble in water – thus, once it’s in the watershed, it’s there for good, free to move through surface and ground waters. High levels of salt are frequently measured in roadside soils, 50 even 100 feet from the road. Salt-tolerant plants such as cattails and the highly invasive Phragmites have largely taken over-taken the fresh-water wetland flora in roadside swales.
Thus, de-icers that cntain sodium chloride may pose one of the most significant threats to freshwater ecosystems in the northeastern United States. The long-term presence of salt in freshwater streams has risen dramatically over the last 30 years, with the highest salinity occurring in the watersheds that have the most roads and parking lots, where infiltration is limited by these impervious surfaces. Worse still, the salinity levels don’t just rise in the winter — they stay high year round: summer levels in urban areas can be over 100 times higher than those in forested areas.
Sujay Kaushal, a researcher at the University of MD, puts it this way: “Human development has a profound effect on salinity. We need to think about runoff from roads and where we place roads and parking lots. Do we really want them near our headwater areas or places that supply public drinking water?”
The City of Charlottesville tested calcium magnesium acetate, an alternative to sodium chloride touted for its stream-friendliness, but it was found to be less than effective in assisting snow removal. Today, the trucks have spread a mixture of road salt and a milky white compound called Magic Minus Zero,– a biodegradable non-toxic compound of magnesium chloride that binds to the crystals of salt and is claimed by the manufacturer to render the salt more effective, thus reducing the amount needed.
We so need this snow to help sustain our reserves in reservoirs and wells and to feed the cold, parched earth in our drought-challenged watershed. Let’s just hope that our efforts to reduce the use of salt – on public and private roadways and sidewalks – will help sustain the relative health of our streams and creeks as well. So if you have driveways and walkways that need clearing, my request is this: shovel early, shovel often, and hold the salt, please.
2008 Copyright by Leslie B. Middleton