Ever wonder what happens to all that rock salt that gets sprinkled on roads and highways, walks and driveways when the snow falls?  It winds up in area streams, ponds and lakes, where research indicates it's altering the development of frogs and other aquatic life.

Salt levels in streams tend to spike after a storm like the one that hit Maryland and the rest of the East Coast this week.  While those peaks do drop within hours or days, the salt washed downstream seems to be building up in some ponds and lakes. 

The salt concentrations in Baltimore's drinking water reservoirs have been slowly rising. A report several years ago found that levels in Liberty had tripled since the 1970s, and quadrupled in Loch Raven, trends that officials attribute to the increased use of salt to de-ice growing amounts of pavement around the region.  Still the treated water supplied by the city remains below the salt threshold recommended by the federal government, says city spokesman Kurt Kocher.

So the water's not too salty to drink, but it may not be quite so kopacetic for the critters that spend their lives immersed in it.  Chris Swan, an assistant environmental science professor at the University of Maryland, Baltimore County, found that the slight elevation in salt seen in area waters is enough to alter the development of grey tree frogs - like the ones that visit my backyard every spring.  They grow faster and larger than normal, he says.  Some insects found in area streams and ponds also thrive in salty water.

But Swan found even modest amounts of salt are bad for zooplankton, the microscopic animals swimming in water that feed on algae, and upon which some fish feed.  Likewise for some of the microbes that help regulate the nutrients in the water.

The long-term effects of this gradual dosing of our freshwater environment are unknown.  Kocher, a spokesman for the Baltimore Department of Public Works, said city officials are keeping an eye on the salt levels in our drinking water, but have no plans to stop using the stuff to maintain safe streets.

"It's not something that anyone wants to have, but we do have to balance that against a car going off the road," he said.

Likewise, State Highway Administration spokesman Dave Buck says road crews try to scatter only as much salt on the pavement as they need to to ensure safe driving.   Trucks are equipped with special spreaders to distribute it evenly and minimize waste, he said.  The state puts down 200,000 or more tons of the stuff every winter, though - with tens of thousands of tons sprinkled in the past few days alone. 

(The truck pictured above, photographed by the Baltimore Sun's Amy Davis, was working for the city schools, treating an alley near Margaret Brent Elementary School in Charles Village.) 

"I'm not going to suggest we should sacrifice human safety for frogs," Swan says, "but we ought to figure out if there are better ways to manage it.