Studies Reveal Little Impact From Sierra’s Acid Snowmelt

When snow begins to thaw each spring, all the man-made pollutants it contains come out in the first flush of snowmelt, entering lakes and streams.

This “pulse” of acidic water in the first runoff of spring, carrying the wind-borne sulfates and nitrates produced by automobiles and factories, is a well-known phenomenon in the Northeast United States and in Scandinavia, where it is harming fisheries and aquatic habitats.

There is no evidence yet that “acid snowmelt” from the Sierra snowpack is having any negative effect on area fisheries, according to researchers who are now in the fourth year of a monitoring program at Emerald Lake, located at 9,200 feet on the western slope of the Sierra in Sequoia National Park.

“We have no information that snow in the Sierra is polluted,” said Danny Marks, a snow hydrologist for UC Santa Barbara. “In fact, just the opposite. The snow in the Sierra is very, very pure.”

UC Santa Barbara is a major participant in the four-year, $18-million study launched in 1984 and sponsored by the California Air Resources Board along with the U.S. Forest Service.

Some experts believe that most of the pollutants in a snowmelt come out in the first 15% to 30% of the water.

Changes With Snow Age

“It has to do with the changes in snow as it ages,” said Neal Berg of the U.S. Forest Service, which operates a snow research station at Soda Springs near Donner Pass.

“As snow changes through time, many impurities in the snow crystals tend to migrate to the edges of the crystals. When it warms up enough for the snow to melt, those impurities at the edge of the crystals are in the right location to be melted first,” Berg said. “So right at the beginning of the snowmelt, the impurities are unleashed and they come out in a slug of relatively polluted water. Then, after that, the remaining snow is pretty clean water.”

Kathy Tonneson of the Air Resources Board said most of the state’s precipitation comes in the form of snow in the Sierra and not rainfall. This is good, she said, because rain picks up air pollution more easily than snow, which is why the Northeastern states--with a mix of rain and snow--are having so many problems with acidification of lakes.

Tonneson gave a slightly different picture of Sierra snow than Marks did. Although there are human pollutants in the first Sierra snowmelt, she said, the volume of the snowpack is so huge that downstream aquatic systems are probably not being affected.

“We have observed no biological impacts as a result of this,” Tonneson said. “There might very well be. But we weren’t monitoring for it at the time or the acidic material went by so fast that we didn’t observe any changes in the fish, or the invertebrates or the zooplankton (tiny animals such as protozoans).”

To further complicate the issue, when the spring snowmelt first begins on the southern-facing slopes above Emerald Lake, the mountain pool is still locked in ice.

“Sampling the biological life underneath the ice is extremely difficult,” she said. “We’ve had some people who want to scuba dive (to search for samples). It’s a difficult thing to look for, a real short-lived biological effect.”

Although the scientists agree that obvious biological impacts are probably not yet occurring, they want to continue the study to find out whether the situation is deteriorating or what might happen if the Sierra began receiving much dirtier snow.

“Four years just isn’t long enough for us to see any trends,” Marks said.