Lime for your drink? Here's a new twist.

Lime for your drink? Here's a new twist

More than 60 years ago, managers of Norwegian salmon hatcheries conducted the first reported "liming," or chemical neutralization, of waters acidified by industrial air pollutants. This treatment, named for the limestones commonly used in the procedure today, typically involves applying mineral powders or pellets directly to affected lakes or streams. Though it yields an almost immediate and potentially revitalizing increase in pH, its benefits vanish as the water containing the buffering agent flushes out of the system and is replaced by untreated water. In lakes, the replacement typically occurs after a year or two, notes Harvey Olem, a Washington, D.C.-based consultant. And that's why researchers are beginning to focus their attention on watershed liming -- an alternative buffering strategy that's expected to provide at least five to 10 years of benefits per treatment, says Olem, who conducted a peer-reviewed survey of liming science and technology for the federally funded National Acid Precipitation Assessment Program.

Rather than liming the acidified waters themselves, this treatment limes the land draining into them. According to Olem, watershed liming can yield a host of additional benefits unattainable with conventional liming. For instance, by parceling out its alkaline therapy more slowly and uniformly, watershed liming should prevent the potentially toxic over-buffering that has resulted from some poorly controlled direct-lake treatments, in which pH levels sometimes rose as high as 9, Olen says. Moreover, by neutralizing water before it enters lakes or streams, the new approach would prevent potentially large pulses of acidic snowmelt or rain drainage from entering a waterway and creating large, undiluted pockets of highly acidic water. Many sensitive aquatic species can die from chronic exposure to a pH of 6 or from acute exposures to more acidic levels. Aquatic biologist Patricia T. Bradt at Lehigh University in Bethlehem, Pa., notes that rain with a pH of 4.2 to 4.8 is fairly common in Pennsylvania.

Researchers in the United States and Europe are currently testing the alternative strategy. One experiment initiated last October used helicopters to shower 1,000 metric tons of limestone pellets onto the forested slopes above two streams feeding Woods Lake in New York's Adirondack mountains. "This is the first watershed liming in the United States, and the first anywhere to involve lots of careful measurements," says project manager Donald Porcella, of the Electric Power Research Institute in Palo Alto, Calif. During the next two years, researchers from five collaborating universities will assist the institute in monitoring water-acidity changes and other effects of the experimental liming on aquatic and terrestrial ecology.

The EPA's National Surface Water Survey has identified 2,500 lakes and 36,000 kilometers of streams as having pH levels of 6 or lower. Though this total may include some naturally acidic waters -- existing in that state for perhaps millennia -- a large fraction are believed to have suffered significant acidification due to industrial air pollutants.

Olem says researchers have estimated that half the U.S. surface waters acidified by air pollutants will eventually recover under the emissions-control strategies most likely to emerge from strengthened Clean Air Act regulations. "The other half will remain acidic," he observes. And for them, "liming may be an option--a tool--for restoring their fisheries."

Harald Sverdrup, a chemical engineer and liming expert from the Lund (Sweden) Institute of Technology, cautions that "liming doesn't solve all [ecosystem] problems -- just a suite of the worst." Nonetheless, he says, it is the fastest remedy for surface-water acidification. And, short of stiff emissions controls, liming is also the "most effective" method known, concludes Olem in his survey report.