Little Rock Lake, the site of a landmark study on the effects of acid rain, has been taken to chemical hell and back, and seemingly recovered from the trip.
The University of Wisconsin-Madison study, spanning two decades, found that while the chemistry of the lake corrected itself naturally - and fairly quickly -- the biological changes took much longer to bounce back.
This year, the northern Wisconsin lake came full circle, returning to its natural condition after its pH levels were dramatically altered beginning in 1984. Scientists separated the hourglass-shaped lake into two basins with a mesh curtain, keeping one side in its natural state while the other was slowly acidified.
From 1984 to 1990, the test basin was taken from an original pH of 6.1 down in two-year intervals to 5.6, 5.2 and 4.7. Then it was allowed to recover without intervention.
It essentially became a tale of two lakes, as the character of the acidified water began to dramatically change, says Thomas Frost, director of the study and site manager of Trout Lake Station in Vilas County. Frost reported his findings this month at the annual meeting of the Ecological Society of America. "We found that the pH levels had a controlling but indirect influence for nearly every biological factor in the lake," says Frost. "The nature of the food web changed completely."
Sport fish in the lake, such as bass and perch, survived the change but the offspring of fish were unable to survive. The zooplankton in the lake, a critical part of the food chain, underwent a complete revolution. Some once-rare zooplankton took over the lake, while once-dominant species almost vanished.
The acidified lake became almost crystal clear in the process, and ultraviolet light penetration increased, he says. Chemical changes helped a long, filamentous algae nicknamed "elephant snot" to spread across the lake bottom.