Thursday, May 31, 2012 - Traveling the western U.S. state of Nevada in the 1860s, a young American writer named Mark Twain heard a "world of talk" about the beauty of Lake Tahoe and so set out one August day to see the lake perched high in the Sierra Nevada Mountains. Determined to make the 11-mile journey on foot, Twain and his companions became briefly discouraged after toiling up one mountain and then another to no avail. But they trudged on until "at last the Lake burst upon us," Twain wrote in his 1872 book, Roughing It.
One hundred and fifty years later, visitors to this border region between California and Nevada still marvel at Lake Tahoe, but sadly the "jewel of the Sierra" is not the same gem it was in Twain's time. Boating on the lake during his trip, Twain said he could see rocks at least 80 feet below the surfacea degree of clarity that scientists attribute to "ultra-oligotrophic" conditions, meaning exceptionally nutrient-poor and pure. Since the 1960s, however, Lake Tahoe's renowned water quality has been in slow decline, and exactly why "is the $64,000 question," says soil scientist Dale Johnson of the University of Nevada in Reno.
Damaging blazes sweep the Tahoe region regularly, and by the time Johnson teamed up with his University of Nevada colleague, Wally Milleran expert on Tahoe's water qualityscientists already knew how catastrophic fires could affect downstream streams and lakes. Wildfire can leave slopes bare of vegetation and unprotected from erosion. Burning also releases nitrogen, phosphorus, sulfate, and other biochemicals locked in plants, wood, and soils, allowing the nutrients to run off downslope or seep into groundwater. But when Miller and Johnson began their studies, they discovered something that few, if anyone, had suspected: Not only could a major disturbance like fire affect Lake Tahoe, but so too could a lack of disturbancethe absence of fire. "The results were very surprising and therefore very har
|Contact: Teri Barr|
American Society of Agronomy