Lake Tahoe clarity improved in 2011, but overall has remained nearly stable since 2000, according to UC Davis scientists who study the lake.
Data released today by the UC Davis Tahoe Environmental Research Center and the Tahoe Regional Planning Agency reported the average annual clarity level for 2011 at 68.9 feet, a 4.5-foot improvement over 2010, when average clarity levels were the second-worst on record.
Winter clarity last year continued a decade-long pattern of improvement, while summer clarity continued to decline at the same rate that it has since the late 1960s, when monitoring began.
Average annual clarity in the past decade has been better than in recent decades. In 1997-98, annual clarity reached an all-time average low of 65.1 feet. From 2001-11 the average clarity was 70.6 feet.
Yet this year’s value is still more than two dozen feet away from the clarity restoration target of 97.4 feet set by federal and state regulators.
Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center, said it is important to remember that long-term trends are a better indication of Lake Tahoe clarity than year-to-year comparisons.
“The factors that contribute to lake clarity are complex, and are not necessarily linked to factors occurring in the current year,” said Schladow. “For example, the 2011 clarity improvement followed a winter that was one of the wettest in recent years, something that is usually associated with clarity declines. Understanding what controls the long-term trends is at the heart of what we are attempting to do.”
Researchers provided measurements for both winter (December-March) and summer (June-September) months. The winter average of 84.9 feet in 2011 was well above the worst point seen in 1997 and a 12-foot improvement over 2010.
Urban stormwater runoff has long been one contributor to reduced clarity at the lake. Most of that runoff occurs during the winter and spring, when rain and snowmelt carry small, inorganic particles from the land into the lake.
Read the complete article at Environmental Protection On-Line