Lake Tahoe clarity improves
April 14, 2015
Researchers with University of California, Davis found that clarity levels at Lake Tahoe last year showed the biggest improvements in more than a decade in comparison to the year before.
The data released by the U.C. Davis Environmental Research Center and the Tahoe Regional Planning Agency (TRPA) reported the average annual clarity for 2014 at 77.8 feet. The average was found from 28 individual readings, of which the deepest was 93.5 feet in July and the shallowest was 57.4 feet in September.
The measurements are taken with a 10-inch white disk called a secchi disk, which is lowered into the water and its depth is measured as it remains visible. Secchi depth is the most widely used method of clarity measurement.
The measurements in 2014 represented a 7.5-foot improvement from 2013.
The research comes from a program led by the TRPA in collaboration with U.C. Davis.
The improvements, the report states, are in part because of continuous work from the Lake Tahoe community to lower pollutants to the lake. They were also influenced by the drought. Reduced precipitation led to fewer contaminants flowing into Lake Tahoe, particularly during the summer, when clarity levels were the highest since 2002.
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"While these latest data are very reassuring, they should not be interpreted as victory in our joint restoration efforts," Director of the U.C. Davis Tahoe Environmental Research Center Geoffrey Schladow stated in the report. "Complete restoration is still decades away, and some of the greatest challenges still lie ahead of us. We are enduring drier and warmer conditions than we have ever encountered, and the restoration consequences of that are still far from understood."
The long-term trend in summer clarity is a result of many factors, including the amount of precipitation in the Basin and the depth to which the lake mixed the previous winter, according to the report. Warmer conditions also resulted in shallow mixing, which usually results in high clarity.
Measurements have been taken since 1968, when the water clarity was measured at 102.4 feet.
Improved real-time monitoring instruments, combined with sophisticated models of the lake currents that transport contaminants, help researchers build a deeper understanding of restoration progress within the entire lake ecosystem.
"Many of the long-held assumptions about lake clarity and conditions in the near-shore areas of the lake are finally being tested," Schladow said.
Ultimately, the coalition is trying to reach a goal of clarity restoration of 97.4 feet set by federal and state regulators.
More information about environmental factors impacting Lake Tahoe will be included in the 2015 State of the Lake Report expected this summer.