Tahoe Lake clarity: fine sediment reduction programs showing promise
SOUTH LAKE TAHOE — Projections for Lake Tahoe’s future clarity continue to show potential, according to Lahontan Regional Water Quality Control Board senior environmental scientist Bob Larsen.
Larsen presented an update on the state of the lake during the department’s board meeting Thursday, May 12.
While researchers from University of California, Davis, recently announced a decline in average lake clarity for 2015, the overall picture appears to be trending toward improvement.
“We’re headed in the right direction,” Larsen said during a Tribune interview following his presentation. “There’s been a lot of good work done.”
He credited the 2010 implementation of the region’s Total Maximum Daily Load Program for managing fine sediments entering the lake.
According to studies, 72 percent of fine sediments entering Lake Tahoe come from highways and other urban runoff, which makes them the largest contributing factor effecting lake clarity.
“It’s overwhelmingly the urban areas,” he said.
During the board presentation, Larsen credited highway redevelopment projects like recent efforts near Kings Beach for playing a significant role in addressing fine sediment runoff and drainage filtration.
Larsen also addressed the UC Davis findings describing last year’s results as more of an outlier that may have been significantly impacted by a record-low snow year.
“The five-year average is still improving,” he said, adding that it will be interesting to see what the results will be for 2016 given a more average winter snowpack.
Echoing that sentiment, Tahoe Regional Planning Agency natural resource analyst Dan Segan said, “We’ve seen the declining trend in clarity level off since 2000. It’s a really encouraging sign. Hopefully the trend continues.”
Segan added the caveat that “it’s hard to discern natural variability from projects around the lake,” in terms of judging lake clarity concerns.
According to annual measurements, 2014’s average lake clarity was the best it had been in a decade.
“We saw transparency approaching 78 feet,” Larsen said.
When annual measurements began in 1968, clarity was recorded at 102.4 feet.
According to Larsen, implementation of Lake Tahoe Basin’s fine sediment management programs is believed to have had a positive impact thus far.
Since the Total Maximum Daily Load Program was adopted, the basin is on track to reach its goal of reducing fine sediments entering the lake by 10 percent at the end of 2016.
The reduction is based on efforts completed since 2004. Officials hope to reach a 21-percent fine sediment reduction by 2021.
“We’ve come a long way in the last decade,” Larsen said, describing the 2016 goal as already “essentially reached.”
NEAR SHORE A QUESTION MARK
Larsen also briefly addressed recent near-shore lake health and algae concerns.
“There’s a lot of uncertainty there,” Larsen said. “We need to better understand what the drivers are.”
While comprehensive long-term data exists for mid-lake water quality, near-shore concerns are more recent.
“We don’t have that same data for the near shore,” Larsen said, adding that it is a point of emphasis moving forward with research funding expected. “We need long-term data. The near shore is extraordinarily diverse.”
While algae growth is a concern, Larsen said there are indications that it could relate to natural variability. He said some evidence exists that algae may have also reached high levels in some locations back in the 1960s.
“The emphasis at this point is to fill in that gap,” Larsen said, regarding the need for more research.
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