Due to this past winter's huge snowpack finally melting, Lake Tahoe is quickly reaching its storage capacity. Wochit
Summertime clarity declines outweigh winter improvements
Lake Tahoe’s famous clarity took a hit last summer thanks to the “continuing effects of climate change,” according to a report posted Thursday.
It’s the second consecutive year climate change contributed to reduced seasonal lake clarity, the report stated.
Although climate change contributed to murkier summertime conditions in recent years, the long-term clarity trend remains steady on an annual basis with sizable seasonal variability, according to the report from the University of California, Davis Tahoe Environmental Research Center.
Clarity measurements are important because they’re a significant indicator of Lake Tahoe’s overall health, said Geoffrey Schladow, director of the center.
Clarity from June through September last year averaged 56.4 feet, a 16.7 foot decline from the previous year.
Schladow blamed the decline on large increases in the production of Cyclotella, a form of algae that suspends in the water column.
He said the algae benefitted from reduced mixing in the water column that’s associated with the effect of climate change on the lake.
“It is pretty definitive,” Schladow said. “One of the consequences of climate change is lakes mix less, especially in summer.”
Algae isn’t the only climate-related problem facing the lake. In 2015 warm layers of turbid water near the surface reduced summer clarity.
Planetary warming due to climate change, largely due to humans burning fossil fuels, has broad ramifications for everything from sea level rise to ocean acidification to melting tundra.
The Lake Tahoe basin isn’t immune to climate change, either. Since 1910 the annual average number of below-freezing days in the basin has dropped from 80 to 60. In the year ending Sept. 30, 2015 the basin only saw 24 days with an average temperature below freezing.
“Lake managers and researchers must continue to work together to better understand the impacts that continued climate change will have at Lake Tahoe, and look for new solutions to mitigate those impacts as we work to restore lake clarity,” Schladow said.
The good news
Despite the recent summertime declines the long term, annual clarity has hovered around 71 feet for the past 15 years.
Clarity from December 2015 through March 2016 increased by 11.7 feet from the prior year to 83.3 feet, the clearest since 2012.
The five-year average clarity is 73.1 feet, which is slightly ahead of the interim target of 71 feet by 2016. That’s an improvement from 64.1 feet in 1997, the lowest recorded average since scientists started tracking clarity in 1968. The long-term goal is to reach 97.4 feet by 2076.
Much of the credit for improvement goes to residents, businesses and government agencies in the Tahoe Basin.
In recent decades they’ve implemented programs and upgraded infrastructure aimed at reducing sediment runoff into the lake, a key contributor to clarity declines.
Since 1997 local and state agencies in Nevada and California have upgraded 729 miles of roads to reduce stormwater runoff and restored 1,558 acres of stream areas.
They’ve also implemented best management practices, or BMPs, to reduce runoff from private property.
According to the Tahoe Regional Planning Agency, which leads the Lake Tahoe Environmental Improvement Program, 43 percent of 43,470 private property parcels in the basin have implemented BMPs.
“The actions TRPA and 50-plus partners have taken to reduce stormwater pollution and restore important natural areas like marshes and wetlands are helping protect and restore Lake Tahoe’s famous water clarity,” said Joanne Marchetta, executive director of TRPA.
Tahoe's future climate risk
The summertime clarity setbacks and overall warming trend show there’s still more work ahead to keep the health of Lake Tahoe heading in the right direction.
Schladow said increasing the implementation rate for BMPs and expanding the restoration of meadows, marshes and streams could help offset problems and make Lake Tahoe more resistant to climate change.
“First, the improvement in winter clarity is evidence that actions being taken are having positive impacts,” Schladow said. “Second, the decline of summer clarity is reminding us that the impacts of climate change are complex, multi-faceted and still evolving.”
Tahoe’s increased exposure to climate risk is happening at a time when support for climate science is in peril.
Although Congress last year authorized $415 million over seven years for the Lake Tahoe Restoration Act the money is yet to be appropriated in a budget. It was a reauthorization of the original restoration act which was set to expire.
President Donald Trump, who has yet to submit a detailed budget proposal to Congress, has shown hostility to funding and regulations aimed at environmental restoration, particularly when it’s tied to climate change.
And an early budget proposal from Trump suggested cutting $230 million raised through the Southern Nevada Public Lands Management Act, also known as SNPLMA. The act directs money from Bureau of Land Management property sales near Las Vegas to environmental projects, including those at Lake Tahoe.
Sen. Dean Heller, R-Nev., and Rep. Jacky Rosen, D-Nev., have vowed to oppose cuts to SNPLMA funds.