Long-term algae impacts to Lake Tahoe murky
Quick highlights of the 2016 ‘Tahoe: State of the Lake Report’
• Only 6.5 percent of precipitation fell as snow in 2015, the lowest amount on record.
• Lake Tahoe’s water temperature is rising at its fastest rate yet.
• Average surface temperature in 2015 was the warmest on record at 53.3 degrees Fahrenheit.
• Lake Tahoe’s mixing depth in 2015 was the lowest ever recorded.
Source: UC Davis Tahoe Environmental Research Center. Visit bit.ly/2aJ43Ne to learn more.
INCLINE VILLAGE, Nev. — Last week, University of California Davis Professor Geoff Schladow broke the news gently before a crowd of residents and scientists that Lake Tahoe is still getting warmer, regional winters are still getting shorter, and overall snowfall is still on the decline.
“Hopefully you’re not like me where you’ve been investing in skis each year,” said Schladow.
The news — highlighted by the fact that 2015 was the warmest year yet for Lake Tahoe — came with the release last week of the UC Davis Tahoe Environmental Research Center’s 10th annual “Tahoe: State of the Lake Report.”
In it, scientists summarize how natural forces, long-term change and human actions have affected Lake Tahoe’s clarity, physics, chemistry and biology over time, concluding that climate change is having a clear impact on Lake Tahoe’s warming waters.
What was less clear in the report, however, is the trend in long-term algae growth.
“Everyone wants to know if there’s more of this stuff, but we don’t know,” Schladow said during a presentation last week at the TERC building on the campus of Sierra Nevada College.
Local researchers study algae growth because it is linked to high levels of nutrients, which enter the lake both atmospherically and through stormwater runoff.
Fertilizer, for example, contains nutrients and can find its way into the lake when it rains, thus contributing to algae growth.
“We have low rainfall and low sediments coming in,” Schladow said. “You would expect the clarity to be better.”
But despite a reduction in the amount of sediment entering the lake last year because of the ongoing Western drought, the concentration of nitrate is actually higher.
“When I saw this, I was concerned because I realized people are going to want answers,” he said.
Schladow said that there is limited scientific data on algae growth because it’s only been measured regularly at Lake Tahoe since the 2000s; there is some intermittent data from the 1990s and 1980s, but nothing older than that.
Because of the lack of scientific data, little is known about what algae levels were like before the 1980s.
“What we’re left to use is anecdotal data,” he said. “We also ask for old photos, so if anyone has some they’d like to share, unfortunately that is the only older data we have.”
UC Davis Staff Research Associate Scott Hackley is one of the scientists working on collecting anecdotal data. He said he and his team frequently hear from people who say that lower algae levels — specifically periphyton — used to be the norm.
“There’s no scientific data, but there’s a lot of anecdotal stories,” said Hackey. “It’d be nice to get some old photos with the year, time of year and the location … to fill in some of the historical gaps.”
Hackey said that he and other UC Davis researchers who study the lake are interested in periphyton, otherwise called “attached algae,” or metaphyton, which is a type of green algae often seen along the South Shore.
What they’re trying to understand is how things like heavy residential and commercial development relate to the growth of algae.
Hackey said he’s worked with archivists at the University of Nevada, Reno, to find old photos, but he and his team are hopeful that the community can help as well.
“What we’re looking for is people who had a nice camera and kept track of dates and locations,” said TERC Education and Outreach Director Heather Segale.
Information on when and where the photos were taken is essential, because it will be used to look up what the Lake Tahoe water level was at the time.
TERC already relies on citizens for current information on lake health with its Citizen Science Tahoe smartphone app, which launched last spring.
“It’s amazing some of the stuff that people send in that I haven’t seen, just because it’s not from one of the beaches that I regularly go to,” said Segale.
As for older photos, Segale and Hackey said they’re looking for images taken before 1990 with a clear view of the Tahoe shoreline, as well as the date and location.
Contact Heather Segale or Scott Hackley at 775-881-7562 or firstname.lastname@example.org if you’re interested in contributing.