Seeking clarity

2019 State of the Lake

Brant Allen, boat captain for the UC Davis Tahoe Environmental Research Center, lowers a Secchi disk into the lake during a clarity test in 2007.

Brant Allen, boat captain for the UC Davis Tahoe Environmental Research Center, lowers a Secchi disk into the lake during a clarity test in 2007.

Courtesy/UC Davis

Living so close to Lake Tahoe, it can be easy to take its emerald blue water, rugged terrain and stunning beauty for granted, and forget that the lake is part of a delicate ecosystem whose health relies on conservation and diligence on the part of naturalists and an informed public. Data collected over the past five decades by the University of California, Davis presents a quantified look at whether we are effective curators by providing comprehensive research on the Tahoe Basin.

UC Davis’ Tahoe Environmental Research Center, or TERC, annually compiles their research into one accessible brief: the State of the Lake Report (SOTL). Since 2007, the report has used an array of technologies across numerous data collection sites to inform researchers about different factors affecting the lake’s health, including its biology, chemistry and clarity.

Clarity findings published by UC Davis on May 23 indicate that the upcoming State of the Lake Report, scheduled for release in late July, will contain more promising data than in 2017, when researchers documented a record low clarity of 59.7 feet. The report measures the depth at which a 10-inch white plate, called a Secchi disk, can be seen from the surface of the water. In 2018, the clarity of the lake increased by more than 10 feet, bringing the depth at which the Secchi disk could be observed to 70.9 feet.

“What the improvement in 2018 shows is that in literally one year the lake can recover from an extreme set of circumstances, and that is really encouraging,” said Dr. Geoffrey Schladow, the founding director of TERC and a UC Davis engineering professor.

However, clarity is only one aspect of ecosystem health, and the Secchi depth findings are not always indicative of the broader conditions of the watershed, which is what the SOTL is designed to monitor.

“A lot of last year’s improvement is a reflection of the fact that the previous year was so bad,” Dr. Schladow explained. “The previous year was bad for two reasons: One, it was a very extreme winter. A lot of snow, a lot of runoff, possibly one of the wettest winters ever recorded. Second, it came at the end of one of the most severe droughts that California and Nevada have experienced. A lot of material that hadn’t been washed out for four or five years suddenly got washed out and eroded and deposited in the Lake.”

For the first time this year, data taken from comparative studies being conducted by TERC researchers at Lake Geneva in Switzerland, as well as Lakes Panguipulli and Villarrica in Chile, will be included in the SOTL Report, demonstrating that an increased understanding of Lake Tahoe can assist researchers around the world in better understanding their respective watersheds.

“Very often, it’s easier to learn about your own system by looking to a similar system and starting to see where the similarities and differences are,” said Schladow. “Lake Tahoe is a unique and iconic treasure. Not just for California or Nevada, but for the whole world. What we learn at Lake Tahoe can be applied literally everywhere.”

As the long-term effects of Climate Change are realized in ecosystems around the planet, the State of the Lake Report, and its conclusions concerning Tahoe’s elasticity following record-breaking weather events, is vital not just to keeping Tahoe blue, but to helping policymakers, scientists and individuals around the globe understand and attempt to mitigate the adverse effects of our rapidly changing climate.