State of Lake Tahoe Report 2022

The University of California, Davis, Tahoe Environmental Research Center, or TERC, released its annual report today Tahoe: State of the Lake Report. The report informs non-scientists of important factors affecting the health of Lake Tahoe and provides the scientific basis for restoration and management decisions in the Lake Tahoe Basin.

The report summarizes data collected in 2021 in the context of the long-term record of research at Lake Tahoe. UC Davis researchers have continuously monitored the lake since 1968.

TERC Director Geoffrey Schladow, professor of civil and environmental engineering at UC Davis, will share highlights from the report in a live presentation and webinar today, July 28 at 6 p.m. Registration for the event is at tahoe.ucdavis.edu/events.

The report describes the collapse of zooplankton and My sister shrimp populations; a sudden change in the phytoplankton community; and the extent of algae growth affecting large sections of Tahoe’s coastline.

“Any of those changes would be a big deal in a single year,” Schladow said. “The three simultaneous events are particularly alarming and provide a huge opportunity to learn lessons that can be used to inform future direction.”

Mysis shrimp up close. (UC Davis TERC)
Scientists from the Tahoe Environmental Research Center at UC Davis night-trawl the invasive Mysis shrimp for a research project at Lake Tahoe. (UC Davis TERC)

Highlights include:

The plankton fall is an obvious opportunity

Zooplankton numbers have dropped over the past year. These tiny aquatic organisms are an important part of the lake’s food web and help regulate algae concentrations. The decline of a non-native zooplankton, the My sister shrimp, marks an opportunity to better understand the clarity of the lake. (The Tahoe Clarity Report was released earlier this month.)

My sister shrimp were introduced to the lake about 50 years ago, feasting on Daphnia and other zooplankton that help purify the water. After My sister abundance decreased in Emerald Bay between 2011 and 2014, Daphnia – and water clarity – increased significantly, resulting in larger kokanee salmon. My sister later returned to the bay, and the process reversed. TERC researchers expect a similar episode to unfold in Lake Tahoe itself within the next four years, with My sister figures already at extremely low levels.

To capitalize on this ongoing natural experiment, the report calls for more comprehensive monitoring to understand the interaction between zooplankton, phytoplankton and clarity.

“Ultimately, My sister will return,” the report said. “The real question is whether the lack of My sister of Lake Tahoe will help restore clarity and, if so, the deliberate removal of My sister justified in the future.

Meanwhile, the phytoplankton forming the base of the food web is also changing its distribution at an unprecedented rate. In 2021, phytoplankton moved closer to the surface as summer progressed. The change may be due to reduced sunlight and UV radiation during wildfire smoke events.

Highest algae growth ever recorded

The growth rate of algae, or “primary productivity”, has increased sixfold over the past 50 years. The abundance of floating algae has also increased by 300% over the past year, reaching a record annual value in 2021.

Algal blooms near the shore are a growing threat, affecting areas of the lake where the greatest number of people congregate. The researchers used aerial imagery to capture the full extent of the periphyton bloom along the northwest side of the lake for the first time.

For the first time, the dominant algae in the lake was cyanobacteria Leptolyngbyaa species favored by the high nitrogen content present in the smoke of forest fires.

A buoy floats in Lake Tahoe under smoky skies in 2021. UC Davis scientists sample the lake from a research vessel in the background. (UC Davis TERC)

Highest fine particles ever recorded

In 2021, concentrations of fine particles, which have a significant impact on clarity, were the highest on record. The wet year of 2017 resulted in a sharp increase in fine particulates in Lake Tahoe from local streams. High average concentrations have been maintained every year since, despite some extremely dry years. Particles from wildfires in 2021 could be a source. Researchers continue to study the drivers and impacts of fine particles.

Meanwhile, nitrogen and phosphorus loads from the Upper Truckee River were the lowest on record in 2021.

Weather and climate change

Climate change is evident in almost all long-term weather trends, including rising air temperatures and decreasing snow cover. In 2021, monthly average temperatures were warmer than the long-term average and the past two years. The year also brought the hottest June and July since these measures began in 2010.

With less than half of the long-term average rainfall, 2021 was the third driest year on record. The report says it is “almost certain” the lake will fall below its natural edge and stop flowing to the Truckee River this summer.

The report also details research related to wildfire smoke, invasive species, microplastics, a new tool on lake conditions, and educational outreach conducted by TERC in 2021.

Production of the State of the Lake Report was funded by the California Tahoe Conservancy, Tahoe Fund, Tahoe Regional Planning Agency, Tahoe Lakefront Owners’ Association, Lahontan Regional Water Quality Control Board, Nevada Division of Environmental Protection, Lake Tahoe Marina Association , Parasol Tahoe Community Foundation, Mountain Workspace, Tahoe Water Suppliers Association, TruePoint Solutions, Truckee Tahoe Airport and Incline Village Waste Not.

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