Microplastics, wildfire smoke, changes in temperature, vast swings in lake clarity from winter to summer, and an increase in rain-on-snow events caused by long-term changes in the climate highlight the annual State of the Lake Report, released on Aug. 8 from the Tahoe Environmental Research Center (TERC).
The State of the Lake report summarizes scientific research conducted by TERC in 2023, noting trends in changes in Lake Tahoe’s ecosystem from its clarity, which dropped to 68.2 feet in 2023, to changes in water temperature, algal growth, aquatic invasive species and precipitation of rain and snow, among other factors.
The clarity report, released on July 30 and first reported on YourTahoeGuide.com, shows the continued trend of improving in the winter and deteriorating in the summer. However, 2023 saw some of the biggest swings in clarity, according to TERC.
Winter lake conditions were the clearest observed since 1983 and the 10th best on record, with visibility of 91.8 feet under the surface, compared with 72.2 feet in 2022, according to the report. The summer of 2023, however, saw the fifth murkiest on record with an average of 53.5 feet, compared with 68.9 feet in 2022. Overall, the annual average for lake clarity dropped to 68.2 feet from its 2022 value of 71.9 feet.
“That’s something that’s really important to understand, is that we’re seeing bigger and bigger changes,” said Dr. Alex Forrest, TERC interim director at the State of Lake Report discussion on Aug. 8 at Granlibakken in Tahoe City.
Read the full State of the Lake report at tahoe.ucdavis.edu/stateofthelake
Rising air, water temperatures
One of the long-term trends being seen as a result of climate change is the increase in air and water temperatures at Lake Tahoe, which leads to more precipitation falling as rain rather than snow, among other changes.
In 2023 the average surface water temperature continued to rise, but the air temperature was colder in the winter than had been trending, according to TERC. The colder temperatures during the winter of 2023 enabled Lake Tahoe to experience a deep mixing event in which water from the bottom of the lake circulates to the top of the lake. This mixing is important to the lake’s health and to the increased winter clarity of 91.9 feet that was recording in 2023.
The clarity then dropped to 53.5 feet during the summer of 2023 as sediment from the large winter snowfall entered Lake Tahoe as it melted, which also contributed to the growth of microscopic plants and algae. The drop was the fifth-worst summer clarity reading on record.
The deep mixing event in early March 2023 and fine particles that were swept into the lake by runoff events in May and June also affected the amount and distribution of nitrogen and phosphorus in the lake, both important nutrients for plankton, according to the State of Lake. These tiny plants (phytoplankton) and animals (zooplankton) are the basis for the food web in the lake.
Impacts of wildfire smoke
TERC researchers are also examining how wildfire smoke in the Tahoe region and smoke that is blown into the Tahoe Basin from fires around the West and as far away as Canada are impacting Lake Tahoe’s health.
“TERC scientists Adrianne Smits and Professor Steve Sadro are studying other lakes in the Tahoe region as part of the California Mountain Lake Network, a set of 15 lakes representing different elevations and environments,” according to the report. “They contributed to research published earlier this year showing that between 2019 and 2021, almost every lake in North America was affected by wildfire smoke on at least one day a year.”
Microplastics
Attendees to the State of the Lake talk on Aug. 8 also expressed concerns about trash around Tahoe’s beaches and in the lake and the impact of microplastics in the environment.
Plastics are found in clothing, packaging, car tires and many items that people use on a daily basis. While not a lot of research has been done to date on the presence of microplastics in Lake Tahoe, microplastics and nanoplastics (which can be as small as a virus) are concerning and need more attention from researchers and the public, according to Dr. Monica Arienzo, assistant research professor at Desert Research Institute and a panelist at the Aug. 8 discussion.
A study by a coalition of researchers discovered that Lake Tahoe has the third-highest amount of microplastics among 38 freshwater reservoirs and lakes around the globe, according to the study published in 2023 in the scientific journal Nature. Read more about microplastics in and around Lake Tahoe at YourTahoeGuide.com/trash.
Human impacts
Visitors and locals alike can do their part to help protect Lake Tahoe and its environment, according to TERC. The public can learn more at the Tahoe Science Center in Incline Village, Nev., the science exhibit at the Tahoe City Visitor Center and at a science exhibit that will open on Aug. 15 at the new Kings Beach Visitor Center (find details on page 14.)
As well, the public can volunteer as citizen scientists by reporting observations on algae, invasive species, litter, water quality and ashfall from wildfires, among other things at citizensciencetahoe.org. | tahoe.ucdavis.edu/stateofthelake
