On a beautiful Tahoe blue day, there’s no other place I’d rather be than on the lake. Fortunately, the weather aligned to allow for me to go out on the UC Davis Tahoe Environmental Research Center’s (TERC) boat with staff research associate Katie Senft and summer interns Megan Root and Katie Fielder. I tag along to see how researchers measure lake clarity.
Our all-woman crew launch from Tahoe City Marina and first head east to visit Tahoe Buoys No. 1 and No. 4 (TB1, TB4). Owned by NASA Jet Propulsion Laboratory (JPL), these are monitoring stations that relay information to the satellites above, sending back near-real-time data to both UC Davis and NASA JPL researchers about how the lake is changing.
Soup pots filled with water at the stations collect deposits, which could be smoke, pollen, bugs and other types of particles at TB4. A plastic one at TB1 collects nitrogen and phosphorus deposits, things that affect the lake’s clarity. Read the annual State of the Lake Report released in late July in this edition or at tahoe.ucdavis.edu/stateofthelake to learn more about lake clarity.
On our way from TB1 to Emerald Bay, Senft tells me how the mysid shrimp population crashed at the end of 2021 in Lake Tahoe. These shrimps were introduced to the lake in the late 1960s and had fully established themselves by 1971. But instead of being food for lake trout as intended, the mysid instead ate all the good zooplankton that helped filter the water and keep it clear. Senft believes that the mysid shrimp population plummeted because Tahoe’s native zooplankton started coming back, something they are still researching.
“It’s always nice to see when the environment comes back naturally without human intervention.”
“We realized that they lay resting eggs in the sediment that can stay dormant for at least 100 years and then they hatch when the conditions are good,” Senft says.
She explains that the Daphnia zooplankton are the “good girls,” who clone themselves when conditions are favorable to keep their species alive.
“It’s always nice to see when the environment comes back naturally without human intervention,” Senft says.
We make our way across the lake and into Emerald Bay, firing up the generator to give power to run the winch. Senft cleans the mesh net for a zooplankton collection to see what organisms are living in the bay. We check the water depth (65 meters or about 197 feet) and she drops the net to about 60 meters, pulling it back up to see the zooplankton stuck to the mesh. Fielder and Root wash it into an attached cup using a squirt bottle to get a more accurate sample. Red and brown plankton flecks wiggle around in the water.
Senft pulls out another instrument called a LISST that measures particle size and count and then a Seabird that looks at conductivity, temperature and depth.
“It allows us to do a full temperature profile all the way to the bottom,” Senft says.
Next, she takes out a 10-inch-wide white disk attached to a weight, called the Secchi disk, created by Father Pietro Angelo Secchi, a scientist, astronomer and advisor to the Pope (learn about Father Secchi at the Aug. 10 TERC Talk). The disk is lowered into the water until it cannot be seen anymore. The disappearance of the disk indicates the transparency of the water.
To keep as much consistency as possible, UC Davis TERC researchers do Secchi readings on the shady side of the boat, within an hour of solar noon. We lose sight of the disk at 11 meters but can see it at 10 meters, so Senft records that day’s reading at 10.5 meters (34.45 feet).
“If we don’t have perfect 20/20 vision then we wear corrective lenses,” Senft says.
There are only four people who’ve historically taken Secchi readings on Lake Tahoe since UC Davis has been monitoring Lake Tahoe and Senft is one of them.
“The first was boat captain Bob Richards [retired] and Brant Allen, who just retired, and now Brandon [Berry] and I are taking over,” Senft says.
She explains that all the Secchi readings are all close together between the four of them, a good sign of accuracy.
The deepest Secchi disk reading was within the last year when the disk could be seen 30 meters down (98.43 feet ) into the water. It was after an upwelling event in which gusty winds drove icy water to the surface, creating phenomenal clarity.
On the way back to the marina, Senft lights up whenever talking about her 13 years with UC Davis TERC.
“I honestly didn’t think anything like this existed. If you were to tell me when I was young that I’d get paid to do this, I wouldn’t have believed it,” she says. | tahoe.ucdavis.edu
Note: This story highlights just a few of the many projects underway by researchers to study and protect Lake Tahoe.
Aug. 10 | “Deep Waters to Deep Space: Father Angelo Secchi’s Amazing 19th Century Science”
Aug. 30 | “The High Sierra: A Love Story” author Kim Stanley Robinson
6-7:30 p.m. | Granlibakken, Tahoe City