{"id":1019,"date":"2023-07-19T17:49:50","date_gmt":"2023-07-20T01:49:50","guid":{"rendered":"http:\/\/www.inedc.com\/23\/?p=1019"},"modified":"2023-07-22T18:00:33","modified_gmt":"2023-07-23T02:00:33","slug":"lake-tahoe-gegaining-its-legendary-clarity","status":"publish","type":"post","link":"http:\/\/www.inedc.com\/23\/news\/lake-tahoe-gegaining-its-legendary-clarity\/","title":{"rendered":"Lake Tahoe Regaining its Legendary Clarity"},"content":{"rendered":"

PLACERVILLE, Ca. (InEDC) Lisa M. Krieger, July 19, 2023 at 11:00 a.m.<\/p>\n

LAKE TAHOE \u2013 At midnight, researchers aboard the vessel John Le Conte \u2014 an old 37-foot diesel-powered salmon trawler \u2014 dropped a net into icy cold waters.<\/p>\n

What was surprising wasn\u2019t what they caught. It\u2019s what they didn\u2019t: Invasive shrimp, which have long held sway over America\u2019s most famous alpine lake, upsetting its balanced ecosystem.<\/p>\n

In a rare piece of environmental good news, the harmful predators are almost gone. In their place are helpful creatures who are safely returning to eat algae and other fine particles. Scientists say this mysterious shift may be restoring the lake\u2019s legendary clarity.<\/p>\n

\"Chart<\/a>Lake Tahoe\u2019s average visibility has increased from 52.8 feet deep to a stunning 71.7 feet in the past three years, although this summer\u2019s runoff has created some temporary murkiness. That\u2019s like seeing seven stories underwater. In the last five months of 2022, the visibility increased to 80.6 feet, a level not seen since 1988, when it was 81 feet.<\/p>\n

\u201cWe haven\u2019t had this level of clarity since the 1980s,\u201d said\u00a0Geoffrey Schladow<\/a>, director of the UC Davis\u00a0Tahoe Environmental Research Center.<\/a><\/p>\n

To study the dramatic restructuring of Lake Tahoe\u2019s food web, the center\u2019s research vessel counts the presence of three different populations: algae; the predatory shrimp, called Mysis;<\/em>\u00a0and a slew of beneficial native species of algae-eating zooplankton, especially Daphnia and Bosmina,<\/em>\u00a0which are harbingers of good water quality.<\/p>\n

In the past, the nighttime netting would capture 100 to 150 of the nocturnal shrimp, which rise to the surface of the lake in darkness.<\/p>\n

Now it\u2019s catching just two or three. \u201cYou can name them,\u201d joked Schladow.<\/p>\n

The lab is also monitoring lake clarity by measuring the depth to which a 10-inch white plate, called a Secchi disk, remains visible when lowered into the water. While 2023 data isn\u2019t yet available, the lake\u2019s average clarity jumped 10 feet between 2021 and 2022.<\/p>\n

Scientists say the lake is clearest when the zooplankton Daphnia and Bosmina, which had once almost vanished, are most abundant.<\/p>\n

\u201cBiologically, things are changing,\u201d said Schladow. \u201cThings that weren\u2019t in the lake before, suddenly they\u2019re there. Things that were in the lake \u2013 they\u2019ve disappeared. It\u2019s very interesting, and we\u2019re trying to piece it together.\u201d<\/p>\n

The mountain-ringed lake, which straddles the Nevada\/California border\u00a0in the Sierra Nevada, has long been considered a natural wonder.<\/p>\n

\"Kayakers
Kayakers and paddleboarders explore the water at Kings Beach in Kings Beach, Calif., on Friday, June 30, 2023. According to research, Lake Tahoe is the clearest its been since the 1980s. (Jane Tyska\/Bay Area News Group)<\/figcaption><\/figure>\n

Awed by its crystalline waters, writer Mark Twain proclaimed it \u201cso singularly clear\u2026that the boat seemed floating in the air. The water was not merely transparent, but dazzlingly, brilliantly so.\u201d The lake owes its clarity to surrounding granite. Additionally, it has a relatively small watershed and is largely free of agricultural pollutants.<\/p>\n

But in recent decades, the lake\u2019s waters had\u00a0grown increasingly cloudy \u2014 losing their world-famous clarity at a rate of nearly a foot and a half a year.<\/p>\n

Lake Tahoe seemed destined to someday look like any other lake: a murky muddle in the mountains.<\/p>\n

Alarmed, management agencies in the region have taken steps to reduce runoff from roads, gardens, golf courses and the construction of new multimillion-dollar homes. They report that more than 500,000 pounds of fine sediment and other clarity-harming contaminants are being kept out of the lake every year through roadway maintenance and erosion-control projects.<\/p>\n

\"University
University of Nevada Reno student intern Katie Fielder displays mysis shrimp in lake water samples at the Tahoe Environmental Research Center in Incline Village, Nev., on Friday, June 30, 2023. According to research, Lake Tahoe is the clearest its been since the 1980s. (Jane Tyska\/Bay Area News Group)<\/figcaption><\/figure>\n

But a natural culprit also emerged: the non-native Mysis shrimp.<\/p>\n

The shrimp\u2019s introduction was an idea gone terribly wrong. In the early 1960s, the California and Nevada Departments of Fish and Game imported it from the Great Lakes, believing the shrimp would provide food for Lake Trout, which was Tahoe\u2019s primary sport fish.<\/p>\n

But the shrimp are sensitive to light \u2014 and once in the lake\u2019s clear waters, they spend their days on the dark deep lake bottom. Every night, they undertake an enormous vertical migration to the surface.<\/p>\n

Most fish are \u201csight feeders,\u201d and don\u2019t occupy the same water column during the day, said\u00a0Katie Senft<\/a>, the Center\u2019s staff research associate. So the shrimp aren\u2019t eaten.\u00a0 And with few predators, they flourished.<\/p>\n

Voracious consumers of zooplankton, the shrimp annihilated the Daphnia and Bosmina, she said. By 1971, those two important species largely disappeared from the lake.<\/p>\n

But now something new is happening.<\/p>\n

\"\"\"Chart<\/a>Starting in 2012, just a few Mysis shrimp were found in samples from the lake\u2019s Emerald Bay. In work that is now being expanded to other lake locations, Daphnia and Bosmina have reappeared in large numbers.<\/p>\n

\u201cFor 50 years, Mysis ruled. Then they disappeared. Gone,\u201d said Schladow. \u201cWe didn\u2019t know why.\u201d<\/p>\n

Microscopic study at the Center\u2019s modern lab, tucked in the tall pines of Incline Village, is revealing a possible cause: The shrimp are starving.<\/p>\n

Once populations of Daphnia and Bosmina plummeted, the shrimp shifted their diet to a different type of zooplankton, called copepods.\u00a0 And those copepods are dying from fungal infections, the lab suspects.<\/p>\n

Magnified, the dead copepods look as fuzzy as a chia pet. To better understand if the fungus is the underlying cause for the current population crash, Center intern Katie Fielder is scanning historic water samples.<\/p>\n

\"Professor
Professor S. Geoffrey Schladow, Phd., oversees as University of Nevada Reno student intern Katie Fielder examines lake water samples at the Tahoe Environmental Research Center in Incline Village, Nev., on Friday, June 30, 2023. According to research, Lake Tahoe is the clearest its been since the 1980s. (Jane Tyska\/Bay Area News Group)<\/figcaption><\/figure>\n

There is likely always some fungus in the lake, and the Center has seen these \u201cfuzzy\u201d copepods in the past, but never at such density. It\u2019s not known why so many are dying now, said Senft.<\/p>\n

All these years, Daphnia and Bosmina have patiently laid in wait. Their eggs can sit dormant in lake sediment for up to a century, said Senft. Now the eggs are hatching \u2014 and, free of predators, they\u2019re flourishing.<\/p>\n

\u201cThey\u2019re very, very, very efficient feeders,\u201d said Schladow. The lake\u2019s cleanup crew, \u201cthey just shovel things into their mouths \u2014 and the food they eat, the algae and very fine particles, are what impact the lake\u2019s clarity the most.\u201d<\/p>\n

Swimming underwater in the lake\u2019s Sand Harbor over the July 4 weekend, \u201cit was serene. Crystal clear. Little minnows were doing something in the water, although it was so cold I\u2019m not sure my brain was working,\u201d said A.J. Kohn, visiting from Minneapolis.<\/p>\n

\u201cAbsolutely beautiful,\u201d said paddleboarder Heather Pratt of El Dorado Hills.<\/p>\n

Darcie Goodman Collins, CEO of\u00a0The League to Save Lake Tahoe<\/a>, welcomed the research, saying that \u201clearning more about this system can help us really understand the \u2018trigger points\u2019 and can help us make management decisions. \u2026 But better annual averages doesn\u2019t mean that the lake is doing better, overall. It\u2019s not time to take a victory lap yet.\u201d<\/p>\n

\"\"\"Boaters
Boaters explore Sand Harbor in Incline Village, Nev., on Friday, June 30, 2023. According to research, Lake Tahoe is the clearest its been since the 1980s. (Jane Tyska\/Bay Area News Group)<\/figcaption><\/figure>\n

\u201cIt\u2019s highly unlikely that the shrimp population is going to be the only component to clarity improvements or clarity loss,\u201d Collins said. \u201cA lot of the impacts are coming from our urban landscape, and could have a significant impact on our ecology, including the Mysis shrimp and our native populations of Daphnia.\u201d<\/p>\n

The lake\u2019s\u00a0clarity is expected to grow over 2023<\/a>, and may return to 1970s levels, despite the expected large runoff from this year\u2019s record snowpack. California and Nevada lake management agencies dream of someday restoring up to 90 feet of visibility.<\/p>\n

Sadly, nature\u2019s food web is a tale of ebb and flow. Mysis will start eating the newly emerged zooplankton and re-establish itself, scientists predict, returning the lake to its perturbed and more clouded status.<\/p>\n

\u201cIt\u2019s temporary,\u201d said Schladow. Once introduced, \u201cyou can never get rid of things completely.\u201d<\/p>\n

But the discovery could support strategies to deliberately remove the shrimp, which could be captured while hovering in its tight 50-foot-deep nocturnal band. While it may not be eliminated, numbers could be held in check.<\/p>\n

\u201cIf we can get the lake back into some balance, then the system is pretty resilient,\u201d said Schladow. \u201cAnd that gives us hope.\u201d<\/p>\n

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