Lake Tahoe’s famed clarity getting substantially murkier
By Katherine E. Hill
Lake Tahoe’s world-renowned water clarity dropped 3.7 feet in 2010 from 68.1 feet to 64.4 feet, the second-lowest clarity level ever recorded.
The drop in clarity is the result of climate change and increased algae growth, according to the UC Davis Tahoe Environmental Research Center in the annual State of the Lake Report released Friday.
Lake Tahoe’s famed clarity can increase or decrease based on any number of factors such as fine articles, algae growth, sediment runoff, snowmelt and others. Researchers say the decrease between 2009 and 2010 in clarity is the result of climate change that may have allowed for the growth of a tiny, free-floating algae named Cyclotella. These tiny algae, which proliferate in warmer temperatures, have grown significantly in recent years.
The Secchi disc is lowered into Lake Tahoe for one of several readings. Photos/TERC
“This year, in particular, these single-cell algae were concentrated very close to the surface, strongly scattering light and thereby impacting lake clarity,” said John Reuter, associate director of TERC in a release about the decline in clarity.
The State of the Lake report also calls for continued joint efforts by California and Nevada to manage the health of Lake Tahoe. The Nevada Legislature passed a bill in June to pull out of the Tahoe Regional Planning Agency Compact by 2015 unless the Regional Plan is amended.
“While land use activities, resource management activities and policy can be controlled to conform to geopolitical boundaries, the waters of Lake Tahoe are not constrained by these human boundaries,” the report states. “What happens in the waters of Lake Tahoe is a direct reflection of activities in both states. If a concrete example of why Lake Tahoe needs to be managed jointly by the two states is needed, then this is one.”
Optimism despite decline
The clarity report also reports a trend in increased clarity during the winter months, with decreased clarity occurring during the warmer, summer months. Researchers stated in the report that improvements in winter clarity measurements may be due to recent efforts to reduce urban stormwater flows, but that those gains are being lost in the summer, which sees higher than normal temperatures due to climate change.
“There is every reason to believe that if it were not for the decades of watershed management, development policy and water quality restoration projects, the lake’s transparency would be worse than it is today,” Geoffrey Schladow, TERC’s director, said in the release.
Despite the drop in clarity, researchers remain positive about the overall health of the lake. The lake clarity chart shows the measurement through the years.
“Taken alone, that decline in clarity is unusual, but it is within the range of normal fluctuations,” Schladow said.
For the first time, researchers also have gleaned a bigger picture of Lake Tahoe’s clarity using remote sensing to record data from around the lake. Most notable in the remote sensing findings is that clarity on the East Shore is lower than the West Shore for most of the year, according to the report. As well, clarity generally improves 1 mile off the shoreline than at points closer to the shore.
How clarity is defined
Lake clarity is measured by several scientific means, but it has been continuously measured since 1968 using a Secchi disc, a 10-inch white disc that is lowered into Lake Tahoe throughout the year to come up with a yearly average. The Secchi measurements are the longest continuous measure of Lake Tahoe’s water clarity.
The Secchi disc was developed in 1865 for use by ships to measure the depths of harbors, but has been used in modern times to measure the clarity of water.
The Secchi disc is the main means to measuring lake clarity.
The Secchi disc measurements are taken by researchers every 10 days at solar noon at the same two locations – off the Tahoe City shelf and off Homewood toward the middle of the lake, according to Heather Segale, TERC’s Education and Outreach director.
The disc is lowered from the boat by a metered wheel and the researcher marks the point on the wheel at which the disc disappears from view, Segale explained, and then marks the point at which the disc reappears as it is raised. The distance between these two points is averaged for the day’s reading.
Since the researchers rely on their eyesight to mark the points at which the disc disappears and reappears, they are required to have their eyesight checked regularly, cannot wear sunglasses, and measurements are performed only during smooth waters, according to Segale. The annual clarity measurement is an average of about 20 to 25 measurements; about 10 are thrown out due to anomalies such as inclement weather, wind and other factors.
While the Secchi disc measurements represent the longest study of the lake’s clarity, researchers also rely on other measurements to gauge clarity. Researchers use several high-tech instruments mounted on a Seabird profiler: a transmissometer that measures how much light of a certain wavelength is received over a fix path; an optical backscatter sensor that measures how much light from a LED is scattered backward by particles; a photosynthetically active radiation sensor that measures solar radiation; and a turbiditimeter that measures the cloudiness of water.
In addition to the annual clarity report, the State of the Lake report also addresses efforts to control aquatic invasive species, such as the Asian clam that were first reported in Lake Tahoe in 2002. The report also addresses the impact of climate change on precipitation, changes in the lake’s water temperature and effect of lake warming on circulation.
To view the report, go online.
C’mon guys we had a record season in terms of rain. Or, lets stop all the erosion control measures-proves they’re waste of time and MONEY.
Lake Tahoe’s famed clarity. Who in the heck besides us locals and a few wack jobs know diddly squat about Lake Tahoe’s “famed clarity?” Maybe “54 40 or fight” or “Tippecanoe and Tyler too” would be a better slogan.
It won’t be too many geological years before this body of water becomes a meadow, then a valley. Then what will the country do to prevent the loss of this “national treasure?”
“the researchers RELY ON THEIR EYESIGHT” ; we’ve spent a billion plus on lake “clarity” using human eyesight? No wonder people are frustrated. The eyesight of a human being changes, the humans used as scientific measuring machines have changed over the years, the differences between the humans have changed and the opportunity for “human error” is astronomical. The reason we use machines instead of humans to build cars is to reduce the human error effect; the reason objective scientific research is used is so that it can be trusted, relied upon to make conclusions.
But we’ve been spending over a billion relying on … Eyesight.
The eyesight of various different people over the years.
The eyesight of people from 30 years ago before measuring and testing of eyesight had the benefit of today’s technology. The eyesight of the first researchers studying lake clarity is used as the baseline from which we compare whether we are losing or gaining in lake clarity.
We’ve spent billions on the results of people “lowering a dish over the side of a boat and looking to see just how far it goes before it’s not visible.” “Hey Sam, I don’t see the dish anymore, how ’bout you?”
Eyesight among all those who “don’t wear glasses” or who see 20/20 is not the same, especially when we’re measuring inch differences.
Maybe we can have some honest discussion one day about the lunacy of how measuring lake clarity was started by eyesight, how measuring eyesight itself has improved over the years, that relying on the human eyesight as a basis for a billion plus in investment is not sound science.
There is no scientifically sound method to measure how clear the lake is (define clear, by the way). And if you can debate the definition of clarity, that debate alone should tell us that there is little and arguable science around what constitutes clarity. How blue is blue?
Plenty of science has already informed the rest of the world that water quality is the key to improved water clarity.
Try to keep dirt, road junk, runoff, litter, ash and a ” boat load” of other junk out of the lake, that should be our focus. Invest in new technology of today to improve storm drains, invest in sidewalks, curbs, gutters, hi- tech modern infrastructure, recycle, reuse, make this falling down place we call home the example of sustainable living, and the lake will stay clear enough for my eyesight and yours and even our kids see really far down below the surface. In the meantime, more importantly, water quality will be improve.
No need to spend another billion paying college students and their professors to lower the dish over the side of the boat as they all lean over to look at know far down it goes and call out when they’ve lost it from view.
Can’t believe we still measure clarity with some guy in a boat looking at a plate. Might be time for some new technology.
Ya think. Well if you take out the dam in tahoe city you will increse lake clarity and the public will have access to the beach, in Nv., when the lake goes below 6223 ft. above sea level.
I am the only person that read the part of the article about the other equipment that is also used? And then there is the explanation about how the disc was being used longer so its interesting for comparison.
Carl there is new technology. But the Secchi disk data set is now over 50 years old.
Also the ranting poster above doesn’t know much about statistics.
Sigh. What’s new in Baltimore?
More conservatives criticizing scientists, asking questions they can answer themselves, not reading the article, demonstrating a basic lack of understanding about the science they are criticizing.
Par for the course.
Here are so amazing excerpts:
“There is no scientifically sound method to measure how clear the lake is (define clear, by the way).”
Except for TDS. And, TDS. Or Turbidity, and NTUs. Both which use fancy science toys.
“little and arguable science around what constitutes clarity. ”
Yeah well other than TDS…. and NTU’s.
Also for that eyesight argument… would secchi disk depths be affected by increasing? And thus showing an increase in clarity?
And then there is statistics….
So much passion, so little substance. Why don’t you cite something?
I have photos taken of our family frolicking at Baldwin Beach in the 1960s, and there’s no question at all about loss of clarity — and that’s based on eyesight. Not the most scientific measure, to be sure, but the most heart-tugging. That was back when raw sewage was still legally allowed to spew into the lake, and plenty of other eco-unfriendly practices I don’t even want to know about, no doubt. What’s key, I think, is that there were far fewer people around then. The permanent population has grown and so has the number of tourists. Human activity always stresses the environment, and the more people there are, the more stressed the environment will be. I’m not convinced that there’s a way to “save Lake Tahoe” that doesn’t involve drastically limiting access to it, and who’s going to go along with that?
She’s a lovely jewel, and we’re killing her. That’s the sad fact.
Sustainability! We need a toll road system or parking or entrance fee for the basin to generate funding for roads which is the primary cause of clarity decline. Improving infrastructure and retrofitting urban stormwater through new LID concepts is critical. If 72% of the loss of clarity is from urban then fund an amount similar to that source. The TMDL will be expensive with uncertain results if diatoms and global warming are the supposed reason for decline. All agencies need to be held to the same standard. Stream restoration is going crazy around here moving huge amounts of dirt in sensitive areas. Some are ok… Some look horrific… Residential BMPs are regulated but not maintained or Inspected. Have you cleaned a dripline gravel BMP? Regional end of pipe infiltration treatment or disconnection is needed. People are frustrated… Over regulated and the town is still in bad shape. With the funding ending in the next few years we need a targeted approach and new way of thinking… Hopefully this is a chance to rethink and rebuild thinking globally. EIP money was funneled through the system and much used by agencies not responsible for tue TMDL. Blending high cost forest health and water quality will be difficult. Different objectives… Improving infrastructure responsibly can can bring economic, environment and social benefits..
and when the Keys was dredged, the lake clarity started going down and hasn’t stopped. What a surprise!
Bike trail from Meyers to the Y parallel with 50. Trains from Sacramento. Trains to accomodate a local system Lake wide.
AND JUST WHAT CLIMATE CHANGE WAS IT THAT CAUSED THE LAKE CLARITY TO CHANGE I HAVE BEEN HERE ALL YEAR AND I CAN NOT REMEMBER ANY CHANGE ALL YEAR.
oye vey….
I must agree with tahoegal. The Tahoe Keys has been the biggest and worst thing ever done to Lake Tahoe. Let’s buy back all those properties and return the Keys to the filtering swamp it used to be before Dillingham got ahold of it. And that does not even address all the foreign seaweed and crap and pollution from boats, lawn chemicals and illegal auto detailing.
Well the worst thing is the dam in tahoe city, cuz the Keys would not exist if there were no dam and the public could use the beach in Nv. as a plus.