Lake Tahoe water clarity improved in 2011

Mar 01, 2012 By Kat Kerlin
 Lake Tahoe water clarity improved in 2011

(PhysOrg.com) -- Lake Tahoe clarity improved in 2011, but overall has remained nearly stable since 2000, according to UC Davis scientists who study the lake.

Data released today by the UC Davis Tahoe Environmental Research Center and the Tahoe Regional Planning Agency reported the average annual clarity level for 2011 at 68.9 feet, a 4.5-foot improvement over 2010, when average clarity levels were the second-worst on record.

Winter clarity last year continued a decade-long pattern of improvement, while summer clarity continued to decline at the same rate that it has since the late 1960s, when monitoring began.

Average annual clarity in the past decade has been better than in recent decades. In 1997-98, annual clarity reached an all-time average low of 65.1 feet. From 2001-11 the average clarity was 70.6 feet.

Yet this year’s value is still more than two dozen feet away from the clarity restoration target of 97.4 feet set by federal and state regulators.

Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center, said it is important to remember that long-term trends are a better indication of Tahoe clarity than year-to-year comparisons.

“The factors that contribute to lake clarity are complex, and are not necessarily linked to factors occurring in the current year,” said Schladow. “For example, the 2011 clarity improvement followed a winter that was one of the wettest in recent years, something that is usually associated with clarity declines. Understanding what controls the long-term trends is at the heart of what we are attempting to do.”

Researchers provided measurements for both winter (December-March) and summer (June-September) months. The winter average of 84.9 feet in 2011 was well above the worst point seen in 1997 and a 12-foot improvement over 2010.

Urban stormwater runoff has long been one contributor to reduced clarity at the lake. Most of that runoff occurs during the winter and spring, when rain and snowmelt carry small, inorganic particles from the land into the lake.

Yet despite a wet winter during 2011, clarity improved. Researchers say this could indicate that efforts led by TRPA, other management agencies, local jurisdictions and private property owners to reduce urban stormwater runoff are having an impact. However, they emphasize that they need more data on stormwater to make definitive conclusions.

Summer clarity levels continued to show a decline. The 2011 value of 51.5 feet was the second worst on record, which the UC Davis data suggest may be due to the large and late spring snowmelt, which carried enormous amounts of fine sediment and nutrients from the watersheds surrounding the lake.

The Tahoe Regional Planning Agency is leading a collaborative Environmental Improvement Program that sets thresholds for various environmental indicators at the lake, with clarity being among the most important.

“We're encouraged that lake clarity is improving and seems to be responding to the substantial restoration investments we've collectively made through the Environmental Improvement Program,” said Joanne S. Marchetta, executive director of the Tahoe Regional Planning Agency.

John Reuter, associate director of the UC Davis Tahoe Environmental Research Center, said environmental improvement efforts in the Lake Tahoe Basin related to water quality, forest health and watershed condition have been significant.

However, Reuter noted that “ecosystem restoration is seen over a time scale of decades and is difficult under the best of conditions. Sustaining the pollutant reduction to any lake that has an urban population and infrastructure like Lake Tahoe is challenging, especially in a faltering economy. In my opinion, the federal, state and public partners at Lake Tahoe are facing this restoration challenge with considerable insight, coordination and determination.”

Clarity is measured by the depth at which a 10-inch white disk, called a Secchi disk, remains visible when lowered beneath the water’s surface. The measurements have been taken since 1968, when the Secchi disk could be seen down to 102.4 feet.

For a complete list of Annual Secchi Depth Data since 1968, visit terc.ucdavis.edu/research/SecchiData.pdf .
Graphs showing the various clarity measurements for summer months, winter months, and the yearly averages, are available at the UC Davis Tahoe Environmental Research Center website at terc.ucdavis.edu .

More information about environmental factors affecting will be included in the 2012 State of the Lake Report, expected this summer.

Funding for the clarity analyses comes from the Tahoe Regional Planning Agency.

Explore further: China says massive area of its soil polluted

Provided by University of California - Davis

3 /5 (1 vote)
add to favorites email to friend print save as pdf

Related Stories

Lake Tahoe Clarity Holds Steady in 2005

Aug 09, 2006

The waters of Lake Tahoe were clear to an average depth of 72.4 feet in 2005, according to UC Davis scientists who have monitored the lake since 1968. That keeps the clarity measurement in the range where it ...

Lake Tahoe Clarity Improved Slightly in 2004

Jul 01, 2005

The waters of Lake Tahoe were clear to an average depth of 73.6 feet in 2004, according to UC Davis scientists who have monitored the lake since 1968. That is a slight improvement from 2003, when the lake's waters were clear ...

Climate change, algae lessen Lake Tahoe's clarity

Aug 15, 2011

(PhysOrg.com) -- Lake Tahoe clarity dropped in 2010, but the rate of decline in clarity over the past decade remains slower compared with previous decades, according to UC Davis scientists who have monitored the lake for ...

Lake Tahoe Clarity Continues to Hold Steady in 2008

Mar 19, 2009

(PhysOrg.com) -- The waters of Lake Tahoe were clear to an average depth of 69.6 feet in 2008, according to UC Davis scientists who have monitored the lake since 1968. That keeps the clarity measurement in the range where ...

Recommended for you

China says massive area of its soil polluted

2 hours ago

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

Book offers simplified guide to shale gas extraction

3 hours ago

The new book, "Science Beneath the Surface: A Very Short Guide to the Marcellus Shale," attempts to offer a reader-friendly, unbiased, scientific guide needed to make well-informed decisions regarding energy ...

New approach needed to deal with increased flood risk

3 hours ago

Considering the impacts of climate change on flood risk may not be effective unless current risk is managed better, according to new research from the University of Bristol published today in the Journal ...

Researchers question emergency water treatment guidelines

23 hours ago

The Environmental Protection Agency's (EPA's) recommendations for treating water after a natural disaster or other emergencies call for more chlorine bleach than is necessary to kill disease-causing pathogens ...

User comments : 0

More news stories

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

First radar vision for Copernicus

Launched on 3 April, ESA's Sentinel-1A satellite has already delivered its first radar images of Earth. They offer a tantalising glimpse of the kind of operational imagery that this new mission will provide ...

Image: Grand Canyon geology lessons on view

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of ...

Book offers simplified guide to shale gas extraction

The new book, "Science Beneath the Surface: A Very Short Guide to the Marcellus Shale," attempts to offer a reader-friendly, unbiased, scientific guide needed to make well-informed decisions regarding energy ...

Cosmologists weigh cosmic filaments and voids

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...