Department of Water Resources
A daily compilation of significant news articles and comment
August 13, 2008
5. Agencies, Programs, People –
Lake Tahoe clearer, but report mostly bleak
The
Tahoe waters stay blue despite threat from 2007 blaze
Editorial:
City, county seek flood of permits
The
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Lake Tahoe clearer, but report mostly bleak
The
The news from
As for global warming, its effects on the entire
All this comes from a 60-page report on Tahoe's condition released Tuesday by UC Davis scientists who have monitored the lake's weather, water and life for more than 40 years.
In the second annual report from the
Here are some highlights:
The Angora Fire that started with an illegal campfire in June 2007 dumped tons of nitrogen and phosphorus into the lake - far more than the amounts in a normal summer, but so far, the fire has had a "negligible impact" on lake clarity and algal biomass," says the report. On the other hand, there was "no significant runoff" from the
Still, long-term algae growth in the lake - a major contributor to its loss of clarity and much of it caused by human-generated pollution - has steadily increased since scientists first started measuring it annually in 1968. Last year, algae concentrations on rocks around the shoreline were above average, and the scientists found that the rate of algae growth was the highest on record - five times greater than in 1959.
However, the water's clarity actually improved slightly in 2007 compared to the year before, say the scientists. To measure the lake's clarity, scientists toss 10-inch white plastic "Secchi disks" - named after a 19th century Italian astronomer and priest named Angelo Secchi who first used them in Rome - into the water throughout the year and measure how deep the disks sink before they can no longer be seen.
Tahoe's average "Secchi depth" has become steadily shallower since 1968, although the loss of clarity has slowed a lot in the past 20 years. Last year, the "Secchi depth" was 70.1 feet, or 2.4 feet deeper than the year before, while in 1968, when fewer summer homes ringed the lakeshore, the water was clear to more than 100 feet in depth.
Tahoe changes
-- The lake's water was clear down to 70.1 feet deep last year, but 40 years ago its legendary clarity extended to 100 feet.
-- Since 1970, the lake's average surface water temperature has warmed from 41.7 degrees Fahrenheit to 42.6 degrees.
-- In 2007, winter temperatures dropped below freezing during 63 days - about 30 days fewer than in 1910, when records began.
-- Compared to 1961, the peak time of snowmelt around the lake is 2 1/2 weeks earlier.
-- With development has come pollution, resulting in a loss of water clarity. Nearly three-quarters of the fine particles polluting
Online resources
The full 2008 report can be found at: links.sfgate.com/ZEMN
For more on the
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/08/12/BARD129KFF.DTL&feed=rss.bayarea
Tahoe waters stay blue despite threat from 2007 blaze
The wildfire that blackened the south
In fact, Lake Tahoe's visibility - widely considered an indicator of the
"We found that within a couple weeks after the fire there was no significant impact," said John Reuter, a water-quality scientist with the University of California-Davis Tahoe Environmental Research Center.
"While some smoke and ash did come into the lake, it didn't seem to affect the lake all that much."
One primary reason, Reuter said, is that this past winter was dry, and there weren't major rainstorms to erode the bare hillsides in the 3,100 acres where the
Also, immediately after the fire, the U.S. Forest Service and state agencies raced to put in place a blitzkrieg of erosion-control measures. They included laying downed logs horizontally along slopes, spraying a mix of sticky straw from helicopters and channeling drainage areas into meadows so silt could settle into the ground rather than rushing into the lake.
In the days after the fire, researchers found a 50 percent increase in phytoplankton, or algae, along the lake's south shore compared with the north shore, because ash is a fertilizer. But within two weeks after the fire, the algae levels had dropped to the same as the north shore.
The study found that although up to seven times as much nitrogen and phosphorus was deposited into the lake from the air during the fire than in a typical June, the amount still represented only about 2 percent of the total that flows in every year from all sources.
This year, new plants have grown up in the burned area, reducing the risk of future erosion. But the biologists, hydrologists and ecologists who study
"We're worried about intense rainstorms - either in the fall or spring - where you have very hard rain falling on bare earth," Reuter said. "This first year was a critical year. Now the patient is out of the ICU. But he's not ready to go home yet."
UC-Davis researchers found the lake clarity in 2007 averaged 70.1 feet. That's an improvement from 2006, when it was 67.7 feet. It also compares well with the worst year, 1997, when it was 64 feet.
But overall, the lake has a long way to go to recover its past ecological health.
In 1968, Tahoe's visibility was 102.4 feet - the distance below the surface that scientists can see a dinner-plate-sized device known as a Secchi Disk that they lower from boats every two weeks.
After steady development that began in the 1920s and accelerated in the 1950s, Tahoe began to lose its clarity because of erosion from construction, fertilizer from golf courses, loss of wetlands and other human disruptions. Over the past decade, the state and federal government have spent hundreds of millions of dollars restoring wetlands, tightening building rules and making other changes to try and stop the 1,645-foot deep lake - America's second-deepest, behind Crater Lake - from becoming a muddy green mess of algae and silt.
Tuesday's news drew cheers from environmentalists and business leaders.
"What science has told us is that everything that we do can affect - negatively or positively - lake clarity. Since we are primarily a tourism community, this is a huge economic issue for us," said Carol Chaplin, executive director of the Lake Tahoe Visitors Authority.
As the lake's south shore went up in a column of black smoke last year from an illegal campfire that would destroy 250 homes, conservation groups braced for an eco-disaster.
"We were very worried. It was a great relief to hear that the lake had not sustained the damage we had feared," said Rochelle Nason, executive director of the League to Save Lake Tahoe.
Nason noted, however, that the lake continues to face a host of threats, including global warming. Tuesday's study found that the lake's average surface water temperature has increased 1.5 degrees since 1970, to 51.9 F. And there are now 30 fewer days a year when air temperatures average below freezing compared with 1910.
Warm weather means less snow and more rain. It also can accelerate algae blooms.
Meanwhile, with $16 million in grants from Congress over the past year, the Forest Service and local fire departments have thinned large areas, but tens of thousands of acres remain to be thinned. And debates remain over how to do it in a cost-effective way that doesn't harm wildlife or increase erosion.
"The good news is, this study today is confirmation we are making progress," said Nason. "But the challenges ahead are tremendous."#
http://www.mercurynews.com/politics/ci_10186072
Editorial:
City, county seek flood of permits
The
Effective on Dec. 8, the federal government will place the Natomas basin in a new flood hazard zone. Any development permitted after that date will have to be elevated three feet or more. The designation will effectively restrict new construction in Natomas until its levees are upgraded in roughly two years.
The real estate industry has long known these restrictions were coming. They became inevitable last year after studies of the basin's levees revealed that, despite decades of levee improvements, Natomas remains vulnerable to an unacceptable risk of flood.
But just to make sure developers know about the deadline, the city and
"Builders and developers who are issued new building permits before the December deadline will be able to build as planned," the press release states.
This is a fine kettle of fish. The federal government, which is trying to protect taxpayers who subsidize flood insurance in Natomas and other flood basins, has called for a "timeout" on new development. The state of
Yet the city and county, supposedly partners with the state and federal governments in upgrading Natomas, are now encouraging developers to hurry up and build in a new flood hazard zone.
Hmm … What is it about the word "hazard" that our local governments don't understand?#
http://www.sacbee.com/110/story/1152246.html
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