UC Davis sees warming trend harming lake's ecosystem
For nearly half a century, UC Davis scientists have been monitoring the environmental health at Lake Tahoe, one of the deepest, largest, highest—and bluest—lakes in the United States.
On Aug. 15, UC Davis released the first in a new series of annual reports designed to give the public an unprecedented amount of information showing the changing water quality and weather conditions in the Lake Tahoe Basin.
Overall, the most striking information in the Tahoe: State of the Lake Report 2007 is the data showing that the Tahoe climate is warming up.
This trend could have profound implications for the natural features that make Tahoe a popular international vacation destination: snowfall in winter and the beautiful cobalt-blue lake in summer.
Troubling signs
The report includes these troubling signs of warming climate:
- Nights are warmer: Night low temperatures have risen more than 4 degrees F. since 1911.
- Cold days are fewer: The number of days with average air temperatures below freezing has dropped from 79 days to 52 days since 1911.
- Less precipitation falls as snow: The percentage of snow in the total precipitation has decreased from 52 percent to 34 percent since 1911.
- Lake waters are warmer: The average July surface water temperature has increased almost five degrees, from 62.9 degrees F. to 67.8 degrees F., since 1999. The lake’s surface waters were the warmest on record on July 26, 2006: 78 degrees F.
In 2006, the waters of Lake Tahoe also grew more murky, UC Davis researchers report. The water was clear to an average depth of 67.7 feet. That is a 4.6-foot loss of clarity compared with 2005, but still an improvement on the all-time low value of 64 feet in 1997.
Science informs policy
Pointing to the persistent increase in water temperature observed since 1978, Geoff Schladow, an expert on lake health and director of the UC Davis Tahoe Environmental Research Center, says:
"The types of algae we see in the lake are changing, and they are starting to be present earlier in the year. The lake is becoming more hospitable to invasive plants and fish, with warm-water species like bass and carp increasingly common.”
Schladow UC Davis' Tahoe Environmental Research Center will continue to provide the solid scientific information to public agencies, homeowners and the business community for developing public policy that balances human and environmental needs.
"Change is a difficult thing, and the lake is changing," he told the San Francisco Chronicle. "…It is going to take a lot of effort and a lot of money. Society will have to decide whether it is worthwhile."
ON THE HOME PAGE: Brant Allen, a staff biologist with the UC Davis Tahoe Environmental Research Center, measures lake clarity using a Secchi disk. Allen charts the depths to which the disk is visible underwater to monitor changes in the lake's water quality. (Karin Higgins/UC Davis photo)