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April 9, 2014
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Scientists: Consistent monitoring of Tahoe’s nearshore critical

INCLINE VILLAGE, Nev. — Over the years, Bob Zimmerman has noticed more algae growth in the shallows of Lake Tahoe.

“(There’s) certainly more density in the summer,” the part-time Tahoe City resident said. “... It’s hard to know how that really translates to lake quality.”

He’s not alone in his observation.

“There have been increases in complaints over the years from the public, even the scientists observe that things are changing anecdotally,” said Alan Heyvaert, a limnologist and acting senior director of the Center for Watersheds and Environmental Sustainability at Desert Research Institute. “‘Oh, my grandfather was here, and he remembers that there was no slime on these rocks.’”

Yet, without consistent long-term data for Lake Tahoe’s nearshore environment, it’s difficult to quantify the change, according to regional scientists.

‘A VISCERAL EXPERIENCE’

A report completed in late 2013 called “Lake Tahoe Nearshore Evaluation and Monitoring Framework” defines the nearshore as the zone from the low water elevation (6,223 feet), or the current shoreline, to a minimum distance of 350 feet from the shore and a depth of approximately 69 feet.

“The nearshore is important because that’s the area that most visitors and residents experience when they come here,” said Heyvaert, who co-authored the report, during a presentation last Thursday at the Tahoe Environmental Research Center. “They look at what’s happening in lake, they go down, they kayak, they swim; they really have a visceral experience with the nearshore.”

Despite its importance, little ­— and sporadic — study has been done.

Instead, limited funds and resources have been invested to monitor the mid-lake, recording Secchi depths, which are gathered by lowering a 10-inch, white disc into the lake until the plate is no longer visible. Such data identifies the lake’s annual clarity and overall trend.

In March, it was announced that lake clarity dropped five feet from 75.3 feet in 2012 to 70.1 feet in 2013. Despite that, clarity levels continued a decade-long trend of stabilization, according to the Tahoe Regional Planning Agency and Tahoe Environmental Research Center at University of California, Davis.

“Some of the year-to-year fluctuations I don’t think are real important to dwell on, even when (clarity) goes up 5 feet,” said Geoffrey Schladow, director of the Tahoe Environmental Research Center, in a previous story. “It’s the trend, and that to me is the big news. For more than a decade, the decline in clarity has been halted, and that is pretty amazing.”

With progress being made in the mid-lake, more attention can be given to the nearshore, Heyvaert said.

“The nearshore is much more complex than the mid-lake, and that’s why, frankly, most of the work was done in the mid-lake to begin with,” he said.

‘IT’S OUR RESPONSIBILITY’

There are many factors that impact the nearshore, some which can be controlled and others not.

Controllable factors include urban stormwater runoff, vehicle emissions, erosion and fertilizer runoff, among others. Uncontrollable factors include wind, the sun, water currents and lake mixing, among others.

Aspects unique to the nearshore environment that can contribute to conditions include a greater vulnerability to increased temperature from climate change, effects of nearshore recreation and fluctuation in lake levels, among others, said report co-author John Reuter, research ecologist and associate director of the UC Davis Tahoe Environmental Research Center, in a statement.

“Therefore, it is recommended that a finer scale of evaluation and monitoring is necessary in this zone,” he said.

The report proposes full perimeter surveys be conducted in the nearshore on a seasonal basis (four times a year) for clarity, periphyton (attached algae), phytoplankton (free-floating algae), benthic macroinvertebrates, aquatic plants and higher-level aquatic species, including fish and crayfish, among others.

Such an effort is considered minimal, and adjustments in sampling design can be considered based on findings and funding over the long-term.

“These are the metrics that are considered response metrics,” Heyvaert explained. “These are particularly sensitive to changes in the nearshore. … They are going to be an early warning indicator — the canary in the mine, if you will — for change in the nearshore.”

Having a comprehensive, sustained monitoring program in place will not only help define current conditions, but the public in defining what conditions it would like to see in the nearshore and driving policy to reach that goal, Heyvaert said.

“Lake Tahoe is certainly one of the premier global environmental assets, and it’s our responsibility, ultimately, to sustain the quality of those assets,” Heyvaert said.


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Tahoe Daily Tribune Updated Apr 14, 2014 06:13PM Published Apr 15, 2014 01:48PM Copyright 2014 Tahoe Daily Tribune. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.