Scientists looking for new ways to battle climate change, increasing populations at Lake Tahoe
This story is adapted from the 2015 summer edition of Tahoe Magazine, a product of the Sierra Sun, North Lake Tahoe Bonanza, Tahoe Daily Tribune and Lake Tahoe Action. The magazine hits newsstands throughout the greater Reno-Truckee-Tahoe region this Memorial Day weekend, so be sure to pick up a copy for your go-to guide to enjoying summer at America’s greatest playground.
LAKE TAHOE — For years, the health of Lake Tahoe was best understood by means of an annual dropping of a white disk — known as a Secchi disk — in the middle of the lake and measuring the depth at which it could still be seen.
While some in the broader scientific community whispered that the annual ritual had more to do with aesthetics or optics than gaining a science-based picture of Tahoe’s health, others assert the decline in lake clarity — which has diminished from 100 feet in 1968 to about 78 in 2014 — is a critical indicator in analyzing the health of North America’s largest alpine lake.
Nevertheless, aside from fluctuations in clarity decline, scientists have developed a broader kit of tools to study different aspects of the lake. And they have a renewed focus on nearshore conditions as anecdotal evidence points to an increase in algae accumulation on submerged rocks.
Recent studies also concentrate on nutrient cycling, which has an impact on biota and Tahoe species’ food web.
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Finally, the research community has essayed a formal engagement with the incontrovertible fact that both the air temperature in the Lake Tahoe Basin and the surface temperature of the water itself is incrementally warming.
“Now we are in a time and place where we haven’t been before,” said Geoff Schladow, director of the UC Davis-backed Tahoe Environmental Research Center. “You can’t go back and look and say this is how the system behaved then.”
THE NEARSHORE — ‘GETTING BETTER, GETTING WORSE’
The Secchi depth reading is typically taken every 5 to 7 days from the middle of Lake Tahoe. Yet, there is a recent movement afoot within the scientific community to devote an increasing amount of data collection, monitoring and reporting to the zone of Lake Tahoe known as the nearshore environment.
The term “nearshore” encompasses an area from the low water level of Lake Tahoe, 6,223 feet, which travels either 350 feet away from the shore in areas where the slope of the lake bottom is steep, or where a 69-foot-deep layer of the lake called the thermocline intersects with the lake floor.
This is the area of the lake where most visitors and locals interact, whether it be hiking along its shore, swimming in the summer, and kayaking and other activities, explained Alan Heyvaert, Director for Watersheds and Environmental Sustainability at the Desert Research Institute in Reno.
“It’s the area of the lake people most directly interact with,” he said. “Over the years, people have noticed an accumulation of more and more algae on the rocks. Even though we as scientists see these changes and hear many people anecdotally saying the situation has gotten worse, it doesn’t tell us much.”
To get a complete picture of nearshore environment conditions, Heyvaert and other water quality scientists realized they needed an overarching program that established a data baseline and provided sustainable monitoring.
“We have to track where these changes are coming, their trajectory, whether they’re getting better, getting worse,” Heyvaert said.
‘THE EFFECTS OF URBAN RUNOFF AND SEWAGE SPILLS’
With this in mind, Heyvaert agreed to spearhead a team of scientists that also includes researchers from the Tahoe Environmental Research Center and the University of Reno, Nevada, to form The Lake Tahoe Nearshore Evaluation and Monitoring Framework.
The project, which was funded by the Southern Nevada Public Land Management Act, is composed of more than a dozen scientists from three prominent research institutions and seeks to establish a data and monitoring baseline for the nearshore environment relative to 10 different metrics.
The metrics relate to obvious items such as lake clarity and algal growth, but also encompass the study of relationships between different biological species, the presence of human-introduced toxins, such as chemical or sewage spills and the health of aquatic habitat.
The collaborative nature of the approach will also limit the silo approach, in which each research institution, and in some cases different scientists within the same institution, work on a specialized area of research without robust engagement with the broader scientific context.
“The integrated approach helps us look at the lake as a whole,” said Heyvaert.
But it also helps pool funding, which is critical to establishing good data.
The project has established six monitoring stations, strategically placed around Lake Tahoe, capable of taking readings relating to temperature, turbidity, wave height and presence of phytoplankton and other invertebrates.
“We are able to take measurements every 30 seconds,” Schladow said. “These monitoring stations tell us what the natural response of the lake is … they will also help understand what some of the unnatural responses of the lake are, including the effects of urban runoff and sewage spills.”
‘LAKE TAHOE IS ON TRACK’
The concerted focus on water quality, which underlies nearly every scientific project in the Lake Tahoe Basin, is also the specialty of Robert Larsen, senior environmental scientist at the Lahonton Regional Water Quality Control Board.
Larsen, along with colleagues in the Nevada Division of Environmental Protection, formulate the annual TMDL Performance Report.
TMDL stands for Total Maximum Daily Load and essentially describes a threshold or maximum amount of fine sediment and nutrients that can be put into the lake without compromising clarity.
“It tracks how we restore Tahoe’s transparency, how we reduce the amount of pollutants and introduces fundamental numerical target settings to reduce sediment loads from the urban landscape,” said Larsen when describing the program.
In the scientific community, two principle culprits have been identified for the continued decline in lake clarity — fine sediment, such as sand that is used to provide traction for automobiles during the winter; and the increase of algae, which has proliferated due to increased nutrient loading in the lake.
“Wintertime traction application to roadways is the primary specific source of (fine sediment particles) in urban stormwater runoff,” said JoAnn Kittrell, spokeswoman for the Nevada Division of Environmental Protection. “Other impervious surfaces such as parking lots, sidewalks and buildings may serve as sources, but to a lesser extent than roads.”
In terms of nutrient loading, the increased presence of nitrogen and phosphorus, introduced primarily by fertilizer and automobile emissions, has given rise to algae.
The Tahoe Regional Planning Agency, with the input of scientists, has developed methods of mitigating the amount of nutrients and fine sediment that reaches the lake, including better management of roads and the introduction of water filtration systems on public and private properties throughout the Lake Tahoe watershed.
The TRPA and other scientists have enacted a clarity challenge, establishing the goal of 78 feet of clarity by 2031.
To achieve that lofty goal, the regulatory agency will have to tackle the increasingly unmanageable problem of one of Lake Tahoe’s greatest foils — nitrogen.
‘THE LIFE CYCLE OF NITROGEN IN THE ECOSYSTEM’
Going back 50 years, there was hardly any nitrogen in Lake Tahoe at all, according to UC Davis’ Schladow. However, in the last half-century, with the influx of car commuters and introductions of all types of fertilizer in the basin, the presence of the element has increased dramatically, spurring the growth of algae and inhibiting the pristine clarity for which the Jewel of the Sierra is famed.
A recent Scripps Institution of Oceanography-led study showed how nitrogen is recycled through the Lake Tahoe ecosystem and how the burning of fossil fuels is impacting the important balance of nutrients in the lake.
“It’s important to study the life cycle of nitrogen in the ecosystem since increasing atmospheric nitrogen deposition can alter the food web in the lake,” said Stuart Goldberg, lead author of the study and a former post-doctoral researcher at Scripps Oceanography. “Just like a home garden, the health of lake ecosystems relies on the balance of nutrients like nitrogen and phosphorus.”
The large problem facing both regulators and scientists presently is that 55 percent of the nitrogen in Lake Tahoe derives from atmospheric deposition.
In other words, it comes from the air, typically via car exhaust, as opposed to tributaries and runoff from the urban environment.
“With all the people driving up to Lake Tahoe, it releases large amounts of nitrous oxide into the air,” Schladow said.
“It’s a significant source of pollutants,” said Larsen of atmospheric deposition. “It’s why our partners in transportation have been trying to effect a decline in vehicle miles traveled.”
While Larsen expressed confidence a reduction in vehicle miles traveled would help alleviate some of the nitrogen loading in Lake Tahoe, he was quick to point out the scope of the problem may exceed a localized approach.
“Nitrogen loading is increasing in the atmosphere globally and I am not sure local regulators have the authority or the ability to meaningfully alter the amount of nitrogen in the atmosphere,” Larsen said.
In other words, as the subject of climate change — how the burning of fossil fuels in massive amounts is altering the climate of planet Earth — plays out on a national stage, leaders in the Lake Tahoe Basin will have to either lend their support to either side, or watch the proceedings.
LAKE TAHOE SHOWING ‘EVIDENCE OF CLIMATE CHANGE’
If Lake Tahoe is some sort of bellwether indicator of a changing climate, one NASA scientist, Simon Hook, who works at the Jet Propulsion Laboratory in Pasadena, Calif., is here to tell you the climate is changing — or, at least the surface temperature of Lake Tahoe is changing, and not just changing, but warming slowly, sporadically and incrementally.
Hook used advanced satellite technology to measure the surface temperature of a number of large lakes around the globe over a 30-year time period.
Tahoe’s surface temperature has ticked up nearly one degree Fahrenheit during the period of study, with periods of plateau followed by accelerated heating.
“We see this as evidence of climate change,” said Hook. “We see warming taking place. Now whether that is attributable to humans or any particular process is difficult to say, but it agrees with numerous other studies that warming is taking place.”
Hook further said that the warming in lake temperatures provides a more integrative picture of various regional factors in the watershed and how they dovetail with snowpack, melting patterns, cloud cover etc.
“Air temperature gives you an instantaneous measurement, but lake temperature is a more integrative measurement,” he said.
Scientists with the Desert Research Institute assert it’s also important to note that a long-term general trend indicates that air temperature in the Lake Tahoe Basin is also on the increase.
“If you look at the temperature trends in Tahoe City, where we have a record that goes back to 1903, you see a steady upward trend, especially in the summertime minimum temperature,” said Nina Oakley, a climatologist with the Desert Research Institute.
The long-term trend in warming has been steady, with a low degree of variability. This trend is particularly troubling when compared with the long-term trend in precipitation, which has a high degree of variability, Oakley said.
Despite the Lake Tahoe Basin’s current position in the throes of a prolonged drought, the data does not point to a conclusive trend.
Thus, the warming of both the lake and the air temperature point to the effects of climate change, but to come full circle back to the lake scientists, they are continuing to grapple with what these implacable warming patterns bode for the future of the lake and its biological inhabitants.
“We think having the small amount of warming is changing the way things get moved around the lake,” said Schladow.
Still, while much work remains, an increasing amount of research and funding is being devoted to studying possible ramifications if these trends continue and perhaps even amplify.
“We don’t definitively know how the rapid changes in the environment will affect Lake Tahoe,” Schladow said. “That’s where we are focusing our research — on what is likely or unlikely to happen.
“It’s an exciting time, but it’s a dangerous time. If we get past these ticking points, you get to a place where you can’t do anything. So we’re working very hard to understand it.”
Matthew Renda is a former reporter for the Sierra Sun and North Lake Tahoe Bonanza and currently is a Santa Cruz-based writer. He may be reached for comment at firstname.lastname@example.org.
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