Warming Lake Tahoe Also Less Blue, Report Finds

     TAHOE CITY, Calif. (CN) — Climate change has caused a spike in the surface temperatures of Lake Tahoe, causing officials and environmentalists to fret over whether a warming planet will thwart their fight to keep Tahoe blue, according to a report.
     The University of California, Davis published its annual report on the state of Lake Tahoe on Thursday, finding the clarity of the famously limpid alpine lake declined by five feet from the previous year and that temperatures were on the rise.
     In fact, the surface temperature of Lake Tahoe, recorded at 53.3 degrees, was the highest ever recorded.
     “We’re not sure if this an extreme year because of the drought, but all of our models show there is a long-term thing going on,” said Geoff Schladow, director of the UC Davis Tahoe Environmental Research Center and one of the authors of the report.
     Indeed, it is not only the one-time temperature reading but the trend that is causing consternation.
     “The lake’s temperature is rising at its fastest rate yet,” the report says, adding the lake’s temperature increased by .48 degrees Fahrenheit from 2014 to 2015.
     In the past four years “the lake has warmed at an alarming rate of over 0.3 degrees per year.” This rate is 15 times higher than the long-term average.
     “It is steadily going up faster by orders of magnitude than it has in the past,” said Darcie Goodman-Collins, executive director of the Tahoe-based environmental group League to Save Lake Tahoe.
     While the second largest alpine lake in North America in one sense acts as a canary in the coalmine for the adverse affects of climate change, the warming trend in temperature also means the lake that is renowned the world over for its clarity could grow more opaque if the trend continues unabated.
     The reasons are due to what is called mixing. Layers of water of different temperature constantly move upward and downward in the lake, carrying oxygen to the bottom, which acts as a seal to the nutrients trapped along the lake floor — nutrients such as phosphorus and nitrogen, the culprits in clouding Tahoe.
     “Its mixing depth in 2015 of 262 feet is the lowest recorded,” the study says. “This lack of deep mixing also led to the highest average nitrate levels ever recorded in the lake, 20.6 micrograms per liter.”
     The warming temperatures also make a more hospitable environment for algae, which can foul conditions of the lake along the shore where residents and visitors spend the bulk of their time. There is also the specter of invasive species.
     “Warmer water makes it much easier for species like quagga and zebra mussels to potentially establish,” Collins said.
     Part of the reason for warmer temperatures and declining clarity can be attributed to not only a decrease in precipitation which has hit the Tahoe region hard over the last five years, but also the type of precipitation when it finally does fall.
     This past winter, when Tahoe finally received a year of average rainfall, only 6.5 percent of it fell as snow — the lowest amount ever recorded. Tahoe set another record with 24 days of below-freezing average air temperatures.
     Typically, when the tributaries that feed Tahoe get less precipitation, it means fewer nutrients get into the water, and clarity increases. But this year, the water running into the lake it was warmer and stayed near the surface, impacting clarity.
     To combat the affects of climate change, Collins said officials need to continue restoration projects around the basin while focusing on keeping sediment from the roads around the basin from reaching the lake.
     “We need to give the lake the tools to be resilient and combat climate change,” Collins said.
     Schladow also said that despite models that show climate change hastens the pace of clouding in the lake, there is a potential to devise methods to reduce the rate at which oxygen is consumed through fishing, getting rid of algae and other tactics.
     “In terms of climate change, things get gloomy and it seems like all is lost,” Schladow said. “But I am optimistic we can find solutions. There are a lot of creative people in Lake Tahoe and elsewhere to find these solutions.”

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