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Boats float on Crater Lake at the dock area accessed by the Cleetwood Cove Trail. AP photo

Crater Lake threat

Climate change could threaten Crater Lake's legendary water quality and possibly alter its deep-water ecosystem, a new study concludes.

The U.S. Geological Survey found that warmer temperatures will hamper or even end the lake's ability to mix surface and deep water, something that's crucial to keeping the United States' deepest fresh-water lake among the clearest in the world.

Deep-water mixing churns nutrients from the lake bottom toward the surface, jump-starting the food web that can cause the lake to become less clear than in years without the mixing, according to the study.

With warmer weather allowing for fewer such events, the years the lake does turn over will bring more nutrients to the surface and create even less water clarity, the study's authors say.

"The clarity of the lake will be more variable year after year," says Tamara Wood, the lead USGS scientist on the study.

Decades of water records show the lake does not mix annually, and climate conditions already are marginal for mixing to occur, Wood says.

"Because the lake is marginal, the future could have a big effect on it," Wood says.

Mixing of the water column in exceptionally deep lakes is rare and requires a special combination of extremely cold near-surface water in winter coupled with strong winds that push this cold water toward one side of the lake, according to the report.

The cold water is heavier and denser than the water on the lake bottom and, given the right conditions, a plume of it can sink to the lake bottom, the report states. The sinking water provides dissolved oxygen for the bottom and forces up water that carries with it nutrients for photosynthesis at the surface, Wood says.

Computer modeling with various wind, solar radiation and atmospheric temperatures created climate and lake scenarios out to the end of this century, according to the USGS.

Currently, the mixing occurs about every other year, Wood says. Modeling shows that mixing will occur, on average, every three years under the least severe warming scenario and possibly stop completely in the worst-case warming scenario.

The less frequent mixing events will mean that more nutrients will gather on the lake bottom to be thrust upward when mixing does occur, creating more plant life that will make the deep-blue lake less clear than in years without the mixing, Wood says.

The model did not predict the ecological effects on the lake, Wood says. However, the cold water that plunges to the lake bottom brings with it dissolved oxygen to support life. Reduced events could leave deep water without oxygen, possibly creating dead zones, she says.

Begun in fall 2013, the study was done in conjunction with the National Park Service and Italy's University of Trento, where researchers previously created a computer model to study the same potential impacts at Russia's Lake Baikal, which is much larger and deeper than Crater Lake, Wood says.

Reach Mail Tribune reporter Mark Freeman at 541-776-4470 or mfreeman@mailtribune.com. Follow him on Twitter at www.twitter.com/MTwriterFreeman.

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