PORTLAND, Ore. — Warming air temperature is predicted to change water temperature and water column mixing in Oregon’s Crater Lake over the next several decades, potentially impacting the clarity and health of the iconic lake, according to a U.S. Geological Survey report released today.

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Researchers from the USGS, University of Trento in Italy and Crater Lake National Park analyzed how climate conditions currently affect the fundamental temperature characteristics and water-column mixing processes in Crater Lake, the deepest lake in the U.S. and one of the clearest in the world.

“We used a one-dimensional computer driven model that was developed specifically for cold, deep lakes to predict mixing events in Crater Lake under six climate scenarios to the year 2100, using wind, solar radiation and atmospheric temperatures as inputs,” said Tamara Wood, lead USGS scientist on the study. “Each climate scenario estimates a different severity of warming over time.”

The USGS modeling showed that warming of the atmosphere caused by climate change could disrupt the deep mixing process in Crater Lake. As the atmosphere warms, deep mixing events will likely become less frequent. Under the least severe warming scenario, deep mixing will occur on average once every three years by 2100. Under the most severe scenario, deep mixing could stop completely.

Mixing of the water column to the bottom in some exceptionally deep lakes requires a special combination of extremely cold water in the upper water column in winter and strong wind events that push that layer of cold water to one side of the lake. Given the right conditions, a plume of cold water can sink to the lake bottom. The deep mixing process requires the presence of cold air in winter. If the surface water does not become colder and denser than the deeper water, deep-water mixing will not occur.

These deep-water mixing events have two major effects on the Crater Lake ecosystem. As the plumes of cold water sink, deeper water is forced upward, which causes upwelling of nutrients that contribute to the growth of algae and can thus affect water clarity. Likewise, these sinking plumes of water are the critical process that replenishes dissolved oxygen near the lake bottom that is otherwise depleted by the decomposition of algae. Organisms that live in the deeper regions of Crater Lake depend on these mixing events in winter to provide the dissolved oxygen needed for survival.

Predicting the effect these changes will have on the ecology of Crater Lake and its famous water clarity will require models that combine the deep-mixing model results with factors that affect algal growth and oxygen use by deep-lake organisms.

“Crater Lake is, of course, well-known for its stunningly clear water and blue color,” said Scott Girdner, a lake biologist at Crater Lake National Park and participant in the study. “So changes in climate that may affect water clarity are of particular interest to the Park from a lake-health perspective.”

The description and results of the Crater Lake modeling can be accessed in U.S. Geological Survey Scientific Investigations Report 2016-5046, “Simulation of Deep Ventilation in Crater Lake, Oregon, 1951–2099.”