Warming temps could affect clarity, quality of famed Oregon lake
Unique climatic conditions that combine to make Oregon’s Crater Lake one of the clearest bodies of freshwater in the world are expected to become more rare as the Earth gets warmer. The changes could impair the lake’s clarity and health, scientists said in a new study published in early May by the U.S. Geological Survey.
The study is based on an analysis of how surface water and deepwater mix, and how a warming atmosphere will affect that dynamic process. For Crater Lake, and other exceptionally deep lakes, the mixing 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.
When that happens, colder, heavier water at the surface sinks to the bottom. If the surface water doesn’t get cold enough, it won’t sink, upsetting the balance of nutrients and algae. The sinking plumes of water carry oxygen to the depths that is otherwise used up by decomposing 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.
The researchers, from the USGS, the University of Trento in Italy and Crater Lake National Park, found that warming is likely to make the deep mixing events 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.
“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.”
“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.”