Future Water Clarity and Dissolved Oxygen in Crater Lake

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Warming air temperature may 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.

The USGS have been exploring how changing climate conditions affect lake temperatures and water in Crater Lake, the deepest lake in the U.S. and one of the clearest in the world. Models show that atmospheric warming could disrupt the deep mixing process in the lake. As air temperatures rise, the deep lake 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.

The 1DDV model was used to simulate daily water temperature profiles through 2099. All future climate scenarios projected increased water temperature throughout the water column and a substantive reduction in the frequency of deep ventilation events. The least extreme scenario projected the frequency of deep ventilation events to decrease from about 1 in 2 years in current conditions to about 1 in 3 years by 2100. The most extreme scenario considered projected the frequency of deep ventilation events to be about 1 in 7.7 years by 2100. All scenarios predicted that the temperature of the entire water column will be greater than 4 °C for increasing lengths of time in the future and that the conditions required for thermobaric instability induced mixing will become rare or non-existent.