MINNEAPOLIS — New research by scientists at the University of Minnesota (U of M) and Rensselaer Polytechnic Institute indicates that oxygen levels in the planet's freshwater lakes are declining rapidly due to climate change and land use.
Published Wednesday in the journal Nature, the project analyzed more than 45,000 dissolved oxygen and temperature profiles collected between 1941 and 2017, from nearly 400 lakes around the globe. Among those lakes are 84 from Minnesota, including dozens of Metro area lakes, Leech Lake southeast of Bemidji and Lake Itasca in southeastern Clearwater County.
Researchers say:
- Oxygen levels in lakes across the temperate zone (i.e., the area between the tropics and polar regions) have declined 5.5% in surface waters, and 18.6% in deep waters since 1980.
- In a large number of nutrient-polluted lakes (e.g., lakes with excess phosphorus), the falling oxygen levels are indicative of rising water temperatures and harmful algal blooms.
- Lakes are releasing increased amounts of methane, a powerful greenhouse gas, into the atmosphere as a result of methane-producing bacteria thriving in oxygen-poor lakes.
Loss of oxygen in deep waters of lakes has a number of implications for biodiversity and ecosystem function, including a loss of habitat for organisms that require cold, oxygenated water (including coldwater fish such as cisco, whitefish, and lake trout), the global greenhouse gas emissions, and nutrient biogeochemistry, which ultimately impacts human health.
“Minnesota is known for lakes with high water quality and these lakes contribute to local economies by supporting popular activities like fishing,” said Lesley Knoll, a freshwater ecologist and associate director at the University of Minnesota's Itasca Biological Station and Laboratories. “We expect to see that with reductions in deep water oxygen, coldwater fish habitat will be lost. Low oxygen environments can also alter nutrient cycles in ways that reduce water quality. Our research highlights highlights how long-term changes in oxygen in lakes may ultimately cascade to people by threatening economic activity and human health.”
Research team members conclude that reducing nutrient loading (pollution) to lakes is possible by protecting forested watersheds and using best management practices on agricultural lands to reduce run-off.
The project was funded by the National Science Foundation, and included work by dozens of collaborators in GLEON, the Global Lake Ecological Observatory Network.
