Oxygen levels in hundreds of freshwater lakes in the U.S. and around the world are plummeting — and climate change is largely to blame, according to a study published Wednesday.
Why it matters: Per a statement from study co-author Kevin Rose, a professor of biology at Rensselaer Polytechnic Institute: "All complex life depends on oxygen. ... when you start losing oxygen, you have the potential to lose species."
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Driving the news: The study published in the journal Nature, analyzed temperature and dissolved oxygen — a measure of how much oxygen is in water — in almost 400 lakes across the temperate zone, mostly in the U.S. and Europe. Several lakes in New Zealand and one in Japan were also examined.
"Warmer surface water temperatures caused by climate change reduce oxygen levels due to lower solubility of oxygen in warmer water," said Rose in an email to Axios Wednesday night.
What they found: The researchers discovered that since 1980, oxygen levels have dropped 5.5% at the surface and 18.6% in deep waters. The fall is 2.75 to 9.3 times faster than the world's oceans.
Warming temperatures are leading to widespread losses in dissolved oxygen across the studied lakes, linked to climate change and human activity.
Some lakes saw increasing dissolved oxygen concentrations and warming temperatures, caused by pollution such as agricultural runoff.
Between the lines: "When there is no oxygen in deep waters, methane is produced, which is a greenhouse gas that is about 23 times as powerful as carbon dioxide," Rose noted to Axios.
A lack of oxygen in deeper waters "permits nutrients to come out of the nutrient-rich sediments, increasing algal growth, and potentially contributing to harmful algal blooms of toxic cyanobacteria," Rose added.
Our thought bubble, via Axios' Andrew Freedman: Just as global warming is fundamentally altering marine ecosystems, making ocean waters more acidic, increasing temperatures, and altering ocean currents, it's now clear that sweeping changes are happening in water bodies on land.
At risk are ecosystems long dependent on a particular temperature and oxygen structure within a lake. In other words, fish and other marine creatures are facing challenges wherever scientists look.
Of note: Researchers have previously documented dissolved oxygen losses in lakes over a sustained period, but "none" have surveyed so many lakes around the globe, noted Samuel Fey, a Reed College biology professor who studies lakes and wasn't involved in this study, to AP.
The bottom line: Rose told Axios that low oxygen can lead to fish kills, and cold-water fish are particularly sensitive.
"This is a particularly severe problem in regions where local populations depend on fish as a primary source of protein," he said.
Editor's note: This article has been updated with comment from Rose.
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