The warming climate and increasingly frequent and dire heat waves are the primary drivers of a worrying trend: lakes are losing their oxygen. A new study published on Friday in Science Advances put some numbers on the declines, and they aren’t pretty.
“Declines in DO [dissolved oxygen] can critically disrupt the delicate balance of an ecosystem,” wrote authors led by Yibo Zhang, of the Chinese Academy of the Sciences. “Adequate oxygen levels are critical for sustaining aerobic life and fostering robust biological communities,” and declines also prompt lakes to emit more nitrous oxide, itself a powerful warming agent.
The researchers combined climate modeling, satellite imagery, and other factors to measure the declines in oxygen and what is driving them at 15,535 lakes around the world. They found that “continuous deoxygenation” occurred from 2003 through 2023 at 83 percent of those lakes; the rate of decline is faster in lakes than it is in either oceans or rivers.
The effect of climate change is, obviously, to raise the temperatures of the lakes’ waters. That, in turn, decreases its solubility, decreasing the amount of dissolved oxygen they can hold. The researchers found that this mechanism is responsible for 55 percent of the overall decline globally. Meanwhile, heat waves can have a rapid and immediate impact on oxygen declines — and they’re getting worse. Those acute heat extremes accounted for another seven percent of the total.
Notably, human impacts beyond climate change also play a role — eutrophication, which occurs nutrient runoff from agriculture, human waste, and other sources, caused 10 percent of the oxygen loss. Our fingerprints are everywhere.
Looking ahead, this is going to get worse. By the end of the century, a high-emissions scenario would see declines in oxygenation of almost nine percent; more middle-of-the-road emissions would still yield a 4.3 percent decline. The researchers looked at some specific examples, like the huge and critical Lake Victoria in Africa. “our predictions for Lake Victoria… indicate a prolonged period of low-oxygen levels,” they wrote. “Repeated exposure to low oxygen may lead to the loss of sensitive species, the death of aquatic organisms, and the collapse of commercial fisheries.”
The answer here, of course, is to get those emissions as low as possible to slow warming and let the lakes stabilize. Other mitigation strategies may also be available, but for something this widespread happening across the bulk of all the lakes in the world, that’s really the only option. “Our findings,” the authors concluded, “suggest more rigorous efforts in the future.”
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