A new study finds that climate change is steadily draining oxygen from rivers around the world, raising concerns for fish and other aquatic life.
WASHINGTON (AP) – Global warming is causing rivers to slowly lose oxygen, threatening fish and other life in the waterways, a new study shows.
Researchers in China used satellites and artificial intelligence to track and analyze oxygen levels in more than 21,000 rivers around the globe since 1985. They found that oxygen levels have dropped an average of 2.1% since 1985, according to a study published Friday in Advances in science. That doesn’t seem like much, but it adds up, and if it continues or accelerates, rivers in the Eastern United States, INDIA and across the tropics could lose enough oxygen by the end of the century to drown some fish and create dead zones, the study said.
Basic chemistry and physics dictate that warm water holds less oxygen, the scientists said. The warmest water, which occurs with human-caused climate changereleases more oxygen into the atmosphere.
If the rate of oxygen loss continues at the current rate, the world’s rivers will on average lose an additional 4% of their oxygen by the end of the century, and in some cases close to 5%, the study found. That’s when the loss of oxygen — called deoxygenation — becomes problematic for fish and people who rely on rivers, according to study lead author Qi Guan, an environmental scientist at the Chinese Academy of Sciences in Nanjing.
More dead zones appear
Scientists worry that oxygen levels in rivers could drop as low as dead zones appear, as they are in Gulf of Mexico, Chesapeake Bay AND Lake Erie. These are areas where fish struggle to breathe and die.
“Deoxygenation is a very slow process. If we have a long period, the negative impact will attack river ecosystems,” Guan said. “Low oxygen levels can cause a number of ecological crises such as the decline of biodiversity, degradation of water quality and possibly some fish will die.”
University of Arizona geoscientist Karl Flessa, who was not part of the study, said in an email that the loss of oxygen in rivers means “a future of stinkier dead zones (hypoxia), especially during heat waves.
Some rivers are in such bad shape that “a small change can put them in the danger zone,” Flessa said. “If your favorite fishing hole gets too warm, the oxygen levels will drop and there won’t be any fish to catch.”
India, the eastern US and the Amazon are hotspots
At the beginning of this century, India was very polluted Ganges River was losing oxygen more than 20 times faster than the global average, the study said. Even with moderate to high increases in global carbon dioxide emission rates — not an implausible worst-case scenario — rivers in the eastern United States, the Arctic, India and much of South America are projected to lose about 10% of their oxygen by the end of the century, the analysis showed.
Guan said he is particularly concerned about tropical rivers, such as the Amazon in Brazil. Since 1980, the number of dead zone days in the Amazon has increased by nearly 16 days per decade, a study last year found.
Professor of hydrology Marc Bierkens of the University of Utrecht in the Netherlands, said a the study he and colleagues did last year showed that oxygen stress in the world’s rivers increased by 13 days per decade and dead zone occurrences increased by nearly three days per decade since 1980. As the world continues to warm, these numbers should jump even higher, said Bierkens, who was not involved in the Chinese study.
Guan’s study found several reasons for the loss of oxygen in the world’s rivers, including nutrient pollution from fertilizers and urban runoff, along with dam construction, flow and wind problems. But nearly 63% of the problem is from warmer water, the study found.
Duke University ecologist and biogeochemist Emily Bernhardt, who was not part of the study, said “as rivers warm, it becomes easier and easier for the same pollution problems as before to cause more severe, longer-lasting, or more widespread hypoxia and anoxia.” Anoxia is the total loss of oxygen.
“Reducing water pollution is more important than ever and will be more difficult as rivers warm,” she said.
By SETH BORENSTEIN AP Science Writer
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