Oxygen Drains From Most Rivers Worldwide; Two Regions Particularly at Risk

Rivers across the globe are experiencing a concerning decline in oxygen levels, according to a comprehensive study published in "Science Advances." Analyzing data from 21,439 river systems between 1985 and 2023, researchers found a global average deoxygenation rate of 0.045 mg per liter per decade.

The most alarming trend is observed in the tropics, within 20 degrees north and south of the equator. Here, the rate of oxygen loss is faster than in polar regions, which were previously considered most vulnerable. This is particularly worrying as tropical river systems are already naturally lower in oxygen and support significantly larger human and animal populations than Arctic areas.

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Metabolism of the ecosystem

Climate change emerged as the dominant factor behind this deoxygenation, responsible for 62.7% of the observed effects. Heatwaves alone accounted for an additional 22.7%. The study, led by Prof. Kun Shi from the Nanjing Institute of Geography and Limnology, also noted that human activities related to water management, such as river regulation and dam construction, can exacerbate the problem by creating shallower waters where deoxygenation occurs more rapidly.

The consequences of declining river oxygen are severe for aquatic life and ecosystems. Fish populations are shrinking, with cold-water species declining and warm-water species attempting to migrate to cooler waters, often finding them only in saltwater seas and oceans. The article references the ecological disaster on the Odra River as an example of the drastic effects, emphasizing that even without such catastrophic events, life in rivers is being steadily depleted. The authors stress that future climate resilience programs must incorporate strategies to prevent and mitigate deoxygenation.

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Extreme weather events, including floods, droughts, and heatwaves, are increasing in severity and frequency, fundamentally transforming riverine ecosystems.