This study looked at how rivers throughout the world are faring — and the findings are disturbing

The impact of continuous dip in oxygen levels of oceanic waters on marine ecosystems — and the lives of humans — is well known. But, the implications of this phenomenon, called deoxygenation, on riverine ecosystems have historically been overlooked.

A new study, however, found rivers are warming and losing oxygen faster than oceans, and deoxygenation could “induce acute death” for certain aquatic species. 

“This is our first real look at how rivers throughout the world are faring — and it’s disturbing,” Li Li, corresponding author of the paper, said in a press statement.

Deoxygenation also drives greenhouse gas emissions and leads to the release of toxic metals, added the study published in the journal Nature Climate Change on September 14, 2023.

An international research team led by Pennsylvania State University used artificial intelligence to reconstruct historically sparse water quality data from nearly 800 rivers across the United States and Central Europe.

The findings of the study showed that of nearly 800 rivers, warming occurred in 87 per cent and oxygen loss in 70 per cent.

While urban rivers showed the most rapid warming, rural rivers witnessed the slowest warming but fastest deoxygenation.

The researchers also forecast future rates. Across all the rivers they studied, future deoxygenation rates were between 1.6 and 2.5 times higher than historical rates.

“We know that a warming climate has led to warming and oxygen loss in oceans, but did not expect this to happen in flowing and shallow rivers,” Li added.

Li called the findings “alarming” because if the oxygen levels get low enough, it becomes dangerous for aquatic life. Within the next 70 years, certain species of fish could die out completely due to longer periods of low oxygen levels, according to the study.

The findings have significant implications for water quality and the health of aquatic ecosystems worldwide, Li said.

Though riverine water temperature and dissolved oxygen levels are essential measures of water quality and ecosystem health, they are poorly understood as they are hard to quantify, said Wei Zhi, the lead author of the study.

Zhi cited the “lack of consistent data across different rivers and the myriad of variables involved that can change oxygen levels in each watershed” as the reasons for flawed assessments.

“We know that coastal areas, like the Gulf of Mexico, often have dead zones in the summer. What this study shows us is this could happen in rivers as well, because some rivers will no longer sustain life like before,” Li said.

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