The researchers analyzed nearly 800 rivers and found that 87 percent exhibited warming while 70 percent showed a decline in oxygen.
The implications of these findings are alarming. The study predicts that in the next seven decades, especially in the southern parts of the US, river systems might encounter such depleted oxygen levels that certain fish species could be at risk of acute death.
“This is a wake-up call,” said study co-author Professor Li Li. “We know that a warming climate has led to warming and oxygen loss in oceans, but did not expect this to happen in flowing, shallow rivers.”
“This is the first study to take a comprehensive look at temperature change and deoxygenation rates in rivers – and what we found has significant implications for water quality and the health of aquatic ecosystems worldwide.”
To investigate, the researchers utilized artificial intelligence and advanced deep learning methods. The goal was to reconstruct historical water quality data from an extensive array of rivers, primarily spread across the US and Central Europe.
The National Oceanic and Atmospheric Administration has noted that most Americans live within a mile of a river or stream, indicating the potential widespread impact of this issue.
“Riverine water temperature and dissolved oxygen levels are essential measures of water quality and ecosystem health,” said study lead author Wei Zhi.
“Yet they are poorly understood because they are hard to quantify due to the lack of consistent data across different rivers and the myriad of variables involved that can change oxygen levels in each watershed.”
Based on deep learning techniques, the experts reconstructed data that allowed a systematic comparison across different rivers. The findings are significant because aquatic life fundamentally depends on the temperature and oxygen levels of the waters they inhabit.
The analysis accounted for variables ranging from annual precipitation rates to soil types and sunlight. The data spanned 580 rivers in the US and 216 in Central Europe.
The researchers found that urban rivers underwent the most rapid warming. While agricultural rivers warmed more slowly, they were faster in losing oxygen.
One model projection indicated that future deoxygenation rates across the rivers could be between 1.6 to 2.5 times higher than what was observed historically.
“The loss of oxygen in rivers is unexpected because we usually assume rivers do not lose oxygen as much as in big water bodies like lakes and oceans, but we found that rivers are rapidly losing oxygen,” said Li.
“That was really alarming, because if the oxygen levels get low enough, it becomes dangerous for aquatic life.”
The model predictions suggest that within the next 70 years, certain species of fish could die out completely due to prolonged periods of low oxygen levels, which Li said would threaten aquatic diversity broadly.
“Rivers are essential for the survival of many species, including our own, but they have historically been overlooked as a mechanism for understanding our changing climate. This is our first real look at how rivers throughout the world are faring – and it’s disturbing.”
The study is published in the journal Nature Climate Change.
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