Freshwater fishing could end within 70 years because rivers are warming and losing oxygen faster than the oceans, new research warns.
The “alarming” study of nearly 800 rivers shows that warming occurred in seven out of eight (87 per cent) and loss of oxygen in 70 per cent.
The study also predicts that over the next 70 years, rivers around the world are likely to go through periods characterized by low oxygen levels, which could lead to “acute die-offs” of certain fish species and threaten aquatic diversity in general.
“We know that a warming climate has led to ocean warming and loss of oxygen, but we did not expect this to happen in shallow, flowing rivers.
“This is the first study to take a comprehensive look at changing temperatures and deoxygenation rates in rivers – and what we found has major implications for water quality and the health of aquatic ecosystems around the world.”
The international research team used artificial intelligence (AI) and deep learning methods to reconstruct historically sparse water quality data from nearly 800 rivers across Europe and the United States.
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The results, published in the journal Nature Climate Change, show that rivers are warming and removing oxygen faster than oceans, which could have serious impacts on aquatic life – and human life.
“River water temperature and dissolved oxygen levels are essential measures of water quality and ecosystem health,” said the study’s lead author, Wei Qi, an assistant research professor at Penn State.
“However, they are poorly understood because they are difficult to quantify due to the lack of consistent data across different rivers and the myriad of variables involved that can alter oxygen levels in each watershed.”
“If you think about it, life in water depends on temperature and dissolved oxygen, which is the lifeblood of all aquatic organisms,” Professor Li said.
“We know that coastal areas, such as the Gulf of Mexico, often have dead zones in the summer.
“What this study shows us is that this could happen in rivers too, because some rivers will no longer support life as they once did.”
Reduced oxygen in rivers, or deoxygenation, also releases greenhouse gases and leads to the release of toxic metals, she says.
To conduct their analysis, the research team trained a computer model on a large data set — from annual rainfall rates to soil type to sunlight — for 216 rivers in Central Europe and 580 rivers in the United States.
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The model found that 87% of rivers have become warmer in the past four decades while 70% have lost oxygen.
The study revealed that urban rivers showed the fastest rise in temperature, while agricultural rivers experienced the slowest rise in temperature but the fastest removal of oxygen.
The researchers also used the model to predict future rates, finding that in all the rivers they studied, future deoxygenation rates were between 1.6 and 2.5 times higher than historical rates.
Professor Li said: “The loss of oxygen in rivers is unexpected because we usually assume that rivers do not lose oxygen to the same extent as in large bodies of water such as lakes and oceans, but we found that rivers lose oxygen quickly.
“That was really concerning, because if oxygen levels get low enough, it becomes dangerous for aquatic life.”
The model predicted that within the next 70 years, some fish species could die out completely due to longer periods of low oxygen levels, which Professor Lee said would threaten widespread aquatic diversity.
She added: “Rivers are essential to the survival of many species, including our own, but have historically been overlooked as a mechanism for understanding our changing climate.
“This is our first real look at how rivers around the world are performing – and it’s worrying.”
