Global warming affects practically every corner of the planet and rivers are no exception. An innovative study in which data from 800 river courses in North America and Europe have been analyzed shows that the increase in temperature in these waters is much faster and more far-reaching than that recorded so far in many of the studies in coastal waters. seas and oceans.
The warming of rivers is associated with the loss of oxygen concentration in these waters, both conditions that alter habitats, endanger various species and cause a deterioration in the quality of this resource, which ultimately also affects humans and society. availability of drinking water.
The results of this work led by experts from Pennsylvania State University (Penn State, United States) have been published (September 14) in the journal Nature Climate Change.
The study also projects that within the next 70 years, river systems, especially in the southern United States, will likely experience periods with oxygen levels so low that the rivers could “induce acute death” of certain fish species and threaten aquatic diversity at large.
"This is a wake-up call," said Li Li, professor of Civil and Environmental Engineering at Penn State and co-author of the paper. “We know that a warming climate has caused warming and loss of oxygen in the oceans, but we did not expect this to happen in shallow, flowing rivers. “This is the first study to comprehensively 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 around the world.”
The international research team used artificial intelligence and deep learning approaches to reconstruct historically scarce water quality data from nearly 800 rivers in the US and central Europe. They found that rivers are warming and deoxygenating faster than oceans, which could have serious implications for aquatic life and the lives of humans. The National Oceanic and Atmospheric Administration estimates that most Americans reside within a mile of a river or stream.
"Rivers water temperature and dissolved oxygen levels are essential measures of water quality and ecosystem health," said Wei Zhi, research assistant professor in Penn State's Department of Civil and Environmental Engineering and author main of the study. "However, they are not well understood because they are difficult to quantify due to the lack of consistent data in different rivers and the large number of variables involved that can change oxygen levels in each basin."
The research team developed novel deep learning approaches to reconstruct consistent data and enable systematic comparison between different rivers, he explained.
"If you think about it, life in water depends on temperature and dissolved oxygen, the lifeline of all aquatic organisms," said Li, who is also affiliated with Penn State's Energy and Environment Institute. “We know that coastal areas, like the Gulf of Mexico, often have dead zones in the summer. “What this study shows us is that this could also happen in rivers, because some rivers will no longer support life as they once did.”
He added that the decrease in oxygen in rivers, or deoxygenation, also drives the emission of greenhouse gases and the release of toxic metals.
To conduct their analysis, the researchers trained a computer model with a wide range of data (from annual precipitation rates to soil type and sunlight) for 580 rivers in the United States and 216 rivers in Central Europe. The model found that 87% of rivers have warmed in the last four decades and 70% have been losing oxygen.
The study revealed that urban rivers demonstrated the most rapid warming, while agricultural rivers experienced the slowest warming but the most rapid deoxygenation. They also used the model to forecast future rates and found that in all the rivers they studied, future deoxygenation rates were 1.6 to 2.5 times higher than historical rates.
"The loss of oxygen in rivers is unexpected because we normally assume that rivers do not lose oxygen as much as they do in large bodies of water such as lakes and oceans, but we found that rivers are losing oxygen rapidly," Li said. "That was really alarming, because if oxygen levels get low enough, it becomes dangerous for aquatic life."
The model predicted that within the next 70 years, certain fish species could become completely extinct due to longer periods of low oxygen levels, which Li said would threaten overall aquatic diversity.
"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," Li said. "This is our first real look at how rivers are faring around the world, and it's disturbing."
