Rivers in danger. Scientists are sounding the alarm

The latest scientific research suggests that rivers around the world are warming up and losing oxygen at an alarming rate, faster than the oceans. As reported by "Nature Climate Change," the studies showed that the temperature rose above a concerning threshold in 87% of the examined rivers, and oxygen loss occurred in 70% of them.

These studies were conducted by scientists from Pennsylvania State University and published in the latest issue of "Nature Climate Change" (http://dx.doi.org/10.1038/s41558-023-01793-3). The authors warn that within the next 70 years, river systems, especially those in the southern USA, may experience periods with such low oxygen levels that some species of fish and other freshwater organisms may become extinct. Such a situation could disrupt the biological diversity of these ecosystems.

Prof. Li Li, one of the authors of the article, emphasizes that this is an alarm signal. "We knew that a warming climate led to rising temperatures and oxygen loss in the oceans, but we didn't expect this to also occur in constant, shallow rivers. Our study is the first to analytically examine the complexities of temperature changes and the rate of deoxygenation in rivers, and what it proves is an important signal for water quality and ecosystem health worldwide."

In their study, scientists used artificial intelligence and deep learning methods to reconstruct historical data on water quality in nearly 800 rivers in the USA and Central Europe. They discovered that these systems are heating up and losing oxygen faster than oceans, which could have serious consequences not only for aquatic life, but also for humans. Over the past four decades, 87 percent of the surveyed rivers have significantly warmed, and 70 percent have undergone deoxygenation.

The study also showed that urban rivers are warming the quickest, while those located in agricultural areas are warming the slowest. However, the latter are experiencing the most rapid deoxygenation. The developed forecasts are also not optimistic: they show that in all the analyzed rivers, future deoxygenation rates will be 1.6-2.5 times higher than historical rates.

"These are very alarming results, because the entire aquatic life depends on temperature and oxygen content," says Professor Li. "We know that in the summer on coastal oceanic areas, such as the Gulf of Mexico, there are often dead zones, or areas devoid of life. This study shows us that this can also happen in rivers, because in some of them, life in the form we know it now simply won't be possible."

Prof. Li adds that we must remember that deoxygenation of rivers leads to the emission of greenhouse gases and releases toxic metals into the atmosphere. "Such a serious loss of oxygen in rivers surprised us, as we assumed that rivers do not lose it as much as large and standing bodies of water, such as lakes and oceans. Reality proved to be the opposite," emphasizes Li. "It's really alarming, because if the level of oxygen drops below a certain limit, it will threaten aquatic organisms. Our model shows that within the next 70 years, some fish species may go completely extinct."

"Rivers are essential for the survival of many species, including our own, but in the past this fact was completely overlooked - the author of the discussed work concludes. - This was the first such extensive and true look at the state of the world's rivers. And it's so deeply disturbing".