There is less and less oxygen in rivers around the world: the alarm comes from research led by Chinese Academy of Sciencewhich shows how climate change is impoverishing these habitat of one of the most important molecules for life, putting entire freshwater ecosystems at risk.
The researchers analyzed nearly 40 years of data from more than 21,000 river reaches around the world, using advanced machine learning techniques to track changes in oxygen levels between 1985 and 2023.
The findings are worrying: on average, rivers are losing oxygen at a rate of 0.045 milligrams per liter per decade, and nearly 80 percent of the rivers studied showed signs of deoxygenation.
Tropical rivers, i.e. those located between 20 degrees south latitude and 20 degrees north latitude, were the most affected: this result contradicts previous predictions according to which rivers at high latitudes would be the most affected due to the intensification of global warming in these regions.
But according to researchers, tropical rivers already have low levels of oxygen and are losing it more rapidly: this makes them extremely vulnerable to extreme oxygen deficiency events, which can cause the death of fish and other aquatic organisms.
The main cause, according to research, is the decrease in oxygen solubility due to climate change, which is responsible for almost 63% of oxygen loss. In fact, warmer water cannot contain the same amount of oxygen as colder water. Furthermore, changes in ecosystem metabolism, which are reflected in temperature, light and water flow, contributed a further 12% to the decrease.
But heat waves also play a significant role: the study found that extreme heat events are responsible for almost 23% of river deoxygenation globally, accelerating the rate of oxygen loss by 0.01 milligrams per liter per decade compared to normal conditions.
Finally, both very low and very high water flow rates can partially slow down deoxygenation: low flow conditions, in particular, reduced the deoxygenation rate by approximately 19% compared to normal conditions, while high flow conditions reduced it by 7%.
Researchers have warned that falling oxygen levels threaten river biodiversity, as fish and other organisms struggle to survive in oxygen-poor waters. They therefore urged policymakers to act, especially in tropical regions, which are most in need of effective strategies to combat deoxygenation crises.
This study provides a fundamental baseline for understanding and mitigating oxygen loss in rivers around the world – explains Shi Kun, co-author of the research – As global warming progresses, protecting the breath of our rivers could become one of the greatest environmental challenges of our time
The study was published on Science Advances.
Sources: Chinese Academy of Science / Science Advances
