Researcher: Climate change drives decline in oxygen levels in rivers
Beijing (ANTARA) - A new study has found that climate change is driving a widespread and sustained decline in oxygen levels in rivers around the world, threatening freshwater ecosystems.
The study, published in the journal Science Advances, was conducted by a team of researchers led by researchers from the Nanjing Institute of Geography and Limnology under the Chinese Academy of Sciences (NIGLAS).
The researchers analysed data collected over nearly 40 years, covering more than 21,000 river sections worldwide. They used advanced machine learning to track changes in oxygen levels between 1985 and 2023.
The results were concerning. On average, rivers lost oxygen at a rate of 0.045 milligrams per litre per decade. Nearly 80 per cent of the rivers studied showed signs of deoxygenation.
Tropical rivers, those located between 20 degrees south and 20 degrees north latitude, including many in India, were among the hardest hit. This finding contradicts previous predictions that rivers in high-latitude regions would be most affected by increased climate warming in these areas. The study found that tropical rivers already had low oxygen levels and are losing oxygen more rapidly. This makes tropical rivers highly vulnerable to extreme deoxygenation events that can kill fish and other aquatic life.
The researchers found that the decline in oxygen solubility due to climate change was the main driver, accounting for nearly 63 per cent of the total decrease in oxygen levels. Warmer water does not hold as much oxygen as colder water. Changes in ecosystem metabolism, reflected by temperature, light and water flow, accounted for another 12 per cent of the decline.
Heatwaves also played a significant role. The study found that extreme heat events were responsible for nearly 23 per cent of global river deoxygenation, accelerating the rate of oxygen level decline by 0.01 milligrams per litre per decade compared to normal conditions.
The study also found that very low or very high water flows could slightly slow down deoxygenation. Low flow conditions reduced the rate of deoxygenation by about 19 per cent compared to normal conditions, while high flow conditions decreased it by 7 per cent.
The researchers warned that declining oxygen levels threaten river biodiversity as fish and other organisms struggle to survive in oxygen-depleted waters. They urged policymakers to take action, especially in tropical regions which are most in need of effective strategies to address the deoxygenation crisis.
“This study provides a much-needed basis for understanding and mitigating the decline in oxygen levels in rivers around the world. As climate change continues, protecting the ‘breath’ of our rivers may be one of the greatest environmental challenges of this era,” said Shi Kun, a researcher at NIGLAS.