Climate change is not only affecting the atmosphere, oceans and ice. According to a new study, rivers around the world are gradually losing oxygen, with tropical waterways emerging as the most vulnerable.
The study, published in Science Advances and led by Professor Kun Shi of the Nanjing Institute of Geography and Limnology at the Chinese Academy of Sciences, analysed data spanning nearly four decades, from 1985 to 2023. Researchers used a machine‑learning algorithm to assess observations from 21,439 river sections worldwide.
The findings reveal a clear global trend of deoxygenation. On average, dissolved oxygen levels in rivers are declining at a rate of 0.045 mg per litre per decade, while 78.8% of the rivers examined showed signs of oxygen loss.
Dissolved oxygen is vital for river ecosystems, supporting aquatic life, biodiversity and key biogeochemical processes. As levels drop, the risk of hypoxia increases, conditions in which oxygen is insufficient to sustain many forms of life.
Greater losses in tropical rivers
Particular concern arises from the finding that the largest losses are occurring in tropical rivers, between 20 degrees south and 20 degrees north of the Equator, including rivers in India.
This surprised researchers, as it had previously been assumed that the greatest risks would occur at higher latitudes, where temperature increases tend to be more intense.
The explanation lies in the fact that tropical rivers already have lower oxygen concentrations, meaning even small decreases can push them closer to critical thresholds.
Flow conditions and dams
The study also examined the role of river flow and dams. Both low and high flow conditions appear to slightly mitigate deoxygenation compared to normal flow levels. By contrast, dams have a more complex effect: in shallow reservoirs they accelerate oxygen loss, while in deeper ones they may reduce it in flooded areas.
Rising temperatures are identified as the main driver behind the global decline, as warmer water holds less oxygen. Reduced oxygen solubility due to climate warming accounts for 62.7% of the observed change. Heatwaves also play a significant role, contributing to 22.7% of global river deoxygenation.
Scientists stress that tropical rivers should become a priority in strategies aimed at limiting oxygen loss, as continued warming threatens to further deteriorate freshwater ecosystems.
Source: lifo.gr
