Global Rivers Experience Declining Oxygen Levels Due to Climate Change, Study Finds

Kathmandu. A new study has shown that oxygen levels in rivers worldwide are continuously decreasing due to climate change, creating serious risks for fresh water. This study has been published in the scientific journal 'Science Advances'.

The research was led by researchers from the Nanjing Institute of Geography and Limnology under the Chinese Academy of Sciences. The research team analyzed data from approximately 40 years, from 1985 to 2023. Advanced computer-based analysis methods were used to measure oxygen levels in over 21,000 river segments worldwide.

According to the study, oxygen levels in rivers are decreasing at an average rate of 0.045 milligrams per liter per decade. Oxygen depletion has been observed in about 80 percent of the rivers studied.

Rivers in tropical regions are most affected. Although it was previously estimated that high-latitude regions would be more affected, the study shows that tropical rivers, already having low oxygen, are losing oxygen even faster.

This can lead to extremely low oxygen conditions, which can cause the death of fish and other aquatic life. According to the researchers, the main reason is the decrease in the solubility of oxygen in water, which accounts for about 63 percent of the total oxygen loss. Warm water can hold less oxygen than cold water.

Similarly, changes in processes related to temperature, light, and water flow have caused an additional 12 percent decrease in oxygen, the study stated.

Extreme heatwaves have also played a significant role in the loss of oxygen in rivers. The study shows that about 23 percent of the global river oxygen loss is related to such heatwaves.

The research also mentioned that extremely low or extremely high water flow can reduce the rate of oxygen depletion to some extent. Compared to normal conditions, the rate of oxygen loss was found to decrease by 19 percent in low flow and by 7 percent in high flow.

Researchers have warned that declining oxygen levels will have a serious impact on river biodiversity. With less oxygen, fish and other organisms will struggle to survive.

They have urged policymakers, especially in tropical countries, to adopt effective strategies. Shi Kun, a researcher at the Nanjing Institute of Geography and Limnology, said,