Freshwater ecosystems require adequate oxygen levels to sustain aerobic life and maintain healthy biological communities. However, both long-term climate warming and the increasing frequency and intensity of short-term heat waves are significantly reducing surface dissolved oxygen (DO) levels in lakes worldwide, according to a study published in Science Advances.

Led by Prof. Shi Kun and Prof. Zhang Yunlin from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, in collaboration with researchers from Nanjing University and the UK’s Bangor University, the study quantifies the effects of continuous climate warming and intensified heat wave events on surface DO levels in lakes worldwide.

The research team utilized an extensive dataset and applied a data-driven model to analyze surface DO variations across more than 15,000 lakes over the past two decades.

The study reveals a widespread decline in surface DO concentrations, with 83% of the studied lakes exhibiting significant deoxygenation. Notably, the average rate of deoxygenation in lakes exceeds that of both oceans and rivers, highlighting the severity of this issue.

The researchers further explored the roles of climate warming and eutrophication in shaping surface DO concentrations. Their findings indicate that climate warming, by reducing oxygen solubility, contributes to 55% of global surface deoxygenation. Meanwhile, increasing eutrophication accounts for approximately 10% of the total global surface oxygen loss.

Historical trends in heat waves were also analyzed, with their impacts on surface DO levels quantitatively assessed. The study shows that heat waves exert rapid and pronounced effects on surface DO decline, resulting in a 7.7% reduction in surface DO compared to conditions under average climatological temperatures.

These findings underscore the profound impact of climate change on freshwater ecosystems, emphasizing the urgent need for mitigation and adaptation strategies to preserve lake ecosystems worldwide. The study provides crucial insights for policymakers and environmental managers working to combat the escalating threat of freshwater deoxygenation.