BEIJING, June 3, Shanghai (Reporter Sun Zifa) -- An environmental research paper was recently published in the internationally renowned academic journal Nature. Researchers found that the oxygen content of temperate lakes has declined in a wide range and over a long period of time. This downward trend may threaten the vital lake ecosystem.

According to the paper, this trend calculated for nearly 400 lakes in 80 years may be related to climate warming and the decline of water transparency.

It is reported that dissolved oxygen concentration in water system will affect nutrient balance, biodiversity, drinking water quality and greenhouse gas emissions. Although the oxygen loss in the ocean has been proved, we have not yet understood the changes of dissolved oxygen concentration in lakes, partly because of the lack of long-term and large-scale research.

In order to solve this problem, the corresponding author of the paper, Kevin Rose of Rensselaer University of Technology and the collaborators compiled the temperature and dissolved oxygen measurement data of 393 temperate lakes (mostly located in Europe and the United States) collected by the government, universities and non-profit organizations from 1941 to 2017. The dissolved oxygen reduction in these freshwater environments is about two to nine times that observed in the oceans. They believe that the rise of water temperature is related to the decline of oxygen concentration in surface water, while the decline of oxygen content in deep water is related to the stronger thermal stratification (different thermocline layers are formed at different depths) and the reduction of water transparency.

The author also points out that there are some exceptions to these trends, such as the rise of water temperature and dissolved oxygen concentration in a large number of lakes (87). However, this anomaly may be caused by water blooms, which may increase the oxygen concentration in the surface layer and decrease the oxygen solubility in the deep layer.

The author concluded that human activities and climate warming are expected to continue to lead to the further loss of dissolved oxygen in lakes, and continuous and strict lake system management measures must be taken to deal with these impacts.