Global warming leads to a decrease in the level of oxygen in freshwater lakes located in a moderate climate belt. It threatens biodiversity and quality of drinking water, reports an international group of scientists, whose article is published in the Nature magazine.
Researchers analyzed more than 4500 temperature and oxygen profiles for almost 400 lakes worldwide collected since 1941. Most long-term records are collected in a moderate climate area covering from 23 to 66 degrees of North and South latitude.
It turned out, the lakes lose oxygen at 2.75-9.3 times faster than oceans. Since 1980, the oxygen level in the surveyed lakes of the moderate zone has decreased by 5.5 percent on the surface and 18.6 percent at the bottom. This is due to the increase in the temperature of fresh water, which increased by 0.38 degrees Celsius over a decade. The concentration of dissolved oxygen in surface waters decreased by 0.11 milligrams per liter during the same time.
Although lakes make up only about three percent of the surface of the land sushi, they contain a disproportionately high concentration of the biodiversity of the planet. The temperature increase also contributes to the reproduction of blue-green algae (cyanobacteria), which distinguish toxins dangerous to the existence of other living organisms. In such lakes, the depth contains little oxygen due to the difficult mixing between different layers, and on the surface, on the contrary, the dissolved oxygen level is growing, which is a sign of cyanobacteria flowering.
The decrease in the oxygen level can also lead to the reproduction of anaerobic bacteria separating methane. As a result of the lake, it will begin to throw out even more greenhouse gases, which is able to strengthen the global climate change.