A new study published in the journal “Nature” on the third of this June confirmed the decrease in the proportion of oxygen and the rise in temperatures significantly in the lakes of temperate regions, such as Europe and the United States of America, which experts view as warning signs of the danger of climate change on the world. face of the planet.
Human pressure and temperature
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In 2016, two studies supervised by the National Institute for Scientific Research in Quebec, with the participation of researchers from the National Institute for Research in Agriculture and Nutrition, on the history of sediments in the lakes of Europe and the world, concluded that the lakes are experiencing a decrease in the proportion of oxygen due to “human pressure”, especially the waste that It is produced by large population centers.
But the new study confirmed that rising temperatures are the main factor in the lack of oxygen and the deterioration of the natural quality of life in temperate lakes.
The study, published by the journal Nature, was supervised by an international team from the World Lakes Environmental Observatory Network, and included more than 45,000 water samples from 400 lakes in temperate regions around the world, mostly in North America and Europe, based on samples spanning time between 1941 and 2019.
Scientists analyzed dissolved oxygen in surface and deep waters, as well as water temperatures. The researchers concluded that the percentage of oxygen began to decline since 1980, at a rate of 5.5% in surface waters, and about 18.6% in deep waters, which is higher than the rate of decrease in the percentage of oxygen in the oceans.
According to the study, the main cause of oxygen deficiency in surface waters is high temperatures, which reduce the solubility of oxygen in water.
Ecological quality of life in lakes
Since the 1980s, with climate change caused by greenhouse gas emissions, the average surface water temperature of the studied lakes has increased by 0.38 degrees Celsius per decade, while the oxygen concentration has decreased by 0.11 milligrams per liter over every 10 years.
The temperature of the deep water remained more stable, but the increase in the temperature of the surface water increased the variance of the degree of density compared to the deep water.
According to the author, this discrepancy impedes the mixing of water from the different layers of the lake, and disrupts the flow of oxygen from the surface towards the deep water, and therefore the oxygen decreases in depth at a greater rate than the surface water.
NASA has published an infographic highlighting the evolution of the Earth’s surface temperature distribution since 1951, with a shift toward hotter that attests to an increase in the planet’s average temperature and an increase in maximum temperatures due to differences in regional warming. https://www.youtube.com/embed/r5xNFx08Vrc?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=ar&autohide=2&wmode=transparent
The concentration of oxygen is one of the main factors that determine the quality of life in lakes, as most living things, such as fish, depend on it, and a very low concentration of oxygen can lead to a decline in the numbers of some species or their disappearance.
In contrast, this reduction in oxygen does not affect microorganisms that do not depend on oxygen for their metabolism, such as bacteria that produce methane, a greenhouse gas.
Low levels of oxygen also alter the chemistry of lake bottom sediments and increase pollution from mineral and food waste.
But what the study revealed that high temperatures are the main factor in the low percentage of oxygen in the lakes of temperate regions, does not cancel – according to the author – the damages of environmental pollution, especially what is secreted by phosphate fertilizers, and understanding the extent of the interaction of these two factors requires further studies.