A decrease in the amount of oxygen is particularly dramatic for fish species which, in summer, depend on colder waters and therefore swim deeper — for example, salmon and trout. If the oxygen level at these depths becomes too low, they cannot survive.
However, in this study, researchers from 18 countries – United States, Canada and a dozen European countries— estimate the oxygen decrease at 5.5% in surface waters, but at 18.6% in deeper waters. The research, published on June 2 in the journal Nature, covers nearly 400 lakes.
Oxygen is one of the best indicators the health of such an ecosystem, the researchers point out, which amounts to saying that with such a decrease, it could be urgent to identify solutions. Although we cannot demonstrate with this one and only study what are the causes of the decrease, suspicion is raised towards global warming and decreasing water clarity due to human activities – among other things, greenhouse gas emissions, as well as sewage and fertilizer discharges into these lakes agricultural.
Other studies had, in recent years, pointed to an apparent decrease in oxygen levels in the oceans –research in 2017 for example, the figure was 2%. But surprisingly, little research had focused so far on such a large number of lakes. If the figures obtained this time were to prove to be representative of hundreds, if not thousands of other lakes, it is to be expected that local and national decision-makers will be pushed more to intervene, while something still lives at the bottom of the lake. their lakes.
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