New research found a concerning drop in oxygen levels in the world’s lakes, with some losing oxygen as much as nine times more quickly than oceans. Between 1980 and 2017, oxygen levels in lakes fell by 5.5% in surface waters and 18.6% in deep waters, a study in Science Advances found.
What’s causing the oxygen loss?
Researchers at the Chinese Academy of Sciences (CAS), headed by geographer Yibo Zhang, analyzed satellite imagery and climate records to determine why this oxygen loss occurred.
They discovered that between 2003 and 2023, nearly 85% of the 15,535 lakes examined experienced more heatwave days per year. These heatwaves lowered oxygen levels by 7.7% since warmer water contains less oxygen.
Beyond rising temperatures, 10% of the oxygen loss was linked to an increase in harmful algal blooms. These blooms happen when too many nutrients, like fertilizer runoff and livestock waste, enter lakes. Algae grow quickly and use up large amounts of oxygen, making it harder for other living things to survive.
What are the effects?
With lower oxygen levels, most lakes are becoming ‘dead zones’, where fish and other animals are unable to survive. Scientists have already witnessed widespread fish deaths globally, including:
Eels in New Zealand
Murray cod in Australia
Fish and mussels in Poland and Germany
Lakes are also evaporating more water as the Earth heats up. This accelerates floods and droughts, complicating life for humans and animals that rely on these lakes. Experts say catastrophes like the devastation of Earth’s fourth-largest lake could recur if no measures are put in place.
Researchers propose placing underwater crops and constructing wetlands to assist the lakes in their recovery. CAS ecologist Shi Kun indicates that these processes can recover oxygen levels and enhance lake health in the future.
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