World’s lakes ‘losing oxygen rapidly due to global warming’

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Freshwater lakes around the world are losing oxygen rapidly as a result of global warming, with potentially disastrous consequences for wildlife, researchers have warned.

A study, published in the journal Nature, suggests oxygen levels in lakes have declined 5.5% at the surface and 18.6% in deep waters over the last four decades – up to nine times faster than in oceans.

The scientists said that while lakes make up only a fraction (around 3%) of Earth’s land surface, they house “a disproportionate concentration of the planet’s biodiversity”.

Kevin Rose, a professor at Rensselaer Polytechnic Institute in New York and one of the study authors, said: “All complex life depends on oxygen.

“It’s the support system for aquatic food webs.

“And when you start losing oxygen, you have the potential to lose species.

“Lakes are losing oxygen 2.75-9.3 times faster than the oceans, a decline that will have impacts throughout the ecosystem.”

The researchers surveyed oxygen levels of freshwater lakes in the temperate zone, covering nearly 400 lakes Canada, Europe, Asia and South America, and tracked oxygen and temperature trends spanning 1980 to 2017.

Oxygen levels in the world's temperate freshwater lakes are declining faster than in the oceans
Oxygen levels in the world’s temperate freshwater lakes are declining faster than in the oceans (Gretchen Hansen/University of Minnesota)

The scientists looked at data on water temperature, clarity and oxygen levels from the lakes.

They found that as surface water temperatures increased by 0.38C per decade, surface water dissolved oxygen concentrations declined by 0.11 milligrams per litre per decade.

This is because because warmer water cannot hold as much oxygen.

The team also discovered that some lakes saw an increase in dissolved oxygen concentrations alongside warming temperatures.

The researchers said these types of lakes were polluted with agricultural waste, favouring the rise of a type of organism known as cyanobacteria, which can create toxins when they flourish in the form of harmful algal blooms.

The researchers said that as well as posing a threat to biodiversity, the concentration of dissolved oxygen in aquatic ecosystems can also influence human health.

This is because freshwater habitats are rich in fish, birds and animals, and are a source of food and water for humans.

Curt Breneman, dean of the School of Science at Rensselaer, said: “Ongoing research has shown that oxygen levels are declining rapidly in the world’s oceans.

“This study now proves that the problem is even more severe in fresh waters, threatening our drinking water supplies and the delicate balance that enables complex freshwater ecosystems to thrive.

“We hope this finding brings greater urgency to efforts to address the progressively detrimental effects of climate change.”

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