"The climate crisis is causing a widespread fall in oxygen levels in lakes
across the world, suffocating wildlife and threatening drinking water supplies.
Falling levels of oxygen in oceans had already been identified, but new
research shows that the decline in lakes has been between three and nine times
faster in the past 40 years. Scientists found oxygen levels had fallen by 19%
in deep waters and 5% at the surface.
Rising temperatures driven by global heating is the main cause, because warmer
water cannot hold as much oxygen. Furthermore, rising summer heat leaves the
top layer of lakes hotter and less dense than the waters below, meaning mixing
is reduced and oxygen supply to the depths falls.
Oxygen levels have increased at the surface of some lakes. But this is most
likely due to higher temperatures driving algal blooms, which can also produce
dangerous toxins. Cutting emissions to tackle the climate crisis is vital, the
scientists said, as well as cutting the use of farm fertiliser and urban sewage
pollution that also damages lakes.
“All complex life depends on oxygen and so, when oxygen levels drop, you really
decrease the habitat for many different species.” said Prof Kevin Rose, of the
Rensselaer Polytechnic Institute (RPI) in the US, who was part of the research
“This study proves that the problem is even more severe in fresh waters [than
in oceans], threatening our drinking water supplies and the delicate balance
that enables complex freshwater ecosystems to thrive,” said Curt Breneman,
RPI’s dean of science.
Freshwater habitats are rich in fish, insects, birds and animals, and are
important for food and recreation for humans. But they have already suffered
great damage, with average wildlife populations having fallen by 84% since
1970. In addition to global heating and pollution, the causes include overuse
of water for farming.
The study, published in the journal Nature, analysed 45,000 dissolved oxygen
and temperature profiles collected from nearly 400 lakes worldwide. Most
records started in about 1980, though one went back to 1941.
Most of the lakes were in temperate zones, particularly in Europe and the US,
but there were a few records from higher latitudes, nearer the poles, and for
tropical lakes in Africa. In both cases, oxygen was falling as in the other
*** Xanni ***
Chief Scientist, Xanadu
Partner, Glass Wings
Manager, Serious Cybernetics