For most life forms on Earth, oxygen may be a necessity, not an optional extra – and due to our warming planet, oxygen is quickly disappearing from our freshwater lakes, putting aquatic life & ecosystems under threat.
Researchers checked out samples & measurements taken from 393 lakes in temperate areas of the world across a period from 1941-2017, finding a widespread decline in dissolved oxygen in both surface & depth water habitats.
That change in oxygen levels features a consequence, all the way from the biogeochemistry of the water to the health of human populations who may depend on these lakes. It could also cause increased greenhouse emission emissions from aquatic bacteria that produce methane.
“All complex life depends on oxygen,” says environmental biologist Kevin Rose, from the Rensselaer polytechnic . “It’s the main support system’ for aquatic food webs. And once you start losing oxygen, you’ve potential to lose species.”
“Lakes are losing oxygen 2.75-9.3 times faster than the oceans, a decline which will have impacts throughout the ecosystem.”
Across quite 45,000 profiles of water temperatures & dissolved oxygen, the researchers found a mean drop of 5.5% in dissolved oxygen in surface waters over the last four decades. That’s right down to simple physics: because the increasingly warm air heats the top-most layers of the lake, gases have a harder time dissolving within the warmer water.
The average drop of 18.6% in dissolved oxygen in high depth water over an equivalent period of time features a different explanation. While temperatures haven’t changed here, less mixing of water layers is happening because the surface stays warmer for long period. This stratification is occurring within the oceans too.
In a subset of lakes – around 1/4 of the entire sample – scientists found both increases in temperature & oxygen. The likely explanation is that these lakes are dominated by cyanobacteria blooms caused by nutrient rich run-off from farms and urban areas, which are producing their own oxygen.
“Lakes are indicators or ‘sentinels’ of environmental change & potential threats to the environment because they answer signals from the encompassing landscape & atmosphere,” says aquatic ecologist Stephen Jane, from the Rensselaer polytechnic Institute .
“We found that these disproportionally more biodiverse systems are changing rapidly, indicating the extent to which ongoing atmospheric changes have already impacted ecosystems.”
Lakes account for just around 3-4 percent of Earth’s non-glaciated surface, yet they’re recognized as particularly rich ecosystems that provide habitat & vital resources for countless species (including humans). Diminishing oxygen supplies threaten not just the aquatic species in lakes, but these biodiverse systems and their food webs as an entire .
What’s more, as oxygen levels drop, it allows numerous sorts of methane-emitting bacteria to maneuver in – as these lakes emit more greenhouse gases, global warming effect is perpetuated, and therefore the cycle continues.
It’s a good bleaker situation than the one we’re seeing happen with the planet’s oceans, & therefore the researchers think it might be just the beginning in terms of oxygen depletion. the single positive is that with more data & more information on the seriousness of problem’, we might take simpler measures to counter it.
“Ongoing research has shown that oxygen levels are declining rapidly within the world’s oceans,” says Curt Breneman, dean of the School of Science at the Rensselaer polytechnic Institute, who wasn’t directly involved within the research.
“This study now proves that problem’ is even more severe in fresh waters, threatening our beverage water supplies & therefore the delicate balance that permits complex freshwater ecosystems to thrive.
“We hope this finding brings greater urgency to efforts to deal with the progressively detrimental effects of global climate change .”
The research has been published in Nature.