For most forms of life on Earth, oxygen is an essential requirement, not an optional extra - and due to our warming planet, oxygen is rapidly leaving our freshwater lakes, putting ecosystems and aquatic life under threat.
Change in Oxygen Levels
Scientists examined samples and measurements collected from 393 lakes in temperate regions of the globe across a period from 1941 to 2017, discovering a general decrease in dissolved oxygen in both shallow and deep water habitats. That change in oxygen levels has a contagion effect, all the way from the water biogeochemistry to the health of human populations who may depend on these lakes.
It could also bring about boosted greenhouse gas emissions from aquatic bacteria that generate methane. Kevin Rose, an environmental biologist from the Rensselaer Polytechnic Institute said: "All complex life relies on oxygen, It's the aquatic food web's support system. And when you begin to lose oxygen, you have the possibility of losing species."
He added that lakes are losing oxygen 2.75-9.3 times quicker than the oceans, a decrease that will have impacts all over the ecosystem." Across over 45,000 profiles of water temperatures and dissolved oxygen, the researchers over the last four decades discovered an average decline of 5.5 percent in dissolved oxygen in surface waters.
That comes down to simple physics: as the increasingly warm air heats the upper layers of the lake, gases have a difficult time dissolving in the warmer water.
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Increase in Oxygen and Temperature
The average decline of 18.6 percent in dissolved oxygen in deep water over the same time duration has a dissimilar explanation. While there hasn't been a change in temperatures here, less combination of water layers is happening as the surface remains warmer for longer. This stratification is occurring in the oceans equally. In a subset of lakes - about a quarter of the whole sample - scientists discovered both increases in oxygen and temperature.
The possible explanation is that cyanobacteria blooms brought about by nutrient rich run-off from farms and urban areas - making their own oxygen - dominated these lakes
Stephen Jane, an aquatic ecologist from the Rensselaer Polytechnic Institute said: "Lakes are indicators or 'sentinels' of environmental alteration and possible threats to the environment since they respond to signals from the surrounding atmosphere and landscape."
Earth's Non-glaciated Surface
Stephen Jane also said they discovered that these unbalanced more biodiverse systems are rapidly changing, showing the extent to which occurring atmospheric changes have already impacted ecosystems.
Lakes are responsible for just about 3 to 4 percent of Earth's non-glaciated surface, yet they are identified as particularly wealthy ecosystems that supply vital resources and provide habitat for numerous species (both humans).
Declining oxygen supplies threaten not only the aquatic species that stay in lakes but these biodiverse systems and their food webs as a whole.
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