Earth’s lakes are experiencing an alarming drop in oxygen levels, new research shows.
Similar trends have also been observed across rivers and seas. But some lakes are losing oxygen up to nine times faster than oceans.
A new study has now identified how much the different mechanisms responsible are contributing to this loss of lake oxygen globally, which between 1980 and 2017 was 5.5 percent in surface waters and 18.6 percent in deep waters.
Chinese Academy of Sciences (CAS) geographer Yibo Zhang and colleagues used satellite images, along with geographic and climate data, to reconstruct the events that led to these oxygen losses. More than 80 percent of the 15,535 lakes they examined now have depleted oxygen levels.
From 2003 to 2023, 85 percent of these lakes experienced a steady increase in the number of heatwave days per year. Higher temperatures reduce oxygen’s ability to dissolve in water.
Zhang and team calculated heatwaves have contributed to 7.7 percent of the oxygen loss witnessed, through rapid and substantial fluctuations in oxygen’s water solubility.
The researchers attributed another 10 percent to increasingly severe algal blooms. These are also being exacerbated by warming conditions, as well as increasing nutrients, including fertilizer runoff and livestock manure, entering our waterways.
However, long-term temperature increases account for the bulk of the lake deoxygenation, according to the research.
Current warming accounts for up to 55 percent of the decrease in lake oxygen levels, the researchers estimate. If this trend continues, Earth’s lakes could have up to 9 percent less oxygen by the end of the century under worst-case climate scenarios, the team warns.
Natural and artificial lakes adorn around 5 million square kilometers of Earth’s terrestrial surface. They’re often home to unique life found nowhere else on Earth.
Declines in dissolved oxygen severely disrupt these ecosystems, creating ‘dead zones’ that are too suffocating for wildlife to tolerate. Acute drops cause mass wildlife deaths, which are increasing in waterways around the world.
In recent years, eels in New Zealand, Murray cod in Australia, and multiple fish species and mussels in Poland and Germany have all served as examples of this macabre phenomenon.
Lakes are also experiencing greater evaporation as our warmer atmosphere holds more water. This is speeding up Earth’s water cycle, causing savage lurches from intensely dry to flooding wet conditions.
All these disruptions are wreaking havoc on lake ecosystems and the economies relying on them, threatening our food security. They’ve already destroyed Earth’s fourth-largest lake.
Beyond our dire need to mitigate global warming, reducing the agricultural waste washing into our waterways would help conserve oxygen availability.
“Planting submerged vegetation and constructing wetlands can also help restore lake ecosystems,” CAS ecologist Shi Kun told Xinhua news.
This research was published in Science Advances.
