By Dana Yamashita
Since 1980, oxygen levels in deep waters of surveyed lakes has declined 18.6% and 5.5% at the surface. Although these numbers don’t seem to be particularly high percentages, lakes are losing oxygen 2.75 to 9.3 times faster than the oceans. Kevin Rose, a professor in the biological sciences department at Rensselaer Polytechnic Institute, says that decline will have impacts throughout the ecosystem.
“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,” he said.
Researchers analyzed a total of over 45,000 dissolved oxygen and temperature profiles collected since 1940 from nearly 400 lakes worldwide. Although lakes make up only about 3% of Earth’s land surface, they contain a disproportionate concentration of the planet’s biodiversity. Stephen F. Jane, who completed his Ph.D. with Rose, said the changes are concerning both for their potential impact on freshwater ecosystems and for what they suggest about environmental change in general.
“Lakes are indicators or ‘sentinels’ of environmental change and potential threats to the environment because they respond to signals from the surrounding landscape and atmosphere. We found that these disproportionally more biodiverse systems are changing rapidly, indicating the extent to which ongoing atmospheric changes have already impacted ecosystems,” Jane said.
The drop in oxygen levels, driven largely by climate change, threaten freshwater biodiversity as well as drinking water quality. Decreasing oxygen levels in surface waters can be an indicator of widespread increases in algal blooms, some of which, Rose explained, can produce harmful toxins. And the decreasing oxygen in deeper waters can lead to clarity losses.
In addition to biodiversity, the concentration of dissolved oxygen in aquatic ecosystems influences greenhouse gas emissions, nutrient biogeochemistry, and ultimately, human health.
This research was recently published in Nature with support from the National Science Foundation. Rose and Jane were joined by dozens of collaborators in GLEON, the Global Lake Ecological Observatory Network, and based in universities, environmental consulting firms, and government agencies around the world.