Oxygen levels in the world’s temperate freshwater lakes are declining rapidly—faster than in the oceans—a trend driven largely by climate change that threatens freshwater biodiversity and drinking water quality. The study published in Nature found that oxygen levels in surveyed lakes across the temperate zone have declined 5.5 percent at the surface and 18.6 percent in deep waters since 1980. Meanwhile, in a large subset of mostly nutrient-polluted lakes, surface oxygen levels increased as water temperatures crossed a threshold favoring cyanobacteria, which can create toxins when they flourish in the form of harmful algal blooms.
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“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,” said Kevin Rose , author and professor at Rensselaer Polytechnic Institute. “Lakes are losing oxygen 2.75-9.3 times faster than the oceans, a decline that will have impacts throughout the ecosystem.”
Researchers analysed a combined total of over 45,000 dissolved oxygen and temperature profiles collected since 1941 from nearly 400 lakes around the globe. Most long-term records were collected in the temperate zone, which spans 23 to 66 degrees north and south latitude. In addition to biodiversity, the concentration of dissolved oxygen in aquatic ecosystems influences greenhouse gas emissions, nutrient biogeochemistry, and ultimately, human health.
Source: The Week
