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A Florida lake with low levels of dissolved oxygen. Photo: USGS
By Amy Lupica, ODP Staff Writer
Oxygen levels in lakes are declining globally according to a new study, and experts say that it could have dangerous implications for the wildlife and humans that rely on freshwater ecosystems. Much like ocean stratification and acidification, this decline is caused by rapidly rising temperatures that prevent the water from absorbing gasses and often result in harmful algal blooms. But unlike oceans, lakes are losing oxygen at much faster rates. Advocates hope that by protecting 30% of all lands and waters by 2030, we can save these crucial freshwater ecosystems.
Why This Matters: Lakes only cover 3% of the earth’s surface, but are some of the most biodiverse ecosystems in the world, providing food and water for millions of people around the globe.
Experts say that these recently observed declines in oxygen may also lead to increased methane production from microorganisms. This creates a vicious cycle of warming and greenhouse gas production that protections against pollution and runoff can’t solve alone.
Out of Breath
“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,” said aquatic ecologist Stephen Jane at Rensselaer Polytechnic Institute. Researchers took 45,000 profiles of water and oxygen content from 393 temperate bodies of water across the globe. They found that from 1941 to 2017, there was an average drop of 5.5 percent in oxygen in surface-level waters. In deeper waters, the average reduction reached 18.6 percent. This is because, as the surface warms, less mixing of water layers occurs. Despite less warming in lower levels of water, oxygen is no longer circulating through the water effectively.
This same process, known as stratification, has been happening in our oceans as well, but lakes are now losing oxygen 2.75 to 9.3 times faster than oceans. “We found that these disproportionally more biodiverse systems are changing rapidly, indicating the extent to which ongoing atmospheric changes have already impacted ecosystems,” said Jane. As oxygen levels drop, however, some lifeforms will thrive. Unfortunately, these microscopic bacteria produce large amounts of methane and will only increase production as oxygen vanishes. In addition, many of the lakes surveyed showed increasing oxygen in surface waters, which is likely due to increased toxic algal blooms — sudden growth of blue-green algae.
Methane can be up to 86 times more effective at capturing heat in the atmosphere than carbon dioxide. Only recently, however, have scientists begun to study how aquatic ecosystems contribute to methane emissions around the world. An April 2021 study found that up to half of global methane emissions come from aquatic ecosystems, especially freshwater ones. Experts say that the key to fighting these rising freshwater emissions is smart water management practices and establishing protections for all lands and waters by 2030. Curt Breneman, dean of the School of Science at the Rensselaer Polytechnic Institute said, “We hope this finding brings greater urgency to efforts to address the progressively detrimental effects of climate change.”
by Amy Lupica, ODP Staff Writer “Glacier blood,” or “watermelon snow,” is sweeping across the Alps, and researchers are eager to survey the snow to figure out what’s responsible for the mysterious phenomenon—the culprit: algal blooms. A new study has found that the same algae that cause dreaded red tide are now blooming en masse on mountains worldwide. […]
One more of the Trump administration’s rollbacks will meet its demise as EPA Administrator Michael Regan and the Biden administration are planning to reinstate protections for many marshes, streams, and wetlands — expanding again the coverage of the Clean Water Act under the “Waters of the U.S.” or “WOTUS” rule.
Why This Matters: Since the late 1700s, 221 million acres of wetlands have been drained in the U.S. for agricultural use. This development has had severe consequences, including fertilizer and pollution runoff threatening drinking water for millions of people.
This year’s historic drought has intensified a century-old dispute over water in the Klamath Lake region on the Oregon-California border. One hundred years ago, the federal government drained lakes and re-routed rivers to make farming easier, but this year’s drought has sent the region into crisis.
Why this Matters: This drought may be the worst in a century — but the trend is likely to only get worse due to climat
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