Blowing tiny bubbles could help protect coral reefs
Could bubbles be the solution to protecting coral reefs, oyster beds, and other marine environments in danger of acidifying oceans?
Scientists at Stanford University think it could help.
According to a new study published in the journal Environmental Science and Technology, blowing tiny bubbles through seawater could be used to remove carbon dioxide from coastal waters, helping offset ocean acidification—one of the main factors threatening to kill 90 percent of the world's coral reefs by as early as 2050.
As the burning of fossil fuels increases the amount of carbon dioxide in the atmosphere, more and more of it dissolving into the ocean, combining with water molecules to form carbonic acid. The chemical compound reduces the amount of calcium carbonate that corals, oysters, mussels, and other hard-shelled organisms need for strength and structure.
It's estimated the ocean has now absorbed about 30 percent of the carbon dioxide released into the atmosphere from human-caused emissions.
"The entire structure of the coral reef ecosystem is built upon the calcium carbonate skeletal remains of dead coral," said David Koweek, lead author of the study and a doctoral candidate at Stanford's School of Earth, Energy and Environmental Sciences.
Koweek got the idea to test "bubble pulsing," as he calls it, while studying the natural 24-hour cycles of marine environments. In the daytime, C02 levels drop thanks to the respiration effects of photosynthesis. But at night, when C02 levels increase, Koweek surmised that bubbling air through seawater could potentially prevent these periods of high acidity and give corals, oysters, and other carbonate-dependent shellfish a chance to grow.
The team ran experiments in a sensor-fitted tank at Stanford's Hopkins Marine Station in Pacific Grove. They bubbled air through seawater for just a few hours in the early morning, and found that transfer rate of C02 between the ocean and atmosphere occurred 30 times faster with bubbling than what would have occurred naturally, significantly lowering the concentration of CO2 in the water.
Stanford earth systems scientist Rob Dunbar, who advised Koweek on the experiment, said bubbling offers a way to turn back the clock and return coral reefs to the conditions they were accustomed to 100 years ago..
"The advantage of this technique is that the technology exists to implement this anywhere in world," Koweek said. The equipment needed—a blower, tubes, and a porous diffuser to restrict the size of the air bubbles—is basically an outsize version of the bubbling system you see in any home aquarium.
Oxygen bubbling has been used for decades as a technique to break up thermal stratification in lakes, where the deepest waters become deprived of oxygen. These deep-water "dead zones" are occurring more and more as a result of algae blooms, an urgent problem around the world that environmental scientists are seeking engineering solutions for.
At the Baltic Sea, a groundbreaking aeration system has recently been installed to breathe life back into a large dead zone in a Swedish fjord, and scientists hope the technology could eventually be used to save the entire Baltic Sea.
The difference in a marine environment is that it's carbon dioxide—not oxygen—that needs to be bubbled. This means that the system would release carbon dioxide back into the atmosphere, but at very low levels that would be easily offset by the potential benefits of renewed reefs, the researchers said.
Bubbling systems are typically constructed with industrial high volume low-pressure blowers, which at the moment are powered by fossil fuels. But, Koweek noted, it wouldn't be an enormous jump to power such a system using a solar array, or even wave power.
In terms of installing bubblers across the world's network of coral reefs, Koweek says an infinitely scalable bubbler system isn't likely because it would be too expensive.
But it could be implemented in targeted areas such as bays and estuaries at high risk of damage.
"If you want to make a lasting impact, you have to do things that people in more resource-poor environments can utilize and benefit from and this is such a technology," Koweek said.
Here's more insight into the history of coral reefs' struggles:
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