Are there microbial answers to carbon emissions?

Susan Ladika, Contributing Writer

What do floating patches of sediment in the beautiful blue Bahamian waters have to do with controlling carbon dioxide emissions in the atmosphere? Probably more than you would think, a team of scientists with the U.S. Geological Survey (USGS) has discovered.

If you’ve ever traveled around the islands, you may very well have come across these white patches. “If you have ever taken milk and poured it in a glass of water, it looks like that,” said Dr. Kim Yates, a research scientist at the St. Petersburg, Fla., office of the USGS.

But those white patches are no liquid. Instead, these “whitings” have been created by two types of single-cell algae, known as cyanobacteria and unicellular green algae. Through the process of photosynthesis, these two algae types use up (“drawdown”) the C02 (carbon dioxide) in the water and give off oxygen.


Left to right: Satellite image of whitings on Great Bahama Bank northwest of Andros Island (photograph courtesy of NASA); aerial view of whiting (~1 Km in length) on Great Bahama Bank; diver in very dense whiting with turbidity and well defined boundaries; floating bell used to measure air-sea C02 gas fluxes in whitings and clear water.
Click here to enlarge image

At the same time, these microscopic organisms generate calcium carbonate, the same mineral that makes up the skeleton of coral. In the process, hundreds of minuscule crystals are formed that entomb the algae, as well as the C02, preventing its re-release into the atmosphere, said Dr. Lisa Robbins, center director, USGS St. Petersburg and Tampa.

As C02 emissions have increased over the years, scientists have searched for viable means to trap and store C02, yet finding biological means to sequester C02 remains one of the most poorly understood–yet environmentally safe–possibilities, Robbins said.

A major objective of Robbins’ and Yates’ whitings research has been to determine whether these patches of sediment were sources of C02, or whether they worked to reduce C02 levels in the atmosphere. A scientific team headed to the Great Bahama Bank, shallow tropical waters in the Bahamas off the southeast coast of Florida.

There, a battery of measurements were taken on many different patches of whitings, as well as in adjacent clear waters for comparison. Using data collected from numerous research cruises, as well as extensive laboratory research, Robbins and Yates found that these whitings can reduce C02 in the atmosphere as the microscopic organisms take in C02 and entomb it in a process called biosequestration. The whitings occur naturally, thriving on the ambient levels of C02 found in the atmosphere.

Field and laboratory experiments on Great Bahama Bank show that blooms of whitings can potentially sequester nearly 1.6 tons of C02 each year. The results may seem small, but the potential is far greater than this, because whiting blooms aren’t just found in the Bahamas. They’ve been identified in tropical locations around the world, including the waters off Cuba, Florida, and Australia, as well as the Arabian Sea and in fresh water environments.

These floating expanses of white sediment can stretch farther than a mile, and can be found in both fresh and marine waters, Robbins said. NASA astronauts have even been on the lookout for these whitings, and taken photographs of them during shuttle flights.

The patches of sediment drift with the tide, so “you can’t just anchor a boat and study them. They just float away,” Robbins said. They also change size and shape, driven by currents and waves. Because the whitings are a natural occurrence, they aren’t harmful to the environment, and in fact, black-tip sharks like to hide in these patches of sediment.

Because the algae are living organisms, some parts of the blooms are growing while others are dying off once they’ve used up the nutrients. When the crystal-encased algae die, they settle to the sea floor and form a white mud.

For scientists to effectively research the patches of white sediment, “you can’t just plunk down anywhere in a whiting and get the same results,” Robbins said. “You have to know what parts of the bloom are growing and what parts are dying, because there are different processes occurring in these areas.”

To successfully sequester C02, “you have to know and optimize that point and timing of the C02 drawdown,” she added.

The scientists’ initial research, funded by the Department of Energy and the Electric Power Research Institute, show promise for future studies.

“It’s possible that mineral formation linked to single-cell organisms has been around since photosynthetic microbes first evolved on earth,” Yates said. “Humans are now seeing the benefits of understanding natural processes like C02 biosequestration in order to balance out overuse of natural resources.”

Robbins and Yates believe that by replicating the process in the laboratory, whitings could be created that could be used to sequester C02 emissions near power plants. “It may not be able to take care of all the C02 emissions in the world, but it might be a way of reducing a part of it,” Robbins said.

Ladika is a freelance editor and writer based in Tampa, Fla., who has written a number of articles on scientific topics. She can be reached at 813-805-9768 or sladika@tampabay.rr.com

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