Microbial degradation of spilled oil and gas comes at a price.

By Janet Raloff

Web edition: June 10, 2010

Every day, Mother Nature burps another 1,000 barrels of crude into the Gulf of Mexico, along with additional quantities of natural gas. They enter from more than 1,000 widely dispersed natural seeps, deposits that University of Georgia oceanographer Samantha Joye has been studying for 15 years. Normally, these hydrocarbons don’t stick around long because local bacteria have evolved to eat them about as fast as they appear.

And that is potentially good news, she explained in testimony during a pair of June 9 House subcommittee events on Capitol Hill, because those bugs are now in place to begin chowing down on oil and gas entering the Gulf from BP's damaged Deepwater Horizon well.

But (and isn’t there always a but), that well blowout apparently spewed an estimated 25,000 to more than 40,000 barrels of oil into the Gulf daily for at least 40-something days — until a cap was successfully installed above the wellhead and began siphoning the oil and gas up nearly a mile to the surface. This cap only collects some of the gushing oil. So the well will continue to spew substantial amounts directly into the water until relief wells shut the flow off, an event expected to occur in mid-August.

In the mean time, the blowout has been throwing far more food at local microorganisms than they can consume. Indeed, the Gulf is developing into a well stocked larder for these bugs, one with sufficient reserves to feed generations for many, many years.

However, Joye explains, without these bacterial residents in place, the Gulf would take even longer to heal, because only they can clean up diffuse underwater clouds of microscopic droplets of oil and bubbles of methane — plumes that she and other scientists have just identified littering large, deep segments of the water column.

And these microorganisms already are doing their best to attack the spilled oil, Joye found during a two-week Gulf research cruise from which she just returned. At sea, she and her colleagues identified a series of plumes hosting dilute oil droplets and whopping concentrations of natural gas. At some of the sites she sampled, “we found a lot of gas,” she told me — anywhere from 100 to 10,000 times the normal background values, concentrations that just shocked me.”

At a briefing before the House Subcommittee on Energy and the Environment, she noted that she has sampled water from above oil and gas seeps and never encountered values even close to this. Clearly, she says, “There’s nothing natural about the concentrations that we were seeing” in some plumes associated with the BP gusher.

Her team also measured substantial oxygen consumption within the newly discovered roaming deep-sea clouds of diffuse hydrocarbons. The plumes most commonly hovered some 1,100 to 1,300 meters below the surface. The presumption, Joye says, is that populations of methane-eating microbes have exploded at these sites, binging on the hydrocarbon smorgasbord around them.

Some could be noshing on oil, she admitted. But methane and related gases are easier to digest, so they tend to be scarfed up first.

This microbial feasting is a good thing, in terms of mopping up spill-related hydrocarbons, Joye acknowledged. But the bugs’ recruitment comes at a price. They use up oxygen as they break down oil and gas. And in some spill-associated undersea plumes that her team sampled, the water showed sharp reductions in dissolved oxygen — drops approaching those that could stress out fish and other oxygen-breathing sea life.

Joye is concerned about the fact that people have been focusing only on the oil they can see floating on the surface or the newly reported plumes hovering at great depths beneath the waves. In testimony before the House Science subcommittee on energy and the environment, she noted that her new cruise data turned up “substantial” evidence of microbes eating oil and gas from the surface to the seafloor, “so the entire water column is being impacted by the oil and gas . . .  from this well.” And any way you look at it, she said, that's not a good thing.