Where’s the Deepwater Horizon Oil?
Microbes are busy, and oil is dispersed but far from gone
The BP/Deepwater Horizon well is now capped but it will be sometime before we understand where the nearly 5 million barrels of oil that gushed from the ruptured well have gone. On August 2nd, the National Oceanic and Atmospheric Administration (NOAA) released its "BP Deepwater Horizon Oil Budget," the agency's assessment of what's happened to the oil. But the report came under stiff questioning last week at the August 17th House Energy and Commerce, Energy and the Environment Subcommittee Hearing on "The BP Oil SPill: Accounting for the Spilled Oil and ensuring the Safety of Seafood From the Gulf." Since then two scientific studies of the underwater oil plume have been released that document the size and persistence of the plume and attest to how much has yet to be learned about the behavior of such a large quantity of oil released as such great depth.
According to NOAA, approximately 25 percent of the oil released was collected or destroyed through skimming and burning; 25 percent evaporated naturally or dissolved, and 24 percent was dispersed into microscopic droplets now somewhere in the Gulf of Mexico. The remaining 26 percent, says NOAA, "is either on or just below the surface as light sheen and weathered tar balls, has washed ashore or been collected from the shore, or is buried in sand and sediments."
NOAA breaks this down further, explaining that about 8 percent of the total oil released was dispersed as a result of chemical dispersant application, some 16 percent "naturally dispersed," while 5 percent was burned on the surface, 3 percent was collected by skimming, and 17 percent recovered directly from the wellhead.
But under questioning by Rep. Edward Markey (D-MA) at the August 17th House Energy and Commerce committee hearing, NOAA senior scientist Bill Lehr presented a somewhat different picture. Recalculating the fate of the oil that actually went into the Gulf (not including what was siphoned directly onto a drillship), Lehr acknowledged that only about 10 to 15 percent was physically removed, leaving the remainder somewhere in some form in the Gulf. "Ten percent; in my mind that's not a passing grade...BP has done a very poor job of cleaning the Gulf," said Markey in response.
Two days later, scientists from the Woods Hole Oceanographic Institution (WHOI) released findings from their research mission to the Gulf in late June to examine the underwater oil plume. While there is much data yet to analyze, the significant findings (published August 19th in Science) thus far include the fact that when the underwater plume was observed it was at least 22 miles long – 1.2 miles wide and 650-feet high – appeared not to have undergone substantial microbial degradation, and that the volume of petroleum hydrocarbon compounds it contained were more than double those to be expected from all natural sources in that part of the Gulf.
The researchers stressed that these results are only a "snapshot" and that not much can yet be said about the plume's bioactivity or toxicity. But, explained lead author Richard Camilli of WHOI's Applied Ocean Physics and Engineering Department, these observations show that the oil" is persisting for longer periods than we would have expected.
"Many people speculated that the subsurface oil droplets were being easily biodegraded. Well, we didn't find that. We found it was still there," said Camilli in a press statement. "Any self-respecting microbe will want to eat oil. But they are like teen-agers and do what they want on their own time," explained co-author Christoper Reddy of WHOI's department of Marine Chemistry and Geochemistry on a call with reporters. "We know there is a plume. We know there are some hydrocarbons there," said Reddy. And while this may seem preliminary, what was learned about the size, shape, and direction of the plume will help scientists understand its fate and impacts.
Also investigating the plume are a group of scientists from the Lawrence Berkeley National Laboratory (Berkeley Lab) whose just released study results will be published in Science on August 26th. They too found a substantial plume at between 3,600 and 4,000 feet underwater. But their sampling found considerable microbial degradation of the oil. They also identified a previously uncharacterized species of microbe at work on the oil and – like the WHOI researchers – found no significant oxygen depletion of the kind that might be expected from such microbial activity at or near the surface.
"We've been sampling continuously since May 25th and what's in the paper is representative of what we've seen," explained lead author Terry Hazen who heads the berkeley Lab's ecology department. These findings include a plume made up of very small oil droplets, light crude oil that's inherently biodegradable in an environment where microbes are naturally adapted to eating oil. What accounts for the specific nature of the plume – its stability while being widely dispersed – may be due to the extreme depth, the pressure, the water temperature, or presence of chemical dispersants, Hazen told me in a phone call.
Asked how is team's findings compare with the WHOI team's, Hazen replied, "We're in perfect agreement. We measured different things."
While these scientists work to understand the nature and impacts of oil that persists deep underwater in droplets smaller than a human hair is wide, extremely visible oil continues to reported on beaches in Alabama, Louisiana, and Mississippi. The New Orleans Times Picayune has a running log of recent oil sightings that include heavy oil, tar balls, sheen, slicks and subsurface oil.
"Massive amounts of oil remain on the beaches of the Gulf, and since the clean up efforts have been pared down to almost nothing I would say that more oil is on the beaches now than ever before," reports Drew Wheelan, Gulf conservation coordinator for the American Birding Association who's spent the past week on Louisiana's southern shore where fall bird migration has now begun.