Pollution and damage to animal life was severe nearly two miles from the wellhead and identifiable more than 10 miles away, Paul Montagna wrote in a report published Tuesday in the online journal PLOS One.
Montagna, a professor of ecosystems and modeling, said the refrigerator-cold water a mile beneath the surface means oil takes longer to decay than in shallower waters, where spill recovery has taken years to decades. That means full recovery could take a generation or more, he said in an interview Tuesday.
"This is the first large-scale examination of the impact on the soft bottom, which is the largest habitat in deep water," said Robert Carney, a deep-sea ecologist and professor in Louisiana State University's department of oceanography and coastal sciences. Carney, who was not part of this study, said Wednesday that it was well done.
He said he wasn't surprised by the extent of the damage, given the size and reach of the plume of oil. BP PLC's Macondo well blew wild for nearly three months starting April 20, 2010, when an explosion on the Deepwater Horizon drilling rig killed 11 workers.
"The plume ... drifted all over the place," so oil that became heavy enough to sink could cover a large area, Carney said.
The study is part of the Natural Resource Damage Assessment that will help decide what damages BP must pay. Montagna said he expects to be subpoenaed as part of the litigation spawned by the oil spill, since he was working for the National Oceanic and Atmospheric Administration and with NOAA scientists.
BP issued a statement expressing skepticism about some details of the report.
"The paper provides no data to support a claim that it could take decades for these deep sea species to recover. In fact, the researchers acknowledge that little is known about recovery rates of these communities following an event such as this," BP said. It said the paper "confirms that potential injury to the deep sea soft sediment ecosystem was limited to a small area in the immediate vicinity of the Macondo well-head" first identified in December 2010.
Because it was the nation's first deep-sea spill, "we're in uncharted territory," said Montagna, who took seabottom cores in September and October 2010, looking for oil. The well had been capped July 15, but cleanup and other vessels kept the survey boats from checking some spots where they wanted samples, Montagna said.
"What was astounding was we found effects out to many, many miles," Montagna said.
He said he was surprised in spite of the extent of the spill, which closed about 88,000 square miles of federal waters to fishing.
"When the spill started, we were saying, 'Oil floats. There won't be effects on the deep sea or bottom. Obviously that wasn't true," he said.
The scientists analyzed core samples from 68 sites between one-third of a mile and nearly 78 miles from the Macondo wellhead, looking for animal life and for pollutants such as the toxic oil components called polyaromatic hydrocarbons and heavy metals such as barium from drilling mud used in unsuccessful attempts to shut the well.
Statistical analysis reduced it to one number — an index of high contamination and low biological diversity — used to map the effects.
The analysis took so much time because one step was counting and classifying animals less than one-hundredth of an inch long and comparing the numbers of nematode worms and the tiny crustaceans called copepods, which are more sensitive to pollution. That is still going on for samples from a follow-up cruise in spring 2011 and hasn't even begun for 102 of the sites checked in 2010, Montagna said.
The team hopes for a spring 2014 cruise, he said.
Carney said "the neatest thing" is that the information is public.
"One of the frustrations for people who are trying to find out what has happened in the Gulf is the legal necessity of the secrecy of the NRDA data. To have this come out so it can get scientific review is great."
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