Researchers
from the University of Rochester and Texas A&M University have
found that, over a period of five months following the disastrous 2010
Deepwater Horizon explosion and oil spill, naturally-occurring bacteria
that exist in the Gulf of Mexico consumed and removed at least 200,000
tons of oil and natural gas that spewed into the deep Gulf from the
ruptured well head.
The
researchers analyzed an extensive data set to determine not only how
much oil and gas was eaten by bacteria, but also how the characteristics
of this feast changed with time.
“A
significant amount of the oil and gas that was released was retained
within the ocean water more than one-half mile below the sea surface. It
appears that the hydrocarbon-eating bacteria did a good job of removing
the majority of the material that was retained in these layers,” said
co-author John Kessler of the University of Rochester.
The results published this week in Environmental Science and Technology
include the first measurements of how the rate at which the bacteria
ate the oil and gas changed as this disaster progressed, information
that is fundamental to understanding both this spill and predicting the
behavior of future spills.
Kessler
noted: “Interestingly, the oil and gas consumption rate was correlated
with the addition of dispersants at the wellhead. While there is still
much to learn about the appropriateness of using dispersants in a
natural ecosystem, our results suggest it made the released hydrocarbons
more available to the native Gulf of Mexico microorganisms. “
Their
measurements show that the consumption of the oil and gas by bacteria
in the deep Gulf had stopped by September 2010, five months after the
Deepwater Horizon explosion.
“It is unclear if this indicates that this
great feast was over by this time or if the microorganisms were simply
taking a break before they start on dessert and coffee” said Kessler.
“Our results suggest that some (about 40%) of the released hydrocarbons
that once populated these layers still remained in the Gulf post
September 2010, so food was available for the feast to continue at some
later time. But the location of those substances and whether they were
biochemically transformed is unknown.”
Previous
studies of the Deepwater Horizon spill had shown that the oil and gas
were trapped in underwater layers, or “plumes”, and that the bacteria
had begun consuming the oil and gas. By using a more extensive data set,
the researchers were able to measure just how many tons of hydrocarbons
released from the spill had been removed in the deep Gulf waters. The
team’s research suggests that the majority of what once composed these
large underwater plumes of oil and gas was eaten by the bacteria.
Professor
John Kessler, recently appointed as Associate Professor in the
Department of Earth and Environmental Sciences of the University of
Rochester, worked with graduate research assistant Mengran Du at Texas
A&M University to analyze over 1300 profiles of oxygen dissolved in
the Gulf of Mexico water spanning a period of four months and covering
nearly 30,000 square miles.
The
researchers calculated how many tons of oil and gas had been consumed
and at what rate by first measuring how much oxygen had been removed
from the ocean. Mengran Du explained that “when bacteria consume oil and
gas, they use up oxygen and release carbon dioxide, just as humans do
when we breathe. When bacteria die and decompose, that uses up still
more oxygen. Both these processes remove oxygen from the water.” Du
added that it is this lower oxygen level that the researchers could
measure and use as an indicator of how much oil and gas had been removed
by microorganisms and at what rate.
The
work was supported by the National Science Foundation with additional
contributions from the National Oceanic and Atmospheric Administration,
the Sloan Foundation, BP/the Gulf of Mexico Research Initiative, and the
Chinese Scholarship Council.
Source: University of Rochester
