Sheila McNulty Oil spill in Gulf could cause ‘dead zone’, further hitting sea life

High concentrations of methane gas – in some cases approaching 1m times the normal level – have been found around the BP oil spill, raising fears it could create an oxygen-depleted “dead zone” where marine life cannot survive.

Dead zones are areas in the water where algae blooms as it feeds on nutrients in high concentrations of foreign matter, such as  methane, in this case, or, more typically, the components of farmland fertiliser runoff into the water. The algae gorge, reproduce quickly and then, in turn, are eaten by bacteria in a process that depletes the immediate area of oxygen. Fish and other sea life cannot survive in these zones, leading scientists to call them “dead”. 

That the spill could cause a dead zone in the Gulf would be yet another negative for the environment, already suffering from the destruction of marine nurseries and bird nesting grounds in the wetlands and projections of negative impacts on sea life along the Gulf Coast. The knock-on effect would be a pocket of the Gulf where fishermen would find no fish or other sea creatures to harvest.

The site where large concentrations of methane has been found is in a six-mile radius around the spill, where John Kessler, assistant professor in the Department of Oceanography at Texas A&M University, has just returned from a 10-day research trip.

From a previous trip last year to the same area, he has identified the rise in methane to the Deepwater Horizon accident. Methane is a key component of natural gas, such as ethane and propane, and it accounts for 40 per cent of the weight of material emanating from BP’s leaking well.

Last year the concentrations of these gases were at normal levels of one to two parts per million. This year, the concentration of methane dissolved in the seawater is 100,000 times more and, in some places, approaching 1m times more, he said.

While methane may be toxic to various marine organisms, one of the focuses of Kessler’s research is investigating if the high concentration of methane could lead to a feeding frenzy by marine microorganizations that feed on this hydrocarbon, depleting the oxygen in the area and creating a dead zone.

“There are some drawdowns in oxygen,” Kessler said. “It’s significant; we notice it. It’s there.”

But whether it will increase enough to cause a dead zone remains to be seen, he said, with significant factors being how high the concentrations of methane will get and how long they will remain at these enhanced levels.

With BP siphoning increasing amounts of hydrocarbons to the surface, there are hopes the amount gushing into the Gulf is on a decline. That said, the leak is expected to continue until the UK company can complete at least one of the two relief wells it is drilling to intersect the leaking well and plug it up. BP is hoping that will be in late July or August.

The National Oceanic and Atmospheric Administration, the US Environmental Protection Agency and the White House Office of Science and Technology Policy said in its first peer reviewed, analytical summary report about subsea monitoring that “dissolved oxygen levels remained above immediate levels of concern.” But it added, “There is a need to monitor dissolved oxygen levels over time.”

The Gulf of Mexico already is home to one of the world’s biggest dead zones – averaging about 17,000 square kilometres, the size of Lake Ontario, over the past five years, according to the Louisiana Universities Marine Consortium.

But researchers do not know if the site of the spill – more than 100 miles from shore – will link up with the one they have been watching over the years. That long-studied dead zone is close to shore, in shallower water, where the Mississippi River drains, over-enriching the waters with nutrients that lead to an abundance of algae that consumes all the oxygen in the water so that it can no longer support marine life.