Gulf Oil Spill Gulf Dead Zone Double Environmental Disaster?

By Erna Buffie
Jun 4, 2010

A dangerous and unplanned scientific experiment is underway in the Gulf, thanks to the combined impact of a massive oil spill and a seasonal dead zone

The gulf oil spill is impacting an ocean ecosystem already under severe stress due to human-induced hypoxia, a drop in seawater oxygen levels.

The BP Oil Spill and the Dead Zone: Environmental Impacts

Every spring and summer for the past 25 years, fertilizer run-off from the Mississippi River has flooded the Gulf with nitrogen and phosphorous, setting off massive phytoplankton or algal blooms. When those blooms die, they sink to the ocean floor where they’re consumed by bacteria that burn up oxygen at a furious rate.The result is a vast, oxygen-starved dead zone, the size of New Jersey, deadly to many ocean creatures that cannot to escape to safer water.

Now, the lethal impact of that dead zone may be compounded by the BP oil spill and a massive slick of oil that’s currently floating on the gulf’s surface waters. In some areas, particularly coastal wetlands and marshes, that thick coating of oil may do double damage – making it impossible for surface waters to absorb oxygen and encouraging even more algal blooms that

But scientists point out that the oil slick could also have the reverse affect, killing off those algal species for which oil is a toxin and blocking the sunlight needed by all photosynthesizing algae. The same may also be true of the chemical dispersants used to break-up the surface oil slicks, which are also toxic to phytoplankton or algae. If that’s the case then the dead zone’s impact may be lessened.

But while the oil and dispersants may inhibit algal growth, most scientists warn that both will likely have a devastating impact on marine animals, poisoning everything from fish larvae and marine birds to sand crabs and sea turtles.

The Gulf Oil Spill, the Dead Zone and the Deep Water Environment

Further off the coast, in deeper waters, the BP oil spill may have a less intense effect on the dead zone, thanks to impact of currents, but its impact may be no less lethal in those deep water areas where the spilling oil originates. That’s because the natural, ocean borne microorganisms that are busy breaking down the oil, also consume oxygen and could form their own dead zones. As a result, gulf mid-waters already naturally low in oxygen may expand down toward the ocean floor and up toward the surface, causing mortality among less mobile creatures like corals, worms and crabs and a loss of habitat and forced migrations for species that are able escape the low oxygen waters.

Scientists to Examine Environmental Impact of Seasonal Dead Zone and Oil Spill

According to reports, there is already one scientific expedition underway in the Gulf examining the combined impact of the oil spill and the dead zone. That expedition is being led by biological oceanographer, Dr. Nancy Rabelais, a scientist with the Louisiana Universities’ Marine Consortium. An expert who has been studying the dead zone for more than two decades, Rabelais’ 2010 survey will examine areas where the oil spill and seasonal dead zone overlap. Other scientists plan on launching similar expeditions over the next few months, aimed at assessing the combined impact of the dead zone and the oil spill.

Source: For more detailed information on the combined impact of the oil spill and the dead zone check out the following report:

David Biello, “How Will the Oil Spill Impact the Gulf’s Dead Zone?” Scientific American, June 3, 2010.

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