Scientists begin to assess how Gulf ‘dead zone’ and oil spill might interact

By By Sharon Schmickle
Thu, May 20 2010 3:07 pm


A few days after BP’s ruptured oil pipes began contaminating the Gulf of Mexico, Minnpost reported that the disaster threatened double environmental trouble.

Unless the gusher was plugged, it could compound problems of a summer-time “dead zone” in the Gulf caused by runoff in the Mississippi River starting as far north as Minnesota.

The odds that will happen grow each day that BP’s deep-sea well continues to spew oil into the Gulf. And scientists are beginning to assess how the two complex problems could interact, according to ScienceInsider, an online publication of Science Magazine.

In the Gulf’s dead zone, oxygen is severely depleted during warm summer months, literally suffocating life in an area roughly the size of Massachusetts. The problem starts with runoff of the nitrogen and phosphorus used to fertilize farms and urban lawns.

After the chemicals from upriver dump into the Gulf, they stimulate an unnatural super bloom of algae. The algae die and sink to the bottom where bacteria decompose them. And the bacteria suck up oxygen, leaving the water in a state known as hypoxia — which means there is inadequate oxygen to support living cells.

In other words, fish must flee for their lives. And creatures like oysters and clams are doomed in the zone.

Satellite images show that the oil slick now overlaps one of the areas where the dead zone typically forms, ScienceInsider said. (You can check the spill’s reach in real time here.)

Scientists are assessing a range of scenarios — from grim to slightly positive.

Here’s the grim prospect, according ScienceInsider:  

“Some factors might worsen the dead zone. The oil’s sheen could prevent oxygen from entering the water, lowering oxygen levels in surface water at a time of year when surface and deeper waters are already stratified. Another negative mechanism: Microdroplets of oil dispersed in the water might set off a feeding frenzy of microbes able to dine on the hydrocarbons, further reducing oxygen levels.”

And here’s the best-case scenario:

“Alternately, the oil could lessen the severity of the dead zone. Oil reflects light, which is needed by the photosynthetic phytoplankton (microscopic plant-like organisms). And toxins in the oil could also diminish the phytoplankton blooms. Both factors could potentially mean fewer dead phytoplankton reaching the bottom, leading eventually to less oxygen depletion.”

The research vessel Pelican is conducting the first measurements of the dead zone since the spill from BP’s rig.

“Besides collecting water and sediment samples, her team is using electronic instruments to measure temperature, salinity, dissolved oxygen, chlorophyll biomass, sunlight penetration, and other parameters at depths from 5 to 30 meters,” ScienceInsider said.

And scientists at Texas A&M University in College Station are trying to add the oil plume into a computer model of the biology and currents of the Gulf. The goal is to try to get an overall sense of the impact on the dead zone from the spill.