By Rod Hill on 2010-09-13
No Dead Zones Observed Or Expected As Part Of BP Deepwater Oil Spill
Report finds decreased, but stabilized levels of dissolved oxygen in gulf areas with subsurface oil.
The National Oceanic and Atmospheric Administration (NOAA), the U.S. Environmental Protection Agency (EPA) and the Office of Science and Technology Policy (OSTP) released a report today that showed dissolved oxygen levels have dropped by about 20 percent from their long-term average in the Gulf of Mexico in areas where federal and independent scientists previously reported the presence of subsurface oil. Scientists from agencies involved in the report attribute the lower dissolved oxygen levels to microbes using oxygen to consume the oil from the BP Deepwater Horizon oil spill.
These dissolved oxygen levels, measured within 60 miles of the wellhead, have stabilized and are not low enough to become “dead zones.” A dead zone is an area of very low dissolved oxygen that cannot support most life. Dead zones are commonly observed in the nearshore waters of the western and northern Gulf of Mexico in summer, but not normally in the deep water layer (3,300 – 4,300 feet) where the lowered oxygen areas in this study occurred. Dead zones, also known as hypoxic areas, are defined in marine waters as areas in which dissolved oxygen concentrations are below 2 mg/L (1.4 ml/L).
“All the scientists working in the Gulf have been carefully watching dissolved oxygen levels because excess carbon in the system might lead to a dead zone. While we saw a decrease in oxygen, we are not seeing a continued downward trend over time,” said Steve Murawski, Ph.D., NOAA’s Chief Scientist for Fisheries and the head of the Joint Analysis Group. “None of the dissolved oxygen readings have approached the levels associated with a dead zone and as the oil continues to diffuse and degrade, hypoxia becomes less of a threat.”
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