Michael T. Slocum
Upstream Technology Editor
While certainly not forgotten, the 2010 Macondo deepwater well blowout in the Gulf of Mexico seems safely in the past. The oil and gas industry responded with improved technology and procedures. The US government passed stricter regulations, gaining tighter control. The American media covered the spill assiduously until other stories surfaced to drive the 24-hr news cycle.
Other than the lingering litigation connected with it, Macondo is no longer front and center. The blowout was sealed, the surge of oil stopped, the spill cleaned up, the blame assigned, and follow-up action taken-nothing more to see here.
For environmental researchers in the gulf, however, Macondo is an ever-present issue. For them, out of sight is definitely not out of mind.
Brownfield, greenfield...Redfield?
A team from Texas A&M University-Corpus Christi, led by assistant professor of chemistry Xinping Hu, has conducted multiyear research based on the spill. The outcome: a new indicator for detecting oil in subsurface water.
This indicator determines just how long oil from spills like Macondo remains in the water, long after it has slipped beneath the waves and out of the public consciousness.
According to the team's study published online in the January 2014 issue of Deep Sea Research Part II: Topical Studies in Oceanography, researchers focused on the water column 3-6 ft above seabed in depths up to 600 ft. They looked at coastal areas near Macondo, between the Southwest Pass of the Mississippi River and Terrebonne Bay.
Previous research into Macondo's oil degradation focused on the open ocean or deepwater, where the water-mass composition is relatively simple. Near the coast, the influx of freshwater makes the hydrodynamics and chemistry much more complex, according to researchers.
Hu and his team looked at samples taken from 2006 to 2012, studying the Redfield ratio of the water. Redfield refers to the specific ratio of carbon, nitrogen, and phosphorus released during organic-matter remineralization.
Tell-tale microbes
This process of turning matter from organic to inorganic is impacted greatly by the dietary habits of microbes.
According to the Gulf Research Initiative, "Marine microorganisms play critical roles in ecosystems by carrying out many biogeochemical processes such as contributing to primary productivity, regulating water quality, and degrading contaminants."
Under normal circumstances, marine microbes release carbon dioxide as they feed on oxygen from decomposing phytoplankton. By analyzing the relationship between oxygen consumption and CO2 microbial respiration then comparing their alignment with the Redfield ratio, the type of organic matter being transformed can be determined.
"We can tell if microbes are using oxygen from plankton-derived carbon or from petroleum," said Hu.
Analysis of pre- and post-Macondo samples from four sites in the Louisiana Bight showed significant deviation in CO2-O2 ratios indicating the presence of oil in 2010. The study claims that petroleum carbon degradation from the spill was the likely culprit. Further analysis determined that those same sites were likely free of oil as early as 2011-12.
These findings have ramifications beyond Macondo.
"If this type of incident occurs again, we can go out and use this method to study the subsurface water and see if the oil degradation signal is present in the water even after it can no longer be seen by the naked eye," said Hu.
Research continues
While the absence of oil in water samples from 2011 on is encouraging, other issues remain to be monitored.
Researchers are studying the impact of the spill on hypoxia-dead zones in the water where marine life can't be sustained. The northern Gulf of Mexico has the world's second-largest hypoxia zone, according to the Louisiana Universities Marine Consortium.
Other research is being conducted to determine if oil is present in the sediment of the sea bed.
"It's all part of the study of the environmental impact of the disaster," said Hu. "Oil in the water can do a lot of damage to sea life. If you know it's there you have to study the consequences."
