New data help show how long impacts will linger on seafloor, where pollutants get into the foodchain
Fall-out from the 2010 Deepwater Horizon oil disaster contaminated more 1,000 square miles of the Gulf of Mexico’s seafloor, but the exact long-term ecological effects are still unknown, said a group of scientists who are tracking 125 major petroleum hydrocarbons settled to the deep ocean floor when the failed Macondo well discharged 160 million gallons of crude oil into the water.
Their new paper, published in the Proceedings of the National Academy of Sciences, outlines the effort to determine how fast each of those compounds will biodegrade. The data came from a federal Natural Resource Damage Assessment of the catastrophic oil spill.
“Now, we can finally take all of this environmental data and begin to predict how long 125 major components of the DWH oil on the deep ocean floor will be there,” said co-author David Valentine, a professor with the University of California, Santa Barbara Department of Earth Science. “The way in which we’ve analyzed all of these different compounds helps answer questions everybody asked right after the 2010 blowout. Yes, we know where a lot of this oil went, and yes, we know what’s happening to it. It is slowly being biodegraded, but each compound is acting a bit differently.”
Numerous other studies have documented the environmental impacts of the spill, from increased coastal erosion to failed dolphin births and other diseases in cetaceans along the Gulf Coast. Last year, a Florida State University researcher estimated that about 6 to 10 million gallons of oil are still buried in seafloor sediments. The oil-infused mud is a conduit for contamination into the food web, the researchers said.
The new study was aimed at establishing how long those impacts could last. Lead author Sarah Bagby created a chemical fingerprint of Macondo oil based on its biomarker compounds. She identified the subset of samples that matched that fingerprint and developed a rigorous statistical framework to analyze each of the 125 individual hydrocarbons studied.
“The data indicates big particles of hydrocarbon that came down to the seafloor are not going away as quickly as smaller ones, which has a variety of implications,” Valentine said. “This hadn’t previously been observed at this spatial scale or in this sort of environment, so this work is important in understanding the fate of oil that reaches the seafloor.”
The study also found, circumstantially, that the chemical dispersant applied at the ruptured well helped spur a rapid biodegradation of oil in the water column, but that the prolonged suspension of oil in the water during the degradation phase may have increase the risk of exposure to some organisms.