On April 20, 2010, an estimated 210 million gallons of crude oil began gushing into the Gulf of Mexico following an explosion on the Deepwater Horizon oil rig killing 11 workers. Oil spewed from the one mile deep well head for a total of 87 days while response efforts added almost two million gallons of dispersants into the Gulf. Both oil and dispersant made their marks on all scales of marine life. Researchers are still studying their impacts six years later and are beginning to see signs of recovery. Studying these impacts are providing valuable new lessons when dealing with future oil spills.
This year marks the 6th anniversary of the Deepwater Horizon oil spill.
The University of South Florida’s College of Marine Science is the lead institution of an international research consortium, the Center for Integrated Modeling and Analysis (C-IMAGE) that studies the aftermath of the 2010 Deepwater Horizon oil spill. Diving into the largest accidental spill in history has provided lessons learned for researchers.
‘What we didn’t know’ during the Deepwater Horizon event is a long list. With an unprecedented amount of research funding steered to the Gulf of Mexico, how has our knowledge evolved over the last six years?
Lesson 1: The need for baseline data throughout the oceans to determine the effects of any disaster
Under the Oil Pollution Act of 1990 (OPA), which was established after the Exxon Valdez spill, the responsible party of a spill is required to pay for cleanup, property damage, to compensate economic losses, and to restore natural resources to its pre-spill condition. An important component of the OPA90 is the Natural Resource Damage Assessment (NRDA) regulation designating government agencies to quantify the damage and to restore the injured ecosystem back to its pre-spill or “baseline” condition.
In a working Gulf pierced with thousands of drilling platforms, this is not an easy task. Additionally, not having a complete picture of the “before” condition for much of the Gulf leaves us blind to the full picture of recovery. Scientists argue that having quality and wide-ranging baseline data provide an invaluable assessment of the “present” condition in any natural system and could have even influenced how responders worked through their risk assessments. The Gulf had been vastly understudied before 2010. In the six years since the spill, federally and privately funded researchers have collected thousands of samples, making the Gulf a little less mysterious than it was on April 19, 2010.
Lesson 2: Oil can sink, even when on the surface
Marine “snow” is a term used to describe the particulate matter (dead and dying plankton) that falls to the seafloor. Marine snow is a pathway through which oil can be deposited on the seafloor through mixing with falling particles. Researchers speculate that the marine snow process has greatest impact on oil spills during spring and summer –plankton bloom seasons, especially during years of high river flow. Adding to the complexity of these marine snow events is the increased toxicity of burned oil compounds. Crude oil is made of thousands of different arrangements of carbon that become more toxic after they are burned. These toxic compounds can be trapped in the marine snow where they can cover the seabed and harm the organisms living on the sea floor.
Lesson 3: Dispersants may not as useful as once believed, particularly in the deep-sea
An unprecedented 2.1 million gallons of dispersants – mostly Corexit 9500A – were released during relief efforts both at the surface and at the well-head. Dispersants are used to break up larger droplets into smaller ones, allowing for increased bacterial degradation. However, studies following the oil spill showed dispersants not only did not stimulate bacterial growth, but may have inhibited bacterial growth, suppressing biodegradation (full study here).
In the deep ocean, the pressure is 151-times greater than the surface and the temperature is about 4º C (40º F), a much different environment than at the surface. Historically, dispersants have been used to break up oil at the ocean’s surface. Little is known about their behavior in the deep sea.
Computer models are used to reenact the impact of dispersant application in the deep sea conditions. Adding dispersants at depth made the sub-surface plumes of oil larger, resulting in larger areas of the sea floor being covered in oil. “Up to 10 percent of the sea floor in the area is covered with oil,” said Dr. David Hollander of USF-College of Marine Science and Chief Scientist of C-IMAGE.
Lesson 4: Prolonged oil toxicity in fish continues even after oil is gone
Fish communities in the Deepwater Horizon (DWH) oil spill were exposed to high levels of polycyclic aromatic hydrocarbons (PAHs), one of the more toxic components of oil. High levels of PAHs can cause severe negative effects on fish health, behavior, and reproduction. USF researchers studied the extent of exposure over time and evaluated fish muscle and liver tissue for PAH since 2010. Both shallow and deep water fish communities were sampled and it was determined that after the 2010 DWH spill PAH concentrations in deep water fish increased 10-fold from 2010 to 2011 while the increase in PAH content in shallow water fish increased 20-fold. After 2012, PAH concentrations in these fish fell to levels closer to baseline levels established in 2007.