Course:EOSC270/2023/DeepwaterHorizonOilSpill

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Overview

On April 20th, 2010, the oil drilling rig “Deepwater Horizon” exploded and sank in the Gulf of Mexico (also referred to as the Gulf of America) resulting in the largest oil spill in history. The rig was built and owned by Transocean, then leased and managed by oil company BP Exploration. It was stationed 66 km (41 miles) south of the Louisiana coast and was positioned to extract oil from the Mississippi Canyon in the continental shelf.

The night of the incident, a burst of natural gas was shot up through the recently installed concrete core of the oil rig.1 The core was too weak to withstand the gas, due to the type of concrete mixture and accelerated curing process, where it fractured and the gas was then directed up the rig to the surface where it ignited. Following the explosion, the rig capsized, fully sinking on April 22nd. The explosion killed 11 workers and injured 17.

Fire response to Deepwater Horizon Explosion.

With no pressure from the rig to contain the oil, it was free to leak into the gulf. Four million barrels of oil were released into the surrounding waters until it was fully contained on July 15th, 2010, nearly 3 months later. The oil leakage was particularly bad due to the failure of several of BP’s failsafes, which were supposed to cover the passage the oil was drawn through in case of an emergency, and stop the flow. The systems, however, were damaged under the pressure of the burst of natural gas and weren't deployed. Failsafe mechanisms like these are meant to withstand immense pressure in case of emergency.

The resulting oil slick was roughly 150,000 square km (57,500 square miles). The cleanup efforts were headed by America’s National Response Team, which were led by the US Coast Guard and Environmental Protection Agency (EPA). There were several methods used to counteract the spill, including 1.8 million gallons of dispersants, booms, and burning.2 The oil travelled all the way to Louisiana’s beaches, where it was manually removed from marshes and estuaries. This resulted in roughly 1,770 km (1,100 miles) of Louisiana’s coast being polluted from this oil spill alone.1 The cleanup effort was not officially closed until April of 2014. The companies responsible—BP and Transoacean—were responsible for paying the billions of dollars that were spent on cleanup and restoration efforts.

Transocean, an offshore oil drilling contractor, had an agreement with BP Exploration and Production, an oil energy company. Together, they planned, built, and maintained the Deepwater Horizon oil rig. BP Exploration was the main contributor, charged with contracting and maintaining the oil rig. Their negligence and corner-cutting regarding the rig’s safety mechanisms were the reasons behind the severity of the oil spill, as all the safety mechanisms failed. Their safety mechanisms were built quickly and cheaply, and the result was the worst oil spill in human history.

Legal Action

There were many legal cases that followed the Deepwater Horizon oil spill, the most notable include:

  1. US vs BP Exploration: Civil Complaint of the US, settled on Dec 15th, 2010.3
  2. BP Exploration’s Criminal Plea: resulting in a four billion dollar settlement on Nov 15th, 2012.4
  3. Transocean’s Settlement: resulting in a one billion dollar settlement on January 3rd, 2013.5 Eighty percent of this money went to the Restore Act,6 and Gulf-related restoration.
  4. Transocean’s Criminal Plea: resulting in a 400 million dollar settlement on January 3rd 2013.7
  5. Ruling on Maximum dollars-per-barrel fine, settled in Louisiana February 19th, 2014.8 This set the maximum financial penalty that would be issued to perpetrators of oil spills per barrel of oil.
  6. BP Exploration’s Civil Settlement: resulting in a 14.9 billion dollar settlement, October 5th, 2015.9

Oil Spills

Oil spills can happen wherever oil is used, transported, or collected. An oil spill is when oil is released into the water, and often damages the ecosystem surrounding the area.10 The negative impacts are specific to the type of oil and the ecosystem impacted, but the general implications are as follows: The toxicity of the oil causes health problems for the flora and fauna in the area, often leading to large decreases in populations, along with immediately impacting the populations. Examples include coating bird’s feathers leaving them flightless, or covering oceanic plants leaving them unable to photosynthesize.

A pelican covered in oil.

In North America, the Coast Guard and NOAA are responsible for cleaning up oil spills. Most oil spills are small and easy for the coast guard to manage. They use booms, which are floating barriers to keep the oil away from sensitive marine life, and can use skimmers to sweep the separated oil off the surface of the water.10 Other styles of oil removal are setting it on fire so it burns out of the ocean, or using chemical dispersants which break up the oil and disperses the compounds.

Oil spills tend to leave lasting damage on the ecosystem they occur in, but with the right response, maintenance, and care, ecosystems are capable of making fantastic recoveries from these events.

Immediate Ecological Impacts

Gulf of Mexico

The Gulf of Mexico harbours a diverse multitude of marine environments including coastal shores, estuaries and coral reefs. Even oil rigs and oil platforms can act as artificial habitats for sessile organisms. The gulf also provides crucial breeding, feeding, and nursing grounds for marine organisms such as Hammerhead Sharks and Frigatebirds.13 The ecosystems of the Gulf of Mexico host one of the most productive marine environments in North America,14 and are home to countless endangered species, like the leatherback sea turtle. The oil produced from the Deepwater Horizon oil spill will not be able to be sedimented for hundreds of years.

The pelagic ecosystems of the Gulf of Mexico are teeming with fish and marine mammals including various species of sea turtles, dolphins, porpoises, whales, and sharks. The mesopelagic, deep ocean, and benthic communities can be found at depths ranging from 100-1300 feet below the surface and are home to numerous marine invertebrates such as sea stars, anemones, corals, sea cucumbers, and sea urchins. The coastal shores which are made up of mangroves, estuaries, and everglades, house diverse marine vegetation such as sea grasses, algae and seaweeds.

Ecosystem Effects

Gulf of Mexico Ecosystems

The Deepwater Horizon oil spill poured 134 million gallons of oil into the Gulf of Mexico, which is equivalent to 5 million barrels of oil.The Deepwater Horizon oil spill is estimated to have killed millions of marine organisms. Oils spills can cause immediate death to marine mammals by means of suffocation (oil and oil sludge can cover gills and smother sessile organisms,) poisoning (through the ingestion of toxins and bioaccumulation,) and a loss of insulating coats on marine mammals and birds, which leaves them vulnerable to extreme temperatures and weather (the oil interacts with their natural oil coating on their fur/feathers, degrading and dissolving it.)15

Pelagic Zones

A sea turtle covered in oil.

In pelagic zones, organisms suffered en masse.  Oil covered and coated mobile species, causing asphyxiation, organ damage and death. Polyacrylic Aromatic Hydrocarbons (PAHs) are considered the most damaging components of oil to marine organisms, as they can negatively interact with species immune systems and when ingested, can be poisonous.16 In 2021, 200 fish were tested for PAH content, and every fish tested positive for PAHs.17 The oil spill also resulted in a significant decrease in reproductive rates and general organ failure across multiple marine species. Reproductive rates have still remained low in fish and dolphins 10 years later. The Deepwater Horizon Oil spill of 2010 has contributed to the “largest and longest marine mammal unusual mortality event ever recorded in the Gulf of Mexico.18” Bottlenose Dolphin populations decreased by 50% in the years following the incident,18 and more than half a million seabirds were killed.19 Oil can be particularly detrimental to seabirds as it can disrupt their feathers' natural oil coating. When the natural coating is disrupted, it reduces the natural buoyancy, insulation, and waterproofing effects of the feathers, leaving the birds susceptible to dehydration, drowning, and hypothermia.20 Sea turtles are an abundant species in the Gulf of Mexico but are an endangered species globally. The spill left the turtles covered in oil. Oil coating decreased sea turtle mobility and dehydrated the turtles. These effects led to their decreased ability to feed and increased risk of predation.15

Benthic Zones

In small oil spills, because oil floats on top of water, often benthic or deepwater organisms can avoid the brunt of the impact and remain unharmed. However, because the BP Exploration rig had deep water leaks, many benthic and deepwater species were affected. Because benthic organisms are either sessile or very slow moving, avoiding oil leakages and spills is almost impossible, especially massive ones like the Deepwater Horizon spill. A survey of the ocean floor in 2019 in the area of the spill determined that much of the biodiversity has decreased and the area remained quite barren. However, in years following the spill, crustacean populations seem to have endured—but not without injury. A 2017 dive expedition found that many existing crabs contained shell deformities or missing limbs.21 Researchers suspect that the deteriorating oil mimics a crustacean sex hormone that draws crabs to the area. But, instead of finding a mate, the oil covers and coats their shells which can prevent the molting of their exoskeleton. Lack of molting can decrease crabs' health as they cannot regrow lost limbs, or shed their body of exoparasites that build up on their shell.21 Sessile invertebrates like coral decreased in population size as, “studies showed that coral larvae exposed to oil and dispersants had lower survival rates and difficulty settling on a hard surface to grow.”22 Oil which coated and covered coral reefs, reduced the coral's access to nutrients and oxygen. Other filter feeders, such as shrimps, copepods, and barnacles were also jeopardized by the oil spill. A 2020 study on the effect of crude oil droplets on filter feeders found that, “[filter-feeding] individuals that ingest crude oil droplets show lower growth rates, lower egg production and hatching rates, higher fecal pellets counts, and higher mortality.”23

Coastal Zones

The impacts of the oil spill on various ecosystems.

On the coast, ocean currents, surface winds, and wave action carried the oil towards shore, affecting coastal ecosystems.  As oil washed up onto the beaches and shores, turtles nesting grounds were compromised. The oil coated and covered the nesting turtle eggs and this negatively impacted the development of the growing eggs. As well, the oil can blanket and bake the eggs in the hot sun, leading to further adverse health impacts and even death of the embryos. Approximately 35,000 sea turtle hatchlings were lost the year of the spill.24 Coastal vegetation, such as sea grasses, mangrove trees and cordgrasses can dampen wave energy and stabilize sediment. As the oil was washed ashore, it became trapped in the coastal marshes, smothering plants, inhibiting their access to sunlight and nutrients, and became incorporated within plant tissues. The integration of oil into plant tissues maintained oil within the ecosystems long after the spill, and led to the bioaccumulation of the toxic oil throughout the coastal shore food chain. As the oil amassed in the marshy ecosystem, plant and animal species declined, and wave action and erosion increased as the ecosystem engineers were absent. Moreover, many clean up activities, including the flushing and washing of marshes, disturbed the coastal environments and stressed and damaged the already vulnerable vegetation. This further delayed the ecosystem's recovery.25 Oysters populations took a significant hit in the Deepwater Horizon oil spill. Experts estimate that between 4 to 8.3 billion oysters were lost in the oil spill and the following clean-up procedures.26 Oysters are a keystone species in the Gulf as they filter the marine water and provide food to higher trophic levels of numerous marine mammals, as well as contribute to the fishing industry of the Gulf. A major factor in the oyster populations’ mass mortality was the use of dispersants in the immediate oil clean-up. In order to break up large floating sheets of oil on the surface waters, dispersant chemicals were used to emulsify the oil into droplets. This increased the oils potential to interact with the oysters, as the droplets became ingestible to the filter feeders.27 Accumulation of oil within oysters led to a decline in survival and reproductive rates, as well as an increase in mortality rates as the oil impacted the fertilization and development of the oysters.

Mitigation and Restoration

Mitigation Efforts

Immediately following the onset of the oil spill on April 20th, the United States federal government mobilized the inter-agency National Response Team to mitigate the damage.28 These initial efforts were intended to collect and/or neutralize the greatest amount of oil possible before it reached vulnerable habitats.

While the spill was active, teams used dispersants injected at the wellhead to prevent the formation of oil slicks. Because oil is hydrophobic and less dense than water, it floats to the surface where it forms a large slick with highly destructive impacts on coastal ecosystems. Dispersants are chemicals that break down oil into smaller particles, facilitating mixing with water and therefore preventing the formation of slicks. In past oil spills, workers sprayed dispersants over the surface to break up existing slicks. However, during the Deepwater Horizon spill, over 1.4 million gallons of dispersants were injected directly into the Macondo wellhead.29

The success of dispersants is debated by researchers. They may have done little to reduce the size of oil particles while inadvertently exposing deep-sea benthic communities to more severe damage by allowing oil to reach the seafloor. The use of dispersants also made oil more easily  consumed by organisms across various ecosystems. For example, the ingestion of oil by seabirds resulted in “anemia, weight loss, hypothermia, heart and liver abnormalities, delayed egg laying, decreased eggshell thickness, gastrointestinal dysfunction, and death”.30

Oil Boom in action.

To address oil already floating on the surface, workers used booms to contain the spill. They then used various techniques to collect the contained oil, including skimmer boats. However, the success of this strategy was limited as only 2-4% of the oil was removed. After skimmers collected most of the captured oil, workers used sorbents to absorb the remaining surface slick. These sorbents could be organic materials, natural inorganic materials, or synthetic materials. Burning was another strategy employed by teams during the mitigation phase. It’s estimated that 5-6% of the total oil spill was removed through controlled burns.31 Activities to contain the spread of oil continued from the onset of the crisis until the beginning of 2011, when clean-up and restoration became the primary focus.

Restoration Efforts

Since 2011, hundreds of projects have been active in order to both assess the extent of the damage and restore ecosystem health. In 2011, the Deepwater Horizon Trustee Council was created to oversee and fund restoration projects.33 In 2012, Congress passed the RESTORE Act which established two programs: the NOAA RESTORE Science Program and the Centers of Excellence Research Grants Program. These programs are governed by five goals:

  • Restore and conserve habitat
  • Restore water quality
  • Replenish and protect living coastal and marine resources
  • Provide and enhance recreational opportunities
  • Provide for monitoring, adaptive management, and administrative oversight to support restoration implementation.34

The trustees comprise federal agencies and impacted states. The federal agencies are the National Oceanic and Atmospheric Administration (NOAA), the U.S. Department of the Interior, the EPA, and the U.S. Department of Agriculture (USDA). The state trustees are Alabama, Florida, Louisiana, Mississippi, and Texas. $8.8 million dollars were initially allocated for restoration projects after the legal settlement with British Petroleum.35 In short, Gulf restoration is an incredibly large-scale and complex process involving countless agencies and hundreds of projects across five states and the open ocean. A full list of projects can be found here.

Unfortunately, many of the reports on restoration projects created by federal agencies are currently inaccessible due to the Trump administration’s recent changes to government websites. It is unclear what impact federal funding cuts and reductions in NOAA’s workforce will have on the ongoing restoration projects; it is likely that the scope of restoration efforts will be greatly reduced.

Across the 1,300 miles36 of impacted coastline, “restoration efforts included mechanically sifting the oil from beaches, cleaning marine animals, and eventually planting new marsh grasses to speed recovery”.37 Marshes were among the most vulnerable and heavily impacted ecosystems. Michel and Rutherford (2014) estimated that recovery would take two to four years for marshes that underwent intensive treatment, and eight years for untreated marshes. The replanting of Spartina in salt marshes and Juncus in freshwater marshes was a crucial element of restoration projects. The benthic communities supported by marshes are expected to recover as the native marsh grass is restored. Indeed, Zengel et al. (2022) confirmed that untreated marshes experienced 100-200% increases in erosion rates while replanting drastically reduced this effect.

Effects of oil spills on marshes.


Due to the complex and diverse impacts of the oil spill, it is difficult to make generalizations about the success of restoration programs. The disaster resulted in the mobilization of vast federal resources and funding for the implementation and monitoring of ecological restoration, a success by any means. However, many coastal and open-ocean ecosystems remain damaged by the event. For organisms with rapid reproduction and short life cycles like the pelagic cyprinodontiformes fishes, recovery occurred rapidly. However, the population of cetaceans and other marine mammals with long lifespans and low reproductive rates remain deeply impacted.39

NOAA’s Gulf restoration projects are projected to continue until 2030 and likely beyond.40 Understanding the true extent of the damage and how ecosystems have recovered in the last 15 years remains a monumental undertaking shouldered by thousands of researchers and dozens of government agencies.

Current Status

Persisting Damages

Of the 134 million gallons of oil spillage caused by the Deepwater Horizon Oil Spill, almost 100 million gallons of combined oil and dispersants are predicted to persist in the Gulf of Mexico.44 Due to the lingering pollutants, various ecological damage continues to impact the environment. For example, destruction of coral communities, threats to oyster fisheries, loss of habitat, and decreases in populations of marine species and sea birds.45 Many of the long-term damages caused by the Deepwater Horizon Oil Spill mainly persist throughout coastal and benthic ecosystems.

Pelagic Zones

Fish in the Pelagic Zone.

In a study41 that researched the availability of 78 endemic species of fish known to be found in the Gulf of Mexico prior to the oil spill, they were unable to find reports of 29 of these species since the oil spill occurred, even with increased sampling efforts aiming to collect data on post-spill distributions.  Due to damaged pelagic ecosystems, decreases in dolphin, sea turtle, and seabird populations have been observed43. These variations in species populations have largely impacted various predator-prey relationships within the pelagic and overall food webs, greatly increasing competition over nutrients and resources. According to the same study43, recovering the natural resources in several areas in the Gulf of Mexico is projected to take over 20 years.

Coastal and Benthic Zones

Hurricane Ian

When researchers44 conducted a study on soil conditions post-spill, they sampled soil from three estuaries found throughout the Gulf of Mexico that were impacted by the oil spill. Each of these were locations that contained a significant amount of vegetation. Within the samples, there were large concentrations of alkanes and aromatics that were calculated to be 1000 times higher than they were before the spill. Furthermore, the concentrations of polycyclic aromatic hydrocarbons, extremely toxic compounds present in oil and petroleum products,45 in the soil samples were also found to be beyond 10 times greater than in samples prior to the spill. The contamination not only decreased the soil strength greatly, but it also killed the vegetation that helps hold the land together, overall accelerating coastal erosion.44 To this day, the soil strength has not recovered fully. With the soil strength damages causing greater risk of erosion, they also found that they lead to greater shore loss during storms.44 They observed, based on satellite imagery, that Hurricane Isaac, a 2012 post-spill Category 1 hurricane, caused a much larger erosion rate of 208% increase compared to the much stronger Hurricane Katrina, a 2005 pre-spill Category 3 earthquake. This suggests that the soil strength damages caused by the spill make the shorelines prone to more damage.

Coral covered in sludge rooting from the oil spillage.

Not long after the spill, a team of researchers found a dense, damaged population of Paramuricea corals at approximately 7 miles away from the spillage site at a depth of 1,370 meters.49 They were covered in sludge consisting of oil and chemical dispersants.

More coral forests in the same condition were found at depths of 1,580 meters and 1,875 meters in a few months. They continued to monitor these sites from 2010-2017, as well as in 2022 and 2023, finding that while the sludge was gone, the corals remained damaged with scarred spots, leaking mucus, weak structures, and exposed skeletons that allowed other parasitic coral species to occupy the damaged space. Unfortunately, many species live within coral habitats, and while the biodiversity of fishes and macroinvertebrates are slowly starting to return to the area, they are still nowhere near the conditions from before the spill47 as many species continue to face habitat destruction and loss due to this continued damage. Some biologists believe that the wildlife in the Gulf of Mexico may never even fully recover to its original state.47

Prevention

The 2010 Deepwater Horizon oil spill remains one of the most devastating environmental disasters in history, releasing approximately 4.9 million barrels of crude oil into the Gulf of Mexico. Despite advancements in oil drilling technology, the spill revealed significant gaps in safety regulations, emergency response preparedness, and spill prevention measures. While large-scale oil spills are in the minority, prevention remains the key to reducing the risk of oil spills. Strengthening prevention policies, enhancing safety training, and improving spill response strategies are essential steps in mitigating future oil spill disasters.

Strengthening Policies and Regulations

One of the causes of the Deepwater Horizon spill was the failure of the blowout preventer (BOP), which is the last resort safety device.51 To prevent similar disasters, it is important to set mandatory monitoring of well pressure and structural integrity to detect issues early. Additionally, regular third-party safety inspections should be required to ensure compliance with safety protocols as well as stronger emergency shutoff systems to reduce the occurrence of large-scale oil spills.

The EPA is responsible for supervising the Spill Prevention, Control, and Countermeasure (SPCC) rule.52 To prevent future oil spills, the agency should require all drilling sites to develop a Facility Response Plan (FRP) for the worst-case spill situation.53 Also, the agency can impose stiffer penalties for non-compliance with safety regulations.

While offshore drilling is a major risk, oil transportation also contributes to spills. Therefore, mandatory use of double-hulled tankers is a significant preventative measure that can reduce the risk of leaks during shipping by featuring two watertight layers on the bottom and sides of the ship.54 Conduction routine underwater pipeline inspections would also help detect leaks before they escalate into major spills. In addition, establishing protected marine routes can prevent vessels from entering areas of fragile marine ecosystems, thus minimizing the impact of oil spills on ecologically sensitive areas.

Enhancing Education & Safety Training

As the Deepwater Horizon oil spill had caused 11 people to lose their lives, it is important for workers and the public to be prepared and educated.55 The oil rig employees should undergo regular safety training on spill prevention, emergency response, and equipment handling. The specialized certification programs could be required for offshore drilling personnel, thus ensuring that only trained professionals operate in high-risk environments. It is also important for the public and government to know the significance of preventing oil spills. The coastal communities and first responders should receive training on oil spill response. Coastal residents and schools could include environmental risk management education to increase the public awareness about the harm of oil spills.

Additionally, collaboration between governments, companies, and environmental organizations is a good way for oil spill response. In this case, by establishing joint training programs with the oil industry, and sharing knowledge and resources for prevention and response can ensure more rapid response capabilities.

More Effective Spill Response Strategies

Oil spills present a serious threat to the environment, polluting marine ecosystems and endangering wildlife. While mechanical and chemical methods can provide immediate containment and removal of oil spills, they may leave residues or cause secondary damage to the environment. Bioremediation is an eco-friendly method that provides a long-term solution by utilizing natural microbes to break down the oil into harmless by-products.56 This method promotes ecosystem restoration while minimizing the introduction of foreign substances.

Bioaugmentation involves the addition of oil-degrading bacteria to a spill site to accelerate the breakdown of hydrocarbons. By introducing specialized or genetically engineered bacteria, bioaugmentation can increase the number of oil-degrading microorganisms to improve efficiency.57 These microorganisms use enzymes to convert oil into energy, making bioaugmentation helpful for sites with low local microbial activity. However, the survival of microbes in harsh environments and competition with native bacteria are challenges to bioaugmentation.

Biostimulation can enhance the growth of existing oil-degrading microbes by modifying environmental conditions. This is usually achieved by the addition of nutrients, such as nitrogen and phosphorus, which are essential for microbial metabolism.57 This method could be more beneficial than bioaugmentation, as it stimulates indigenous bacteria that were already more competitive. However, overuse of nutrients could lead to eutrophication.

Biosurfactants are naturally occurring surfactant compounds that help disperse and break down oils.57 They are amphiphilic compounds that can modify microbial cell surfaces and increase the surface area of hydrophobic substances. In contrast to synthetic chemical dispersants, biosurfactants are biodegradable and less toxic, thus representing a promising alternative. Additionally, biosurfactants are stable under extreme conditions and can act over a wide range of temperatures, salinities, and pH values.

The other advanced technologies have also significantly improved oil spill prevention and response. For instance, the spill modeling has been improved to use simulation to predict how oil will spread under various conditions.58 In addition, remote sensing and satellite monitoring can provide real-time data, which allows early detection and rapid containment of spills. The Satellite Analysis Branch (SAB) plays a crucial role in monitoring oil spills, which uses advanced imaging techniques to track their movement. The Synthetic Aperture Radar (SAR) can detect oil film on the ocean’s surface by distinguishing the roughness of the Earth’s surface.59

References


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