20 April 2011 Last updated at 01:31

BP oil spill: The environmental impact one year on

In April 2010, the Deepwater Horizon explosion in the Gulf of Mexico killed 11 people and resulted in 4.9m barrels of oil being discharged, threatening marine life and hundreds of miles of coastline. Yet, one year on, what environmental impact did one of world's largest accidental oil spills have on the region's wildlife and habitats, and has it been as bad as it was feared at the time?

Marine mammals

A sharp increase in the number of bottlenose dolphin deaths following the incident has concerned scientists. Some researchers suggest the mortality rate could be up to 50 times higher than reported figures. In the first birthing season since the spill, data shows a spike in the number of dead young dolphins being washed ashore. The exact cause is unknown.

Wetlands

The region is home to a number of coastal wetland areas that play a vital role in supporting migratory species. Favourable weather conditions and a prompt response from official agencies prevented the worst-case scenario being realised. However, oil still managed to penetrate a number of marshlands and wildlife havens and affected hundreds of miles of coastal areas.

Sea turtles

Even before the disaster, conservationists had identified the Gulf's sea turtles as species in need of special attention as a result of habitat disturbance and being caught in fishing nets. Following the spill, 25,000 eggs were transported from the Gulf to Florida's Atlantic coast. The move was seen as necessary in order to prevent an entire generation of sea turtles perishing in oil-tainted waters.

Birds

Thousands of birds from more than 120 species were affected, with more than half dying as a result of being oiled. Among the most affected species was the brown pelican, possibly because of its habitat to dive into water to catch fish. Conservationists say it could have been much worse if agricultural land was not flooded to create alternative wetlands for migratory species.

Fisheries

On the face of it, fish seem to be one of the "winners" because large parts of the Gulf were closed to fishing. Surveys recording surprising increases, such a 400% increase in sharks and a rise of up to 200% of small fin-fish and shrimps. However, scientists say the figures are for just one year and they cannot say whether there has been a long-term disruption to the marine foodchain.

Shoreline affected

Oil began washing ashore in June 2010 and went on to affect hundreds of miles of coastline along the Gulf states from Florida to Louisiana. Favourable weather condition kept the oil offshore in the initial few weeks of the spill. This gave the authorities time to put defensive measures in place, such as more than 4,000km (2,500 miles) of protective booms, to limit the volume of oil reaching land.

Oil footprint

At its largest extent, the spill covered thousands of square miles during the three months the well 1.5km (5,000ft) below the surface released crude oil into the Gulf. Of the estimated 4.9m barrels discharged, 800,000 barrels were recovered, the equivalent of 265,000 barrels was burned off the sea surface and 1.8m gallons of dispersants were used.

Coral

Gulf of Mexico is home to some of the northernmost tropical reefs, and it is difficult at this stage to assess what impact the oil has had on the fragile ecosystem. Conservationists warn that if a reef has been completely coated in oil, then it is probable that the slow-growing coral, which can take centuries to become established, will have died.

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By Mark Kinver Science and environment reporter, BBC News

Scientists have warned that it is too soon to attempt to offer a considered assessment on what impact the Deepwater Horizon oil spill, the largest of its kind, has had on the Gulf of Mexico's wildlife.

In short, they said, nature did not work in such a way that the full picture will present itself within just one year.

Also, they added, more data needed to be gathered in the months and years ahead to gauge the full extent of the incident, which covered such a vast area.

Kemp's Ridley turtle hatchlings Turtles are among the animals affected by the leak

Dr Jane Lubchenco, the administrator of the National Oceanic and Atmospheric Administration (Noaa) - one of the federal agencies leading the clean-up operation - said there were reasons to be optimistic.

In an interview with the AP news agency, she said that the health of the Gulf is "much better than people feared", but the jury was out about what the end result would be.

"It's premature to conclude that things are good. There are surprises coming up - we're finding dead baby dolphins," she observed.

Researchers and conservation groups said it was difficult to access information being gathered as part of an investigation by a federal Natural Resource Damage Assessment (NRDA) process.

The NRDA is a formal framework in which government agencies look at the damage caused by the spill to natural resources and services - such as fisheries, wetlands, protected species, agricultural land - and calculate how much it would cost to repair the "injuries".

"What we know is very sketchy," said Claude Gascon, chief science officer for the National Fish and Wildlife Foundation.

"We have tried, and many others have tried, and it is almost impossible to get any idea what that group of agencies and researchers are actually finding.

"The simple reason for that is that there is going to be so much potential litigation in terms of settlements etc, " Dr Gascon told BBC News.

"So it is very difficult to know at the moment, the scale of the impact has been and will be in the future.

Graphic

"All of us, including conservation organisations, professionals and academics, are keenly awaiting whatever the federal process will release into the public domain."

There was also agreement that it was too soon for long-term impacts to manifest themselves, such as disruptions to ecosystems' food chains.

This is why it was important for the data collection currently being carried out by the NRDA to continue, even if there was an out-of-court settlement, said Stan Senner, director of conservation science for Ocean Conservancy.

"It is too soon to draw any conclusions about impacts, especially within the marine environment," he told BBC News. "We certainly cannot gauge long-term effects just 12 months after the spill.

"For example, there were things like the massive use of dispersants, which was unprecedented. And because the well was so far offshore (50 miles), there were undoubtedly many, many impacts that were out of sight and we may never have the capacity to work out what really happened.

"Right now, there are far more questions than answers."

Understanding risks

Referring to the NRDA, Dr Senner said: "If the process runs its full course, it could take several years, may be more, to go through the damage assessment studies, then develop a restoration plan and present a claim for the cost of restoration to the responsible parties."

Russian flag on the seabed at the North Pole (Image: AP) In 2007, Russians planted a flag on the North Pole's seabed, staking a claim to the region's resources

During a similar process following the 1989 Exxon Valdez spill, Dr Senner - at the time - worked for the US government.

"We started that process and did our damage assessment studies," he explained. "But two years after the spill, the government and Exxon settled their claims out of court so that process never had to go through its full course.

"That may or may not happen [in the Deepwater Horizon] case, but one point I want to make very clear is that regardless of whether there is settlement or not, we strongly advocate that the scientific work continues.

"This will help us understand what happened, how long will the impacts last, how long recovery will take etc."

He said that the information would be vital for assessing the risk associated with future oil and gas activities.

The Arctic, with its vast untapped wealth in oil and minerals, has become the focus for a number of nations that are keen to stake their claim to the natural riches.

However, Dr Senner urged caution: "There is simply much less that is known about the Arctic region where oil development is proposed.

"If you look in the Gulf of Mexico, there is a relatively good baseline of environmental information compared with the Arctic.

"Also, there is a lot more capacity to respond to an oil spill in the Gulf; there is no capacity in the Arctic - there is not even a harbour on the Arctic slope of Alaska, which could be a staging base to respond to a spill."

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