The oil spill is under control – now it's time to count the ecological cost

 guardian.co.uk

When BP's chief executive, Tony Hayward, said in May that the Gulf oil spill was a drop in the ocean – "tiny in relation to the total water volume", he was pilloried by Barack Obama and the US press, but he was technically correct.

In the 85 days of the leak, the worst oil disaster in history, nearly 184m gallons of crude oil is estimated to have gushed into the Gulf of Mexico, the ninth largest body of water in the world. That is a lot, but no more than Americans burn every five hours and 10 minutes. Indeed, in the 24 hours since BP temporarily capped the Deepwater blowout, Americans have used over 840m gallons in their cars, planes, kitchens and factories which will have soiled the air, land and sea.

The US can now look back on the Deepwater spill and count itself ecologically lucky, in many ways. It was not just a mile deep, allowing much of the oil to be diffused in the ocean, but it was 50 miles offshore in a warm sea. Many other oil spills have been far more injurious to wildlife and the marine and terrestrial environments, because oil breaks down much more slowly in cool seas. The 11m gallons spilt from the Exxon Valdez in the Alaskan waters in 1989 still threaten the whole ecosystem. That spill killed at least 36,000 sea birds. So far, Friends of the Earth US reported today, only 1,387 birds, 444 sea turtles, and 53 mammals have been found dead in the Gulf.

Nonetheless, the damage yet to be revealed will be far worse than a few dead birds and tar balls along 500 miles of coast. Dolphins, whale sharks and sea turtles numbers will almost certainly have been hit hard, and some populations may not recover for years. Fish and shrimp-breeding habitats will have been hit. Deep coral reefs, which can take centuries to grow, may also have been affected.

Furthermore, the ecological damage done in the last three months is made far more serious because it comes on top of years of man-made degradation of the Gulf environment. Many of the wetlands and estuaries that take the brunt of any oil spilt had already been seriously degraded by man's interference with river flows. These could now disappear even faster if the oil has got into the roots of the grasses.

The oil that gushed also added to natural oil and gas leaks into Gulf waters. These occur all the time from the sea bed, and the US Department of Energy estimates that there may be 5,000 active "seeps" in the northern Gulf alone. One researcher calculated in 2000 that 500,000 barrels of oil – 84m gallons – naturally gets into the Gulf each year, but is never cleaned up.

The Gulf is also heavily polluted by nitrogen and phosphorus from fertilisers and livestock waste washed down the vast Mississippi river from farms and industry. Every year, a massive oxygen-starved region known as the "dead zone" develops off the coast of Louisiana in which nothing can live. Last month, the US government's National Oceanic and Atmospheric Administration (NOAA) said it expected this year's "zone" to be between 6,500 and 7,800 square miles, the 10th largest ever. No one knows yet how the oil spill may affect it. Some marine scientists think the oil may make it larger, but others say it could help to limit its size – a scenario that could, absurdly, see BP claiming to be clearing up pollution in the Gulf.

Fish will have suffered, but paradoxically the US government's decision to ban commercial fishing from 88,000 sq miles of the Gulf during the clean-up in order to safeguard human health could actually help regenerate depleted fish stocks. The Gulf is one of the most overfished seas in the world, with many species in serious decline and some fisheries near collapse.

Closing off nearly a third of the waters is likely to have given many species a chance to increase numbers. The oil spill will have killed some fish, but vastly more are caught by industrial fishing operations every year. Stocks of fish such as red snapper and bluefin tuna, which spawn in the Gulf, could benefit greatly.

One wild card yet to be played is a major hurricane tearing through the Gulf of Mexico, as is likely to happen before the end of the season in November. Rough seas will hamper efforts to finally seal the well and clean up the oil. The associated storm surges could also drive oil over barriers and further onto coastal land and into sensitive habitats. But the raging of a storm could also break up the oil slick, allowing the bacteria that break it down to act more rapidly.

Posted via email from Jim Nichols