That's because even before the spill, up to 8,000 square miles of Gulf waters would turn every year into Dead Zones -- vast areas of the coast so depleted of oxygen that shrimp, crabs and other marine animals could no longer live.
Now, scientists fear the BP spill will make a bad situation worse. Despite blithe predictions that the Gulf fishing industry will bounce back like Alaska's after the Exxon Valdez disaster, the already-expanding Gulf Dead Zone presents a uniquely dangerous scenario that many fear poses a long-term threat to ocean life.
First noted by scientists in the 1960s, Dead Zones are formed when huge amounts of nutrients -- as found in agricultural fertilizers, municipal sewage and other wastes -- overload the water, leading to explosive algae growth that ultimately robs oxygen from marine life below, a process known as hypoxia.
A 2008 study found over 400 Dead Zones around the world, and the Gulf of Mexico's is one of the largest. Snaking along the Louisiana and Texas coasts, the expanding Gulf Dead Zone has drastically reduced seafood stocks and pushed fishers further out to sea.
The primary culprit? Nitrate-laced runoff from agricultural operations along the Mississippi River, which eventually drain into Gulf waters. One study found that 51% of nitrogen load in the Mississippi was from commercial fertilizer, with livestock manure, human sewage and runoff from other crops contributing to the mix.
Fall weather brings cooling air and churning waters that dampen algae growth, but scientists are now seeing a "legacy" effect where lingering decomposed organic matter continues to steal away oxygen. This means that even if nitrate levels hold steady or decline, past pollution can still cause Dead Zones to expand in the future.
Now add the BP disaster. Gushing oil is the most immediate threat to marine life, but scientists see another looming danger: methane, which BP itself has estimated constitutes 40% of what's flooding out of the Deepwater Horizon drill site.
Last week, John Kessler of Texas A&M University measured methane levels at 35 different locations near and far from the BP disaster, and here's what he found:
What's wrong with methane? Like nitrates, it stimulates the growth of shallow-water life -- in this case, feeding microbes -- that sucks up ocean oxygen and kills off deeper-water animals life seabed shellfish. In some places, Kessler's team found "depletions [of oxygen] up to 30 percent."
Levels of methane in deep-ocean waters near the Deepwater Horizon oil spill are 10,000 to 100,000 times higher than normal, and in some very hot spots "we saw them approaching 1 million times above" what would be normal, says ocean chemist John Kessler.
While BP's spilled oil has already killed much marine life, a growing threat to the Gulf comes from another energy source further up the Mississippi River: ethanol.
Most U.S. ethanol comes from corn; in fact, ethanol accounts for over a third of U.S. corn production. And corn is one of the worst crops when it comes to Dead Zone-causing pollution runoff, because it depends on higher concentrations of nitrates to grow.
That problem will only grow worse as the U.S. ramps-up production of ethanol fuel. The Energy Independence and Security Act of 2007 set a goal of the U.S. using 36 billion gallons of renewable fuels by 2022, including 15 billion gallons of corn-based ethanol -- triple the current amount. President Obama affirmed the country's commitment to ethanol in a directive last year.
The result would be "a disaster for the Gulf of Mexico," says Simon Donner, a geographer at the University of British Columbia. Along with scientist Chris Kucharik, Donner published a study in the March 18, 2008 Proceedings of the National Academy of Sciences which showed that:
[S]caling up corn production to meet the 15-billion-gallon goal would increase nitrogen loading in the Dead Zone by 10-18%. This would boost nitrogen levels to twice the level recommended by the Mississippi Basin/Gulf of Mexico Water Nutrient Task Force, a coalition of federal, state, and tribal agencies that has monitored the Dead Zone since 1997. The task force says a 30% reduction of nitrogen runoff is needed if the Dead Zone is to shrink.
Groups like the American Farmland Trust are pushing for solutions: Their Best Management Practices contest pays farmers to reduce fertilizer use and therefore nitrate runoff. But these are still small-scale answers to a national problem that demands a federal response.
Until Washington comes up with a plan to address the growing Gulf Dead Zones, thousands of square miles of ocean waters -- and the thousands of families who depend on them for a living -- face a grim future, long after news headlines of the BP disaster fade away.
Follow Chris Kromm on Twitter: www.twitter.com/chriskromm