Biology Comics

Oily Dreams: the Deepwater Horizon Disaster

The well drilled by the drilling ship Deepwater Horizon in a mile of water continues to pour oil and gas into the deep sea. Some of the oil floats to the surface, where the lighter fractions evaporate (up to half the oil), the rest floats in rafts on the sea, until driven by winds and currents onto the beaches and marshlands of the gulf coast. Turtles or whales that swim through the oil become disoriented; some die. Birds that land in it die. The film of oil kills the larvae of fish and crustaceans that float in the spring waters of the gulf; including the larvae of such long distance swimmers as the western Atlantic population of the bluefin tuna.

Much of the oil and gas disperses underwater to form deep plumes of tiny droplets under the sea surface, that oxidize, or are oxidized by bacteria, and use up the oxygen in the water. The water in the plumes may become too depleted of oxygen for animals to survive. Such plumes are also toxic to the larvae of gulf animals and to the animals (deepwater corals, fish, crustaceans) themselves.

Some summer anoxia in coastal bays and estuaries (like those of the gulf) is normal. The upper layer of the ocean is ventilated by storms mixing surface water, rich in oxygen, with the waters below. Oxygen also diffuses downward into the water column, but slowly. Currents bring deeper waters to the surface, renewing their nutrients and being renewed with oxygen.

In summer storms are fewer. The sun heats the surface waters, which tend to form a lid over the colder waters below. The water column stratifies. Fresh water from rivers pouring into the sea, less dense than salty ocean water, also sits on the sea’s surface, helping keep the lid in place. So the oxygen content of the deeper waters falls.

If the water’s oxygen content falls too low, fish and benthic organisms (corals, anemones, worms, sponges) suffocate. One July evening in 1987, lobsters started crawling out of Long Island Sound onto shore: insufficient oxygen was left in the water. Bluefish gasped in the shallows. Modern summer anoxias are made more extreme by the nutrients (from sewage effluent, pet poop, burning fuel, fertilizer) we put in the ocean. These materials cause algae to grow. The algae grow and die, sink to the bottom of the sea and decay, using up the available oxygen. (This process also sequesters carbon.)

Fertilizer from farms and lawns running off into the Mississippi River has created a so-called dead zone of anoxic water in the Gulf of Mexico for several decades. The size of the zone increased dramatically after the 1993 floods, which increased the runoff of nitrogen and pesticides into the gulf. It continues to grow.

I would guess its growth is related to the size of the American corn crop. The nitrogen runoff is caused by poor agricultural practice in the Mississippi basin: not rotating corn and sod crops; applying too much fertilizer; putting too much land in crops, period. Fertilizing the tens of millions of acres of suburban lawn grasses in the Mississippi basin also adds nitrogen. Rotating cornland into hays would reduce the size of the corn crop by a third and help heal the river and the gulf. With the price of corn so low, people burn it instead of wood and transform it into a motor fuel; but corn is a food. Even agricultural economists say we have too much corn.

The nutrients and soil running off poorly managed farms also degrade rivers, and their fisheries.

So the anoxia caused by the oil adds to the anoxia caused by foolish agricultural policies in the fertile center of the continent.

The rafts of evaporating oil also drift into the marshes at the mouth of the Mississippi and onto coastal beaches.

On the beaches it is removed. (Some sinks below the surface.) Removing it from marshes is more difficult.

Thousands of people have been organized to remove the oil. They drive vehicles through colonies of nesting birds and over low coastal dunes, flattening them. They walk through pelican nests (whose adults will die anyway).

Some biologists say it would be better to leave the oil alone. Over time most of it (perhaps 70%) will evaporate or biodegrade. In Prince William Sound in Alaska, high pressure washing with warm water of rocks along the shore after the Exxon Valdez spill drove the oil underground, where it remains, mobilized from time to time by digging animals or rock shifting storms. (Once out of reach of oxygen oil breaks down extremely slowly. Adding nutrients like nitrogen may help.) The herring fishery in the sound never recovered and other fisheries remain much reduced many years after the spill. Fish living near a 40 year old spill on Cape Cod show elevated levels of liver enzymes many years later. (Fuel oil there also remains under the surface of the beaches, driven down by gravity and storms.) No one knows the continuing effects on fish eggs and larvae and thus on fish abundance; but our use of oil is a sort of tax on the wild world. Oil on the surface of the ocean or land will eventually be broken down by bacteria and archaea (natural asphalt lakes are full of life) but in the case of heavy tarry oils eventually is a long time.

Oil and gas seeps in the gulf may release a million barrels a year (not a small amount). This oil is used by bacteria, which are eaten by large worms and other creatures in so-called dark ecosystems on the seafloor. (‘Dark’ because they are out of the reach of sunlight.) So oil is not new to the gulf.

Booms are used to keep the oil from reaching the beach and people scoop up and bag the oil that does. Hair (human and otherwise) makes an excellent absorbent and afterwards the oil soaked material can be burned. Behind the booms, skimmers remove the oil from the surface of the sea.

Booms and sleeves stuffed with hair are cheap but oil companies don’t want to pay for buying and storing the material against emergencies. (Renting the drilling ship Deepwater Horizon cost about $500,000 a day.) Absorbent booms are probably better than plastic ones but are more expensive.

Any cleanup is a big mess. Nothing really works. Storms and waves cause problems. Marsh vegetation will come back after one oiling but several oilings will kill it, leaving the marshland open to erosion by the sea.

But gulf marshlands have been receding for decades, a matter that is well known. Modern levees keep the muddy waters of the Mississippi from flowing over the marshlands and rebuilding them. Rather, the river water is sent straight out into the gulf, where its muds and fertilizers add to the dead zone, rather than fertilize and maintain the protective marshlands of the delta.

Canals dug by oil companies through the marshes (10,000 miles of them) let the sea in to erode the marshes.

Salt water penetrates inland and as the marshes become more saline, their vegetation changes. They become less desirable to migratory waterfowl. Cypresses and other trees die.


The receding marshlands expose the coast to storms.

The Caribbean, of which the Gulf of Mexico is part, once had tens of millions of sea turtles grazing its seagrass meadows and coral reefs, manatees nibbling seagrasses along its coasts, seals eating its forage fish and many whales. Its spawning fish came from nearby and far away. Like the water birds most of these animals are reduced by 90-95% from their original abundance. Some losses were deliberate (turtles and manatees were hunted for food and oil), some a consequence of human settlement.

The Ixtoc spill of 1979-80 in the Mexican section of the gulf, released 10,000-30,000 barrels a day for ten months until contained. Much of the oil ended up on Texas beaches. The Deepwater Horizon spill is putting out 25,000-60,000 barrels a day. If the relief wells work and end the spill by August, it will only have lasted half as long. (The Ixtoc relief wells did not work at first.)

As of June 5th a temporary containment system seems to be capturing half the oil.

Such oil spills are only a part of our mismanagement of the ecosystems of the gulf. The Louisiana sport and commercial fisheries are worth about 8 billion dollars a year. In general, we have no idea of our place amidst the natural systems of the planet.

And as long as we place no value on nature, we will treat it like shit.