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Oil and water don't mix

The effects of oil on ecosystems

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Oil is always in the news for some reason or another, whether for fluctuating barrel prices, oil-rig fires, or tanker crashes and leaks. Recently, it is because of the gigantic semi-submersible Mobile Offshore Drilling Unit (Modu), called Deepwater Horizon, that exploded on April 20, resulting in millions of litres of crude oil gushing into the pristine waters of the Gulf of Mexico. The oil rig is leased by BP Plc, fka British Petroleum, a British-based global energy company. 

Unfortunately, the world still needs oil, but oil is becoming increasingly scarce. Oil companies find that they must drill in more dangerous, less accessible places, such as 1.5km below the ocean's surface, near the middle of the Gulf of Mexico, the site of this disaster.

Deepwater Horizon

On April 20, the Deepwater Horizon, situated about 64km off the Louisiana coast along the Gulf of Mexico, burst into flames after a blowout due to pressure in the pipelines, resulting in the deaths of 11 platform workers and injuries to 17 others.

The rig burned for two days and sank on April 22, leaving behind oil gushing from the pipelines on the seafloor. Deepwater Horizon is the deepest subsea blowout, and, at about 1.5km deep, it is extremely difficult to cap the leak due to not only the great depth, but because of the sheer lack of oil industry experience in dealing with leaks at great depths.

There have been many tried-but-failed attempts to plug the leak, and at the time of writing, the Deepwater Horizon oil spill is still continuing, with sadly no real end in sight for the immediate future. This incident arguably has already become the largest oil spill in history.

Dangers of the spill

There have been many oil spills, and one famous oil spill springs immediately to mind: the Exxon Valdez spill in 1989. The oil tanker Exxon Valdez ran aground off the coast of Alaska and spilled millions of litres of oil into Prince William Sound. Although by no means one of the largest oil spills, its remote location in a fragile wilderness was simply devastating to the local ecology, wildlife and fishing industry. The Deepwater Horizon tragedy shares these characteristics.

Off the southeast US coast along the Gulf of Mexico are various unique and fragile ecosystems. The mangrove wetlands, marshlands and swamps in that area, as well as the Mississippi delta and the Everglades, will inevitably suffer long-term effects from the spill. These directly and negatively affect regional tourism. The short-term conseqences are already evident.

Effects on ecosystems

Birds suffer greatly from oil spills. Sea birds that rely on coastal habitats and those that hunt fish for food inevitably come into contact with the oil. Birds secrete a natural oil that waterproofs their feathers and serve as insulation against the cold.

Petroleum oil interferes with their natural insulation and can cause birds to be vulnerable to varying temperatures. Birds constantly preen their feathers with their beaks to keep their feathers in good condition.

When they are covered in oil, preening means birds necessarily ingest the toxic oil. The heavy crude oil (see "shovel" picture, at left) also inhibits a bird's ability to fly, making it susceptible to predation and mental anxiety. Without human intervention, the birds would most certainly die.

Thousands of birds have already died, with more inevitable casualties around the corner. And even if the birds are cleaned by humans, as their ecosystem is all but destroyed, there is nowhere to release them. Fur-covered seals and otters suffer similarly to the birds, as the oil renders the animals unable to insulate their body once their fur is soaked in oil.

Dolphins and whales also suffer the consequences of oil. They need to breathe air and therefore have to surface through the oil as it floats on top of the water due to its having a density lower than that of water.

This can lead to ingestion, and therefore poisoning of these marine mammals. Sea turtles, all of which are endangered to some extent, also have this problem as they, too, are air breathers. Apart from direct ingestion, marine mammals, reptiles and birds also rely on other organisms for food. Many of these creatures are piscivores (fish eaters), and fish stocks are rapidly dying.

The toxicity to fish is severe and acute, and many fish species may become locally extinct in the region. Many fish have floating eggs that will be poisoned, whereas others will be poisoned through ingestion. There is also a chance of bioaccumulation occurring, wherein toxins from ingested oil by animals or absorption by plants can accumulate up food chains leading to the intoxication and deaths of top predators.

If any links are broken in food webs, the shift in the ecological balance can be devastating to whole species or communities.

But food webs themselves are nothing without producers like marine plants and phytoplanktons, which are the basis of all the ocean's food webs.

Oil floating on top of the water can seriously inhibit sunlight from penetrating into the water, which directly affects the rate of photosynthesis by producers, which in turn reduces the amount of biomass available for the rest of the organisms in the ecosystem.

There is also a threat of reduced oxygen levels due to heightened bacterial action digesting the oil, which again could spell disaster for the immediate ecosystems and produce "dead zones". Simply put, the effects of oil spills on ecosystems are nothing short of catastrophic.

Self-cleaning oceans

Despite the decreasing oxygen levels as a result of increased microbial activity, the job that bacteria do is essential as this is how the oil, in fact all oil from spills that haven't been burnt off or evaporated, will gradually be removed from the oceans, thereby leaving "clean" oceans behind.

The term used to describe the action of microorganisms like bacteria that break down contaminants such as oil, thereby returning the contaminated area back to its natural state, is called bioremediation.

Bacteria of certain species have the ability to naturally biodegrade the hydrocarbons that make up oil. In the Deepwater Horizon oil spill, though, the amount of nutrients such as nitrogen and phosphorus, essential to the bacteria, are lacking in sufficient amounts to produce a "swift" clean up.

Either way, some normality in the oceans will be restored eventually, but it is impossible to say when, and that is taking into account that there will be no more oil spills happening in the area. The damage to ecosystems may have very far-reaching effects and may even affect human health. Let's just hope the damage is not permanent.

Dave Canavan has an MSc in Behavioural Ecology and is the Head of Secondary at Garden International School. Dave is fascinated by science and loves animals, especially the dangerous kind! You may discuss this article with Dave at davidc@gardenbangkok.com.

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