Image Source: Wikimedia Commons

As the years roll by, the Earth’s waterways become more and more polluted. Sometimes, it may be due to litter or the illegal dumping of waste. In other cases, oil spills or pipe bursts happen. Over the past year alone, we saw quite a few incidents, including spills in the Timor Sea and San Francisco Bay, plus the more recent pipe burst in China that caused thousands of gallons of oil to be swept away; some clear to the Yellow River.

There is, however, one oil spill incident that still stands out when compared to all the rest: the 1989 Exxon Valdez oil spill. Many of you may remember the incident, but for those who don’t (or perhaps were not even born yet), here is a recap:

It all began on the night of March 23, 1989, when the Exxon Valdez departed from Alaska’s Valdez oil terminal and headed south for Long Beach, California. There were many icebergs in the area at the time, so a harbor pilot guided the ship through the Valdez Narrows.  Sometime after 11 pm, the ship was on autopilot and the outbound shipping lane was completely crowded with icebergs. Captain Hazelwood requested and received permission from the Coast Guard to go through the inbound lane. Shortly after midnight, the ship had struck Bligh Reef and 10.9 million gallons of oil quickly made their way into Prince William Sound.

Many animals were instantly killed by the spill, while some suffered and died later on. The death toll is estimated to include between a quarter and half million seabirds, 1,000 sea otters, 300 harbor seals, 250 bald eagles, 22 orcas and 12 river otters. It also included billions of salmon and herring eggs.

Nearly 21 years later, and imprints or traces of the spill are still being found throughout miles of gravel beaches along Prince William Sound. To look at the picture in this article, you wouldn’t think that such a place was ever touched by an oil spill. Despite all clean up efforts, at least 20 thousand gallons of crude still remain in the sound.  Until recently, no one could quite figure out why all this oil remained; but Michel C. Boufadel did. Boufadel is chairman of the Department of Civil and Environmental Engineering at Temple University and he conducted his own study of the sound.

Boufadel took a team and dug approximately 70 pits, between 3 and 5 feet deep, across 6 beaches. The focus of his study comes from information collected on Eleanor Island—15 miles from Bligh Reef and the grounding site of the Exxon Valdez.

His study—which can be found in Nature Geoscience—explained that Prince William Sound’s gravel beaches are trapping the oil between larger rocks and finer gravel. He discovered that water moved through the gravel layer up to 1,000 times slower than it did through the larger rocks. Water helps oil to biodegrade, but since the water and oil were trapped in the gravel—an environment that was practically oxygen and nutrient-free—the oil biodegrading process became much slower. He explained:

“The oil could be maybe one foot below the beach surface and in contact with sea water with a lot of oxygen, but the oxygen doesn’t get to it.”

As for the upper, larger rock layer, he notes that the water table falls within it as fast as the tide, due to its permeability. According to the study:

“As global warming is melting the ice cover and exposing the Arctic to oil exploitation and shipping through sea routes such as the Northwest Passage, the risk of oil spills on gravel beaches in high-latitude regions will be increased.”

Unfortunately, animals are still affected by the spill, as well. Sea otters, ducks and other birds in the area have been producing an enzyme, which shows that they’ve been exposed to oil. Right now, it’s uncertain how long it will take for the rest of the oil to biodegrade, but Boufadel predicts it will be a long time.