How did Deepwater Horizon’s spill affect the coastal soils and wetlands in the Gulf of Mexico?

April 2020, is the 10th anniversary of the BP Deepwater Horizon oil spill in the Gulf of Mexico. We are dedicating this months’ Soils Matter blogs to the topic of the wetlands and soils, how scientists helped determine and solve some related issues – and where the wetlands are in their recovery.

British Petroleum’s Deepwater Horizon oil platform exploded in the Gulf of Mexico Apr. 20, 2010. Over 87 days, the resulting leak created about 5 million barrels of crude oil. Although crews attempted to contain the spill to the ocean, it couldn’t be done.

Clean up crews working on beaches contaminated with oil from Deepwater Horizon. Credit: National Institute for Occupational Safety and Health

By June, large doses of this crude oil were washing up on the Gulf’s coastal wetlands. This included Louisiana, Mississippi, Alabama and Florida wetlands and beaches. In later months, Texas shores were also affected.

And, it wasn’t just the crude oil that caused problems. Chemicals used to try to keep the oil contained and away from land added to the pollution. During the two-month journey to the Gulf’s shores from the wellhead, the oil also was exposed to sunlight. This caused further chemical reactions to take place before it washed up on coastal shores. We’ll refer to this as “weathered oil.”

Not only are wetlands vital elements to our ecosystem, they are also home to a diverse group of fish, birds, and other animal life. Wetland soils are home to soil microbes and many other soil-dwelling animals.

The arrival – and continued deposition – of the oil from Deepwater Horizon’s spill started a cascade of environmental and human health issues. The economy along the coastal shores was deeply affected. The shoreline at the time supported tourism and jobs valued at $34 billion annually.

Natural presence of hydrocarbons

Hydrocarbons – which is what crude oil is made of – have stored energy. That’s what makes them great fuels. They easily react with other chemicals, like oxygen in the air. The coastal area of the Gulf of Mexico has enormous oil reserves close to shore. These have been naturally seeping up to the surface – leaking if you will – for millions of years. An annual oil seepage of approximately 20 million gallons is natural, but its year-long, and slow.

Why isn’t the Gulf full of oil? Soil microbes and some plants use these hydrocarbons as their source of “food” if the process is slow. Sunlight and oxygen can also degrade these slowly leaking oils too. In fact, they become the source of food for whole communities of animals in the deep sea.

Impact of the spill on marsh soil

The slow, chronic natural leaks are something that Mother Nature can handle on its own. It’s man-made disaster spills causing acute levels of oil that cause real issues. Instead of 20 million gallons spread over 365 days, Louisiana wetlands received 200 million gallons in the course of almost three months during Deepwater Horizon. This completely overrode the natural way of handling hydrocarbon seepage.

One study reported that just over 1100 miles of shoreline was oiled. Half of that was beaches, marshes 45% and the remainder was other shoreline types. Shoreline cleanup was authorized for 73% of oiled beaches and only 9% of oiled marshes. The intensity of oiling differed along the Gulf Coast and across habitats.

Contracted cleaning crews use machinery to sift tar balls from sand along the beaches of Grand Isle, La., August 2010. Seth Johnson, US Coast Guard

Some marshes received so much oil, it created a solid “pavement” on top of the marsh soil. In other areas, only a small amount washed up. This oil became incorporated into the porous peat soil and was buried.

Research showed that the weathered oil was less toxic to the soil microorganisms than the fresh oil. One study did report that submerged oil had an impact on wetland plants’ roots. This could potentially increase their stress and damage the plants.

Erosion happened in areas where the oil washing up on shore was too thick. The plants’ roots died in some locations, and roots are important to prevent erosion. Without plant roots, wetland soils were at the mercy of tidal movements and weather.

Scientists from many disciplines started to contribute to relief efforts. Some made direct impacts on removal of waste. Others helped wildlife. And others helped determine how much oil was present. Our next blogs will discuss the detection of oil in the area as well as a recap on wetland life 10 years after the spill.

By Susan Fisk (SSSA) with John White and Ed Overton, Louisiana State University

Read our other blogs about Deepwater Horizon here:

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