|The colonization of marsh grasses fuels the food web, binds the soil, and slows down the flow of water / Photo by Getty Images|
Oil spills are dangerous to organisms and the environment, which may not recover depending on the damage. A new study investigated the ongoing impacts of the Deepwater Horizon oil spill in the Gulf of Mexico. Their investigation showed the key to the overall recovery of the region.
The investigation of the continuing effects of the Deepwater Horizon oil spill was led by Louisiana State University and collaborators, including the Virginia Institute of Marine Science. Their findings revealed that marsh vegetation serves as the vital component to the recovery of contaminated marsh sites. They published the results in the journal Estuaries and Coasts.
The Deepwater Horizon Oil Spill
On April 20, 2010, a leak began from the drilling rig called Deepwater Horizon. The old rig was leaking crude oil into the Gulf of Mexico and no one knew that it would become the largest oil spill in human history. Its magnitude was between 8 and 31 percent greater than the volume of oil unleashed by the Ixtoc I oil spill, a separate incident in the same region. The US government estimated the discharge of at least 210 million US gallon of crude oil, according to the US Department of Homeland Security.
Nine years later, the Gulf of Mexico is still enduring the toxic effects of crude oil on its natural habitats. While efforts are in place to push recovery, the impacts remain as big challenges. One of the subsequent responders in the sites is a group of investigators who monitored everything since the day after the spill was contained.
"Our study highlights the crucial role that plants play in the recovery of important links in the Gulf of Mexico's coastal food web," said David Johnson, an author of the study and an assistant professor at VIMS. Certain types of plants were discovered to be key elements that could keep the recovery path of the region. If some efforts could be pooled into these plants, coastal wetlands affected by oil spills would improve at a steadier pace.
The Key Plants on the Road to Recovery
Since the team has been collecting samples after the containment, they were able to learn about organisms that survive the incident. In the salt marshes of the Gulf Coast, researchers noticed specific plants that dominated the area. Two plants called the smooth cordgrass (Spartina alterniflora) and the black needlerush (Juncus roemerianus) were seen to be abundant despite the oil spill.
When they examined the coast closely, they also detected the benthic microalgae populating the marsh surfaces. The microalgae have been described as single-celled, plant-like organisms. Their close examination uncovered small invertebrates in the area as well, which included amphipods, copepods, nematodes, and snails, among others. These invertebrates were found on the grass blades or any underlying root zone.
Interested with the surviving organisms, researchers obtained measurements between 2011 and 2016 with six-month intervals. They measured the organisms' population levels and biomass in several areas of Barataria Bay in Louisiana. They retrieved biomass samples from heavily oiled, moderately oiled, and un-oiled locations.
|Findings revealed that marsh vegetation serves as the vital component to the recovery of contaminated marsh sites / Photo by Getty Images|
An early sampling of plants in the coast determined that nearly every species died in heavily oiled areas. The same happened as well in affected places where microalgae and invertebrates thrive. But later sampling indicated signs of recovery being led by benthic microalgae and the cordgrass Spartina. After the cordgrass reestablished itself, the invertebrate community started to return full swing in the area.
Johnson said that the very foundation of salt marshes is vegetation. They serve as shelter and source of food for small invertebrates. The colonization of marsh grasses fuels the food web, binds the soil, and slows down the flow of water. This means efforts on the restoration of marsh plants are needed to help the recovery rate of the salt marshes.
So, if someone plants a marsh plant, invertebrates will likely learn about the new vegetation. If the plants grow, more small invertebrates will go to plant-rich areas to create habitats.
The Recovery Rate in Different Soils
Aside from the key components for recovery, the study also discovered the recovery rate of marsh sites in the Gulf Coast. The heavily oiled soils exhibited the slowest recovery rate in over six years after the oil spill, compared to moderately oiled soils and oil-free marsh sites.
Analyses of heavily oiled soils expressed the high concentration levels of oil and its byproducts, substantial slow growth of black needlerush, reduced supply of plant detritus and similar organic materials, and altered soil density. These conditions were expressed as well by small invertebrates that failed to thrive in such soils.
But what shocked them the most has been the very low population of the Manayunkia aestuarina worm. The population of this worm typically indicates the health of marsh sediments, and their rarity in the Gulf Coast affects the food web in the marsh sites.
Overall, the recovery rate of heavily and moderately oiled marsh sites has been estimated to be longer, probably more than 10 years. Still, the team is optimistic in the long-term recovery of affected areas. They said fertilizing Spartina plantlings will make a huge difference in marsh sites.