Yesterday marked nine years since the Deepwater Horizon crude oil started to leak into the Gulf of Mexico. The leak ended up being the most devastating oil spill in history and there is much evidence to show that almost a decade later its effects are still being felt by habitats on the Gulf Coast. Salt marshes are one of those habitats and new research published in Estuaries and Coasts reveals just how crucial marsh grasses are aiding ecological recuperation after a spill.
Co-author David Johnson, an assistant professor at William & Mary's Virginia Institute of Marine Science, explains: "Our study highlights the crucial role that plants play in the recovery of important links in the Gulf of Mexico's coastal food web." The study was part of the 10-year Gulf of Mexico Research Initiative program to track recovery after the spill.
The study focuses on the abundance and biomass of two species of grass: smooth cordgrass Spartina alterniflora and black needlerush Juncus roemerianus. Throughout 2011-2016, the team of scientists collected measurements in heavily oiled, moderately oiled, and oil-free areas of Louisiana's Barataria Bay. They also analyzed the impact on benthic microalgae communities and small invertebrates like amphipods.
Their data show that Spartina is key in kickstarting the recovery process. After two to three years, Spartina's growth was having a noticeable impact on the rest of the marsh ecosystem and it was only after Spartina had repopulated areas that small invertebrates came back. This took time, as the researchers noted that almost all the plants in heavily oiled areas died.
This finding concludes that Spartina is a foundation species, meaning that it "enhances recovery by providing habitat and reducing sediment erosion," says co-author Irving Mendelssohn. The authors hope that this discovery can be used to guide mitigation strategies for future spills, suggesting that Spartina should be planted as part of any clean-up process. "Plant growth enhances recovery by improving soil quality. Plants generate organic matter that accumulates belowground, while their roots and rhizomes release oxygen, bind sediments, and increase sediment volume. Breakdown of plant tissues also provides nutrients that further stimulate plant growth and beneficial microbial processes in the marsh," Mendelssohn explains.
While this finding was positive, the research team also determined that the heavily oiled marsh areas are still suffering from the spill years later, with higher levels of oil, slower growth of black needlerush, and severely impacted small vertebrate populations, compared to moderately oiled and oil-free areas. This is a concern because previous studies had implied that recoveries after spills would take less time.
"We're starting to see the salt marsh in the Gulf of Mexico rebound," says Johnson, "but it will likely be a decade or more before we see a complete recovery."