Figure: Percent cover of smooth cordgrass (Spartina alterniflora) from Louisiana sampling sites, 1994-2016 Smooth cordgrass is the most ubiquitous coastal marsh plant in Louisiana, forming the base of the ecosystem’s food web. It provides habitat and food for many coastal marsh species, stabilizes the marsh against land loss from erosion and storm damage, and helps sequester carbon.
The dense under-surface network of roots enables smooth cordgrass to resist sediment erosion, making it an important land builder on the Louisiana coast. When cordgrass goes, coastal marshes go with it. Smooth cordgrass is the most ubiquitous coastal marsh plant in Louisiana, forming the base of the ecosystem’s food web. It provides habitat and food for many coastal marsh species, stabilizes the marsh against land loss from erosion and storm damage, and helps sequester carbon. In 2001, a major drought caused high salt concentrations in the marsh, leading to the browning and die-off of over 100,000 acres of smooth cordgrass. A state of emergency was declared in 4 coastal parishes due to the extensive die-off. Although the grass recovered within 5 years, the event highlighted the fragility of this important species, and the susceptibility of the marsh ecosystem to the effects of climate change.
More than 224,000 kilometers of Louisiana’s coastal marshes were damaged during the 2010 Deepwater Horizon oil spill, increasing already-rapid erosion rates by destabilizing the roots of marsh plants. Although cordgrass was not affected as dramatically as in the 2001 event, coastal marshes were highly degraded, and die-offs of oiled smooth cordgrass were observed following the spill in 2010-11. Oiled sites had returned to semi-normal functioning 11 months post-spill, but many areas that had experienced severe erosion due to cordgrass die-offs were unable to recover. Additionally, heavy metals and toxins that accumulated in the soil following the spill are still detectable to this day, and have greatly affected the smooth cordgrass’s ability to withstand further environmental stressors. Studies into the effects of the Deepwater Horizon spill on smooth cordgrass indicate that oil spills have the potential to accelerate land loss of Louisiana.
References: Herbaceous marsh vegetation data compiled from the Coastal Information Monitoring System (CIMS) via the Coastal Protection and Restoration Authority (CPRA) (https://cims.coastal.louisiana.gov/monitoring-data/)
CIMS provides geospatial, tabular database and document access to CPRA’s suite of protection and restoration projects, Coastwide Reference Monitoring System (CRMS) stations, the 2017 Master Plan, project scheduling, geophysical data, and coastal community resiliency information.
Silliman, B. et al. 2012. Degradation and resilience in Louisiana salt marshes after the BP-Deepwater Horizon oil spill. PNAS 109:11234-11239: (https://doi.org/10.1073/pnas.1204922109)