Coastal Ecosystem Resiliency after Major Disturbances

Abstract

Disturbances are a common occurrence in coastal ecosystems and can provide opportunity for adaptation and renewal in healthy systems; hurricanes bring mineral accretion to a marsh, floods provide a pulse of freshwater and nutrients to estuaries, and fires increase species diversity and abundance in forests. Humans, however, have depleted the resiliency of many coastal systems via top down and bottom up mechanisms, leaving these ecosystems more vulnerable to both natural and anthropogenic disturbances. Louisiana’s wetlands have been modified for centuries via canals, levees, agricultural impoundments, etc., leading to a decreased resiliency to land loss. The Deepwater Horizon (DWH) oil spill had the potential to further reduce marsh resiliency, potentially precipitating a “regime shift” where natural disturbances that were once a subsidy to the system are now a stress. The DWH oil spill released 4.9 million barrels of oil into the northern Gulf of Mexico, covering 2,000 km of shoreline from Florida to Texas in the world’s largest accidental marine oil spill. I examined the direct and indirect impacts of the oil spill on salt marsh erosion rates in southeastern Louisiana on varying spatial (from cm to km) and temporal scales (from hours to years). I chronicled the effects using multiple techniques of documentation including field data collection of the marsh edge for 5 years, GIS analysis spanning 15 years, and time-lapse photography for one year. The DWH oil spill directly increased erosion rates for 2 years and also left a continuing land loss legacy of cascading erosional effects lasting for 3+ years. The salt marsh shoreline eroded unevenly, leaving behind micro-headlands that eroded at an accelerated rate, leading to cascading heightened land loss along the study area. The shoreline erosion rates immediately after the DWH oil spill that included Hurricane Isaac were higher than any time period in the last 15 years, including after the hurricane seasons of 2004 and 2005. The oil depleted the resiliency of the marsh, making it more susceptible to erosion precipitated by natural disturbances, and leaving a land loss legacy much greater than the initial impacts.