LAND LOSS AND LARGE SCALE DISTURBANCES
Boom surrounding a Louisiana marsh to try and prevent oil from the 2010 Deepwater Horizon oil spill from reaching land.
Knowing the historical resiliency of a system and how it has changed with human impact, as well as how the system responds to disturbances, is important in determining strategies for restoration and management.
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, and agricultural impoundments, leading to a decreased resiliency to land loss.
I studied the direct and indirect impacts of the Deepwater Horizon (DWH) oil spill and hurricanes 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 two years and also left a continuing land loss legacy of cascading erosional effects lasting for over three years. The salt marsh shoreline eroded unevenly, leaving behind micro-headlands that were lost at an accelerated rate. This uneven shoreline led to cascading heightened land loss along the study area.
Multiple disturbances also lead to negative synergistic effects, as the DWH oil spill increased the land loss caused by a hurricane. 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.
Effects of both anthropogenic and natural disturbances can last much longer than the initial impact. In fact, the cascading indirect effects can many times be larger than the initial; ensuring that disturbances are studied on the appropriate spatial and temporal scale is paramount to capturing the full impact of an event. Healthy coastal ecosystems can withstand stressors such as sea level rise and hurricanes, but this research has shown that the resiliency quickly diminishes as human modification increases.