Wetland accretion rates along coastal Louisiana: Spatial and temporal variability in light of Hurricane Isaac’s impacts

Coastal wetlands in southern Louisiana are vanishing rapidly due to a host of environmental stressors including sea level rise, subsidence, and lack of sediment deposition. Since these wetlands provide significant environmental and economic value, their stability and preservation are critical issues for scientists and policyholders. A key question concerns the spatial and temporal variability of wetland accretion rates, particularly the role of hurricanes as an agent in wetland sedimentation. Since 1996, thousands of wetland accretion measurements have been determined at 390 sites across South Louisiana as a result of a regional monitoring network (Coastal Reference Monitoring System, or CRMS), under the collaboration of the Louisiana Office of Coastal Protection and Restoration (CPRA) and the United States Geological Survey (USGS). We utilized this voluminous dataset to analyze the spatial and temporal patterns of wetland accretion by mapping the rates during three time periods around the landfall of Isaac, a category 1 hurricane, in August 2012. By analyzing sites with sampling dates no more than 7 months from establishment, the results indicate that wetland accretion rates averaged about 2.89 cm/yr from stations sampled before Isaac, 4.04 cm/yr during the period containing Isaac’s impact, and 2.38 cm/yr from sites established and sampled after Isaac. Wetland accretion rates determined from the period containing Isaac’s impact were 40% and 70% greater than rates before and after the hurricane, respectively. Wetland accretion rates associated with Isaac were highest at sites along the Mississippi River and its tributaries instead of along the path of the hurricane, suggesting that freshwater flooding from rivers and streams, rather than storm surge, is the main mechanism responsible for increased wetland accretion.