MEASURING COASTAL LOUISIANA WETLAND RESILIENCE TO RELATIVE SEA-LEVEL RISE USING LARGE-SCALE REGIONAL MONITORING DATA

Coastal wetlands are critical for both ecosystem services and coastal protection from storm surge, and their response to accelerated sea-level rise is a key issue in long-range coastal management. In coastal Louisiana, the question is whether wetlands are able to prevail while facing some of the world’s highest rates of relative sea-level rise (RSLR). Here we analyze a regional dataset of unprecedented size, derived from 239 rod surface elevation table-marker horizon (RSET-MH) stations established within the framework of the Coastwide Reference Monitoring System, to understand wetland resiliency potential. Measurements of vertical accretion (VA) and surface elevation change (SEC) are used to determine shallow subsidence (SS). SS is then incorporated into an overall RSLR (SS + deep subsidence + sea-level rise) value at the wetland (mostly marsh) surface. Comparison of VA rates to overall RSLR rates provides insight into potential wetland resiliency as wetlands must gain elevation at or above the rate of RSLR in order to survive. Our results show great variability in VA rates from site to site, emphasizing the importance of a large data set to elucidate coastwide conditions. We find that almost half of Mississippi Delta sites are experiencing an elevation deficit compared to local RSLR rates while conditions in the Chenier Plain are much worse, with nearly three-quarters of sites falling short. Considering the expectation of continued acceleration of global sea-level rise, the longer term future of Louisiana’s marshes is therefore highly uncertain.