Quantifying Mississippi Delta Wetland Resilience 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 the Mississippi Delta (MD), the question is whether wetlands are able to prevail while facing some of the world’s highest rates of relative sea-level rise (on the order of ~10 mm/yr). It is important that coastal restoration policy decisions be made after considering the most robust scientific data available to maximize potential impact and efficacy. Here we analyze a regional dataset of unprecedented size, derived from 168 rod surface elevation table-marker horizon (RSET-MH) stations established within the framework of the Coastwide Reference Monitoring System, to determine present-day surface-elevation change (SEC) rates and to understand the relative contributions of vertical accretion and shallow subsidence to SEC. Comparison of SEC rates to RSLR rates provides insight into potential wetland resiliency as wetlands must gain surface elevation at or above the rate of RSLR in order to survive. Our results show great variability in SEC rates from site to site, emphasizing the importance of a large data set to elucidate coastwide conditions. While 93% of sites exhibit at least some surface elevation gain, we find that the mean SEC rate is 6.6 ± 7.9 mm/yr and only 21% of sites are gaining elevation at a rate that meets or exceeds the mean RSLR rate. We conclude that over this short timescale (5 to 10 years), only a small portion of MD wetlands is somewhat resilient to the high rates of RSLR.