Microtidal wetland losses and hydrologic stressors as sea level rise accelerates in the Gulf of Mexico: running with Alice

Abstract Global sea level rise (SLR) is a widely appreciated threat to coastal wetlands. Modeled estimates of SLR thresholds beyond which coastal wetlands convert to open water suggest that landscape scale estimates of wetland loss vary with geomorphic setting, upland barriers to migration, vegetative tolerances to flooding, sediment supply, and tidal ranges among others. Landscape scale examples from long-term observations are sparsely available but needed to interpret the significance of data collected from small and large sampling plots, after occasional storms, of various observation lengths, and regional SLR variations. A long-term data set in 15 min Quadrangle maps from the northern Gulf of Mexico is available to evaluate some of these threshold factors. Dredging for canals is the dominant stressor for losing 27% of the 14,501 km 2 of microtidal coastal lands existing in 1934. There is a strong linear relationship between dredging canals and wetland loss from 1934 to 1990. Compared to 1980 to 1999, SLR in the GOM doubled from 2000 to 2022 at a steady 10 mm yr −1 . This recent doubling presented an opportunity to test if there was a SLR impact effect on wetland loss vs. canal density from 1934 to 2016 compared to from 1934 to 1990. No acceleration in the slope or change in intercept was observed as SLR accelerated and there was a coincidental rise and fall in both coastal wetland loss and the number of dredging permit issued in the last 95 years. We conclude that a 10 mm yr −1 SLR has not (yet) become a synergistic stressor on wetland loss on this coast, where human-driven effects on wetland loss continue to accumulate. We anticipate that the legacy effect of canal dredging will eventually work together with SLR to accelerate the rate of wetland loss.