IMPACTS OF SALINITY ENCROACHMENT ON COASTAL MARSHES IN SOUTHERN LOUISIANA

Anthropogenic climate change has exacerbated sea level rise in coastal Louisiana, causing vegetation dieback from subsidence and saltwater intrusion. Tribal communities that reside along the Louisiana coast have been made increasingly vulnerable as a result of vegetation dieback, which occurs when coastal land becomes too wet or salty for certain species to grow. Saltwater marshes protect coastal communities from storm surges and wave erosion, absorb excess nitrogen and phosphorus runoff which prevents algal blooms and hypoxia, and provide habitat to hundreds of aquatic and terrestrial organisms. Here, we present our findings of vegetation dieback and salinity encroachment at the locations of three tribal communities based on remote sensing: the Grand Caillou/Dulac and Isle de Jean Charles bands of Biloxi Chitimacha Choctaw, and Point au Chien. We determined changes in the Normalized Difference Vegetation Index (NDVI) and Salinity Index (SI) from Landsat imagery from 1987-today (May-August). Using 1991 as our baseline, we distinguished areas that were consistently vegetated (NDVI > 0.1) throughout our study period from those that transitioned to bare surface or water (NDVI < 0.1). From 1991 to 2020, NDVI significantly and gradually decreased across all consistently vegetated sites at each of the field locations, indicating a decrease in vegetation health. In 1999, 6% of Dulac experienced decreases in vegetation due to salinity increases and 6% experienced inundation or die-off. By 2011, 37% of Dulac experienced saltwater intrusion, and 22% experienced inundation or die-off. Although the study areas need to be expanded to provide a more robust sense of vegetation change across the Louisiana coastline, our results indicate that the impacts of sea-level change are increasingly stressing marsh habitats in ways that are magnifying the vulnerability of tribal communities.