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Browse  abstracts

The Interplay Between Salt Concentration, Mangrove Vegetation, and Die-Back: A case study of islands with complex geometries in Southern Puerto Rico

Isamar Cortes, Montclair State University Montclair , United States. cortesi1@montclair.edu

Although mangroves provide several beneficial ecosystem services, such as blue carbon storage, coastal protection, and nursery habitats, they rapidly decline due to human development and climate change. In particular, in areas in the Caribbean, such as Puerto Rico, climate change will likely lead to an increase in evaporation over precipitation. Such an increase in drought-like conditions will drive porewater salinity to increase exceeding the threshold beyond which mangroves can survive. To improve our understanding of this interplay, we developed a numerical model using the Landlab Python library that describes the spatial distribution of vegetation and die-back in low-lying and undeveloped mangrove islands where freshwater inputs come solely from precipitation. We apply the model to a series of islands with elongated and asymmetric die-backs in La Parguera, a bay environment in southern Puerto Rico. Our model can explain the die-back shape and location for all islands as a function of the average net evaporation rate (i.e. evaporation – precipitation), the island's edge water salinity, and the mangrove soil dispersion coefficient, or the porewater exchange through tidal flushing. We gathered evaporation data from the Woods Hole Oceanographic Institute's OAFLUX project and precipitation data from the Tropical Rain Monitoring Mission, and quantified the soil dispersion as a function of the area of red mangroves, which was calculated via satellite imagery analysis. Additionally, we infered the outer edge salinity from the maximum canopy heights, gathered from Goddard's LiDAR, Hyperspectral, and Thermal Imager. In our model results, some islands presented a subtle bayward shift of the die-back. This can be explained by a higher island's edge water salinity on the landwards side, where bay depths are shallow and mixing with the rest of the bay is low. This spatial difference in salinity was consistent with the differences in canopy heights derived from LiDAR, and fell within the range of values reported in the literature. This portable modeling framework can be applied to other low lying mangrove carbonate islands with complex geometries.