EXPLORING THE RELATIONSHIP BETWEEN MANGROVE ISLAND MORPHOLOGY AND ASYMMETRIC STRESSOR CONCENTRATIONS: COUPLING NUMERICAL MODELING WITH FIELD OBSERVATIONS

Mangroves are facultative halophytes thriving in tropical and subtropical coastlines. Mangroves provide ecosystem services such as coastal protection, blue carbon storage and biodiversity. Despite their global importance, mangroves are currently under threat due to anthropogenic influence and climatic forcing. In certain regions, mangroves are susceptible to high evaporation rates, which reduce freshwater availability, and therefore lead to an increase in soil interstitial salinity and sulfide. Despite their ability to thrive in saline environments, mangroves die off when a certain salt concentration threshold is surpassed. To better understand the relationship between net evaporation rates, salinity, and mangrove response, we built a database of mangrove low-lying islands in the Caribbean, a region with a wide range of net evaporation (i.e. evaporation – precipitation) rates. Additionally, we developed a model that relates mangrove vegetated surface area with the hydraulic conductivity of the soil, ocean salinity, and net evaporation rates. We estimated evaporation rates using OAFLUX evaporation datasets from the WHOI and precipitation datasets from the Tropical Rain Monitoring Mission. Hydraulic conductivity was calculated as a function of the area of red mangroves using remote sensing techniques. Assuming a symmetric salt concentration profile across islands (i.e., salt concentration on both sides of islands is equal), we find a strong relationship between estimated and observed vegetated area. We also find, however, that a number mangrove islands can be exposed to different salinity levels on each side, which affects the location of the die off area within the island. For example, there are mangrove islands in Venezuela with one side facing the lagoon and the other face the open ocean, which results in a shift of the dye off towards the lagoon side, which has higher salt concentration. Additionally, there are a number of mangrove islands in Florida bay that are exposed to large gradients in salt concentration around them due to inputs of freshwater from the Everglades. Consequently, die off in these islands is also shifted towards the side with higher salt concentrations. We find good agreement between the magnitude of the shift estimated by the model and the field observations.