Exploring the Role of Evaporation and Precipitation Rates on Mangrove Island Morphology

Mangroves are salt tolerant species of trees that grow in tropical and subtropical environments. Mangroves provide ecosystem services to societies along marine environments, including storm protection, coastal biodiversity, and blue carbon storage. However, as the importance of mangrove ecosystems has become clearer over recent years, their coverage has been reduced through mismanagement and climate impacts. For instance, in terms of climate warming, mangroves cannot survive under abnormally high rates of net evaporation when soil stressor concentrations (e.g., sulfate, sulfide) increase above threshold conditions. To study the effects of this climate driver phenomenon on mangrove islands, we are examining mangrove islands, which typically grow on carbonate platforms, isolated from human activities. In high net evaporation zones (where evaporation is greater than precipitation) such as Florida, Bahamas or Puerto Rico, the soil moisture potential is altered by high net evaporation, which affects mangrove islands by undergoing species zonation and die off within the interior. In contrast, mangrove islands within a low or negative net evaporation zone (relative to precipitation), such as Belize, are typically large and grow to the maximum extent allowed by the carbonate platform. We quantified this phenomenon with a simple mathematical model that relates island vegetated area with the rate of net evaporation, the hydraulic conductivity of the soil, and the salinity threshold for mangrove growth (used as a proxy for soil stressor concentration). We estimated net evaporation rates in the Caribbean using existing meteorological data for the last ~20 years, and the hydraulic conductivity as a function of the area of red mangroves versus black mangroves, which requires remote sensing analysis. Areas with a greater proportion of red mangroves can tend to have higher hydraulic conductivity while those with a greater proportion of black mangroves tend to have lower hydraulic conductivity. Preliminary model results coupled with data from a number of mangrove islands in the Caribbean support the initial premise that an increase in net evaporation reduces mangrove vegetated area. Future work will focus on expanding the mangrove island database and better constrain the input parameter values with local observations