Net Evaporation Rates and Mangrove Island Morphology: Caribbean Examples
Abstract
Mangroves are halophytic species of trees that grow in tropical and subtropical regions. At the interface between aquatic and terrestrial ecosystems, mangroves provide ecosystem services for coastal communities including coastal protection, biodiversity and blue carbon storage. Despite their importance, global mangrove extent is shrinking due to development and climate forcing. Specifically, changes in evaporation and precipitation can affect species zonation, mangrove mortality and increases in stressor concentrations such as sulfide. Consequently, in high net evaporation zones (where evaporation over-exceeds precipitation) such as Florida, mangrove islands tend to exhibit zonation and die off within the interior. In contrast, mangrove islands within a low or negative net evaporation zone, such as Belize, are typically large and grow to the maximum extent allowed by the carbonate platform. To test these observations further, we first use data from the NASA/Japan Aerospace Exploration Agency Tropical Rainfall Monitoring Mission (TRMM) and Woods Hole Oceanographic Institute to build an average net evaporation map for the Caribbean. For the purpose of this study, we focus on low-lying mangrove islands located far from anthropogenic influence. We develop a theoretical framework that describes mangrove vegetated as a function of the net evaporation rate, ocean salinity, and the hydraulic conductivity of the soil. This framework assumes a circular shape for islands, and a critical salt concentration beyond which black mangrove forest stands cannot survive. We estimate the hydraulic conductivity of the soil using the area of red mangroves in each island, using near infrared false color composite imagery from the European Space Agency's Sentinel-2 mission. Areas with a higher ratio of red mangroves are expected to have a higher hydraulic conductivity as their stressor concentration is never met. As we decrease hydraulic conductivity, salt tends to accumulate in the soil instead of flushing out of the system, resulting in a steeper succession of mangrove species from red to black, and die off in the interior. Preliminary model results coupled with data from a number of mangrove islands in the Caribbean support the initial premise that as net evaporation increases, mangrove vegetated area decreases.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP11E2085C
- Keywords:
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- 3020 Littoral processes;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS;
- 4316 Physical modeling;
- NATURAL HAZARDS;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL