Mangrove forest-atmosphere interactions in the Florida coastal Everglades

This presentation will report two new findings concerning mangrove forest-atmosphere interactions. First, we will report the unique hydrologic and local climate forcings deduced from eddy covariance studies for a mangrove forest in the Florida coastal Everglades. These forcings control and contribute to unusually high rates of forest carbon assimilation and energy partitioning patterns different from those observed for terrestrial forests. While mangroves are inundated with and surrounded by water, fresh water is precious and must be manufactured from a saline environment. Consequently, these forests exhibit one of the highest water use efficiencies among the C3-plants. With transpiration rates limited, forests respond by converting most of the available energy into sensible heating. Second, we will present results obtained from a mangrove biophysical model that predicts for the first time the onset of midday photosynthesis deactivation under high (>1000 W m-2) radiational loads, warm (>30oC) air masses, and a hypersaline soil environment. The model captures the negative feedback loop of reduced evapotranspiration, elevated leaf temperatures (>35oC), and nearly negligible rates of foliage carbon assimilation in the forest crown. Still, mangroves represent a large sink for atmospheric carbon dioxide when assimilation rates are integrated over the period of days and an entire growing season. Also, feedback processes occur less frequently during fresh water inputs from upstream flow or from local precipitation. As pore water salinity declines, the model predicts higher rates of transpiration, lower leaf temperatures, and higher carbon assimilation rates. The model reproduces flux measurements of water vapor, carbon dioxide and energy.