Salinity and Hydrology Control Evapotranspiration From a Degraded Coastal Swamp

Evapotranspiration is a primary water efflux from swamps, especially ones that have been impounded by roads, levees, or other human activities. There is generally a poor understanding of how meteorological conditions, salinity, flooding, and resulting physiological processes control evapotranspiration in wetlands. In this study, we investigate how natural variability of salinity, hydrology, and meteorological conditions affect evapotranspiration from a forested wetland. Strawberry Swamp, on Winyah Bay in coastal South Carolina, is a partially impounded swamp that receives periodic salinity influxes. Over the past 100 years, salinity has changed a tract of swamp forest into a marsh-shrubland-swamp gradient. Salinity remains a stressor to many of the species found in the extant wetland community. Latent heat fluxes were measured by Bowen ratio energy balance techniques and with an open-path infrared gas analyzer – eddy covariance system (EC150/CSAT3, Campbell Scientific, Inc.) at 13 m height, with the sampling footprint primarily comprised of wax-myrtle shrub-forest. Preliminary results show evapotranspiration corresponded with meteorological forcing, but latent heat exchange increased and sensible heat exchange decreased as the site water table dropped. These findings are indicative of increasing transpiration and decreased stomatal resistance as saline flood waters dropped, possibly below the root zone. These energy exchanges are fundamentally different from most terrestrial systems, in that more water availability appears to reduce the partitioning of energy to evapotranspiration.