Halophyte die-off in response to anthropogenic impacts on tidal flats

This study analyzed an abrupt change in halophyte populations, especially the annual plant Suaeda japonica. The boundaries and distributions of S. japonica and Phragmites australis were determined based on the decision tree classifier of TerraSAR-X, SAVI of Landsat ETM+, and density slicing of aerial photography. A large patch of S. japonica in the eastern parts of Donggum-do, South Korea, disappeared in 2007, while populations have been stable in the western parts of the island. To understand the reason behind the sudden die-off, mean sea level was analyzed based on gaged tidal data. Sedimentation rate was measured using Vernier caliper and RTK leveling data. Sedimentation rate between 2006 and 2007 was above the threshold at which S. japonica can germinate. After the loss of an 11-ha S. japonica patch from the eastern part of Donggum-do, sedimentation was accelerated because of a decrease in tidal current caused by a series of land reclamation projects. The increased monthly exposure duration due to continuous sediment accretion altered the type of salt marsh. Our results imply that accumulated effects from a series of coastal construction projects around Ganghwa-do can change not only tide and current hydrodynamics, but also sedimentation and erosion rates, which can cause large halophyte patches to disappear.