Altamaha Basin > Hydrology > Water Quality > Environmental Threats > Human Impacts > Cultural Features > Coastal Habitats > Tributaries > Plants > Animals > Sapelo Island |
||
 |
||
|
The intertidal habitats consist of unvegetated creek banks and mud flats, including small tidal creeks that drain completely at low tide, and the vegetated marsh surface, which contains several distinct zones (see figure above). Plant zonation is controlled by a combination of interacting factors including elevation and hydrology. Although the marsh surface is covered by water less than half of each tidal cycle, there is a perched water table which maintains the sediments of all but the highest intertidal elevations in a near waterlogged condition. Near creek channels the hydraulic head created by difference in the level of the water table and water level in the channel results in a slow seepage of interstitial water through the creekbanks into the channels. At a distance from the creeks, however, there is little subsurface water movement except that due to water loss near the surface via evaporation and transpiration. That water is replenished by the subsequent flood tide, but the difference in water exchange near creeks and at a distance from them results in large and constant differences in redox potential, salinity, sulfide concentration and plant productivity. |
||