15 Salt marshes
The single most important ecological feature of salt marshes along coastal rivers is their immersion/exposure cycle. The lower the marsh, the longer the surface is immersed in tidal waters. Low marshes in North Carolina are dominated by smooth cordgrass (Spartina alteriflora). These plants form a monoculture in the areas of the marsh that are regularly flooded by salt water. They have salt glands on their stems that excrete salt. Areas slightly higher in the marsh are dominated by the species you saw in Figure 13, black needle rush (Juncus roemarianus).
These plants have a very high tolerance for salinity variation. In the high marsh, the salt content of the soil goes up when freshwater evaporates on hot, dry days. As a result, the soil salinity may be more than double that of nearby estuarine water. When it rains, of course, the soil salinity drops rapidly, sometimes to levels near fresh water.