Here the soil is washed regularly with sea water, which keeps changes in salinity and temperature to a minimum and continually supplies nutrients to the plants on the creek banks. The smooth cordgrass on the levees usually grows to its full height of 6 feet. Behind the levees is the low marsh which makes up most of the southern marshlands. Incoming tidal water overflows the banks of the numerous small creeks and floods the low marsh for several hours a day. The relatively shallow water moves slowly over the black mud, exposing the water to the sun's radiant energy.
Increased evaporation accompanies the elevated temperatures, causing a rise in salt concentration.
These conditions, coupled with the intermittent exposure to air and water, make the low marsh a less optimal living environment than the levee marsh. Here the cordgrass grows I to 3 feet high. With a slight rise in elevation, the low marsh gradually changes into high marsh with sandier soil which, during high tide, is flooded by barely enough water to cover the surface for an hour or less each day. Continued evaporation of the soil water makes the salt left behind a severe limiting factor for the plants living in this area. A slight elevation above the high marsh prevents tidal inundation except during spring and storm tides.