THE SALTMARSH:

At first glance, the Sapelo saltmarsh appears to be composed only of smooth cordgrass (Spartina alterniflora). There are numerous other plants present also, but Spartina is dominant in most of the lower lying, tide dominated areas. Closer inspection will show that the Spartina in the vicinity of the creeks and levees is much taller and more luxuriant than that on the marginally higher ground, where growth is shorter and more sparse.

A number of factors may be influential in determining the height and luxuriance of Spartina. The pattern of water flow through the creek bank is active and the mud is “flushed” by tidal action even though it remains largely anaerobic (all oxygen is used up). On the other hand, the water trapped in the mud of the high marsh behind the levees is not flushed out on neap tides and becomes more saline and stagnant with time. Nutrients are used up, and toxic substances such as sulphide build up. Differences between the creek banks and the high marsh are evident not only in the above ground growth, but also in the root growth and the bacterial interactions occurring within the soil itself. All marsh soils are anaerobic except for the surface few millimeters and around the roots and burrows. The soil bacteria responsible for the breakdown of accumulated organic matter require just such an anaerobic environment. However the rate at which such breakdown occurs and hence the rate at which plant nutrients are made available for new growth appears to be related to the water flow characteristics and the rate of removal of waste products.

Nitrogen and phosphorus are two major nutrients required by plants. Phosphorus is readily available both in the soil and in the tidal waters. Nitrogen is not so freely available. Despite the fact that nitrogen gas is the most abundant element in the air, it is not usable in that form. Higher plants require it to be converted to ammonia, nitrate or nitrite before they can use it. Blue green algae on the marsh surface, and nitrogen transforming bacteria within the soil, convert nitrogen into conveniently utilizable forms. Nitrogen is ultimately exported from the saltmarsh in the form of dissolved and particulate nitrogen-containing organic matter. These are important nutrients for the algae and simple animals of the water column.

Spartina is predominant largely because it is so well adapted to its environment, having developed with time the physiological mechanisms which enable it to cope with the estuarine salinity and temperature ranges. The only other plants in the lower marsh areas are the microalgae already referred to, such as blue greens and diatoms, and the occasional occurrence of such simple macroalgae as sea lettuce (Ulva lactuca).

Generally, a little higher on the marsh, glasswort (Salicornia sp.) plants become more obvious and saltgrass (Distichlis sp.) also appears as patches amongst the stands of Spartina. The black needle rush (Juncus) forms thick stands and is readily distinguishable by its fine stalks, sharp points and greyish appearance. Sea-purslane (Sesuvium sp.), saltmarsh bulrush (Scirpus sp.), sea ox-eye (Borrichia sp.) and the saltmarsh cordgrass (S. patens) are all present in the “high marsh”, an area of higher ground, but shorter Spartina growth. Another feature of this area is the presence of salt barrens, a highly saline area where nothing but diatoms grow.

The hammocks are areas of high ground above all normal tides and support tall vegetation such as redcedars, wax myrtles and yaupon holly (Ilex vomitoria). The hammocks stand out conspicuously from the low lying marsh, both in terms of height and difference in the color of the vegetation. Pumpkin and Fishing Hammocks on the Duplin River are Pleistocene bases surrounded on three sides by Holocene marshes.