THE BIOLOGY OF SALT MARSH
Salt marshes began to appear in the United States approximately 50,000 years ago with the retreat of the Laurentide Glacier, which stretched across northern Canada to the northern United States. As the climate grew warmer, the glacier began to melt and the water eroded the bases of many forests, forming streams and rivers. Moreover, the water carried with it a new soil that contained a mixture of rock flour and sand; it began to settle, mixing with the mud of many uncovered areas, and the amalgam created a fertile environment where vegetation could take seed. 
Torrential rains, along with the melting of once-sheltered ice patches in the north, caused the level of the sea to rise. As the heavy ice disappeared, the land rose up. Marsh development began once the glacier ceased melting and the land finished its rapid rebound. At this point, plants as well as the climate and sea level began to alter the face of the earth. Birds began to settle along the shorelines, carrying with them the seeds of different plants. Where the birds came to rest seeds were deposited, and soon salt marsh vegetation including Spartina alterniflora and Spartina patens germinated. In some areas the fledgling marsh was drowned by the sea, while elsewhere its growth continued as rivers and streams brought in sediment from the recently exposed earth. Plant roots bound this sediment into a firm peat, which in turn grew and increased the level and size of the marshes. Once the marsh reached the high-water level and above, S. patens established itself prominently in the higher areas of the marsh. 
These grasses, along with the increased number of animals moving into the marsh, caused decomposing organic matter to continually form a layer of peat. The new layers formed fast enough to keep the marsh rising at the same level as the sea, while compressing preceding layers. As the layers were crushed under the weight of the new peat, the marsh expanded outward, encroaching upon the edges of solid land. Fresh-water plants were replaced by marsh grasses that could better withstand the high salinity of bay and ocean waters. This process continued as the marsh expanded and storms blew saltwater inland, killing fresh-water plants. As a result, with no barrier between the saltwater and the land, the sea continued to encroach, and Spartina grasses flourished in conjunction with the marshes. Despite the fact that the marsh is well established, gradual and continual changes still occur that alter both the environment and landscape. Salt marshes expand according to the rate of plant growth and the supply of sediment as they adjust to changes in sea level. 
The effects of the glacier age varied according to the location of the marshes, falling into two categories, glaciated and unglaciated. The area between the St. Lawrence River south to the northern edge of New Jersey is part of the glaciated coast. The marshes that existed here were destroyed by the glacier as it moved south; once the glacier melted, the marshes were re-established but smaller in size. No such significant areas are found until the Bay of Fundy, which includes fifty square miles of salt marsh (Fig. 6). A portion of this marsh, near the Tantramar River, has been diked since the early seventeenth century. Large masses of marsh along the Eastern Seaboard do not reoccur until New Hampshire and they only encompass twenty square miles. These marshes continue sporadically along the coast in Massachusetts, Rhode Island, Connecticut, and down into New York. 
The unglaciated coast runs from southern New Jersey to Florida. The only major break in the marshes along here is the Chesapeake Bay; marshes are frequent along the eastern side of the bay but not the west. The most abundant example runs from Albemarle Sound in North Carolina to the northern coast of Florida. Most of the grass found in these southerly marshes consist of S. alterniflora and a coarse black rush called Juncus roemericanus. 
The marsh through here is intact because it was never covered by ice. Without the pressure from the glaciers, the soils and sands of the marshes were not scraped away, nor was its bedrock exposed. Moreover, the rivers carried great amounts of sediment that helped feed and extend the marshes. In the Delaware Bay region there are approximately 350 square miles of salt marsh; the New Jersey side consists more of S. patens, the Delaware side of S. alterniflora (Fig. 7). 
As with any marsh, that along New Jersey's Atlantic and Delaware Bay varies in elevation depending upon sea level. Some of the marshland is only inches above sea level, while others could be several feet higher (Fig. 8).  The lowest marshes are inundated with every high tide. Only sedge grass survives in this environment, making the area worthless agriculturally. An increase in elevation means that the land will only be slightly covered with water at every high tide, allowing nutrients to soak into the soil and the agricultural quality to improve. 
Moving toward the upland where the marsh is high enough that it is not covered by daily tides, sedges and joint grasses survive. If there is a slight rise in the high-tide level due to wind, storm or moon changes, the marsh will be covered. The burrowing action of the resident fiddler crabs allows for drainage, as needed, which prevents stagnation and mosquito infestation. 
The marsh closest to the upland is only fully flooded during extreme spring tides and storm tides. Salt marsh vegetation such as Spartina grass and Juncus grows on this level. This marsh attracts many types of animals besides fiddler crabs because flooding is infrequent. Creeks and streams dissect this marsh at various intervals. Waterways vary in width and usually have sharply defined banks, making them excellent outlets for ditches. Unfortunately, the natural drainage of these marshes is limited, and stagnating water attracts mosquitoes. The presence of valuable marsh grasses and the waterways with sound banks, however, make these marshes ideal for reclamation. Once reclaimed, the improved drainage decreases the stagnate mosquito breeding grounds. 
Spartina grass, especially S. patens, is perhaps the most important feature in the higher-level salt marsh (Fig. 9). In addition to its roots holding the soil together, the dead grass decays and becomes part of the peat that helps the marsh expand. S. alterniflora is a big, coarse grass that can grow up to 10' tall with leaves 1/2" wide at the base (Fig. 10). S. alterniflora grows near creeks and the outer edges of the marsh; thus, it is found in both the second and third types of marshes, those exposed to tidal currents more often than S. patens. S. patens is a fine, small grass that grows to be no more than 2' tall. It is often the most valuable grass, and the one used as salt hay. Because of its location in the marsh, the previous years' growth is not washed away by the tide as often as that of S. alterniflora. Instead, the dead grass creates a protective covering that keeps the soil moist and fertile. 
Both S. alterniflora and S. patens have adapted to a lack of oxygen in the soil and the high salinity of the surrounding environment. The process of osmosis within its cells has much to do with the fact that the plant can survive a salt-marsh environment. The solution in the cells has adjusted by increasing the amount of salt in its internal water; the amount of salt within the cell is a higher concentration than that found in water absorbed from the air. As a result, salt-marsh plants selectively absorb sodium chloride from the moisture in the air to keep the cells from exploding and the plants from wilting.
Though Spartina grass has little competition, other marsh grasses exist. Many of these, as well as the Spartina grass, are referred to generically as "marsh grass," "salt hay," and "salt grass." The Latin and Greek names associated with the prominent grasses include Distichlis, Juncus, and Salicornia. The different species within these genera include Distichlis spicata, Juncus gerardi, Juncus roemerianus, Puccinellia phryganodes, Avicennia nitida, and Rhizophora mangle (Fig. 11). Other genera with several different species present in the marsh include Iva, Sabatia, Salicornia, Atriplex, Suaeda, Salsola, and Chenopodiaceae. 
Living among the salt-marsh grasses are many types of animals, characterized by their ability to dig down into tidal flats and marsh-creek banks. The ability to burrow allows them to seek shelter in a relatively stable environment. The animals who live here year-round include razor clams, quahogs, clam worms, soft-shelled clams, lugworms, and burrowing shrimp, to name a few. Other creatures associated with marsh life are various shorebirds, such as rail-birds and ospreys; ducks, including wood-ducks and teals; reptiles, such as snapping and diamond-back turtles; mammals, including raccoons and muskrats; and insects, such as mosquitoes and greenhead flies.  Like indigenous vegetation, these animals have adapted to conditions specific to the salt marsh: changes in temperature and salinity, and periods of exposure and lack of oxygen at low tide. 
Despite their ability to adapt to salinity and water conditions, marsh environments are fragile and are adversely affected by fluctuations caused by human intervention and natural conditions. According to Ralph Tiner's Wetlands of New Jersey, human actions that destroy this fragile environment include discharging hazardous materials, and infilling dredged soil for roads, highways and other commercial ventures. In addition, dredging and stream channelization for navigation channels, digging of drainage ditches for crop and timber production and mosquito control, and mining of the soil for sand and gravel have negative effects. Tiner includes the building of dikes, dams and levees for flood control, cranberry production, water supply, and storm protection as being threatening to wetlands. While this is true, in the case of land reclamation for agricultural purposes, the land can be returned to wetlands once the dikes, dams or levees are removed. He adds that "marsh creation and restoration of previously altered wetlands can also be beneficial." However, marshes that have been filled, polluted, or damaged are permanently lost. In addition to human activity, wetlands are also damaged by the natural rise of sea level, droughts, storms, erosion, and muskrats and other burrowing animals.