Wetlands and Marshes

Salt marshes with lighthouse and Savannah River in the background
A marsh is a wetland where the main vegetation is non-woody plants like grasses and succulents. There are both fresh and salt water marshes. In a salt marsh, salt water floods the area at high tide and creates different zones for a diversity of plants and animals based on the elevation of the land and the height of the water. Because many plants and animals cannot tolerate high levels of salt, the salt water flooding limits what can survive in the marsh.

Because of Georgia’s low coastal elevation and high tidal range, salt marsh habitat covers a large amount of area along the Georgia coast - an estimated one-third of all the salt marshes on the east coast. The one hundred miles of Georgia’s coast has approximately one-half million acres of marshland, each marsh ranging from 4 to 8 miles wide.

Twice a day, the tides along the coast rise and fall 6 to 8 feet, bringing in nutrients, oxygen, water, and even animals, and carrying away wastes. The salt marsh is one of the most productive ecosystems in the world, and plays an important role in the ecosystem by providing habitat for animals, reducing floods, and filtering the water.
The marsh is a harsh environment for wildlife, and few animals actually live in the marsh. The temperature can change quickly with the shifting tides, and the inconsistent influx of salt water creates and irregular expose to air and salt water. Most wildlife are visitors in search of food or shelter. Many, such as crabs and shrimp, enter the marsh as plankton (microscopic drifters) and leave as adults. The shallow tidal water of the marsh is home to the young of many marine species before they return to the open sea. Other organisms, such as periwinkle snails and oysters, enter to stay. Each has adaptations to help them survive in the changing salt marsh environment.
FOPU salt marshes

The salt marsh has three major zones, defined by their vegetation type which is controlled by their elevation and daily water coverage.
Low Marsh High Marsh Transition Zone
The low marsh makes up the majority of the southern marshlands. It is flooded with salt water for 6-8 hours per day when the incoming tides overflow the banks of the small surrounding creeks. Because of the ponding water in the low marsh, the sun is able to increase the temperature of the water, which increases evaporation, leaving behind large amounts of salt. A natural monoculture of Spartina alterniflora (Smooth Cordgrass) is often present as few other plants have adapted to survive the harsh and irregular conditions of the low marsh. Dark, squishy soil with a distinctive musky smell is characteristic of the low marsh because of the bacteria hard at work decomposing dead plant material and turning it into nutrients for plants and planktonic creatures. Low marshes are populated with species like the mud fiddler crabs, purple marsh crabs, oysters, ribbed mussels, worms and snails. After a slight rise in elevation, the low marsh gradually transforms into high marsh. The high marsh has sandy soil that is covered with water only at the highest tides, which occur when the moon is new or full and during stormy weather. Much of the surface water evaporates, exposing the soil surface is to air for long periods of time, increasing salt concentrations and making it difficult for many plants to survive in the high marsh. Bare sandy areas known as salt pans may develop in the high marsh where the salt concentration has become great enough to prevent all plant life. The high marsh has a high diversity of plants including sea oxeye, glasswort, needle rush, and saltwort and is home to sand fiddlers and wharf crabs. A small transition zone, referred to as the marsh border, separates the forest from the marsh. During large storms and very high tides, the marsh border gets flooded by salt water, so the plants in this area, including cedars, palms, palmettos, and groundsel tree, are all salt tolerant, but require less of a salt tolerance than plants in the marsh areas because they also receive fresh water inputs from rain and runoff from nearby uplands.

Last updated: February 11, 2020

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