Problem
Does the change in elevation in a brackish salt marsh affect the distribution of marsh plant species?
How does diversity change over an elevation gradient in the marsh?
Introduction
This project deals with the zonation and distribution of marsh grasses over an elevation gradient. It consists of the collection of data on the frequencies of plant species, their heights, biomasses, percent covers, elevations, distances from marsh edge, salinities, total dissolved solids, and pH values. A comprehensive procedure has been designed to collect the above data in Deer City Marsh on Wye Island, with the initial assistance of Jill Rooth at Horn Point Environmental Laboratories. A modified version of the devised procedure will also be used to collect data in a marsh at Assateague Island.
This project was chosen because of an increased interest in the marsh restoration projects currently going on in the state of Maryland, as well as all over the United States. Marsh areas are rapidly declining because of increase in development world-wide and rising sea level. Knowing the living habitat of various species of marsh plants is essential to marsh ecology. This project will be the first step to determining the habitat qualifications of each plant species.
Background Information
The Marsh
Salt marshes are one of the most important ecosystems in the Chesapeake Bay. Formed between 10,000 and 12,000 years ago, salt marshes have plays a vital role in the Bay ecology. Salt marshes serve as buffers, protecting the shorelines from erosion by absorbing and dissipating the force of waves. Such marshes also absorb and filter contaminants from the land and produce fuel for living organisms.
Today, many problems are leading to the loss of hundreds of acres of marshland. Human expansion and development, such as the building of highways, railways, and roads built through marshland block the daily ebb and flow of the tide. Erosion from agricultural fields and construction projects accelerate the process of siltation, which in turn chokes vegetation and leaves marsh soil vulnerable to wave action.
In comparison to the fresh water marsh, the salt water marsh supports a less diverse community of vegetation. Salinity is a limiting factor in a salt marsh, because very few plants can survive the harsh conditions of a saline environment. Therefore, 90 percent (Silberhorn, p.8) of the salt marsh is inhabited by Spartina alterniflora, a plant accustomed to high salinity and heavy wave action.
The vegetation in a salt marsh is separated into zones. The edge of a salt marsh is inhabited by Spartina alterniflora (tall form-dark green), then Spartina alterniflora (short form-yellow green), and finally, a mixture of Salicornia spp., Limonium carolinianum, Atriplex patula, and Suaeda maritima. Five centimeters above the mean high tide one will find a mixture of Spartina patens and Distichilis spicata, with a few Fimbristylis spadicea, then Iva frutescens and Baccharis halimifolia, and finally, Myrica pensylvanica and Hibiscus palustris. There are other grasses that inhabit the marsh and they include Scirpus americanus, Phragmites australius, and Aster tenuifolius.
S. alterniflora (or Salt marsh Cordgrass) inhabits a medium saline environment and is found along the edges of marshes and other areas subjected to daily flooding. There are two forms of S. alterniflora. The tall form is approximately four to seven feet tall and has a dark green color. The short form is approximately one to two feet tall and has a yellow green color. The short form is usually found at a slightly higher elevation than the tall form, at the upper limits of the daily tidal influence. The tall form produces a flower in August, but the short form does not. Both forms of S. alterniflora produce seeds, but as far as reproduction goes, it relies mostly on underground rhizomes which send up young plants in nearby areas. The seeds that are not eaten by waterfowl remain lodged in the soil, where it is possible that they will germinate in the spring.
S. alterniflora has many adaptations that enable it to thrive in a saline environment. This unique marsh grass has the ability to regulate the salt concentration inside of its cells. By increasing the concentration of sodium chloride within its cells, it is able to maintain osmotic pressure and prevent water loss from the cell, which would kill the plant. The sodium ion has very little function in the plants cells and therefore does not disrupt important cell processes when it increases the amount of concentration.
The Salicornia genus (saltworts or glassworts) contains Salicornia virginica, Salicornia europaea, and Salicornia bigelovii. These species are approximately six inches to two feet tall and are found in the drier and sandier areas of the marsh. S. virginica is sometimes found mixed with the short form of S. alterniflora. They have fleshy, thick green stems that are the color of jade. The stems of the species in this genus have the ability to retain water, which helps to maintain water balance, which is necessary for survival in a highly saline environment. In the autumn, S. europaea turns a deep pink or ruby red, while the other two species change to a brown or yellow.
Limonium carolinianum (or Sea Lavender) is a plant containing basal rosettes of fleshy, leathery, smooth leaves that surround a stem leading up to spreading inflorescences of tiny lavender or blue flowers. The basal rosette stands two to four inches high and four to eight inches wide, and the flower stem stands approximately 1 and 1/2 to 2 and 1/2 feet tall. Sea Lavender is another plant that is tolerant of a highly saline environment. It is thought that its protection against this environment is a woody substance, called lignin, which is found in the plants epidermal cell walls.
Atriplex patula (sometimes referred to as Orach or Spearscale) is found just above the mean high tide. The plant has gray-green triangular shaped leaves. A. patula is lax and prostrate, often growing like a vine. The branches may extend more than three feet from the main stem. Orach produces small green flowers on the terminal ends of the branches, and also produces small green, triangular shaped fruit.
Suaeda maritima, or Sea Blite, consists of tiny, button-like, white flowers. The plant stands 3 to 12 inches in height and has leaves that are pointed and fleshy to the touch.
Spartina patens is a smaller member of the Spartina genus. It lives approximately five centimeters above the mean high tide and grows to a height between 1 and ½ to 5 feet tall. This grass has long, tapering leaves, which are rolled inwards towards the central stem and appear round. The flower itself is brown. This grass is commonly referred to as Saltmeadow Hay.
Found mixed with patens, one will find Distichilis spicata. Commonly called Salt Grass, it grows in the upper marsh to a height between 1 to 2 feet tall. The leaves of this plant are 1 to 5 inches long, trough shaped, and found arranged all in one plane. This plant invades new areas by way of rhizomes.
Fimbristylis spadicea, or Marsh Fimbristylis, is a grass often found in the upper marsh along with S. patens and D. spicata. The rigid stem of this plant is triangular in cross-section and emerges from dense set of round basal leaves. The stem leads up to a cluster of cylindrical, sometimes cone-shaped seed heads.
Iva frutescens, or Marsh Elder, lives in the upper levels of the marsh. Rarely growing over ten feet tall, this plant has a woody stem and thick, leathery leaves. Small flowers are arranged in a head and are often found on the terminal stems, appearing as green globular fruit.
The Groundsel Tree (Baccharis halimifolia) is found in the most upper limits of the marsh. This woody stemmed plant may grow to heights above 15 feet. The upper leaves on this plant are smaller, about ½ to 1 inch long, and lack teeth. The lower leaves are longer, approximately 1 and ½ to 2 and ½ inches long, and lack teeth.
Myrica pensylvanica, known to many as Bayberry, is a woody stemmed plant that is fragrantly spicy. The leaves are dark green in color and are approximately 2 and ½ to 4 inches long and 1 to 2 and ½ inches wide. This plant has waxy, bluish gray fruits and inconspicuous flowers are produced below the leaves on the stems.
Hibiscus palustris, commonly referred to as Swamp Rose-Mallow, is identifiable by its huge pink flower. The plant stands between 5 and 7 feet. H. palustris forma peckii (Crimson-eyed Rose-Mallow) is the white form of the above description. This white flower also contains a red center.
Scirpus americanus is commonly referred to as Olney Threesquare. The stem is three winged when cross sectioned and stands knee-high to above the height of a man. Blunt-tipped, brown spikelets appear ½ to 1 inch below the tip of the stem. When ripe the spikelets become a brownish-gray.
Phragmites australius, stands higher than a man to three times as high. The plant contains alternating grayish-green leaves that are approximately two feet long and two inches wide. At the top of the plant there is a large seed or flower cluster, approximately 1 and ½ feet long. Each individual spikelet on the seed head contains 3 to 7 flowers with long hairs between the flowers. When young the seed head is often purple in color, but when old the seed is whitish-brown in color.
Aster tenuifolius, or the Perennial Salt Marsh Aster, stands 1 to 2 feet high. The flower is purple or white in color, with dimensions of ½ to 1 inch across. The leaves are very slender and fleshy to the touch.
Methods and Techniques
Elevation:
The elevation in a marsh is a dominant factor in the distribution of grass species. Factors induced by elevation are the extent of the tidal influence, water saturation in the soil, and soil salinity. For measuring elevation, one needs to construct an elevation meter (for the building instructions, see Part I, Letter B of the procedure). The elevation meter allows water to run through the clear tube whenever one side is lifted higher than another. By finding the difference between the two readings, one will know the change in elevation over a certain area.
Above Ground Biomass:
Above Ground Biomass is defined as the dry mass of all living plant species found in a given sample area where the shoots emerge from the ground to the top of the shoots. The root and the subterranean portions of plants are excepted. For accuracy, the biomass samples are dried to remove additional mass of water. The Above Ground Biomass indicates the size, infers general health, and gives a point of comparison other than the frequency count.
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