An Examination of Marsh Grass Diversity in a Brackish Marsh

Abstract

The salt marsh is an important ecosystem in the Chesapeake Bay. Salt marshes serve as buffers, protecting the shorelines from erosion by absorbing and dissipating the force of waves. These marshes also filter contaminants from the land and produce fuel for living organisms. Industrial expansion such as the building of roads, farming processes, and construction projects block the daily ebb and flow of the tide. This leaves the marsh extremely vulnerable to wave action, encouraging erosion (Latane, 1989).

The vegetation in a salt marsh is separated into zones. Along the edges of a salt marsh, lives Spartina alterniflora (tall form-dark green), then S. alterniflora (short form-yellow green), and a mixture of Salicornia spp., Limonium carolinianum, Atriplex patula, and Suaeda maritima. Five centimeters above the mean high tide, one finds a mixture of Spartina patens and Distichilis spicata, with a few Fimbristylis spadicea, then Iva frutescens and Baccharis halimifolia, and Myrica pensylvanica and Hibiscus palustris along the back extent of the marsh. Other grasses that inhabit the marsh include Scirpus americanus, Phragmites australius, and Aster tenuifolius.

The purpose of this project was to determine the factors involved in dividing the marsh vegetation into zones. A comprehensive procedure was designed to examine all aspects of the marsh, including elevation, salinity, pH, total dissolved solids, temperature, and their affects on the distribution and diversity of each species found. A salt marsh at Wye Island NRMA was chosen because of its accessibility and limited intrusion of P. australius.

From the data collected, the frequencies of S. alterniflora (both forms), S. patens, D. spicata and A. tenuifolius were statistically proven to have a relationship to elevation, with a 95% degree of certainty. At certain elevations, the frequencies of these plants tended to be higher, or lower. I. frutescens, F. spadicea, and P. australius were not found to be significant proving that no elevation is preferred by these species.

To calculate species diversity, the Simpson index was used. As calculated, the diversities at each of the eight data stations were all below 0.5 on a zero to one scale. The diversities failed to prove a correlated change over the elevation gradient. However, the transects did not run the entire distance of the marsh possibly affecting the diversity correlations with elevation. Had the transects been extended beyond the marsh meadow, up, into the surrounding woods, a significant drop in salinity and an increase in diversity could have been observed. Salinity is certainly a limiting factor in plant distribution because only certain species can tolerate a halos water or soil environment. Diversity would be consequently affected by such change. When moving to the far extent of where the marsh meets the woods, salinity would decrease to minute proportions, providing a suitable habitat for plants not tolerant to a saline environment.

Conclusions were drawn from a statistical analysis. From the analysis, the soil core sample data for pH, salinity, and temperature were not proven to have any affect on the zonation of the plant species. No correlation between these factors and species frequency or diversity was observed. By the nature of this study, elevation was concluded a limiting factors in plant frequency and diversity.

Latane III, Lawrence. "Wetlands: The Irreplaceable Link Between Land and Water." Richmond Times-Dispatch July 9, 1989: 16+.

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.