An Examination of Marsh Grass Diversity in a Brackish Marsh
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+.