Date of Award

2010

Document Type

Campus Access Thesis

Department

Biological Sciences

First Advisor

James Morris

Abstract

Standing biomass of Spartina alterniflora Loisel. (Spartina) has been shown to correlate with the relative elevation of the sediment surface and anomalies in mean sea level. Aboveground biomass, stem density, stem height and percent organic nitrogen were measured as a function of relative elevation. Marsh surface elevations were extracted from LIDAR data collected in 2003. An optimal elevation for Spartina standing biomass was identified at about 35 cm NAVD88. The upper and lower elevation limits for Spartina are related to tidal flooding duration and frequency. We speculate that the lower limit (around 0 cm NAVD88) is probably controlled by hypoxia while the proximate determinate of the upper elevation (around 80 cm NAVD88) is salt stress, desiccation, and/or competitive pressure from other species.

The equilibrium elevation of the marsh surface has been hypothesized to be inversely proportional to the rate of sea level rise (Morris et al. 2002). Consequently, the skewness of the frequency distribution of elevations may be useful as a diagnostic of stability for marshes imminently threatened by rising relative sea level (Morris et al. 2005). A right skewed marsh, gathering about the lower vegetative limit, would be least stable, a marsh with left skew, gathering about the higher vegetative limit, would be most stable, and a marsh with a normal distribution would be in equilibrium with the current rate of sea-level rise or in transition.

In North Inlet, South Carolina, we hypothesized that marshes at greater distances from the major sediment sources would have elevations that were right skewed relative to marshes nearest sediment sources. Marshes at greater distances from sediment sources were hypothesized to be sediment starved and possibly not keeping pace with rising sea level. We found that the elevations of marshes farthest from sediment sources were lower then those of marshes closest to the sediment sources at the mouth and southern area near Winyah Bay. However, the differences in mean elevations among geographical areas were small and the frequency distributions of elevations were all approximately normal. We found no evidence that marshes in any of the areas are nearing collapse due to submergence.

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