Master of Science (MS)
Oceanography and Coastal Sciences
Floating marshes are wetlands of emergent vascular vegetation which have a significant mat of live and dead roots, decomposing and dead organic material, and mineral sediments. This mat moves vertically as ambient water levels rise and fall. These marshes have unique hydrology in that overland sheet flow is reduced or eliminated leaving no inorganic sediment input, but there is extensive belowground water exchange. The effect of significant sediment introduction into wetlands with floating marshes is unknown. The purpose of this study was to observe the marsh mat response to Mississippi River sediment addition and measure species composition change and growth response of vegetation. Study sites were Cypress Canal in Barataria Basin and Turtle Bayou in Terrebonne Basin, Louisiana, USA. Both are thin-mat floating marshes dominated by Eleocharis baldwinii. At each site, twenty plots were constructed around a boardwalk built on the marsh. Each 1 m2 plot was randomly assigned one of five treatments: low, medium, and high sediment additions, and two controls. With increasing sediment addition, there were significant increases in bulk density and significant decreases in percent organic matter in the top 25 cm of the marsh mat. No significant differences in water level over the mat were found between treatments, indicating that buoyancy was not affected by sediment addition. Vegetation species composition after one growing season was not affected by the addition of sediment to the marsh mat. The number of species present was not affected. Aboveground biomass showed trends of increase with sediment addition, though these trends were not statistically significant. Belowground biomass was not significantly affected by the addition of sediment. Neither plant tissue nutrients nor soil nutrient levels showed much significant change with the addition of sediment to the marsh. Most of the sediment added remained in the top 25 cm of the marsh mat. Results presented suggest that some addition of sediment to the surface of a fresh water thin-mat floating marsh will not negatively affect the buoyancy of the mat. Increased bulk density facilitates increased vegetative growth, as is found in prior studies. Future data must be collected to determine more definite results.
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Carpenter, Kate, "Effects of adding sediment to a fresh water thin mat floating marsh" (2005). LSU Master's Theses. 192.