Date of Award
Doctor of Philosophy (PhD)
Irving A. Mendelsohn
Three experiments were conducted to evaluate the response of freshwater-oligohaline marsh macrophytes to increased water depth and salinity. In the first experiment, marsh sods containing Sagittaria lancifolia were manipulated in the field to decrease elevation (i.e., increase water depth) by 7.5 and 15 cm. Marsh sods at 15 cm below the marsh surface had the lowest redox potential and highest interstitial water sulfide concentration. Plants in the 15-cm water depth treatment had higher mean and maximum leaf heights than disturbed control plants, but aboveground biomass was not affected. In the second study, the effects of salinity pulses on plant growth and ability to recover following stress alleviation were examined in a greenhouse experiment that included monocultures of four species: Eleocharis palustris, Panicum hemitomon, Sagittaria lancifolia, and Scirpus americanus. Effects of final salinity reached, salinity influx rate, and duration of exposure were investigated. All species responded to final salinity level to a greater degree than salinity influx rate. The magnitude of growth suppression increased for all species with exposure duration. The species were ranked as follows in order from least to most salt tolerant: Panicum hemitomon $<$ Sagittaria lancifolia $<$ Eleocharis palustris $<$ Scirpus americanus. Within a species, ability to recover under freshwater conditions varied with final salinity level and duration of exposure, and to a lesser extent with salinity influx rate. Scirpus americanus was the only species able to recover under all experimental conditions. In the final greenhouse experiment, two common oligohaline marsh communities were subjected to salinity pulses; influx rate, duration of exposure, and water depth were manipulated. The two communities included one species in common, Sagittaria lancifolia; the sub-dominants were Eleocharis palustris and Scirpus americanus in community 1 and community 2, respectively. Species richness in both communities was reduced in the most extreme treatment. Community 1 total biomass and stem density were reduced, as were biomass and stem density for both dominant species. Community 2 had reduced biomass and stem density overall and for Sagittaria lancifolia; Scirpus americanus was not affected. Considered together, the three experiments indicate that different responses of existing plant species to environmental stressors can ultimately influence community structure and composition.
Howard, Rebecca J., "Increased Salinity and Water Depth as Constraints on Growth of Freshwater Marsh Plants." (1995). LSU Historical Dissertations and Theses. 6107.