Master of Science (MS)
Renewable Natural Resources
Coastal wetland forest ecosystems rely on the intimate interactions of hydrology, salinity, and coastal forest vegetation. The boundary between marsh and forest is often where hummock-swale terrain exists. It remains unknown as to the degree to which trees may experience varied salinity level within hummocks provided with freshwater flux. This study examined the hydrological regime of the hummock-swale terrain that resulted in salinity variation and whether freshwater source exists for baldcypress. Natural tracers of stable isotopes of water and salinity were applied to understand the sources of water. To better examine the tracers used, we conducted several experiments to gain a clearer understanding of the variability in isotopic compositions in throughfall and by extracting water from wood and soil. The studies indicated that baldcypress are able to avoid saline flooding from hummocks. We found that the throughfall process does correspond with the canopy structure enough to strongly influence throughfall amount but only weakly influence isotopic composition. Also at microtopographic scale, salinity of the groundwater in hummocks remained chronically high and vertical solute exchange was little. The shallow subsurface of hummocks was a zone characterized by slow dilution and episodic salinization rather than slow salinization and episodic flushing. Rainfall and frequent inundation by generally low-salinity water flushed salts and maintained lower salinity in upper layers. Thus the baldcypress forest overall occupies a nonsaline site, but the episodic influxes followed by slow leaching occurs superimposed on a layer of salinity that lies presumably beneath the root zone for most of the growing season. In addition, the systematic errors were little considering the isotopic fractionation during water extraction from wood.
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Hsueh, Yu-Hsin, "Microtopographic Ecohydrology of a Forested Wetland in Louisiana" (2015). LSU Master's Theses. 864.
Keim, Richard F.