Master of Science (MS)
Oceanography and Coastal Sciences
Although the Earth may be in the early stages of the projected trends of global warming, several ecological responses to recent warming are already evident. The timing of seasonal activities of plants and animals has begun to shift, and the advancement of species poleward is occurring in several regions of the world. One unique distributional shift is the movement of Avicennia germinans (black mangrove) northward into temperate salt marshes dominated by the marsh grass, Spartina alterniflora. In Louisiana, black mangroves were historically restricted to the southernmost barrier islands and beaches; however, in recent years a noticeable expansion of Avicennia northward into Spartina marshes has been observed. To date, no research documents the effects mangroves may have on ecosystem processes within salt marshes. The goal of this research was lessen this gap in scientific knowledge by examining the effects of expanding populations of Avicennia on the ecosystem processes of accretion, organic matter production and decomposition, and carbon assimilation. Study results indicate that, to date, Avicennia expansion has had no major effects on essential ecosystem processes within the salt marsh. No differences were detected in accretion rates, using sediment trap, feldspar, or 137Cs techniques, decomposition rates, belowground production, or carbon assimilation rates between Avicennia and Spartina areas. However, edaphic parameters such as elevation, redox potentials, bulk density, and soil ammonium were slightly higher, while soil moisture and porewater salinity were somewhat lower where Avicennia expanded into the surrounding Spartina salt marsh. Also, differences were detected in the relative rates at which mangrove and salt marsh tissues decomposed. Decomposition of Avicennia leaves (0.63-1.0% loss d-1) and roots (0.055-0.30% loss d-1) was quicker than that of Spartina leaves (0.52-0.83 % loss d-1) and roots (0.074-0.25% loss d-1). Moreover, root biomass belowground degraded quite slowly, with 50-60% of roots remaining after 384 days. In contrast to quick leaf degradation and the export of leaf litter, slow root degradation and retention within the soil suggest that roots have more potential to contribute organic matter to this Louisiana salt marsh, particularly Spartina roots which degraded even more slowly than Avicennia roots.
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Perry, Carey Lynn, "Ecosystem effects of expanding populations of Avicennia germinans in a southeastern Louisiana Spartina alterniflora saltmarsh" (2007). LSU Master's Theses. 3599.
Irving A. Mendelssohn