Browsing by Subject "salt marsh"
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Item Quantification of Salt Marsh Carbon Stocks: Integration of Remote Sensing Data and Techniques with Field Measurements(2013-12-02) Kulawardhana, Ranjani WRecent climatic change projections have increased scientific and public attention on the issues relating to carbon cycling patterns, its controls, and the importance of ecosystems in the cycling and sequestration process. Global carbon studies, however, primarily have focused on dry land ecosystems that extend over large areas and have not accounted for the relatively small and scattered, though highly carbon rich, ecosystems such as mangrove swamps and salt marshes. Using data from a Spartina alterniflora dominated salt marsh in Galveston, Texas this study integrates remote sensing data (multispectral and Light Detection and Ranging - lidar) with field measurements for the quantification of carbon pools in salt marsh ecosystems. Findings in this study show the capability of remote sensing data for the characterization of salt marsh terrain and vegetation heights and the estimation of above-ground biomass quantities. The best biomass prediction models using lidar heights reported considerably low errors, i.e. the percent root square errors (% RSEs) are close to 20%, which is the recommended error threshold for remote sensing based forest biomass prediction models. Our findings also demonstrate that lidar as compared to spectral data can provide better estimates of above-ground biomass and carbon, even in the herbaceous and low-relief context of a salt marsh. A clear zonation of terrain, vegetation characteristics and the distribution of biomass quantities within the marsh extent was also observed. Distribution of biomass quantities revealed linkages with the elevation. Variations in soil properties (i.e. carbon and bulk density) in the soil profile were linked to the temporal changes in soil carbon accumulations on the marsh surface, relative sea level history and resulting vegetation transitions as corroborated by historical aerial images. In general, the amounts of soil carbon stored in recently established Spartina alterniflora intertidal marshes were significantly lower than those that have remained in situ for a longer period of time. These findings indicate that, even though salt marshes can respond to relative sea level rise by migrating landward, their status as a carbon sink varies as a function of both space and time. Thus, in order to predict carbon in a wetland, researchers need to know not only the elevation, the relative sea level rise rate, and the accretion rate ? but also the history of land cover change and vegetation transition. Findings of this study contribute to carbon quantification efforts in these vulnerable ecosystems. Further, these findings will also contribute to the increased understanding of the capabilities of remote sensing datasets and techniques for the quantification of these important carbon stocks.Item Spatial and temporal patterns of Lycium carolinianum Walt., the Carolina Wolfberry, in the salt marshes of Aransas National Wildlife Refuge, Texas(Texas A&M University, 2006-08-16) Butzler, Rachel ElizabethUnderstanding the salt marsh ecosystem in the Guadalupe Estuary is needed because wetlands in this system support the endangered whooping crane (Grus americana). The marsh plant research and monitoring described herein were based in the salt marshes at Aransas National Wildlife Refuge (ANWR), which are utilized by the cranes each winter. Past research indicates that the Carolina wolfberry (Lycium carolinianum) contributes 21-52% of crane energy intake early in the wintering period (Chavez 1996). Beginning in Fall 2003, vegetation transects were sampled along an estuarine gradient at ANWR. Species diversity and composition was similar at the three sites, with all sites containing the same 6-7 common species. While Spartina alterniflora is only a minor part of this vegetation community, it dominates the few low inter-tidal, fringe areas present. Species composition exhibited little variability from Year 1 to Year 2 of the study. Densities and biomass of L. carolinianum were not significantly different between sites or years. L. carolinianum, while important to salt marsh ecology, accounts for only a small portion of the overall productivity. Based on correlation coefficients, L. carolinianum was found in association with some of the common species in the vegetation community, indicating that its growth and survival requirements are typical to the salt marshes at ANWR. Also beginning in Fall 2003, I repeatedly sampled L. carolinianum in permanent plots along the estuarine gradient. L. carolinianum exhibits strong temporal patterns. Leaf production peaked in early spring and again just prior to peak berry abundance. Flowering of L. carolinianum occurred in October and November. Peak berry abundance coincided with the cranes?? arrival in late October and early November. Berry production occurred in October, November, and December; berries were virtually non-existent in the marshes for the remainder of the year. Stepwise regression showed stem diameter alone was a good estimator of aboveground biomass of this species in ANWR marshes, accounting for 94% of the variability (p<0.001). Changes in aboveground biomass followed no distinct patterns in the year of monitoring, perhaps due to the woody stem of the plant. Spatial patterns in L. carolinianum were not explained by water quality parameters alone; it is suggested that soil properties may help to account for the spatial variability.Item Spring phytoplankton dynamics in a shallow, turbid coastal salt marsh system undergoing extreme salinity variation, South Texas(Texas A&M University, 2005-08-29) Hebert, Elizabeth MicheleThe contribution of phytoplankton productivity to higher trophic levels in salt marshes is not well understood. My study furthers our understanding of possible mechanisms controlling phytoplankton productivity, abundance, and community composition in salt marshes. Across three consecutive springs (2001 to 2003), I sampled the upper Nueces Delta in south Texas, a shallow, turbid, salt marsh system stressed by low freshwater inflow and wide ranging salinity (<15 to >300 ppt). Water column productivity and respiration were estimated using a light-dark bottle technique, and phytoplankton biovolume and community composition were determined using inverted light microscopy. To determine their effect on the phytoplankton community, zooplankton and bacterioplankton abundance and several physical parameters were also assessed. Meaningful relationships among the numerous variables evaluated in this study were identified using principal component analysis (PCA). Despite high turbidity, phytoplankton productivity and biovolume were substantial. Resuspension appeared to play a major role in phytoplankton dynamics, as indicated by a positive relationship between ash weight and biovolume that explained up to 46% of the variation in the PCA. Negative relationships between zooplankton grazers and pennate diatoms of optimal sizes for these grazers suggested a functional grazing food chain in this system. Salinity also may have been important in phytoplankton dynamics, whereas nutrients appeared to play a minor role. Salinity increases may have been responsible for a decoupling observed between phytoplankton and grazers during late spring. Findings suggest hypotheses for future studies focused on the role of phytoplankton in salt marshes, particularly those stressed by reduced freshwater inflow and high salinities.Item The effect of cattle grazing on the abundance and distribution of selected macroinvertebrates in west Galveston Island salt marshes(Texas A&M University, 2004-09-30) Martin, Jennifer LynnThe effect of cattle grazing on the abundance and distribution of vegetation, burrowing crabs (Uca rapax, Uca pugnax, and Sesarma cinereum), marsh periwinkles (Littoraria irrorata), horn snails (Cerithidea pliculosa), and salt marsh snails (Melampus bidentatus) was evaluated over four seasons (summer 2000, fall 2000, winter 2001, and spring 2001) in grazed and ungrazed treatments. A Galveston Island salt marsh adjacent to Snake Island Cove was sampled at five elevations, from the water's edge to the high tidal flats. Data were analyzed for statistical differences using a two-way ANOVA in SAS. Cattle grazing may affect the vegetation and macroinvertebrate communities in salt marshes through trampling and herbivory. Vegetation resources available to other herbivores are decreased by the direct consumption of plant material by cattle. Spartina alterniflora and Salicornia virginica heights were significantly greater in ungrazed treatments than grazed for every season in the edge, upper, and middle elevation zones. Total aerial vegetative cover was also reduced significantly in grazed treatments, with the greatest impact in the edge and upper marsh. In the ungrazed treatments, S. alterniflora stem density was significantly greater in edge elevations, while both S. virginica percent cover and stem density in the edge elevation was greater. Burrowing crab populations were greater in the upper marsh and edge habitat of ungrazed treatments, while significantly greater in most of the middle marsh habitats of the grazed treatment. Size of burrowing crabs was generally significantly greater in ungrazed treatments. Cerithidea pliculosa size decreased in grazed treatments, but population had an overall increase in grazed treatments. Littoraria irrorata had very few differences between treatments, although few specimens were found. Melampus bidentatus populations were too small to evaluate thoroughly. Macroinvertebrate populations could be used to assess the overall health of grazed salt marshes.