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Publications Theses - Dissertations Modeling Growth and Production Dynamics of Spartina Alterniflora
Abstract - The goal of this work is to investigate the growth and production dynamics of the dominant salt marsh grass in the southeastern United States, Spartina alterniflora, including documenting non-structural carbohydrate pools and investigating seasonal changes in translocated biomass between above- and below-ground tissues.In Chapter 2, the dynamics of several non-structural carbohydrates (NSC) stored in S. alterniflora is investigated. Results show that sucrose is the dominant NSC in both above- and below-ground tissues and that the total NSC as a percentage of total biomass is highest in the summer through to early winter. The study suggests that sucrose is likely used for long-term storage whereas glucose is preferentially utilized for short-term storage.In Chapter 3, the growth and production dynamics of short, medium, and tall height forms of S. alterniflora are investigated using a phenology-based growth model (PG model), which includes the effects of light, temperature, and salinity on plant production. The model is used in combination with field observations of biomass to estimate values of physiological parameters such as mass-specific rates of carbon translocation. Once parameterized, the model is used in forward mode to predict whole-plant production, growth, respiration, mortality, and translocation. Model results indicate that the short height form of S. alterniflora translocates a higher proportion of photosynthates or remobilization of assimilates to below-ground tissues during periods of growth and senescence periods than medium or tall S. alterniflora, although the absolute amount of carbon translocation to below-ground tissues is greatest in the tall form of S. alterniflora because of its larger above-ground biomass.In Chapter 4, the model is used to compare the production and translocation dynamics of S. alterniflora along a latitudinal gradient using sites in Delaware, South Carolina, and Louisiana. Model results indicate that photosynthates make up the main source of carbon translocated to below-ground tissues at low latitudes, whereas at high latitudes, both photosynthates and remobilization of assimilates in senescing shoots are preferentially used. This shows the importance of taking into account the different translocation dynamics of the plants when comparing growth and production across sites at different latitudes.
(contributed by Yeajin Jung, 2018)
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    Salt Marsh Dieback: The response of Spartina alterniflora to disturbances and the consequences for marsh invertebrates
Abstract - Spartina alterniflora is a foundation species that plays a disproportionately critical role in salt marshes, as it ameliorates chemical and physical stress to other plants and animals, provides essential habitat, protection from predators, and a source of organic matter to associated fauna. Disturbances including sudden dieback, herbivore overgrazing, and wrack deposition can lead to a loss of Spartina and thus, indirectly affect the invertebrate community. My goals were 1) to examine the effects on the invertebrate communities in 2 different geographical regions (GA, LA) and among 4 different disturbances within a region (GA), 2) to determine whether various disturbances would elicit a similar and predictable physiological response (the DMSO:DMSP ratio, and metal load) in Spartina that could be used as a sensitive and predictable indicator of stress among various disturbance types, and 3) to document the never before described long-term trajectory and patterns of recovery from sudden dieback in a Spartina and Juncus roemerianus marsh. Spartina loss in GA and LA led to similar decreases in Littoraria irrorata (periwinkle snails), but there were strong differences in the responses of infauna between the states and among years. These results suggested context-dependency in both the effect of foundation species within a geographical region and in the evaluation of the ecosystem service provided at the time of sampling. Overall and despite differing results, it was found that Spartina was ultimately important in maintaining the invertebrate communities in both states. However, within a geographical region, both the physiological response of Spartina and the indirect response of the invertebrates to Spartina loss were similar and predictable among four different disturbances. The DMSO:DMSP ratio and metal loads were increased in affected Spartina plants (often responsive in otherwise green leaves) and periwinkle snails and benthic macroinfauna (density, taxon richness, and diversity) were significantly decreased in affected areas, regardless of disturbance type. Vegetation recovery at sudden dieback is occurring slowly (on the order of a decade) via rhizomes extension from healthy areas, and thus understanding the effects to invertebrates is important, as disturbances such as these are expected to increase with climate change and anthropogenic effects.
(contributed by Caroline R. McFarlin, 2012)
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    Geographic Variation in the Structure of Salt Marsh Arthropod Communities
Abstract - The natural environment shows variation at multiple scales, and determining how large-scale patterns relate to the local community's structure and function is a fundamental goal of ecology. Salt marshes along the Atlantic and Gulf coasts are similar in many ways, and are inhabited by the same plant and insect species. However, the Atlantic and Gulf coast areas have different tidal regimes, which may result in the two areas not functioning exactly the same. In addition, abiotic factors that vary with latitude or longitude may lead to differences between northern and southern or eastern and western sites. I hypothesized that structure and function of the coastal salt marsh varies geographically. To test this, I characterized abiotic conditions and the plant and arthropod communities at 11 sites along each coast in the late summers of 2009 and 2010. I also manipulated wrack (dead plant stems) and nutrient availability in 2 x 3 m plots at each site to evaluate geographic differences in community response. The experiment was established in 2009 and allowed to run to 2010. My sampling documented that some abiotic factors varied geographically, as did plant height, nitrogen content, and thatch cover. Although the total number of arthropods collected did not differ geographically, the trophic composition of samples showed marked variation among regions. Large-scale differences in latitude and mean tidal range are likely driving much of this variation. Arthropod community structure was little affected by wrack addition, but responded strongly to fertilization; and, the effect of fertilization varied geographically for some trophic levels. Although salt marshes are superficially similar from Maine to Texas, they may be structured differently throughout this geographic range. Therefore, extrapolating results from one geographic region to another should be done with caution.
(contributed by Brittany DeLoach McCall, 2011)
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    Geoarchaeological analysis of two back-barrier islands and their relationship to the changing landscape of coastal Georgia, U.S.A.
Abstract - This study examines the past human settlement system on the coast of Georgia from 12,000-1,000 B.P. (the Paleoindian through Late Woodland periods) in relation to landscape change. I take a landscape approach to understanding settlement, incorporating geomorphology, formation processes, a distributional approach to archaeological data, and landscape ecology metrics. Archaeological surveys of two back-barrier islands, Mary Hammock (9MC351) and Patterson Island (9MC493), are combined with non-archaeological paleoenvironmental data, and compared to changes in sea level, and to archaeological surveys from other environmental settings, to understand the change in human occupation in McIntosh County, GA. Numerous environmental datasets, including present-day elevations, former surfaces under the marsh, bathymetric data, soils, and wetlands, were incorporated together. These data were combined with changes in sea level over time, creating a dynamic model of landscape change. This model is used to create predictions about human settlement patterns in relation to the marsh-estuarine system for McIntosh County in general, and the back-barrier area specifically. These predictions were then tested with prehistoric site distributions of McIntosh County, as well as to prehistoric sherd densities of various surveys. Analysis revealed that terminal Middle Archaic sites (~5,000 B.P.) with evidence of coastal adaptations should be found within present-day McIntosh County. Because there are no such sites, I suggest that there may have been an abandonment of the coast at this time. The explosion in Late Archaic sites, then, may have been from an influx of people to the Georgia coast. Back-barrier islands were always part of the settlement system. The intensity of back-barrier island utilization may be related to their proximity to larger landmasses (the mainland and major barrier islands), and the different types of settlement systems associated with those landmasses. The intense utilization of back-barrier islands at certain times suggests that they may have been permanently settled. Another explanation for their intense use may be that these are relatively small islands where activities would have been concentrated. The predictions of the model were not always substantiated, indicating that changes in sea level and marsh-estuarine resources were not the only reason for changes in settlement and subsistence patterns.
(contributed by John A. Turck, 2011)
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    Application of the Water Quality Analysis Simulation Program (WASP) to Evaluate Dissolved Nitrogen Concentrations in the Altamaha River Estuary, Georgia
Abstract - The Water Quality Analysis Simulation Program (WASP v.7.4) and a water flow model, SqueezeBox, were used to model concentrations of dissolved nitrogen (DN) in the Altamaha River estuary, Georgia. Model development was guided by previous studies using WASP, literature surveys, and sensitivity analyses. The model was calibrated and validated against observations from the Georgia Coastal Ecosystems Long Term Ecological Research project. Average error between model predicted and observed concentrations was 39.8 % for NH3, 23.6 % for NO3-, and 7.8 % for DON. Results from the calibrated model showed that riverine DN input had an approximately 6-fold greater influence on predicted DN in the estuary than either flow or temperature. Overall, predicted DN concentrations were highest for high DN input, high flows, and low and medium temperatures.
(contributed by Galen Kaufman, 2011)
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    Microbial Ecology and Biogeochemistry of the Coastal Ocean: New Insights from Metatranscriptomics
Abstract - In the oceans, the transfer of energy and cycling of elements is predominantly controlled by bacterioplankton, such that any understanding of marine ecosystems requires knowledge about bacterial activities and functional capabilities. Metatranscriptomics, the direct retrieval and sequencing of environmental RNA, is a powerful tool that can identify active community members and their expressed functional capabilities. This dissertation is composed of three studies that used metatranscriptomics to gain fundamental insights into the ecology and biogeochemistry of coastal microbial communities. In the first study, an internal standard approach was developed to make absolute (per liter) estimates of transcript numbers, a significant advantage over proportional estimates. Expression levels of genes diagnostic for transformations in the marine nitrogen, phosphorus and sulfur cycles were determined, as well as the total size of the mRNA pool. By representing expression in absolute units, metatranscriptomics extends beyond relative comparisons, allowing for direct comparisons with other biogeochemical measurements. In the second study, a metatranscriptomic dataset revealed an unexpected abundance of transcripts to Candidatus Nitrosopumilus maritimus, an ammonia oxidizing Archaea whose presence has significant implications in the carbon and nitrogen cycles. Reads assigned to genes for ammonia uptake and oxidation accounted for 37% of N. maritimus transcripts. In contrast, transcripts from co-occurring ammonia oxidixing Bacteria were in much lower abundance, with no transcripts related to ammonia oxidation or carbon fixation. This study suggests that these two members of the ammonia oxidizing functional guild respond differently to the same environmental cues. The third study used metatranscriptomics to examine how differences in expression among taxa can be indicative of niche diversification. The sequencing of transcripts from four coastal bacterial communities revealed the expression and activity of thousands of different taxa. The genes carried by these taxa have extensive overlap, and the majority of highly expressed genes were for redundant functions. To identify unique ecological roles for these taxa, a method was developed to classify genes both by their expression level and their frequency in genomes. The results show clear functional delineations across broad phylogenetic groupings and provide insights into the diversity of lifestyle strategies that supports complex microbial assemblages.
(contributed by Scott Gifford, 2011)
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    Smouldering oceans: on the photochemically mediated oxidation of dissolved organic matter in coastal waters
Abstract - Marine dissolved organic carbon (DOC) is one of the largest and most dynamic pools of reduced carbon on earth. Photochemical processes have the potential to significantly affect the content of this DOC pool. Photochemical oxidation to carbon monoxide and carbon dioxide are two direct pathways for the removal of DOC from the marine system. Indirectly, photochemical processes can lead to the removal of DOC through the alteration of chemical structures rendering them more biologically labile. In order to assess the influence of photochemistry on the coastal carbon cycle the variability of these processes must be well constrained. To calculate photochemical production in marine waters, it is crucial to know how light is absorbed by chromophoric dissolved organic matter (CDOM), as well as the spectral efficiency of the resulting photochemical reactions (i.e. the apparent quantum yield (AQY) spectra). The challenges of using visible wavelength CDOM absorption data to model ultraviolet absorption data are investigated. Direct measurements of ultraviolet absorption data model photochemical processes best. When this is not possible, visible data can be used with an accuracy of +/- 10% in coastal waters. Either a hyperbolic absorption model or one using correction factors applied to a traditional exponential model will allow for similar accuracy in the ultraviolet portion of the absorption spectrum. The variability of photochemical oxidation of dissolved organic carbon in a coastal system was studied in order to constrain remote sensing calculations. The variability of CO and CO2 AQY spectra were relatively well constrained in three estuaries of Georgia, USA. The AQY for CO varied within +/- 12.7% year-round while CO2 varied within +/- 33.6% year-round. Hyperspectral remote sensing reveals finescale hydrodynamic structure in estuarine systems and is readily adaptable to photochemical modeling applications. Defining the variability of photochemistry?s influence on the biological lability of DOC is a complex undertaking. Unlike direct photochemical oxidation of DOC to CO and CO2, the biologically labile products (BLPs) of incomplete oxidation can themselves be photochemically reactive. Competition between production and destruction of BLPs during irradiation is a significant consideration when determining the quantitative influence of photochemistry on marine systems.
(contributed by Heather E. Reader, 2011)
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    Synoptic comparison of salt marsh spatial structure using hyperspectral imagery at NOAA National Estuarine Research Reserves
Abstract - As a dynamic system, salt marshes are highly productive habitats. Exceedingly dependent on specific tolerances to tidal regimes, temperature, elevation, and salinity, the plant composition and structure of a salt marsh are highly variable. Due in part to their visible spatial patterns and the impracticality of large scale field observations, aerial and satellite remote sensing has provided an effective alternative for studying these plant communities. This research focused on the use of hyperspectral remote sensing to advance an overall understanding of salt marsh ecosystem productivity, diversity, and abundance within specific National Estuarine Research Reserves (NERRs) using AISA (Airborne Imaging Spectrometer for Different Applications) imagery.The overall goal of my thesis was to create a synoptic overview and site comparisons of salt marsh vegetation for seven NERRs, within their respective growing seasons, using three remote sensing vegetation indices. Additionally, within and between site geospatial patterns were examined using two landscape metrics. The seven sites were located in a range of climates, tidal, and river discharge regimes between Texas and Delaware.Across all sites, the NDVI and MSAVI indices were well suited for distinguishing structural differences and illustrating variations in relative biomass and plant vigor at each site. They both showed latitudinal and longitudinal shifts in histogram distributions, relatable to nutrient, tidal, and climate regimes. These indices were also useful for discriminating features unique to individual sites, such as exposed, intertidal mud flats (Georgia site) and robust Phramites australis stands (Delaware site).The VARIgreen index, more closely captured the photosynthetic capacity and "greenness" of salt marsh vegetation, and was more sensitive to phenological changes and foliage pigment densities. This index was more responsive to spring greening and late summer senescence. As a result, VARIgreen's distributional patterns appeared more sensitive to growing season patterns.Patches per unit area (PPU) was an effective landscape metric for measuring patchiness of vegetation index classes for the entire landscape. The Texas, Georgia, and South Carolina sites displayed the highest PPU values, while sites in Mississippi and West Florida had the lowest values. Although PPU illustrated the abundance of different patches in a single area, it was biased towards dominant classes. In comparison, the Shannon Diversity Index (SDI) captured the degree of equitability of all classes of patches. The largest class diversity and SDI values were found in the Delaware and West Florida sites.Ultimately, the vegetation indices and landscape metrics helped to show spatial variations at each site. As a result, site characterizations, unique to each site helped to explain the structure and productivity of the eight datasets.
(contributed by Drew N. Seminara, 2010)
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    Temporal and Spatial Variability of Transport and Mixing Mechanisms: Using Heat and Salt in the Duplin River, Georgia
Abstract - A study of the Duplin River, a shallow, sinuous, tidal creek which connects the salt marshes of Sapelo Island, on the central Georgia coast, with the waters of Doboy Sound and the coastal Atlantic Ocean, was conducted to quantify the physical processes which regulate the flux and zonation of heat and salt throughout the creek system.Three water masses are identified with differing temperature and salinity regimes. Hourly scale heat budgets are constructed for the upper (warmer) and lower (cooler) areas of the Duplin River showing the diminishing importance of tidal advection away from the mouth of the creek along with the concomitant increase in the importance of both direct atmospheric fluxes and of interactions with the marsh and side creeks. The heat budget is re-examined on daily averaged scales revealing the decreased importance of advective fluxes relative to direct atmospheric fluxes on this scale but the constant importance of marsh/creek interactions regardless of time scale or season. Tidally averaged along channel salt fluxes are calculated and a contrast is drawn between the lower and the upper Duplin. The main channel of the lower Duplin is bordered by creekless marsh, marsh hammocks and hard upland and salt fluxes are largely constrained to the main channel with salinity in the lower Duplin closely tracking observed salt fluxes. The upper Duplin is isolated from the lower Duplin by a sinuous channel and is subject to significant local fresh groundwater input. The upper Duplin acts as a reversing estuary on a fortnightly time scale. Salt fluxes are not constrained to the main channel but show a significant influence of the marsh. Vertical mixing is shown to be modulated on both M4 and fortnightly frequencies with turbulent stresses being generated near the bed and propagating into the water column on periods of max flood and ebb and being significantly greater on spring tide than on neap. Horizontal mixing is driven by tidal dispersion, which is modulated by the fortnightly spring/neap cycle. Net export of salt from the lower Duplin is shown to be due to residual advection modified by upstream tidal pumping which, in the absence of external forcing, exhibits a pulsating character with net export taking place for a short period on spring tide followed by a longer period of net import of salt.A box model is developed to explore subtidal inputs of groundwater and salt into the three water masses of the Duplin River. The results of this model are examined to draw insights into the magnitude and spatial distribution of these processes and their effect on the Duplin River water masses.
(contributed by Paul McKay, 2008)
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    Benthic Microbial Food Webs: Spatial and Temporal Variations and the Role of Heterotrophic Protists in Salt Marsh Sediments
Abstract - In order to determine if the loss of bacterial biomass varies over time, I investigated the microbial food web structure at two time scales in the salt marsh sediments of Sapelo Island, Georgia. Samples were collected monthly for one year at three contrasting subtidal locations: a high energy sandy beach, a muddy Spartina marsh, and a tidal creek bed. Concentrations of benthic microalgae (BMA), bacteria, heterotrophic protists, and metazoan meiofauna were measured at each location. Additionally, short-term dynamics of sediment microbial populations and bacterivory rates were investigated over a diel period in an intertidal creek bed to determine if variable rates of protist grazing could significantly impact bacterial standing stock. Although bacterivory rates were variable throughout the day, there were no periods of the day when protists could effectively reduce bacterial biomass. Yearly sampling revealed high variation in the microbial food web structure, mostly among sample locations. However, I observed a shift from a BMA-dominated community in the spring/ early summer months to a bacterial-dominated food web in the late summer/fall at all locations. Bacteria and heterotrophic protist concentrations were significantly related to porewater volume (6.9±1.2 x 10 and 5.1±1.1 x 10 -1 cells ml, respectively, ±SE). The low abundance of protists (relative to high bacterial concentrations) may be due to top-down pressure by large ciliates and nematodes. This top-down pressure in the autumn months (when BMA are proportionally less abundant) may contribute to high concentrations of bacteria during this season. Microbenthos displayed a clumped distribution pattern in Fluorescently Labeled Embedded Cores (FLEC). The aggregation of microbenthos indicates that the importance of protists in microenvironments may be overlooked by their total concentrations in the sediments. The common benthic ciliate, Uronema marinum, was capable of ingestion of fluorescently-labeled dextran (a high molecular weight carbohydrate) at low concentrations (3 microM DOC). However, the ingestion of starch, glucose and acetate did not significantly improve the growth or biomass production for this ciliate. Instead, I hypothesize that the initial breakdown of recalcitrant organic carbon compounds (and egestion of fermentation byproducts) can stimulate sulfate reducing bacteria and indirectly benefit bacterivorous protists through increased bacterial production.
(contributed by Matthew R. First, 2008)
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    Biogeochemical dynamics in coastal sediments and shallow aquifers
Abstract - Patterns of benthic metabolism and the relative importance of assimilatory and dissimilatory processes as sinks for nitrate (NO3-) in intertidal sediments were examined. Under illuminated, nitrogen (N)-replete conditions, sequential nutrient limitation of benthic microalgae (BMA) was observed, with N limitation preceding silicate limitation; and biological assimilation dominated nitrate uptake. Conversely, under dark hypoxic and anoxic conditions, water column NO3- uptake was dominated largely by three competing dissimilatory reductive processes; denitrification (DNF), dissimilatory nitrate reduction to ammonium (DNRA), and, on one occasion, anaerobic ammonium oxidation (anammox). High sulfide concentrations negatively impacted DNF and DNRA rates, while high dissolved organic carbon (DOC):NO3- ratios favored DNRA over DNF. Under baseline conditions sediments exhibited tight coupling between photosynthesis and respiration. Nitrogen addition shifted the metabolic status of the sediments from a balance between autotrophy and heterotrophy to net autotrophy, and the sediments became a source of DOC. The role of groundwater as a source of nutrients and organics to the coastal ocean was evaluated using a combination of radium isotopes and geochemical characterization. Geochemical data indicated significant spatial variations in groundwater chemical composition and radium activity ratios indicated geographically distinct hydrological regimes. Spatial variations in microbially mediated processes, DOC distribution, and/or groundwater residence time contributed to this pattern. Radium based geochemical loading rates illustrated a substantial groundwater contribution of organics, DIC, nutrients, methane and nitrous oxide to the Okatee estuary. The groundwater biogeochemical dynamics along a shallow monitoring well transect on a coastal hammock were evaluated by density-dependent reaction transport model. A switch in the redox status of the DIN pool occurred during the spring-neap tidal transition (spring high NO3- low NH4+; neap low NO3- high NH4+). The observed N redox-switch was evaluated with regard to the relative roles of nitrification, DNF, DNRA, ammonium adsorption, and variations in inflowing water geochemistry between spring and neap tides. The latter was found to most significantly affect the observed pattern in DIN dynamics. Additionally, the fate of DOC and DIN originating from a septic system was studied. Simulation results indicated that while DNF increased ~15 fold, higher N removal rates could not keep pace with the increase in DIN loading, resulting in higher export of DIN to coastal waters.
(contributed by William P. Porubsky, 2008)
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    Centrifugal organization in a Georgia salt marsh plant community
Abstract - In this study I evaluate whether a centrifugal model helps explain vegetation patterns in a Georgia salt marsh using a combination of sampling data and manipulative experiments. The centrifugal model predicts that multiple stress gradients radiate out from a shared core habitat and that plants should occupy discrete ranges along these gradients. The results from this study indicated that there were two clear stress gradients, salinity and water-logging, along which species and habitats occupied discrete ranges, supporting the centrifugal model. The centrifugal model predicts that productivity should be greatest at the benign end of each stress gradient and least at the most stressful end. The results from this study generally supported the centrifugal model. Juncus and Borrichia, which occupied the most benign habitat, had the highest biomass. The stressful ends of the gradients, occupied by Salicornia virginica, short Spartina alterniflora and medium Spartina alterniflora, all had relatively low biomass. The centrifugal model predicts that diversity should be highest in intermediate levels of stress. Salicornia virginica and Spartina alterniflora zones always had the lowest species richness and diversity, supporting the centrifugal model. However, the Borrichia zone always had the greatest or second greatest level of species richness and diversity, not supporting the centrifugal model. The centrifugal model predicts that when species are transplanted outside of the benign habitat they will do poorly, with or without neighbors present, where species at the stressful ends of the gradients will do well when transplanted into the benign habitat without neighbors, but poorly when neighbors are present. The results of the transplant experiments strongly supported the centrifugal model. In conclusion, I found strong evidence that the centrifugal model was useful in explaining plant community structure in a Georgia salt marsh. This model also provides a unified theory for vegetation patterns in northeast and southeast USA salt marshes, where zonation due to high salinities caused by increased evapotranspiration in the low-latitude climates can be equated to the disturbance-caused temporary increases in salinity in high-latitude climates.
(contributed by Alana R. Lynes, 2008)
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    Molecular description of ascomycete fungal communities on Spartina spp. in the U.S.
Abstract - Ascomycetous fungi play a crucial role in the decomposition of salt marsh vegetation. The first part of this research used molecular methods to examine whether physical associations exist between individual bacterial and common ascomycetous fungal species that co-occur on decaying smooth cordgrass, Spartina alterniflora, in a southeastern U.S. salt marsh. We found that bacterial communities were unaffected by the identity of initial fungal decomposers, suggesting that few species-specific associations exist between those members of the Spartina decomposer community. The next part of the study involved a characterization of ascomycetes involved in the decomposition of different species of Spartina in different environments. In California, the fungi associated with S. alterniflora, S. foliosa, the hybrid between them, and S. densiflora were all characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis of their internal transcribed spacer (ITS) region of rRNA genes as well as clone libraries. Although we found no effect from the hybridization of two host species, we did see significant differences in the fungal decomposer communities both within and among species. S. densiflora hosted several unique ascomycetes. Two previously described ascomycetes, Phaeosphaeria spartinicola and Mycosphaerella, were ubiquitous on all samples analyzed. On the east coast, ascomycete communities on samples of S. alterniflora and S. patens collected in four states (Georgia, North Carolina, New York, and Massachusetts) were compared, again using T-RFLP analysis of the interspacer region. Results show that diversity of the ascomycete taxa on S. patens hosts a higher number of unique ascomycete species than S. alterniflora, and that it has significantly higher diversity, but there were no consistent differences among states. P. spartinicola and Mycosphaerella again dominated most T-RFLP profiles. The data suggest that two fragments (147 and 149 bp), although not confirmed to represent separate taxa, were specific to host plant species. Preliminary data from samples of the same species of grass collected in states along the Gulf coast (FL, LA, MS, AL) confirm all conclusions drawn for samples collected along the east coast, including the higher diversity on S. patens, omnipresence of P. spartinicola and P. halima, and species-specificity of fragments at 147 and 149 bp.
(contributed by Justine I. Lyons, 2007)
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    Determination of gas exchange velocities based on measurements of air-sea CO2 partial pressure gradients and direct chamber fluxes in the Duplin River, Sapelo Island, GA
Abstract - CO2 fluxes were determined directly, using a floating chamber for ten to fifteen minute intervals over the winter between 2006 and 2007 from Marsh Landing Dock on Sapleo Island, Georgia. Air-Sea pCO2 differences were measured alongside the fluxes using a coupled equilibrator and infrared gas detector whereby gas transfer velocities (k) were calculated. In addition, current speeds were measured using an acoustic doppler current profiler and correlated with gas transfer velocities along side wind speeds. In the Duplin River, with the exception of spring tides, wind is an important variable controlling k in agreement with prior empirical measurement of estuarine k values. However, bottom generated turbulence was responsible for more than half of the magnitude of measured gas transfer velocities for 17 out of 100 of the deployments. In addition, gas transfer velocities during spring tides may be able to substantially increase k, however independent verification with an un-tethered floating chamber is needed to verify this in the Duplin River.
(contributed by Justin Hartmann, 2007)
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    Patterns of plant diversity in two salt marsh regions
Abstract - Although ecologists have been interested in explaining the diversity of ecological systems for many years, there is still no generally accepted theory to explain what determines diversity. Patterns of diversity are determined by which species are able to colonize a particular site and persist in a particular abiotic environment, and by biological interactions between species that may expand or contract their range across an abiotic gradient. By examining these patterns we can begin to understand which biotic and abiotic mechanisms are important for shaping the overall diversity of a system. I compared the salt marshes of Texas to those of Georgia to determine what differences in plant diversity patterns existed between these two systems with similar species pools and general abiotic environments. Both Gulf Coast and Atlantic Coast salt marshes are tidal systems and therefore plants must be tolerant to flooding, salinity, and anoxia. The major abiotic difference between the salt marshes of these two regions is the relatively irregular schedule and lower amplitude of tides in Texas. Tidal schedule and amplitude might affect plant distribution patterns by creating abiotic conditions that vary over time as much or more than over space, thereby altering competitive relationships between plant species.I quantified diversity patterns (richness and relative abundance) on transects across elevation at 59 salt marsh sites in Georgia and 49 sites in Texas. Diversity was measured at global, regional, site, and plot scales to consider processes occurring at all levels. Species pools were similar between regions. Texas had greater diversity at the site and plot scales, which was primarily due to processes occurring at the site level. The greater diversity of Texas was partially explained by the fact that Texas marshes had more middle marsh (a high diversity zone) and less low marsh (a low diversity zone) than Georgia marshes, and by the fact that most species were more widely distributed across the marsh landscape in Texas than in Georgia (i.e., zones were less discrete). Biomass data from a subset of plots and sites suggested that high diversity in Texas was not caused by lower productivity; instead, Texas marshes had greater standing biomass than Georgia marshes. Irregular flooding of Texas marshes might allow more species to exist in the marsh by making abiotic conditions more variable over time, thereby making the outcome of competitive interactions less predictable and rapid.This work suggests that Gulf Coast marshes may function differently in some ways than Atlantic Coast marshes. Managers of Gulf Coast marshes should not assume that paradigms based on the Atlantic Coast will automatically apply. In addition, because salt marsh diversity is determined by site-scale processes, protection efforts should focus on maintaining a range of different marsh types rather than simply maximizing the total marsh acreage protected in a region.
(contributed by Amy E. Kunza, 2006)
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This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.