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Publications Theses - Dissertations Tidal marsh vertical carbon fluxes across spatial and environmental gradients: enhancing satellite-derived blue carbon modeling
Abstract - Tidal marshes, with other tidal wetlands collectively known as blue carbon (BC), are important ecosystems in the global carbon (C) cycle. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate highlights the importance of quantifying BC in combating climate change. Satellite remote sensing (RS) models fusing surface reflectance and weather/climatology products are often used to quantify and predict gross primary production (GPP) at broad spatiotemporal scales. However, existing RS GPP models are not parameterized for tidal wetlands, and only a few studies have investigated this issue. Therefore, research was needed to determine specific drivers of vertical C fluxes in tidal marshes across space and time. We focused on a bottom-up approach to study the influence of marsh heterogeneity on ecosystem scale vertical C fluxes. Specifically, we looked at how changes in emergent leaf area (ELA) through the tidal cycle across Spartina alterniflora morphological canopy types altered C fluxes. We then determined a simple RS-based relationship between a vegetation index (NIRv) and ELA, allowing data capturing inundated marshes to be used in GPP models. Next, we increased our scale to the marsh domain and measured the differences and drivers of interannual net ecosystem exchange (NEE) by S. alterniflora canopy type. This work highlighted the spatial heterogeneity of C exchange across a single tidal marsh. Then, expanding to a comparison between two marshes in Georgia and Mississippi dominated by different species, we identified and ranked the environmental gradients impacting each marsh’s light use efficiency, the ratio of gross productivity and light absorption, a key variable in GPP modeling. Finally, we broadened our scale to assess the C and greenness phenologies of different tidal marshes and used our previous research findings to parameterize and tidal marsh specific GPP RS model. Our new model could predict tidal marsh GPP with an accuracy of 7.4 g Cm-2 per 8-day, representing a 10.5% error. Our research highlighted how important spatial heterogeneity is in marsh C fluxes and will inform future work measuring and modeling C dynamics under future climate conditions.
(contributed by Peter Hawman, 2024)
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    Remote Sensing of Georgia Tidal Marsh Habitats Using Aerial Photography and Planetscope Satellite Imagery
Abstract - Globally, tidal marshes cover about 90,800 km. Within the state of Georgia tidal marshes are primarily located behind the barrier islands and total 1,619 km2 . The combination of high salinity environments and daily inundation, and being dependent on river output, make these dynamic systems. Tidal marshes provide numerous ecosystem services such as carbon and nitrogen sequestration, flood control, coastal protection, and numerous biogeochemical processes. Due to their unique position, tidal marshes are under threat from sea level rise, drought, coastal development, and large-scale disturbance events. Tidal freshwater marshes are especially susceptible to these threats due to their geographic location and small extent which have been historically understudied. By mapping tidal marshes, species composition is better understood and can be used to scale up ecosystem services, biogeochemical processes, and above ground biomass using remote sensing imagery. This study uses aerial orthoimagery along with a digital elevation model, National Wetland Inventory, and vegetation indices to map salt, brackish, and tidal freshwater marshes along the entire coast of Georgia. Higher spectral and spatial resolution PlanetScope 4- and 8-band satellite imagery was also used to map salt, brackish, and tidal freshwater marshes of the three main watersheds in coastal Georgia which include the Ogeechee, Altamaha, and Satilla Rivers. The aerial orthoimagery classification had an accuracy of 86.3% with salt marshes making up 67.8%, brackish 28.7%, and tidal freshwater 3.5% of the classified image and showed the importance of using a DEM and NWI for tidal marsh mapping. The PlanetScope classifications were comparable to the aerial classification with an accuracy of 86.5% (Ogeechee), 88.1% (Altamaha), and 75.9% (Satilla). Differences between the 4-band and 8-band PlanetScope imagery proved to be minimal. Due to the vulnerability of salt marshes to climate change, this study aims to contribute and expand upon current remote sensing studies on tidal marsh mapping.
(contributed by Harrison Currin, 2023)
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    Using Machine Learning Classification and ESA Sentinel 2 Multispectral Imager Data to Delineate Marsh Vegetation and Measure Ecotone Movement in Coastal Georgia
Abstract - Tidal marshes are unique communities that are subjected to environmental stressors including sea level rise, salinity change, and drought, resulting in constant change. It is important to monitor these changing areas because of the ecosystem services they provide to us, such as protection from storms and carbon sequestration. The Georgia coast is home to a large section of marsh on the Atlantic coast of the United States. This thesis project focused on the study of tidal marshes, and the dynamics between the vegetation species within them, on Broughton Island, Georgia. The aim of this project was to use geospatial technology and analyses, along with machine learning classification methods, to monitor change in these valuable ecosystems. The two objectives of this study are to 1) examine multiple machine learning algorithms to determine the best supervised classification method for the Broughton Island, Georgia, and 2) quantify the relationship between species-specific aboveground biomass of vegetation with ecotone movement between the three tidal marsh domains. Objective one of this study compared two different supervised classification methods, Random Forest and Artificial Neural Networks, to determine which supervised classification performs best in mapping vegetation species and ground cover within the study area. In objective 2, the most accurate classifier will be used to examine ecotone movement over time and quantify the relationship between aboveground biomass, using vegetation indices as a proxy, of vegetation and ecotone movement.
(contributed by Thomas Pudil, 2023)
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    Grazers vs Grazers: Large Mammal Herbivores Influence Salt Marsh Invertebrate Communities
Abstract - Large mammals cause disturbances in the environments in which they graze by dramaticallychanging the physical structure of habitats. The response of plant and animal communities tomegafaunal herbivory is highly variable among ecosystems, geographic location, and species ofinterest. Past research has often only focused on the response of a single taxa, and effects ofgrazing in North American salt marshes is understudied. I conducted field studies on threebarrier islands on the coast of Georgia, USA. Each island served as a site for one of three grazingtreatments (cattle, feral horses, and artificial grazing by clipping). Treatment and control plotsat the three sites were sampled for vegetation metrics and invertebrate abundance anddiversity. All three grazing types altered invertebrate community composition, and eachrepresented a different level of grazing intensity. Cattle grazing had a particularly negativeimpact, while artificial grazing produced some opposite effects. Some vegetation characteristicsand taxa had varied responses, but others responded similarly to all three grazing types. Plantheight and katydid density were consistently reduced by the three grazing types, indicating thatgrazed vegetation does not provide katydids with ideal conditions. To further investigate this, Iperformed two katydid feeding experiments and found that a more nutritious diet may notnecessarily be more palatable. The responses of different taxonomic groups and invertebratecommunities and the underlying mechanisms should be considered when making livestock andland management decisions that aim to promote ecosystem functioning.
(contributed by Kori Lugar, 2022)
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    Evaluation of tidal fresh forest distributions and tropical storm impacts using Sentinel-2 MSI imagery
Abstract - Situated in the transitional zone between non-tidal forests upstream and tidal fresh marshes downstream, tidal fresh forests occupy a unique and increasingly precarious habitat. The threat of intensifying anthropogenic climate change, compounded by the effects of historical logging and drainage alterations, could reduce the extent of this valuable ecosystem. The overall goals of this project were to identify forest communities present in the Altamaha tidal fresh forest; develop satellite imagery-based classifications of tidal fresh forest and tidal marsh vegetation along the Altamaha River, Georgia; and to quantify changes in vegetation distribution in the aftermath of hurricanes Matthew and Irma. Based on vegetation data gathered during our field survey, we identified at least eight distinct forest communities with hierarchical clustering methods. Using Sentinel-2 Multispectral Imager (MSI) satellite imagery and a balanced random forest classifier, we mapped land cover for six anniversary images from 2016 to 2021 to examine changes in vegetation distributions. Overall classification accuracies ranged from 80 to 86%, and we were able to accurately discriminate between several classes at the species level. Over our six year study period we did not observe any substantial changes in land cover, including the forest-marsh transition, suggesting resilience to tropical weather impacts. We postulate that this stasis may be due to the large volume of freshwater delivered by the Altamaha River and the extensive tidal marshes of the Altamaha estuary, which protect freshwater wetlands from the short-term effects of saltwater intrusion by reducing salinity and buffering them from acute pulse events such as hurricane storm surges.
(contributed by Galen Costomiris, 2022)
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    Refining cultural and environmental temporalities at the late Archaic-early woodland transition along the Georgia coast, UGA
Abstract - The Late Archaic in the Southeast U.S. (c. 4500–3100 B.P.) was a time of increased sedentism and social complexity, long-distance trade, and relatively large-scale societies. Along the coast, societies constructed monumental shell rings that functioned as persistent places on the landscape and the focal points of village sites that were occupied year-round. Estuaries provided bountiful resources for these villages, including the oysters whose shells comprise the majority of the ring sites. In the terminal Late Archaic, however, a major cultural shift occurred. Shell ring sites were depopulated, and groups became smaller and more mobile. Evidence from various world regions points to a global climatic transition occurring in the mid-Holocene whose regional timing and manifestations varied. On the Georgia Coast, evidence has long pointed to the localized effects of this climatic shift as including one or more sea-level shifts. In this examination of culture and environment at the end of the Late Archaic, we model new and existing radiocarbon dates from shell-bearing archaeological sites and interpret use and depopulation dates within the framework of a high-resolution paleoenvironmental proxy data source – a 5,177-year tree-ring chronology, a site-level standardized representation of annual tree growth, (and an earlier 529-year floating chronology) derived from ancient buried bald cypress (Taxodium distichum) trees at the mouth of the Altamaha River that provides insight into annual environmental conditions on the North Georgia Coast. This chronology and associated analyses indicate that Late Archaic societies weathered a 493-year period of enhanced environmental fluctuation that lasted from 2355 – 1863 B.C.E. and included salinity intrusion events, unreliable rainfall patterns, numerous drought years, and possible hurricanes, speaking to the resilience of both Native American societies of the ancient Southeast as well as the estuary ecosystems that provided their resource base.
(contributed by Katharine Napora, 2021)
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    Groundwater flow and transport at the forest-marsh boundary: A modeling study
Abstract - The forest-marsh boundary, where tidally influenced salt marshes meet a forested upland, is hydrologically complex due to its multiple water inputs. Groundwater flow and salinity transport at this boundary are not well understood. In order to make predictions about salinity at this boundary as it responds to climatic factors, a two-dimensional model was built to simulate groundwater flow and solute transport at a salt marsh on Sapelo Island, Georgia. After calibration based on observed data from wells at the study site, the model can be used to identify patterns in groundwater movement and solute transport that may influence the vegetation and consequently the migration of the forest-marsh boundary. Additionally, the model is designed to be a first step toward identifying the impacts of press and pulse disturbances, such as sea level rise or drought, on the marsh.
(contributed by Sophia C. Sanders, 2021)
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    Dissolved organic matter dynamics in coastal aquatic systems
Abstract - Dissolved organic matter (DOM) is a critical component of aquatic environments and global carbon cycling; it has multiple sources including terrestrial runoff, riverine input, phytoplankton excretion, viral lysis, among others. These inputs have varying levels of contribution depending on temporal and spatial scales as well as environmental variables, making the characterization of the DOM increasingly complex. This dissertation used bulk (dissolved organic carbon - DOC), optical (chromophoric DOM - CDOM), molecular (FT-ICR MS) analyses as well as microbial incubation experiments to investigate changes in DOC concentration, DOM composition, and lability in coastal ecosystems in the southeastern U.S. In CHAPTER 2, changes in DOC concentration and DOM composition were analyzed monthly over a year at the Altamaha River and at the head of Sapelo Sound in coastal Georgia, USA. Results showed that river discharge was the primary driver that changed the DOM composition in both locations. In October 2016, the Georgia coast was hit by Hurricane Matthew, which increased the average DOC concentration by ~ 4 times and strongly augmented the terrigenous signature of DOM. In CHAPTER 3, changes in DOM composition and bacterial processing were investigated at fifteen sites across a riverine-estuarine gradient system as part of the GCE-LTER domain over four seasons. The terrigenous-marine gradient in organic matter sources explained the most variation in DOM composition throughout the year. Increased microbial degradation rates were observed for DOM that had a stronger terrigenous character, especially for samples collected ~ 30 days after Hurricane Irma had impacted the studied area. Finally, in CHAPTER 4, changes in DOC concentration and DOM composition of ambient seawater were characterized after interaction with a loggerhead sponge, Spheciospongia vesparium, in the Florida Bay, USA. The sponge-microbial holobiont removed small, oxygen-depleted, nitrogen-rich compounds and the DOM composition was significantly different than that of the ambient seawater. Microbial incubations suggested that sponge exhalent seawater was less labile than ambient seawater, possibly due to holobiont removal of nitrogen-rich compounds. Overall, this dissertation illuminates the merits of combining different chemical analyses and microbial experiments to better uncover and understand the dynamics of different DOM pools across complex coastal environments.
(contributed by Maria L. Letourneau, 2020)
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    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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    A spatial and temporal investigation of estuarine and shelf flows on the Georgia Coast
Abstract - A series of hydrographic surveys and monitoring instrument deployments were performed within the Georgia Coastal Ecosystem Long Term Ecology Research domain and across the adjacent region of the South Atlantic Bight (SAB). The result were also compared to the finite volume community ocean model (FVCOM) for the Georgia Coastal Ecosystem domain for the year 2014. The region contains three major sounds - Sapelo, Doboy, and Altamaha Sounds - and lies adjacent to the widest portion of the SAB. In 2014, the Winter and Spring seasons experienced high river discharge from the Altamaha River, while Summer and Fall seasonal discharges were relatively low. There was also a strong nor’easter event in early April that corresponded to high northerly winds. Bottom mounted acoustic Doppler current profilers (ADCP) within the sounds indicate that the tides are dominated by the lunar semidiurnal constituent (M2) and the shallow water overtide (M4). Removing the dominant tidal constituents from 24 hour surveys spanning the width of the navigable portion of each of the Sounds results in a net residual export of estuarine waters across all four seasons, with exports being somewhat higher and more to the south during periods of high discharge. Hydrographic surveys on the SAB also show the extent of freshwater intrusion on the shelf with maximal extent during high discharge. Empirical orthogonal function analysis of moorings placed on the SAB during April, 2014 indicate that there are two major modes driving cross shelf flows within the region: along-shore wind stress and freshwater discharge in the coastal waters. Bottom cross shelf flows dictated by wind stress and the impact of winds is larger further offshore. There is only a single major mode apparent in the along shelf flow of coastal waters. The spatial observations are in agreement with model output generated by the FVCOM for the GCE domain.
(contributed by Trevor Richards, 2018)
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    Historical analysis of 70 years of salt marsh change at three coastal LTER sites.
Abstract - Salt marshes are dynamic ecosystems that change in response to natural and human factors. This study used digitization of historical charts and imagery and the Analyzing Moving Boundaries Using R toolkit to measure approximately 70 years of change in lateral marsh extent and the distribution of interior features (ponds, upland, channels, and flats), in marshes of the Georgia Coastal Ecosystems (GCE), Virginia Coast Reserve (VCR), and Plum Island Ecosystems (PIE) LTER sites. Measuring the marsh edge exposed to high fetch and along channels was important for providing complete information on marsh change. Although GCE was dynamic, total marsh area was conserved. VCR experienced marsh loss to flat expansion, which was offset by marsh migration, and overall marsh area was conserved. PIE was erosional, losing marsh along the outer edge, channel widening, and ponding. GCE was considered the most resilient because of its tidal range, sediment supply, and elevation.
(contributed by Christine Burns, 2018)
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    Elucidating natural and anthropogenic marine processes using molecular biomarkers.
Abstract - Molecular biomarkers were first used in fossil fuel geochemistry, marking the beginning of the organic geochemistry field, but soon their utilization expanded to environmental research. This thesis uses both nonpolar and polar biomarker analysis of environmental samples to track inputs, transport, and transformations of organic carbon in the marine environment. In the second chapter, the results showed a massive accumulation of petroleum-derived compounds in Gulf of Mexico sediments after the Macondo well blowout that reached a maximum in the fall of 2010, followed by a strong decrease in concentration. In the third chapter, increased levels of energy reserve compounds (e.g. sugars) and n-alkanols were determined to be an indicator of seasonal thermal stress that corals located in the Florida Keys were subjected to in 2000, and possibly in previous years, providing a chemical distinction between bleaching resistant and nonresistant zooxanthellae (a symbiotic dinoflagellate species that lives in the coral tissue).
(contributed by Lydia Babcock-Adams, 2016)
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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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44 Records
LTER
NSF

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.