No description available.

A high-resolution, finite element-based, shallow water equation model is developed to simulate the tides in the South Atlantic Bight. The model is constructed to include all of the estuarine features along the southeastern United States seaboard: coastal inlets, rivers and tidal creeks, sounds and lagoons, intertidal zones including salt marshes and mangrove swamps, and the Atlantic Intracoastal Waterway. The estuaries are represented in the finite element mesh using triangular elements with side lengths on the order of tens of meters. Also incorporated into the model is a spatially distributed bottom friction parameterization, based on the various landcover and benthic characteristics in the domain. The motivation to use this comprehensive representation of the system was inspired by a desire to capably account for the full estuarine tidal physics. In this approach, no calibration is performed and the model is used as a tool to assess the physical processes it describes. Upon its development, the model is first validated by accurately simulating tidal hydrodynamics in the South Atlantic Bight including the described estuaries. Variants of the model are then constructed by selectively removing estuarine features from the domain. All model representations are subsequently applied in nearly identical simulations: the only differing factor between the simulations being the inland extent of the estuaries described. The solutions are compared with respect to including versus excluding the estuarine features of the domain. Where water surface elevations are shown to be unaffected by the estuarine features of the South Atlantic Bight, tidal velocities exhibit far more sensitivity. This effect is pronounced locally, with regional effects extending offshore. Further analysis is performed on cross-sectional flows recomposed locally and on tidal energetics diagnosed throughout the domain. It is discovered that the high frictional environment of the vast estuarine surface area plays a role in local and regional tidal circulation in the South Atlantic Bight.

No description available.

El Salitral de la Vidriera (Part. Villarino, Prov. Buenos Aires) presenta una gran cantidad de factores de estrés (sequía, salinidad, alta radiación, etc.) que impiden la implantación de muchas plantas; sin embargo, permite la existencia de otras que han logrado adaptarse a tales condiciones ambientales. El objetivo de esta tesis doctoral ha sido analizar la anatomía vegetativa de especies vegetales que conforman la comunidad xero-halófila que se desarrolla en dicho Salitral y la distribución espacial de las mismas en relación al gradiente de salinidad. A partir de esta relación se buscaron especies bioindicadoras que permitan estimar el grado de salinidad del suelo. Se ha estudiado la anatomía vegetativa (foliar y caulinar) de 35 especies pertenecientes a 15 familias botánicas. Hojas y tallos fueron tratados con técnicas tradicionales para estudios anatómicos y epidérmicos, así como también para la descripción de los macropatrones de cristales de oxalato de calcio. Se analizaron, además, muestras de la capa superficial del suelo a fin de cuantificar su salinidad. En gran parte de las especies estudiadas se identificaron características morfológicas y anatómicas que demuestran una alta adaptación al ambiente, siendo las hojas los órganos con mayor variedad de estas características. En general las adaptaciones están relacionadas con la reducción de la pérdida de agua por evapotranspiración y con los mecanismos de regulación de la concentración de sales. Entre las estrategias comunes pueden citarse: reducción del área foliar (por microfilia o plegamiento de las hojas), epidermis con células de paredes engrosadas, estomas pseudo-hundidos o protegidos por tricomas, tejido acuífero, etc. Particularmente en la organización del mesofilo se observaron diseños dorsiventrales, isolaterales y céntricos, siendo éste el carácter más variable entre los estudiados. En general en los tallos se encontraron caracteres que complementan los efectos de las variaciones anatómicas presentes en las hojas. Entre éstos pueden citarse: gran cantidad de tejidos de sostén mecánico (colénquima y esclerénquima) y rápido desarrollo de crecimiento secundario (típico o atípico). La distribución de las especies muestra una estrecha relación con las características del suelo. Ocho especies vegetales fueron consideradas como buenas bioindicadoras de salinidad debido a que su distribución espacial coincide con rangos estrechos de salinidad; con ellas se confeccionó una clave dicotómica que facilita su utilización como bioindicadores. Los estudios sobre especies vegetales de ambientes hostiles revisten especial importancia debido a los profundos cambios ambientales a los que se enfrenta el hombre; este conocimiento permitirá encontrar nuevas aplicaciones y/o utilidades para estas especies. / The Salitral de la Vidriera (Part. Villarino, Prov Buenos Aires) presents a lot of stress factors (drought, salinity, high radiation, etc.) that impede the implantation of many plants, allowing the existence of others which have successfully adapted to such environmental conditions. The objective of this thesis was to analyze the vegetative anatomy of plant species that form the xero-halophytic community of the mentioned salitral and the spatial distribution of these plants in relation with the salinity gradient. From this relationship, bioindicator species were sought to estimate the degree of soil salinity. The vegetative anatomy (leaf and stem) of 35 species belonging to 15 plant families were studied. Leaves and stems were treated with traditional techniques for anatomical and epidermal studies and also to describe their calcium oxalate crystals macropatterns. Samples of topsoil also were analyzed to quantify their salinity and then to find potential bioindicator species. In most of the studied species morphological and anatomical characteristics showed high adaptation to their environment, the leaves being the organs with the greatest variety of these characteristics. Adaptations are generally related to the reduction of water loss by evapotranspiration and mechanisms for regulation of salt concentration. The common strategies found include: reduction in leaf area (by microfily or folding of leaves), epidermal cells with thickened walls, pseudo-sunken stomata or protected by trichomes, aqueous tissue, etc. Particularly in the organization of the mesophyll were observed dorsiventral, isolateral and centric designs, this being the most variable character among those studied. In general stems characters complement the effects of anatomical variations present in the leaves. Among these may be mentioned: great development of mechanical supporting tissues (collenchyma and sclerenchyma) and rapid developing of secondary growth (typical or atypical). Relating the distribution of species with soil characteristics, it was observed that there is a relationship between them. Eight plant species were considered good salinity bioindicators, because their spatial distribution coincides with narrow ranges of salinity; they were compiled in a dichotomous key to simplify their use as bioindicators. Studies on plant species of hostile environments have particular importance due to profound environmental changes that men are facing to, this knowledge will contribute to find new applications and/or utilities for these species.

Increasing human pressure combined with sea level rise and increased storminess is threatening coastal ecosystems around the world. Among these ecosystems, saltmarshes are particularly endangered due to their position in temperate areas with low wave action where human density is often high (e.g. estuaries). Around the UK, centuries of land reclamation have led to a substantial decrease of the area of saltmarsh. Over the past decades, restoration schemes have been implemented in numerous coastal locations in an attempt to counteract this loss. Such schemes involve allowing sea water to inundate a previously embanked area and letting the vegetation develop naturally, thereby reverting to saltmarsh through natural colonisation. However, surveys of restored areas that have looked at the recovery of plant species diversity or functional characteristics often show that restored saltmarshes do not reach the state of a natural saltmarsh ecosystem. While there is much data at the species level, recovery of plant intra-specific diversity (genetic diversity) has not been assessed in restored saltmarsh although this component of biodiversity is receiving increasing attention for its effect on ecosystem function. This thesis represents the first attempt to (1) characterize the nation-wide genetic structure of two important north-west European saltmarsh plant species, the common saltmarsh grass (Puccinellia maritima) and the sea arrowgrass (Triglochin maritima) and (2) compare levels of genetic diversity and structure between restored and natural ecosystems. Microsatellite molecular markers were developed for both species. Using innovative methods to analyse the genetic data obtained for these two polyploid species, this thesis highlights that genetic diversity at the national scale is organised regionally for both species, although gene-flow is still restricted between populations within the same region. Gene-flow between populations is determined by different processes depending on the species. While coastal processes mainly influence gene dispersal in P. maritima, overland routes of dispersal are involved for T. maritima. These differences are believed to be due to differences in dispersal ecology between the two species. Although gene-flow exists between distant saltmarshes, the genetic analysis of P. maritima and T. maritima colonists arriving on restored sites highlighted their local origin and reaffirmed that it is preferable to restore saltmarsh where a nearby natural saltmarsh can act as a source of colonists. A multiple paired-site comparison identified similar genetic diversity between restored and natural saltmarshes indicating that restoration of local genetic diversity is rapid for both species. A single site comparison at Skinflats in the Forth estuary compared fine-scale spatial genetic structure between the restored and natural saltmarsh. Interestingly, no structure was detected for T. maritima either in restored or natural saltmarsh. In contrast, a strong genetic structure organised along the elevation gradient was observed in the natural saltmarsh for P. maritima but was absent in the restored saltmarsh. The origin of this structure is not clear but could be due to restricted gene-flow between individuals from different elevations due to strong post-zygotic selection, as suggested in previous work. In any case, this lack of structure in the restored saltmarsh indicates that genetic recovery is incomplete in this respect for P. maritima. This thesis introduces the growing field of restoration genetics to saltmarsh ecology and identifies the principal population genetic trends in two of the species dominating the vegetation of north-west European saltmarshes community. The information given here will be useful for restoration practitioners and provides a strong foundation for future work characterizing the importance of genetic diversity for saltmarsh function.

Salt marshes provide critical ecosystem services, such as shoreline stabilization, biogeochemical cycling and habitat for wildlife, to much of the world's population living on the coasts. Emergent vascular plants are a critical component of these ecosystems. This study was a comprehensive effort to gain a better understanding of the ecology of salt marsh plants in the Nueces River delta on the south Texas coast. This knowledge is essential to understand the potential anthropogenic impacts on salt marshes, including sea-level rise, global warming, reduced freshwater inflow and coastal erosion. A combination of remote sensing analysis, field studies and experiments were used to allow analysis across spatial scales ranging from landscape patterns of vegetation to leaf level measurements of the dominant species. A novel method of image classification was developed using high-resolution multi-spectral imagery integrated with ancillary data to map the major plant communities at a landscape scale. This included a high marsh assemblage composed primarily of Spartina spartinae and a low marsh community dominated by Borrichia frutescens and Salicornia virginica. Geospatial analysis determined that the location of these plant communities was related to the distance from the tidal creek network and elevation. The B. frutescens and S. virginica assemblage was more abundant at lower elevations along the waters edge, making it vulnerable to loss from shoreline erosion. At a finer spatial scale, gradient analysis was utilized to examine the relationship between elevation, which creates environmental gradients in salt marshes, and species distribution. I discovered that elevation differences of less than 5 cm can influence both individual species and plant community distribution. One interesting finding was that the two dominant species, B. frutescens and S. virginica, share similar responses along an elevation gradient yet are observed growing in monotypic adjacent zones. I constructed a large reciprocal transplant experiment, using 160 plants at 4 sites throughout the marsh, to determine what causes the zonation between these two species. The results of this study found that S. virginica fared well wherever it was transplanted but was a weak competitor. B. frutescens survival was significantly lower in the S. virginica zone than in its own zone suggesting that abiotic factors are important in determining the zonation of this species. However, high spatial and temporal variability existed in environmental parameters such as salinity. This variability may have been caused by the semi-arid climate and irregular flooding typical in the Nueces Marsh. Therefore, I utilized a greenhouse experiment to directly test the importance of the two dominant physical factors in salt marshes, flooding and salinity. The results found that for B. frutescens the effects of flooding were not significant, however salinity at 30% reduced growth. Salinity did not influence growth of S. virginica. The greater ability of S. virginica to tolerate salinity stress has important implications because reduced freshwater inflow or climate change can increase porewater salinity, thus favoring the expansion of S. virginica, and altering the plant community structure. / text

Present models of Holocene estuary evolution are driven largely by changes in relative sea-level (RSL) with little reference to long-term changes in fluvial regime and regional climate. Recent US studies of estuarine sequences have shown that decadal-centennial scale fluctuations in river discharge and freshwater inflow can be inferred by changes in estuarine palaeosalinity and that the timing of these events reflect changes in regional precipitation. It is therefore becoming apparent that estuarine sequences may hold an archive of mid-late Holocene climate change information, as well as being recorders of RSL change. The principal aim of this study is to produce a palaeosalinity-based climate record for southern England during the late Holocene, based on changes in climate-driven freshwater influx into the estuarine environment. The late Holocene palaeosalinity record of the inner Taw Estuary will be reconstructed using diatom salinity index as a proxy for salinity. Nine periods of below-average or above-average palaeosalinity have been recognised in the Taw Estuary since 300 cal.yr.BC. Four intervals of high river discharge are identified at 520-780, 850-1030, 1215-1315, and 1420-1900 cal.yr.AD. Five intervals of low river discharge are identified at 300-520, 780-850, 1030-1215, 1315-1420, and 1900-2000 cal.yr.AD. This shows that there has been significant climatic variation in southern Britain since c.300 cal.yr.AD, with climatic shifts evident in the estuarine record. In order to validate this record, the fluvial geomorphic history of the lower Taw valley was also investigated. There is a strong correspondence between the dry and wet climatic periods identified in the estuary and the geomorphic fluvial history and flood record of the lower Taw valley. Comparisons with other proxy climate records in the UK and Europe show a high degree of correspondence with the Taw Estuary palaeosalinity-based climate record. As the inner estuary environment will also be influenced by RSL change during the late Holocene, RSL change since c.6600 cal.yr.BP was successfully reconstructed in the Taw Estuary, with eleven new validated SLIPs providing evidence of former MSL. The magnitude and rates of RSL rise in north Devon are compared with other RSL records in southern Britain, suggesting that the isostatic history is similar to other areas bordering the Bristol Channel and with the central south coast of England. Fluctuations in palaeosalinity in the late Holocene are seen to be mainly controlled by centennial-scale changes in climate-driven river discharge, rather than RSL change.

Herbivores and pathogens pose a consistent threat to plant productivity. In response, plants invest in structural and/or chemical defenses that minimize damage caused by these biotic stressors. In salt marshes along the Atlantic coast of the United States, a facultative mutualism between snails (Littoraria irrorata) and multiple species of fungi exert intense top-down control of the foundation grass species Spartina alterniflora. Since exposure to herbivores and pathogens are tightly coupled in this system, I investigated whether S. alterniflora utilizes chemical and/or structural defenses to deter both snails and fungi, and examined how plant defenses varied among S. alterniflora individuals and populations. I also assessed how other marsh plants prevent snails from establishing farms, and considered whether interspecific variation in plant chemical defenses influences marsh community structure. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that plant secondary chemistry was the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that differences in plant chemistry were the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability against S. alterniflora. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future.

Saltwater marshes in the Bay of Fundy act as greenhouse gases sinks and reservoirs by fixing atmospheric carbon dioxide and storing it in carbon rich deposits. There are approximately 3,131.5 hectares of saltwater marsh in the Bay of Fundy, of which 958 ha are currently owned by the government or conservation organizations and 2,173.5 ha are owned by private landowners. A multiple bounded discrete choice contingent valuation survey was conducted to estimate landowners' willingness to accept compensation for selling their saltwater marshes to a conservation program. A multiple bounded model developed by Gregory Poe and Michael Welsh (1995) was used to analyze the responses. Mean willingness to accept compensation for one hectare of saltwater marsh was estimated to be $1,004.22, and aggregate willingness to accept compensation for the total of 2,173.5 ha of saltwater marsh owned by private landowners was approximately $2,180,000. Using these estimates and the rate of carbon dioxide-equivalent absorption of saltwater marshes, the opportunity cost of one tonne of carbon dioxide-equivalent sequestered by saltwater marshes in the Bay of Fundy was calculated to range between $16.70 and $19.95. Decision-makers can use this result for policy purposes concerning the achievement by Canada of its greenhouse gases emission reduction commitment under the Kyoto Protocol (1997).

xviii, 160 p. : ill. (some col.) / Salt marshes are intertidal communities dominated by halophytic vascular plants that are subjected periodically to tidal inundation. These species have developed various adaptations to this stress, including tolerances of fluctuating salinity, extended periods of inundation and intervals of anoxic conditions. The marshes are divided into zones of different plant communities based on species' tolerances of ambient estuarine conditions. Abiotic stresses change along the estuarine salinity gradient (marine to riverine), potentially altering development and composition of plant communities. Abiotic gradients associated with tides are not the only factors that contribute to development of plant community composition in salt marshes. Both negative (competition) and positive (facilitation) biological interactions are also important. Factors that influence community structure in salt marshes, particularly on the eastern North American seaboard, have been well studied. In contrast, salt marshes along the Oregon coast are smaller and more discrete and have received comparatively little attention. The community structure and seed bank composition of six marshes along an estuarine salinity gradient were evaluated. Four major community types dominated marshes that varied in the salinity of inundating tidal waters. Community types were relatively consistent throughout the estuary despite the distances between the marshes. Unlike the emergent plant communities, marsh seed bank composition was more similar within a marsh than within a community type. The low and high marsh community types were separated by a distinct boundary in the marine marshes. Although abiotic factors influence the physical separation of communities, competitive interactions commonly determine the upper limit of a species. In Metcalf marsh, however, the upper boundary for two dominant low marsh species was not determined by competition with the high marsh dominant species. Positive biotic interactions between seedlings and existing vegetation in a community are important factors in determining species distributions, particularly in stressful estuarine environments. In salt marshes, where abiotic stress can be harsh, presence of existing vegetation can ameliorate these conditions and enhance germination and seedling establishment. However, interaction between seedlings and the emergent marsh community was highly competitive, though germination of one species was enhanced in the presence of existing vegetation. This dissertation includes un-published co-authored material. / Committee in charge: Dr. Scott Bridgham, Chairperson; Dr. Richard Emlet, Advisor; Dr. Steven Rumrill, Member; Dr. Alan Shanks, Member; Dr. Gregory Retallack Outside Member