Coastal marshes and wetlands are vital natural resources that offer habitats for plants and animals, serve as ecological filtration for soil and water pollutants, and act as protection for coastlines. Fishing, both commercial and sport, has a large economic impact in the study area – the Gulf Coast between Galveston Bay, TX and Oak Grove, LA. The objective of this research was to determine the contribution of Hurricane Ike storm surge sedimentation to long-term marsh aggradation in Texas and Louisiana coastal marshes. The research hypothesized that Hurricane Ike’s storm surge deposit would be equal to decades and possibly even a century’s worth of the average annual non-storm sedimentation. A quantitative field study was performed. The storm surge deposit was examined in a series of 15 transects covering approximately 180 km east of Hurricane Ike’s landfall. Nine of the 15 transects were re-surveyed a year after the initial measurement to assess preservation of the deposit. The results demonstrate that Hurricane Ike contributed between 10 to 135 years’ worth of sediment to coastal marshes along the coasts of Texas and Louisiana, and the sediment deposits have been preserved for over two years.

The Dee estuary, one of the most important British estuaries in terms of size and conservation value, has been subject to extensive colonisation and development of intertidal mudflats by salt marsh vegetation. In the last century, acceleration of this process has been attributed to the ability of Spartina anglica C.E. Hubbard to colonise bare sediment. The research in this thesis aims to investigate the ecological patterns and processes involved in the development of salt marsh vegetation. These have been examined using a large-scale approach involving remote sensing techniques and a small-scale approach to examine ecological processes at the level of the individual plant and species. Large-scale temporal patterns in the distribution were investigated by analysing a sequence of monochrome aerial photographs dating from 1955 to 1997. At the marsh apex, initial rapid colonisation was followed by a decreased rate of expansion and a reduction in the pioneer zone. This suggested a steepening of the marsh elevation gradient, which is interpreted as the marsh approaching its natural limit of expansion. The rate of salt marsh expansion was consistent across the time sequence for the second target area, a cross-section of the marsh gradient, but with S. a«g/zca-dominated colonisation of mudflats changing to colonisation by a pioneer community co-dominated by S. anglica and Salicornia europaea. Large-scale spatial distribution patterns were further investigated using multispectral remote sensing data from 1997. Radiometric data were used to define the spectral characteristics of the major types of salt marsh vegetation. Airborne Thematic Mapper data were used to classify the reflectance data from the whole marsh to determine the spatial distribution of plant communities based on their spectral characteristics. Mapping of these communities provided a baseline that will be a useful tool for future management of the salt marsh. An experimental approach was used to examine the role of abiotic and biotic factors on the growth and interactions between S. anglica and Puccinellia maritima (Huds.) Parl. In two series of competition experiments, P. maritima exerted a one¬way effect over S. anglica. The intensity of this interaction was increased in environmental conditions favourable to P. maritima, and was greater in terms of above-ground than below-ground biomass. In both experiments, S. anglica exhibited a disproportionate reduction in below-ground competitive interaction in abiotic conditions less favourable to P. maritima. A corresponding increase in rhizomes suggested that this is a potential mechanism by which S. anglica may evade competitive neighbours at low marsh elevations. An appreciation of the importance of scale has led to a multi-scaled and holistic view of the ecological process of salt marsh colonisation and development. Integration of both large and small-scale approaches has provided valuable information on the ecological patterns and processes, and has important implications for current and future management of salt marsh in the Dee estuary.

A detailed record of the Late Holocene sea level rise and landscape evolution that has taken place on the Georgia coast is contained within the sedimentary stratigraphy of its salt marsh depositional basins. Global relative sea level (RSL) has risen during the Late Holocene, and the rate of rise has accelerated during the Anthropocene. Jones Narrows marsh stratigraphy and radiocarbon analysis indicate increasing rates of RSL rise for the late Holocene on the Northern Atlantic Coast of Georgia, while FPXRF analysis of the marsh sediments facilitates a chemostratigraphic study of Jones Narrows salt marsh deposition and landscape evolution. Sedimentation and hydrology at the site have been heavily influenced by recent local anthropogenic impacts, which are examined through stratigraphic and spatial methods.

I carried out several large, manipulative greenhouse and controlled-setting experiments to elucidate Panicum hemitomon growth response as influenced by environmental conditions associated with restoring thick-mat floating marsh. Initially, Panicum hemitomon growth response was assessed in conjunction with manipulated nutrient availability and hydrology. Next, I assessed Panicum hemitomon growth response in conjunction with a suite of substrate and mat or containment materials. Finally, I evaluated Panicum hemitomon growth response, as well as overall created floating marsh vegetated development, using both a multi-species planting approach and a suite of Panicum hemitomon establishment techniques. All partitions of Panicum hemitomon biomass (shoot, rhizome, and root material) were enhanced under nitrogen, and to a lesser extent, phosphorous enrichment. Saturated (not inundated) hydrologic conditions were most conducive for robust growth by all partitions of Panicum hemitomon biomass. Substrate and mat or containment materials had a significant effect on Panicum hemitomon vigor, with peat and peat-containing blended substrate materials being most conducive for vigorous Panicum hemitomon growth. Duralast coconut fiber was the most suitable mat or containment material based not only on measures of plant vigor, but also for reasons associated with strength and stability, as well as buoyancy. The combination of Panicum hemitomon and Ludwigia peploides was superior to any other multi-species treatment tested. Ludwigia peploides was highly resilient to transplanting, grew vigorously in a lateral fashion, produced significantly more biomass than any other secondary species, and enhanced overall mat buoyancy, all key metrics regarding successful floating marsh restoration. Equally as important, the large amount of biomass attained by Ludwigia peploides was not totally at the expense of vigorous Panicum hemitomon growth. With respect to establishment technique, the positive response of Panicum hemitomon rhizome growth to humic acid amendment warrants further study. This research generated data that not only advance the body of general ecological knowledge pertaining to Panicum hemitomon, the dominant macrophyte of thick-mat floating marsh, but equally as important, data that are likely to augment or enhance the creation and restoration of this important freshwater marsh type.

Thesis advisor: Tara Pisani Gareau / Salt marshes provide important ecosystem services, including carbon sequestration. Permanently inundated ponds are prominent features in the marsh landscape, encompassing up to 60% of the total marsh area, but they are rarely considered in biogeochemical assessments. I investigated two ponds in Plum Island Estuary, MA to measure and analyze their metabolism. The ponds varied in size and vegetation cover. Oxygen concentrations and pH values were recorded in 15-minute intervals during the entire study period. The ponds regularly become hypoxic or anoxic during night. This is a problem for the estimation of respiration rates which are based on nighttime measurements. To investigate this potential underestimation, several approaches to estimate respiration were used. First, additional measurements of surface water concentrations of dissolved inorganic carbon were made. A comparison of respiration estimates based on oxygen and DIC changes during tidal isolation revealed a reasonable agreement for the most time but not during periods of high productivity during the day or late at night. At this point, oxygen concentrations are so depleted that a change in concentration – the indicator of respiration – is barely detectable. However, DIC based respiration rates indicate that respiration is occurring under these hypoxic/anoxic conditions. This saturation changes during periods of tidal inundation, when a nighttime peak in oxygen concentrations indicates that the flood water is relatively enriched in oxygen compared to the pond water. On three days, it was tested whether under these conditions the oxygen-based respiration rate was higher than under hypoxic conditions (i.e., during tidal isolation). The rates were indeed higher than those under tidal isolation but still not in the range of DIC-based rates. Overall, metabolic rates differed between the two ponds in magnitude, which is likely caused by different vegetation cover, but may be influenced by size, sampling period, and duration as well. / Thesis (BS) — Boston College, 2018. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Earth and Environmental Sciences.

Plant interactions (e.g., competition, facilitation) are critical drivers in community development and structure. The Stress Gradient Hypothesis (SGH) provides a predictive framework for how plant species interactions vary inversely across an environmental stress gradient, predicting that facilitation is stronger with increasing levels of stress. The SGH has been supported in numerous ecosystems and across a variety of stress gradients, but recent research has demonstrated contradictory results. These discrepancies have led to SGH revisions that expand its conceptual framework by incorporating additional factors, such as other stressor types and variations in species life history strategies. In this dissertation, I examine a further modification of the SGH by proposing and testing a Multiple Stress Gradient Hypothesis (MSGH) that considers how plant interactions vary along a continuous gradient of two co-occurring stressors using mangrove and salt marsh communities as a case study. In Chapter 1, I outline the predictive framework of a MSGH, by creating a series of predictions of species interactions. The components of the MSGH predict that stressors of similar types (e.g., resource and nonresource) will have similar effects and be additive. On the other hand, varying species life history strategies and life stages will lead to extremes of plant interactions. In Chapter 2, I performed a series of experiments to test the various components of the MSGH. In Chapter 3, I performed a large-scale observational study to test whether multiple co-occurring stressors altered the cumulative effects on plant interactions, and if these stressors should be grouped (e.g., resource and non-resource, abiotic and biotic, etc.) to enhance predictability. From a series of studies conducted herein, I concluded that co-occurring stressors are important factors that control complex species interactions as shown in my MSGH modeling approach. Further, future theories need to incorporate species-specific and stressor specific grouping when modeling how species interactions shape communities. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2013.

Salt marshes are some of the most productive and valuable landscapes on earth, but they are vulnerable to the effects of sea-level rise, erosion and eutrophication. These processes act on a wide range of temporal and spatial scales, which complicate assessments of the health and stability of marsh ecosystems. High-frequency monitoring using in situ sensors captures the complete range of these dynamics, but extracting meaningful physical and ecological information from these signals requires process-based models coupled with statistical techniques. I develop and apply such methods to study two coastal landscapes, a coastal pine forest on the Eastern Shore of Virginia and a mesotidal salt marsh complex in the Plum Island Estuary, Massachusetts. Observations from groundwater wells in the Virginia pine forest indicate that storms are the dominant controls on the hydrology of the forest and that tidal influence is nonexistent. This forest exhibits a distinct spatial pattern in age structure in which young trees do not grow at low elevations. This pattern can be explained by a model that includes the interaction of sea-level rise, storms and the age-dependent variation in tree stress response, which predicts that the long-term evolution of the boundary is an ecological ratchet. Stresses due to sea-level rise slowly push the boundary at which young trees can survive upslope. Powerful storms then kill the mature, persistent forest at low elevations, which quickly pushes the forest boundary up to the regeneration boundary. Salt marshes need to accumulate sediment to replenish material lost as sea-level rises and creek banks erode. Fluxes of sediment can be monitored with simultaneous high-frequency observations of flow from acoustic Doppler current profilers and turbidity from optical backscattering sensors. I first investigate the relationship between water level and flow in marsh channels and develop predictive stage-discharge models to simplify the monitoring of fluxes. I then construct sediment budgets for eleven salt marshes in the Plum Island Estuary. The observed budgets depend strongly on the unique hydrodynamic conditions of each marsh channel. Variability in these conditions leads to the observed spatial and temporal variability in sediment fluxes from these marshes.

Extensive shell ridges frame the edges of marsh platforms in parts of the Biloxi Marsh of southeast Louisiana. The exact sources of the shells in these accumulations have not been clearly identified but the most likely source is a combination of shells from modern offshore and shells excavated from buried St. Bernard delta deposits. Larger or fetch-protected ridges remain stable through time, whereas ridges facing open water are more mobile, moving as much as 38 m inland from July 2017 to January 2018. Behind stable ridges, marsh platform biomass is relatively unaffected. When ridges are mobile, vegetation is smothered, leaving an exposed platform that lacks aboveground vegetation to dampen wave energy and fragments into “blocks” along its terraced edge, which in turn are deposited onshore. In the future, marshes will likely erode fastest in areas where shell ridges are mobile and remain resistant where shell ridges are stable.

The Bandon Marsh is a large marsh restoration project located in southwest Oregon. The land has been previously used for dairy farms and much of the marsh was used for cattle grazing. The goal of the restoration is to recreate a natural habitat for shorebirds and fish. The purpose of this thesis is to gather and analyze data on the geology of the marsh and both ground and surface water quality to evaluate its ability to support biology. The US Fish and Wildlife Service began restoration on the Bandon marsh in 2005. Research on the Ni-les'tun Unit began in that same year with Geoprobe coring, Ground Penetrating Radar (GPR), piezometer well installation, and surface water analysis. Twelve cores were taken with the Geoprobe in 2006 and later analyzed for this thesis. A total of 50 GPR lines were run across the marsh ranging from ~25 m to 1,200 m in length for a total of about 9,700 meters (9.7 km). The ten piezometer wells were sampled to collect groundwater pH, oxidation-reduction potential, salinity, temperature, and well water elevation. Twelve channel sampling sites were chosen to be sampled in three field runs taking place in winter 2011, summer 2011, and winter 2012. The summer 2011 and winter 2012 sampling runs were done after tide gates had been removed from the marsh. The Geoprobe core samples were retrieved for extensive lab analysis. Analyses included; bulk density, porosity, permeability, and grain size studies. Lab results revealed a low permeability fine grained upper sedimentary unit ranging from ~0.5 to ~2.5 meters depth with a coarser grained higher permeability lower unit. GPR lines were analyzed for groundwater surface depths and buried channel cut and fill features (Peterson et. al., 2004). GPR results showed a fairly shallow groundwater surface around 0.5 meters in the north down to 2.0 meters in the south. The piezometer wells showed a seasonal variation in well water elevation with higher elevations in the winter and lower in the summer. Well water chemistry showed both seasonal and spatial variations. Values for pH and dissolved oxygen were lower in the north side of the marsh and higher in the south side, and pH was higher in the summer than in the winter. Wells that were more proximal (within ~400 m) to the Coquille River Estuary showed higher conductivity (salinity) values than those that were more distal (greater than ~400 m). Channel sampling results showed similar trends as the groundwater results. The lower pH values tended to be in the north side of the marsh as well as lower dissolved oxygen values. Again, there was a spatial variability in conductivity with the higher values found closer to the Coquille River. Conductivity in the channel water showed a great seasonal variability with the highest values occurring in the summer time and much lower values in the winter. As expected, channel water increased about 10°C on average from winter to summer. The results of all of these observations and analyses are combined to put together a generalized flow model showing the different water inputs into the channel waters on the Ni-les'tun Unit. Once these inputs were derived, conclusions can be made on the quality of the water and its ability to support small aquatic life.

Redhead duck (Aythya americana) nesting and habitat change was studied in Knudson Marsh, Utah, in 1974 and 1975, and compared with earlier studies from 1950 and 1955 on the same marsh. Water condibons in 1975 were found to be similar to those in 1950, both years of favorable habitat, yet there was a decline in numbers of redheads from 500 pair s in 1950 to 50 pairs in 1975. The number of nests found also declined from 151 in 1950 to 49 in 1975. Water conditions were poor in 1955 and slightly more favorable in 1974, but there was a decline from 95 pairs and 49 nests in 1955 to 50 pairs and 23 nests in 1974. Success of active nests was greater in the present study than in 1950, but hatching success in successful nests was greater in 1950. No appreciable change in the vegetational composition of the marsh was detected between 1950 and the present study.