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Consistent shoreline development and urbanization have historically resulted in the loss of wetlands. However, some construction activities have inadvertently resulted in the emergence of new tidal wetlands, with prominent examples of such anthropogenic wetlands found within the Hudson River Estuary. Here, we utilize two of these human-induced tidal wetlands to explore the sedimentary and hydrologic conditions driving wetland development from a restoration perspective. Tivoli North Bay is an emergent freshwater tidal marsh, while Tivoli South Bay is an intertidal mudflat with vegetation restricted to the seasonal growth of aquatic vegetation during summer months. Using a combination of sediment traps, cores, and tidal flux measurements, we present highly resolved sediment budgets from two protected bays and parameterize trapping processes responsible for their divergent wetland evolution. Utilizing a 16-year tidal flux dataset, we observe net sediment trapping in Tivoli North for most years, with consistent trapping throughout the year. Conversely, sediment flux measurements at Tivoli South reveal net sediment loss over the study period, with trapping constrained to the summer months before being surpassed by large sediment exports in the fall and early spring. The timing of the transition from sediment import to export marks the end of the invasive water chestnut growing season and the onset of the associated exodus of both sediment and organic material from Tivoli South. When sediment cores collected for this study are compared to sediment cores collected in 1996, 137Cs profiles confirm little to no sediment accumulation in Tivoli South over the previous two decades. These results support the hypothesis that water chestnut is serving to inhibit sediment trapping and facilitate sediment erosion, preventing marsh development in Tivoli South. The longevity of this dataset highlights the capacity of aquatic vegetation to regulate sediment exchange and geomorphology in enclosed bays when provided an opportunity to colonize. Results of this project provide evidence to inform the management of restoration projects in river systems with freshwater tidal wetlands, especially those affected by invasive species of aquatic vegetation. In bays where tidal sediment supply is not limited, water chestnut removal may present a viable strategy to facilitate marsh restoration.

Background: Majority of cancer interventions today are performed percutaneously using needle-based procedures, i.e. through the skin and soft tissue. Needle insertion is known as one of the recent needle-based techniques that is used in several diagnostic and therapeutic medical procedures such as brachytherapy, thermal ablations and breast biopsy. The difficulty in most of these procedures is to attain a precise navigation through tissue reaching target locations. Insufficient accuracy using conventional surgical needles motivated researchers to provide actuation forces to the needle’s body for compensating the possible errors of surgeons/physicians. Therefore, active needles were proposed recently where actuation forces provided by shape memory alloys (SMAs) are utilized to assist the maneuverability and accuracy of surgical needles. This work also aims to introduce a novel needle insertion simulation to predict the deflection of a bevel tip needle inside the tissue. Development of a model to predict the behavior of the needle steering in the soft tissue has been always a point of interest as it could improve the performance of many percutaneous needle-based procedures. Methods: In this work first, the actuation capability of a single SMA wire was studied. The complex response of SMAs was investigated via a MATLAB implementation of the Brinson model and verified via experimental tests. The material characteristics of SMAs were simulated by defining multilinear elastic isothermal stress-strain curves. Rigorous experiments with SMA wires were performed to determine the material properties as well as to show the capability of the code to predict a stabilized SMA transformation behavior with sufficient accuracy. The isothermal stress-strain curves of SMAs were simulated and defined as a material model for the Finite Element Analysis of the active needle. In the second part of this work, a three-dimensional finite element (FE) model of the active steerable needle was developed to demonstrate the feasibility of using SMA wires as actuators to bend the surgical needle. In the FE model, birth and death method of defining boundary conditions, available in ANSYS, was used to achieve the pre-strain condition on SMA wire prior to actuation. This numerical model was validated with needle deflection experiments with developed prototypes of the active needle. The third part of this work describes the design optimization of the active using genetic algorithm aiming for its maximum flexibility. Design parameters influencing the steerability include the needle’s diameter, wire diameter, pre-strain, and its offset from the needle. A simplified model was developed to decrease the computation time in iterative analyses of the optimization algorithm. In the fourth part of this work a design of an active needling system was proposed where actuation forces of SMAs as well as shape memory polymers (SMPs) were incorporated. SMP elements provide two major additional advantages to the design: (i) recovery of the SMP’s plastic deformation by heating the element above its glass transition temperature, and (ii) achieving a higher needle deflection by having a softer stage of SMP at higher temperatures with less amount of actuation force. Finally, in the fifth and last part of this study, an Arbitrary-Lagrangian-Eulerian formulation in LS-DYNA software was used to model the solid-fluid interactions between the needle and tissue. A 150mm long needle was considered to bend within the tissue due to the interacting forces on its asymmetric bevel tip. Some additional assumptions were made to maintain a reasonable computational time, with no need of parallel processing, while having practical accuracies. Three experimental tests of needle steering in a soft phantom were performed to validate the simulation. Results: The finite element model of the active needle was first validated experimentally with developed prototypes. Several design parameters affecting the needle’s deflection such as the needle’s Young’s modulus, the SMA’s pre-strain and its offset from the neutral axis of the cannula were studied using the FE model. Then by the integration of the SMA characteristics with the automated optimization schemes an improved design of the active needle was obtained. Real-time experiments with different prototypes showed that the quickest response and the maximum deflection were achieved by the needle with two sections of actuation compared to a single section of actuation. Also the feasibility of providing actuation forces using both SMAs and SMPs for the surgical needle was demonstrated in this study. The needle insertion simulation was validated while observing less than 10% deviation between the estimated amount of needle deflection by the simulation and by the experiments. Using this model the effect of needle diameter and its bevel tip angle on the final shape of the needle was investigated. Conclusion: The numerical and experimental studies of this work showed that a highly maneuverable active needle can be made using the actuation of multiple SMA wires in series. To maneuver around the anatomical obstacles of the human body and reach the target location, thin sharp needles are recommended as they would create a smaller radius of curvature. The insertion model presented in this work is intended to be used as a base structure for path planning and training purposes for future studies. / Mechanical Engineering

The needle-based procedures are usually considered minimally invasive. However, in insertion into soft tissues such as brain and liver, the tissue damage caused by needle insertion can be very significant. From the literature, it has been known that reduction in needle insertion and extraction forces as well as tissue deformation during the insertion results in less invasive procedure. This work aims to design and develop a new bioinspired design for surgical needles which reduce the insertion and extraction forces of the needle, and its damage to the tissue. Barbs in honeybee stinger decrease its insertion force significantly. Inspired by that finding, a new honeybee-inspired needle was designed and developed, and its insertion mechanics was studied. To study the insertion mechanics of honeybee-inspired needle, insertion tests into artificial and biological tissues were performed using both honeybee-inspired and conventional needles. The barb design parameters effects on needle forces were studied through multiple insertion and extraction tests into PVC gels. The design parameters values of the barbs were experimentally modified to further reduce the ultimate insertion and extraction forces of the needle. Bioinspired needle with modified barb design parameters values reduces the insertion force by 35%, and the extraction force by 20%. To show the relevance, the insertion tests into bovine liver and brain tissue were performed. Our results show that there was a 10-25% decrease in the insertion force for insertions into bovine brain, and a 35-45% reduction in the insertion force for insertions into the bovine liver using the proposed bioinspired needles. The bioinspired and conventional needles were manufactured in different scales and then used to study the size scale effect on our results. To do so, the insertion tests into tissue-mimicking PVC gels and liver tissues were performed. The results obtained for different sizes of the needle showed 25-46% decrease in the insertion force. The tissue deformations study was conducted to measure tissue deformation during the insertion using digital image correlation. The tissue deformation results showed 17% decrease in tissue deformation using barbed needles. A histological study was performed to accurately measure the damage caused by needle insertion. Our results showed 33% less tissue damage using bioinspired needles. The results of the histological study are in agreement with our hypothesis that reducing needle forces and tissue deformation lead to less invasive percutaneous procedures. / Mechanical Engineering

<p dir="ltr">Non-native biological invasions are one of the leading concerns for global biodiversity. The establishment of invasive species reduces local biodiversity, shifts species composition, changes successional trajectories, and alters ecosystem functions. This thesis examines two aspects of invasive plants: (1) the distribution and the most important climatic and anthropogenic drivers of invasive trees across the eastern United States, and (2) an evaluation of invasive plant removal and herbaceous recovery from a government cost-share program that provides financial support for invasive plant management by private landowners.</p><p><br></p><p dir="ltr">Our first study focused on identifying the distribution of invasive trees, and the factors associated with their distribution. This is essential to predicting spread and planning subsequent management. Using USDA Forest Inventory Analysis (FIA) data and random forest modeling, we examined the distribution, and variables associated with the distribution, of invasive tree species. Invasive trees were found in 10,511 out of 299,387 FIA plots. Invasive species basal area and density (trees per ha; TPH) were highest within the central and southern Appalachian Mountains, Michigan, the Northeast, and the southern Coastal Plain of the United States. A random forest model of invasive species basal area (R²= 0.47, RMSE = 0.47) and density (R²=0.46, RMSE=0.50) vs. environmental variables found that both invasive basal area and density were most strongly associated with human footprint, followed by various climatic variables. An equivalent model of native tree basal (R²=0.53, RMSE=9.25) and TPH (R²=0.47, RMSE=8.64) found that native tree basal area and density were most strongly associated with aridity followed by various climatic variables. As human footprint increased, invasive tree basal area and density increased. These results suggest that the distribution of invasive trees is reliant on human alterations to forests.</p><p><br></p><p dir="ltr">Our second study focused on Environmental Quality Incentives Program (EQIP), a federal cost-share program that has provided $25 billion of financial assistance to farmers and non-industrial private forest owners. Few studies have examined whether this program facilitates the recovery of the herbaceous layer while decreasing the dominance of invasive plant species. We surveyed the herbaceous layer of EQIP-treated and untreated (reference) forests across three physiographic regions of Indiana. Using non-metric multidimensional scaling (NMDS) ordination and linear mixed effects models, we evaluated the species composition, richness, diversity, evenness, floristic quality index, and herbaceous-layer cover of EQIP and reference sites. We also used linear mixed models to evaluate how EQIP site treatment affected the diversity of native plant species. Sites treated with EQIP contracts typically had significantly higher native species richness, Shannon’s diversity, and floristic quality than reference sites. There were significant separations in species composition between EQIP treated and reference forests state-wide and in the southern non-glaciated region of Indiana, although composition overlapped between EQIP and reference forests. Our study suggests that EQIP-funded treatments promote increased species richness and diversity. However, the persistent overlap in species composition we observed may signify biotic homogenization due to a long-shared history of anthropogenic disturbances between EQIP and reference sites. Therefore, active restoration of the herbaceous layer might be needed to allow a full recovery after invasive removal.</p>

Water hyacinth (Eichhornia crassipes) is a floating non-native plant that has been reoccurring in Lake Chapala, Jalisco, Mexico for more than 100 years. In this research, I explore the effects of water hyacinth on freshwater ecosystems worldwide and specifically on Lake Chapala. In chapter 1, I reviewed studies conducted on water hyacinth worldwide and found that the effects of water hyacinth on water quality are similar but the magnitude of effects is dependent on the percent cover and potentially the spatial configuration of water hyacinth mats. Water hyacinth's effect on aquatic invertebrates, fish, and waterbirds is less predictable and dependent on conditions prior to invasion. In chapter 2, I tested for relationships between percent water hyacinth cover and waterbird abundance, species diversity, community composition, and habitat use. In general, I found a weak positive relationship or no relationship between these variables. In Chapter 3, I monitored habitat use by American Coots (Fulica americana) in a variety of habitats around Lake Chapala. I found that the time spent in water hyacinth positively corresponded to the percent water hyacinth cover and that the time foraging in water hyacinth was positively related to the time spent in water hyacinth. In Chapter 4, I compared invertebrate assemblages in open water to those within and at the edge of water hyacinth mats, emergent vegetation, and submerged trees. I also examined invertebrate assemblages within the roots of water hyacinth plants and compared assemblages between patch and shoreline water hyacinth plants. I found that density and taxonomic richness of water column invertebrates were generally higher in association with water hyacinth, but that mean percent cover of water hyacinth affected the magnitude of differences among habitats and vegetation types. I did not find significant differences in root invertebrate density and taxonomic richness between patch and shoreline water hyacinth plants. In chapter 5, I discuss how water hyacinth affected dissolved oxygen and water transparency on a small, localized scale, but was not the driving factor for seasonal differences. The overall results suggest that water hyacinth had a minimal ecological effect on Lake Chapala during this study. / Ph. D.

Nonnative fishes are a major threat to biodiversity and new species continue to be introduced. In this dissertation, I described patterns and assessed determinants of fish invasions in the Mid-Atlantic region of the United States. Data on nonnative fish distributions were obtained from the United States Geological Survey's Nonindigenous Aquatic Species Database (NASD). Nonnative fishes are introduced by a variety of pathways, and prevention efforts can be optimized by focusing on pathways posing the greatest risk of new invasions. To assess the importance of existing pathways, I described the species associated with each pathway, analyzed the number of species introduced by decade for certain pathways, and estimated the detectability and probability of establishment of species introduced by each pathway. Additionally, I reviewed the efficacy of existing regulations for preventing introductions via each pathway. Historically, the intentional introduction of centrarchids and salmonids for sport was the dominant pathway. Pathways currently posing the greatest risks included bait release, illegal introductions, stocking of private ponds, and several pathways associated with economic activities. These pathways involved cyprinids, catostomids, and species exotic to North America. Regulations varied considerably among states, and I suggest that region-wide prohibitions on the release of nonnative species into the wild would help prevent additional introductions. Mid-Atlantic region watersheds differ considerably in nonnative species richness (NNSR), suggesting they are not equally invasible. I analyzed relationships between ecosystem characteristics and invasibility by compiling data on watershed characteristics and correlating these with NNSR. I included measures of colonization pressure (i.e., the number of species introduced) and research effort, which can bias patterns of NNSR. After controlling for these factors, the range in elevation in a watershed explained the greatest variation in NNSR. Highland watersheds had greater NNSR, probably because of greater habitat heterogeneity due in part to human activity. I suggest that NNSR can be reduced by restoration activities that reduce the diversity of artificial habitats available in highland watersheds. Ecosystems with similar NNSR may be invaded by different species, because differences in ecosystem characteristics may regulate the types of species that are able to establish. To explain differences in nonnative species among ecosystem types, I grouped Mid-Atlantic region watersheds by nonnative community and tested for differences in ecosystem characteristics among groups. Four groups were identified. A large, speciose group in the north-west portion region was characterized by smallmouth bass (Micropterus dolomieu). A large, speciose group in the south-west portion of the region was characterized by largemouth bass (Micropterus salmoides). Two smaller groups with few species were found on the coastal plain; one to the north, characterized by black crappie (Pomoxis nigromaculatus) and a second to the south characterized by white crappie (Pomoxis annularis). Nonnative community type was correctly predicted 80% of the time by models based on temperature and range in elevation. Relatively uninvaded watersheds in the south-east part of the region were predicted to host the most diverse nonnative community, suggesting that risks of invasion are high there. These results demonstrate the importance of species identity in determining ecosystem invasibility. There is no consensus on how to estimate the relative impacts of nonnative species. I developed and compared several approaches for doing so. I estimated impact by surveying fish biologists regarding the abundance and socioeconomic and ecological impacts of each species. I obtained fish collection records as an additional estimate of abundance and consulted reports of impacts in the NASD. I consulted reports of impacts in global invasive species databases as a basis for comparison. I compared top-ranked species among approaches, and game and non-game biologists' ratings of game and non-game species for each survey question. Top-ranked species differed considerably among approaches. Non-game biologists gave higher ecological impact ratings to both game and non-game species. Approaches assessing socioeconomic impacts are most appropriate for informing social decisions, such as restricting the possession or trade of a species. A combination of data from approaches assessing ecological impacts and abundance is most appropriate for studies of ecological patterns, such as testing for differences in traits between high- and low-impact species. These approaches are transferrable to other regions and taxa, and can inform management decisions and improve efforts to identify factors correlated with high-impact invaders. Collectively, my results can aid in reducing the effects of nonnative fish invasions by enabling managers to focus prevention efforts on high-impact species likely to invade particular ecosystems via known pathways. For example, bait releases, illegal introductions, private stocking, and several pathways associated with economic activities present the highest risks of future invasions, and warrant attention aimed at preventing invasions. Prevention could also be focused on several watersheds in the south-east part of the region, which currently have few established species but were predicted to be invasible by bluegill (Lepomis gibbosus), bluntnose minnow (Pimephales notatus) channel catfish (Ictalurus punctatus), and warmouth (Lepomis gulosus). This work represents major advancements in invasion biology, including new links between species identity and ecosystem invasibility and the development of methods for quantifying impact. / Ph. D.

Ailanthus altissima (Mill.) Swingle is a tree native to Asia that was intentionally introduced into the United States in the late eighteenth century. Ailanthus altissima has become an invasive species that has spread throughout most of North America. Lack of effective management tactics for suppression of A. altissima has lead to alternate control methods. Investigations into using biological control with the weevil Eucryptorrhynchus brandti were initiated in 2004. Studies were conducted to understand the general biology of E. brandti, rearing efficacy, and host specificity. Eucryptorrhynchus brandti is univoltine, has a life cycle similar to the closely related species Cryptorhynchus lapathi (L.), with 6 instars, and completes development in 126 ± 6.5 d at 25°C. Efficient egg to adult rearing was accomplished by caging 12 m and 12 f for 7 days on 23 – 92 cm long billets. Males and females can be differentiated by the structure of the metathoracic sternite and 1st abdominal segment. Host specificity experiments show that E. brandti preferentially feeds on North American A. altissima when tested against 29 species from 14 families. Larval development in the rare species Leitneria floridana Chapm. was apparent. Additional studies show that A. altissima does not occur across L. floridana distribution but may have the potential to invade L. floridana sites. / Ph. D.

Exotic invasive plants have become a significant issue in the Southeastern United States for private landowners. These plants possess characteristics that allow for rapid growth and easy adaptation to many growing conditions, often outcompeting native vegetation and altering wildlife habitat, especially in disturbed areas. Disturbance, including access roads, trails, harvest sites, powerline corridors, and fence rows, is common on private land. Private landowners are often left to combat these problems without many monetary or expertise resources that are available to federal lands. Three field sites, each in a different physiographic province in Virginia, were surveyed for exotic invasive populations and sampled with nested overstory, understory, and regeneration plots and wildlife point intercept transects using paired plots during the summers of 2006 and 2007. Species richness of the overstory and understory did differ, but native percent understory cover and sapling density remained unchanged. Tree density and forest basal area were reduced with presence of exotic invasive plants. Regeneration diversity and density decreased in areas of exotic plant invasion. Eastern cottontail habitat suitability increased with the presence of exotic invasive plants. Suitability of habitat for the gray squirrel, downy woodpecker food, black-capped chickadee reproduction, and eastern wild turkey cover declined with the occurrence of exotic invasive plants. Twenty three of thirty seven total invasive plots were within twenty feet of a disturbance area. Continual assessment of impacts will help provide a better understanding of the nature of exotic invasive plants to landowners and may help them to manage and prevent plant invasions. / Master of Science

Peatlands are a diverse type of wetland ecosystem, characterized by high levels of soil organic matter, that provide a wide array of ecosystem services including water storage and filtration, carbon sequestration, and unique habitats. Draining peatlands degrades their resilience to future disturbances, notably including high intensity, soil-consuming fires. Peat soil fires are unique in that they can smolder vertically through the soil column, with consequences ranging from large carbon emissions to altered hydrology and dramatic shifts in vegetation communities. In this work we had two complementary objectives to understand both the drivers and impacts of smoldering fires at the Great Dismal Swamp (VA and NC, USA). First, we developed and verified a new method to model peat burn depths with readily available water level and peat hydraulic property data. Our findings suggest that drainage weakens both short- and long-term controls on peat burn depths by reducing soil moisture and by decreasing peat water holding capacity. To address the impacts of smoldering fires, we quantified the abundance of the noxious Phragmites australis in a large fire scar and the extent to which altered hydrology influenced its occurrence. We did so by leveraging satellite imagery, random forest models, LiDAR data, and water table observations. Our results suggest that P. australis is aided by a hydrologic regime generated, in part, from the combined effects of drainage and deep smoldering fires. Our conclusions from these two studies contribute to the scientific understanding of smoldering peat fires and can inform management efforts. / Master of Science / Peatlands are a diverse type of wetland ecosystem that have characteristically thick levels of organic-rich soil, known as peat. Peatlands are home to a variety of unique plants and animals, store large amounts of carbon, and provide water storage functions. Peatlands were historically drained to enable development and conversion to other land usages, which had many unintended consequences like increasing their risk to wildfires that consume soil organic matter. An intense peat fire can smolder down through the peat, with impacts ranging from large releases of carbon to changes in water levels and vegetation communities. In this work we had two objectives aimed at understanding the drivers and impacts of smoldering peat fires in the Great Dismal Swamp (GDS) (VA and NC, USA). First, we developed and verified a new method of modeling how deep peat fires burn by using readily available water level and soil property data. Our findings suggest that drainage weakens both the short- and long-term controls on peat fire burn depths by reducing soil moisture and by limiting the ability of peats to hold water. We also studied how water levels in a post-peat consuming fire environment influence the amount of the weedy Phragmites australis. We did so by using satellite imagery, elevation data, and water table observations. Results from this investigation suggest that the combined effects of drainage and deep smoldering fires help to create ideal conditions for P. australis invasion and establishment. Our findings from these two studies add to the scientific understanding of smoldering peat fires and may inform land management decisions.