Environmental Science & Technology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2748

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End date: 2019Subject: search.filters.subject.Ecology

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    Anthropogenic disturbance alters plant and microbial communities in tidal freshwater wetlands in the Chesapeake Bay, USA
    (2019) Gonzalez Mateu, Martina; Yarwood, Stephanie A; Baldwin, Andrew H; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Tidal freshwater wetlands are often found near urban centers, and as a result of human development they are subject to multiple environmental stressors. Increases in nutrient runoff, sedimentation, and hydrologic alterations have had significant impacts on these systems and on the ecosystem services they provide. One of the consequences of these stressors is the expansion of invasive species that can affect native biodiversity and the many biogeochemical processes that are key to wetland ecosystem function. This research looked at how human activities affect microbial communities in tidal freshwater wetlands, and explored various aspects of an invasive plant’s ecology in the Chesapeake Bay. In our first study, we found that microbial community composition differed along a rural to urban gradient and identified microbial taxa that were indicators of either habitat. Rural sites tended to have more methanogens and these were also indicators in these system, whereas in urban systems nitrifying bacteria were the main indicator taxa. This study suggested that urban wetlands have different microbial communities and likely different functions than those in rural areas, particularly concerning nitrogen and contaminant removal. Our second study looked at management of an invasive lineage of Phragmites australis which is commonly found in wetlands impacted by nitrogen enrichment. We evaluated the effects of different C:N ratios on the competitive ability of this lineage and a native North American lineage. Even though carbon addition did not improve the native’s competitive ability, we identified facilitative interactions when both lineages were growing together. This suggests that native and invasive Phragmites might coexist if there are no additional disturbances to the system. Our last study focused on plant-fungal interactions, and found that both Phragmites lineages benefitted from inoculation with fungal endophytes under salt stress. These results suggest that studies of plant-fungal interactions can yield insights into mechanisms of invasion, and could be further investigated in native wetland plants susceptible to increased salt stress following sea-level rise. Our results provide insights into plant and microbial ecology in the Chesapeake Bay’s tidal freshwater wetlands, and improve our understanding of the invasion process and management strategies of Phragmites australis.
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    Quantifying the Ecosystem Metabolism of a Tidal Estuary as a Consequence of Aeration
    (2019) Gotthardt, Zachary; Harris, Lora A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    As anthropogenic activity affects shallow estuaries it is imperative to quantify how these systems respond to changing conditions. Ecosystem metabolism is an integrative, metric to measure how ecosystems change, and can act as the focus of comparative experiments. We leveraged an aeration system, to examine the ecosystem metabolism of the estuary through comparative experiments. The aeration system allows us to study a normoxic, eutrophic ecosystem. Chapter 1 explains the causes and effects of eutrophication, with an emphasis on the connection between hypoxia and eutrophication. In chapter 2, we describe an experiment focused on quantifying the ecosystem metabolism in a tidal, eutrophic estuary where engineered aeration has been operational since the 1980s. The aeration system provides an ideal site for addressing some of the difficulties inherent to studying eutrophication. In our experiments, we observed evidence of chemoautotrophy when the aerators were operational. Bottle methods and open water methods provided conflicting results.
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    Spatio-temporal mechanisms of urban mosquito coexistence in Baltimore, MD
    (2019) Saunders, Megan Elizabeth Maria; Leisnham, Paul T.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Understanding the interactions governing species distributions and community structure are of fundamental ecological importance. Mosquitoes that utilize container habitats at their larval stage usually engage in strong competition and competitive exclusion is expected; however, numerous container-utilizing mosquito species co-occur in the same individual container habitats and regionally coexist. I investigated spatial and temporal mechanisms governing the distributions and abundances of the competitively superior invasive Aedes albopictus and resident Culex spp. mosquitoes in four neighborhoods with varying socioeconomic status in Baltimore, Maryland. Specifically, I investigated if the findings from both field surveys and field and laboratory experiments were consistent with four spatial and temporal hypotheses for species coexistence that act at different scales: spatial partitioning among neighborhoods and blocks, seasonal condition-specific competition, aggregation among individual container habitats, and priority colonization effects within individual containers. I found modest but important evidence for all hypotheses that could each facilitate Culex spp. coexistence with Ae. albopictus. I found clear neighborhood effects, with low SES neighborhoods supporting higher abundances of mosquitoes than high SES neighborhoods overall, but with the highest abundances of Ae. albopictus in low SES neighborhoods and Culex spp. being more variable among neighborhoods. Culex spp. abundances were higher in the early summer compared to mid-summer peaks in abundance for Ae. albopictus. Laboratory competition trials showed increased aggregation of Ae. albopictus had a slight positive effect on Culex spp. population performance, and aggregation conditions sufficient for coexistence among experimentally placed ovitraps and negative associations of Aedes and Culex genera in resident containers in the field. Lastly, I found that priority colonization of a container leads to stronger population performance for both species, and that resource availability seems to affect Culex spp. more than competition. The results of my dissertation have revealed the role of several ecological mechanisms that may facilitate the regional coexistence of Culex spp. with Ae. albopictus and is among the first bodies of work to do so. Due to their roles in the transmission of human pathogens, future examination of other spatial and temporal mechanisms of coexistence between Ae. albopictus and resident Culex spp. is warranted.
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    Soil microbial processes and community structure in natural and restored tidal freshwater wetlands of the Chesapeake Bay, Maryland, USA
    (2017) Maietta, Christine E.; Yarwood, Stephane A.; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Tidal freshwater wetlands are integral to downstream water quality because they capture, store, and transform nutrients. Unfortunately, anthropogenic stressors are negatively impacting these habitats. While wetland restoration is helping to reinstate their presence in the landscape, restored wetlands frequently differ physically, chemically, and biologically from their natural counterparts. This research examined plant, soil, and microbe relationships and how their interactions affect soil carbon (C) storage and cycling in natural and restored tidal freshwater wetlands of the Chesapeake Bay, MD, USA. This research yielded important findings regarding differences between natural and restored habitats. First, we discovered soil microbial community composition of an urban tidal freshwater wetland retained similar composition as their less disturbed, suburban counterpart, and wetland sites constructed using similar restoration methodology produced similar microbial community structure and soil function. Additional research revealed that a natural and a restored wetland store soil C quite differently: A majority of soil C in the natural site was associated with large macroaggregates (> 2000 μm) whereas most soil C in the restored site was associated with smaller macroaggregates (> 250 to < 2000 μm). The distributions of six chemical compound classes (i.e., carboxylics, cyclics, aliphatics, lignin derivatives, carbohydrates derivatives, N-containing compounds) were relatively similar across the five soil fractions from both sites, however. In the final study, anaerobic laboratory mesocosms were used to evaluate the effects of clay content (%) and leaf litter quality on soil C cycling processes over time. This study found restored soils, regardless of clay content, mineralized more C as carbon dioxide (CO2) and methane (CH4) compared to natural wetland soils. Natural soils respired approximately half the volume of gas as restored soils, suggesting the addition of high- or low-quality C substrates to low C systems elicit a greater response from the heterotrophic microbial community. The results of these three studies suggest site history and edaphic features of restored wetlands are important drivers of microbial communities and their function. We propose that practitioners and researchers work together to identify practices that will enhance soil functions, particularly C storage, in tidal freshwater wetlands of the Chesapeake Bay region.
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    SECRETIVE MARSHBIRDS OF URBAN WETLANDS IN THE WASHINGTON, DC METROPOLITAN AREA
    (2016) Nielson, Patrice; Bowerman, William; Baldwin, Andrew; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Secretive marshbirds are in decline across their range and are species of greatest conservation need in state Wildlife Action Plans. However, their secretive nature means there is relatively sparse information available on their ecology. There is demand for this information in the Washington, DC area for updating conservation plans and guiding wetland restoration. Rapid Wetland Assessment Methods are often used to monitor success of restoration but it is unknown how well they indicate marshbird habitat. Using the Standardized North American Marshbird Monitoring Protocol, I surveyed 51 points in 25 marshes in the DC area in 2013 – 2015. I also collected data on marsh area, buffer width, vegetation/water interspersion, vegetation characteristics, flooding, and invertebrates. At each bird survey point I assessed wetland quality using the Floristic Quality Assessment Index (FQAI) and California Rapid Wetland Assessment (CRAM) methods. I used Program Presence to model detection and occupancy probabilities of secretive marshbirds as a function of habitat variables. I found king rails (Rallus elegans) at five survey sites and least bittern (Ixobrychus exilis) at thirteen survey sites. Secretive marshbirds were using both restored and natural marshes, marshes with and without invasive plant species, and marshes with a variety of dominant vegetation species. King rail occupancy was positively correlated with plant diversity and invertebrate abundance and weakly negatively correlated with persistent vegetation. Least bittern occupancy was strongly negatively correlated woody vegetation and invertebrate abundance and weakly positively correlated with persistent vegetation. Species-specific models provided a better fit for the data than generic marshbird models. A comparison model based on important habitat variables in other regions was a very poor fit for the data in all sets of models tested. FQAI was a better indicator of secretive marshbird presence than CRAM, but neither method had very good predictive ability or goodness of fit. These results underscore the importance of having species- and region-specific models for effective conservation. Based on these findings, decreasing woody vegetation and managing for a variety of co-dominant species to avoid monocultures would improve habitat for marshbirds. Rapid Assessment Method scores should be interpreted with caution when applied to marshbird habitat conservation.
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    The Ecology of Urbanization: A Study of Soil Microbial Community Rosponse
    (2016) Epp Schmidt, Dietrich Jonathan; Yarwood, Stephanie A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Urbanization is associated with global biodiversity loss of macrophauna and flora through direct and indirect mechanisms, but to date few studies have examined urban soil microbes. Although there are numerous studies on the influence of agricultural management on soil microbial community composition, there has been no global-scale study of human control over urban soil microbial communities. This thesis extends the literature of urban ecology to include soil microbial communities by analyzing soils that are part of the Global Urban Soil Ecology and Education Network (GLUSEEN). Chapter 1 sets the context for urban ecology; Chapters 2 addresses patterns of community assembly, biodiversity loss, and the phylogenetic relationships among community members; Chapter 3 addresses the metabolic pathways that characterize microbial communities existing under different land-uses across varying geographic scales; and Chapter 4 relates Chapter 2 and 3 to one another and to evolutionary theory, tackling assumptions that are particular to microbial ecology.
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    An Ecological Analysis of the Potential for Moss-Based Green Roof Design
    (2016) Prince, Benjamin Alan; Kangas, Patrick C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Green roofs are a maturing application of best management practices for controlling urban stormwater runoff. The majority of green roofs are planted with drought resistant, higher plant species, such as the genus Sedum. However, other plant varieties, such as mosses, may be equally applicable. Residential roofs and natural terrestrial communities were sampled in both Maryland and Tennessee to determine moss community structure and species water composition. This served as a natural analog for potential green roof moss communities. During sampling, 21 species of moss were identified throughout the 37 total sites. The average percent moss cover and water composition across all roof sites was 40.7% and 38.6%, respectively and across all natural sites, 76.7% and 47.7%, respectively. Additional maximum water holding capacity procedures were completed on sedum and 19 of the 21 sampled moss species to assess their individual potential for stormwater absorption. Sedum species on average held 166% of their biomass in water, while moss species held 732%. The results of this study are used as a basis to propose moss species that will improve green roof performance.
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    Estimating Population Trends in American Woodcock (Scolopax Minor) Using Population Reconstruction Models
    (2016) West, Brent Hopkins; Bowerman, William W; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The American woodcock (Scolopax minor) population index in North America has declined 0.9% a year since 1968 prompting managers to identify priority information and management needs for the species (Sauer et al 2008). Managers identified a need for a population model that better informs on the status of American woodcock populations (Case et al. 2010). Population reconstruction techniques use long-term age-at-harvest data and harvest effort to estimate abundances with error estimates. Four new models were successfully developed using survey data (1999 to 2013). The optimal model estimates sex specific harvest probability for adult females at 0.148 (SE = 0.017) and all other age-sex cohorts at 0.082 (SE = 0.008) for the most current year 2013. The model estimated a yearly survival rate of 0.528 (SE = 0.008). Total abundance ranged from 5,206,000 woodcock in 2007 to 6,075,800 woodcock in 1999. This study represents the first population estimates of woodcock populations.
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    Design and Performance of a Wetland-Inspired Green Bulkhead and a Grassland-Inspired Green Wall
    (2015) Stanley, Lela; Kangas, Patrick C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Green walls are technologies that provide benefits to the human, natural, and built environments including building shading and cooling, aesthetics, and habitat. Using natural ecosystems as templates, it should be possible to design green walls to provide enhanced ecological functions and play a role in urban reconciliation ecology. This thesis describes the design and performance of two types of green wall drawing inspiration from Mid-Atlantic ecosystems. The first, a wall modeled on Chesapeake Bay brackish marshes, was operated in the Baltimore Harbor for five months and successfully replicated some conditions of wetlands including supporting the growth of native macrophytes throughout the growing season. Notably, this model is the first functional green wall designed for an urban waterfront. The second design tested native grass survival in a dry grasslands-inspired green wall model. In this model, which was moisture-limited with a very shallow substrate, both planted grass species gave way to an invasion of volunteer species.
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    Back to Earth: Molecular Approaches to Microbial Ecology Must Consider Soil Morphology and Physicochemical Properties
    (2015) Dlott, Glade; Yarwood, Stephanie A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This project studied the influence of different long-term agricultural management regimes on soil microbial communities, and compared survival strategies of individual prokaryotic OTUs in diverse soils subjected to long-term incubation. Together these would show whether alterations to microbial communities affect rates of soil carbon cycling. Agricultural soils were sampled at arbitrary depths above and below the plow layer, and relative abundances of microbes were measured using high-throughput sequencing. `Activity' (rRNA:rDNA) ratios were calculated for individual OTUs identified by high-throughput sequencing of tropical rainforest and temperate cornfield soils after incubation for one year with differing water and carbon availabilities. It was found that depth controls microbial communities to a greater degree than agricultural management, and that the characterization of microbial trophic strategies might be complicated by the often-ignored DNA preservation potential of soil. The study highlights the need for holistic approaches to testing hypotheses in modern microbial ecology.