1,721,018 research outputs found
The biology and management of bark beetles in old growth pine forests of Itasca State Park
Get PDFAyres, Matthew P; Lombardero, María J; Ayres, Bruce D.; Shumate, Alice M.; Santoro, Alyson E.. (1999). The biology and management of bark beetles in old growth pine forests of Itasca State Park. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/172553
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Microbial remineralization of sinking particulate organic matter in the mesopelagic ocean
Get PDFMicrobial remineralization of sinking particulate organic matter (POM) drives flux attenuation in the mesopelagic ocean and regulates the transport of carbon to the ocean’s interior. As POM sinks, environmental conditions and substrate bioavailability can set microbial community structure on the particle, influencing remineralization rates. However, directly measuring these rates in situ and connecting them with shifts in microbial community composition is difficult, resulting in few studies that are able to do so. My work combines measurements of sinking particle fluxes and particle-associated respiration rates with 16S rRNA sequencing to examine the relationships between environmental conditions, microbial community composition, and POM remineralization.In the first chapter, we evaluate the effect of preservatives (formalin and RNAlater) on POM-attached microbial communities collected using sediment traps. When preservatives were deployed inside sediment trap tubes, significant differences in microbial community composition among preservation method across deployments. Several copiotrophic taxa were overrepresented in RNAlater, suggesting each preservative differs in its ability to halt microbial activity.The second chapter aims to establish cross-basin relationships between environmental variables, POM-attached microbial community structure, and rates of microbial production and respiration of POM. No significant relationships were observed between environmental variables (i.e. temperature and oxygen) and microbial production and respiration of POM at a cross-basin scale, suggesting an important role for other factors. Despite differences in microbial community composition among ocean basins, copiotrophs generally dominated the community and were actively growing on POM. We identified a few of the same amplicon sequence variants (ASVs) on POM across ocean basins, including two Pseudoalteromonas ASVs that demonstrated a significant positive relationship with carbon-specific respiration rates. These results suggest that POM remineralization is primarily driven by a small number of taxa in the community who may be better adapted to the consumption of the available substrate present at the time.Finally, in the third chapter we examine the connections between environmental conditions, microbial community composition, and sinking particle fluxes in a coastal environment. Using part of a long-term moored sediment trap timeseries in the Santa Barbara Basin, we paired measurements of fluxes and 16S rRNA amplicon sequencing with CalCOFI water column data from November 2020 through May 2024. Sinking particle fluxes varied widely over this period but followed seasonal patterns of upwelling. C/N ratios of sinking particles declined throughout the sampling period and were associated with shifts in particle-attached microbial community composition. Random forest model results identified several microbial groups that were good predictors of sinking particle fluxes, further establishing the connection between microbial community structure and organic matter export in the Santa Barbara Basin.Together, this dissertation provides insights into the relationships and complex interactions between environmental conditions, microbial community composition, and the remineralization and eventual export of POM in the ocean
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Linking biological and physical processes to understand microbial diversity and nitrogen dynamics along the aquatic continuum
Get PDFThis dissertation examines the effects of anthropogenic perturbation on microbial diversity and freshwater and marine nitrogen cycling, with a particular focus on nitrification and the production of the greenhouse gas nitrous oxide (N2O).In the first chapter, headwater stream microbial communities were characterized across a gradient of urban and agricultural land use using 16S rRNA gene amplicon sequencing and compared to traditional physiochemical and biotic indicators of stream health. Stream microbial diversity differed in watersheds with high agricultural, urban, and forested land uses, and community structure differed in streams classified in good, fair, poor, and very poor condition using benthic macroinvertebrate indicators of water quality. Along with changes in diversity, stream community respiration correlated with forest cover and negatively correlated with nutrients associated with anthropogenic influence. Additionally, N2O concentrations negatively correlated with forested land use and positively correlated with dissolved inorganic nitrogen concentrations. The findings suggest stream microbial communities and ecosystem processes are impacted by watershed land use and can potentially assess ecosystem health.The physical and biological controls on N2O production in the eutrophic Chesapeake Bay were investigated in the second chapter using gas measurements (N2O and N2/Ar) and stable isotope tracer incubations. Nitrification rates were highest following wind events that mixed oxygenated surface water below the pycnocline into ammonium-rich bottom waters, resulting in the accumulation of nitrite (NO2-) and N2O. During periods of weak vertical mixing, both N2O concentrations and nitrification rates were lower, and lower oxygen (O2) concentrations below the pycnocline allowed for N2O consumption by denitrification. A three-layer box model provided estimates of N2O production demonstrating the importance of both biological (production and consumption) and physical (advection and vertical exchange) processes in driving the observed large fluctuations in N2O concentrations. The results demonstrate physical processes affect the net balance between N2O production and consumption, making Chesapeake Bay a variable source and sink for N2O.The final chapter investigates the seasonal coupling of primary production and nitrification, and the relationship between these processes and N2O production in the Southern California Bight (SCB). Over two seasonal upwelling cycles, nitrification rates fueled by ammonia and urea-derived N were measured using stable isotope tracer additions and N2O concentrations were measured using gas chromatography. Nitrification rates were highest at the onset of upwelling and correlated with rates of primary production. Similar ammonia and urea-derived N oxidation rates suggest urea is a significant nitrogen source fueling nitrification in the SCB. Nitrification supplied a large proportion of phytoplankton nitrogen demand, demonstrating significant nitrogen remineralization within the euphotic zone. The SCB was always a source of N2O to the atmosphere, which likely was advected into the system from the eastern tropical North Pacific. Together, the results suggest nitrification is an important control on the amount of organic carbon available for export, and the coupling of nitrogen remineralization and primary production may export a smaller fraction of primary production out of the surface ocean, but physical transport dominates over local production of N2O in the SCB
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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