Flow-induced failure of granular materials is relevant to a broad range of geomechanical applications. Plasticity, which is the inherent failure mechanism of most granular materials, enables large deformations that can invalidate linearised models. Motivated by fluid injection into a borehole, we develop a steady-state model for the large deformation of a thick-walled, partially-permeable, elastic--perfectly-plastic annulus with a pressurised inner cavity. We account for pre-existing compressive stresses, as would be present in the subsurface, by subtracting a compressed initial state from our solutions to provide the additional disturbance due to fluid injection. We also introduce a simple parameter that allows for a smooth transition from an impermeable material (i.e., subject to mechanical loading at the inner wall) to a fully permeable material (i.e., subject to an internal pore-pressure gradient), which would be relevant to coated boreholes and very-low-permeability materials. We focus on the difference between poroelastic and poroelasto-plastic deformations, the role of kinematic and constitutive nonlinearity, and the transition from impermeable to fully permeable. We find that plasticity can enable much larger deformations while predicting much smaller stresses. The former makes model choice increasingly important in the plastic region, while the elastic region remains insensitive to these changes. We also find that, for a fixed total stress at the inner wall, materials experience larger deformations and generally larger stresses as they transition from impermeable to fully permeable.

Large poroelasto-plastic deformations due to fluid injection from a borehole

Increasing the Pierre Shale Reservoir Volume Using Heat - Part I

Plant parasitism and soil microbes: A tripartite interaction driving plant community structure Jordan C. Argrett1, Nina Wurzburger1, Y.A. Chung2 (1) Odum School of Ecology, University of Georgia (2) Department of Plant Biology, University of Georgia Hemiparasitic plants are common in many natural ecosystems and are known to influence community structure and ecosystem function. They connect to host plants through unique root structures called haustoria to establish a direct connection to its vascular system and form a living physiological bridge by which some nutrients, carbon, and water are extracted. In nutrient-limited ecosystems, hemiparasitic plants influence ecosystem processes and increase productivity through two primary pathways. (1) Hemiparasitic plants produce nutrient-rich and labile litter, stimulating microbial activity and increasing local decomposition rates (litter pathway). (2) Hemiparasitic plants reduce the abundance of dominant species via parasitism, thus facilitating the increase and coexistence of diverse co-occurring species (parasitism pathway). While past work on hemiparasites has focused on the direct impact on aboveground responses like host species and plant diversity, little is known about how these plants affect belowground processes. We aim to investigate the effects of hemiparasitic plants on neighboring plant population and community dynamics, nutrient cycling, and soil microbial communities by assessing their direct and litter-mediated effects. This work will provide a comparison of the two pathways, ultimately contributing to a greater understanding of how hemiparasites impact surrounding plant communities and ecosystem cycling. The gut microbial diversity of a Chagas disease vector varies across single and coinfection status throughout central Panama Kaylee M.H. Arnold1,2, Christina Varian1,2,3, Troy Kieran2,4, Azael Saldaña5, Franklin Samudio5, Jose Calazada5, Nicole Gottdenker1,2,3 (1) Odum School of Ecology, University of Georgia (2) Center for the Ecology of Infectious Diseases, University of Georgia (3) College of Veterinary Medicine, University of Georgia (4) Environmental Health Sciences, University of Georgia (5) Gorgas Memorial Research Institute, Panama City, Panama Chagas disease is caused by the parasite Trypanosoma cruzi that is carried in the guts of bloodfeeding triatomine (kissing bug) vectors. Triatomines are often coinfected with the parasite T. rangeli, which is non-pathogenic to mammals but can reduce the fitness of their triatomine hosts. This study examined the gut microbial diversity of T. cruzi single-infected, coinfected, and uninfected triatomines (n = 288) throughout central Panama. We hypothesized that single and coinfected triatomines would have greater gut microbial diversity than uninfected individuals due to pathogen-microbe interactions within the gut, which may facilitate the proliferation of less dominant bacterial taxa. Coinfections were found in 13% of individuals (40/288), and there was significantly greater alpha diversity in coinfected individuals when compared to both single and uninfected samples (Dunn's test of multiple comparisons, p < 0.001). Furthermore, single T. cruzi infections were found in 32% of sampled individuals (91/288) and also displayed significantly greater alpha diversity when compared to uninfected individuals (Kruskal-Wallis H test, p < 0.001). Finally, the beta diversity of single and coinfected samples was significantly different to uninfected samples (PERMANOVA: p = 0.001). These results highlight triatomine gut microbial diversity patterns that may be influenced by infection status and will be important to consider when developing vector control strategies. Fish habitat associations in the Conasauga River and implications of climate change effects on species conservation Anna Y. Baynes1,2, Seth J. Wenger1,2, Mary C. Freeman1,2, Kyle S. McKay1,3 (1) Odum School of Ecology, University of Georgia (2) River Basin Center, University of Georgia (3) U.S. Army Corps of Engineers Flow is a key determinant of the ecological structure of a riverine ecosystem, but climate change could alter flows to which fishes have evolved. In the Southeastern US, a global hotspot of biodiversity, changing flows are a potential threat to fish communities that have already experienced declines in abundance and richness due to other anthropogenic factors. Our objective was to understand fish relationships with flowrelated microhabitat variables such as depth, velocity, Reynolds number and Froude’s number, while accounting for the effects of other habitat features such as vegetation, to guide fish conservation in a changing climate. We used a long-term data set of annual fish samples in the highly biodiverse Conasauga River, GA, to estimate occurrence and counts of 21 fish species as a function of habitat variables using generalized linear multiple regression models. Results showed that microhabitat models explained a substantial amount of the variation in counts for some species, although other species were poorly predicted. Associations with depth and velocity varied greatly among species, indicating different flow niches. We found some species had associations with specific habitat features, such as aquatic plants and woody debris, but not all our hypotheses about these associations were supported. The characterization of depths and velocities used by shoal-dwelling fish will allow us to understand the effects of future changes, such as increased frequency and severity of droughts, on populations. A wide variety of habitats need to be maintained in a changing climate to support the large fish diversity in the Conasauga River. Life stage specific effects of environmental stressors on epigenetic aging Emily M. Bertucci1,2, Marilyn W. Mason2, Junsoo Bae2, Benjamin B. Parrott1,2 (1) Odum School of Ecology, University of Georgia (2) Savannah River Ecology Laboratory, University of Georgia Age-associated patterning of DNA methylation (“epigenetic aging”) is a strong predictor of biological age as it is correlated with chronological age, the onset of age-related disease, and all-cause mortality. Using measures of epigenetic age to explore the discrepancies between chronological and biological aging offers insight into the molecular determinants of variable life history trajectories. While previous work demonstrates that adverse environmental conditions are associated with accelerated biological aging, it is not clear if some life stages are more sensitive than others to environmental conditions. Given that age-associated methylation patterns are most dynamic during early life, we hypothesized that early life exposures to environmental stress would have disproportionate effects on epigenetic aging relative to adult exposures. We tested this hypothesis by investigating the relative contributions of environmental stressors applied during different life stages of medaka (Oryzias latipes). At two distinct life stages (early life: 7-weeks post hatch and adult life: 4-months post hatch) fish were exposed for 21 days to either methylmercury or exogenous cortisol. After exposure, all fish were reared to a common age of 6-months and assessed for biological age acceleration via several measures epigenetic age estimates, telomere length, and the degree of epigenetic drift. Our results shed light on life stage sensitivity of epigenetic aging and the potential mechanism by which the epigenome translates environmental stressors into accelerated biological aging trajectories. The adaptive significance of temperature-dependent sex determination in the American alligator Samantha Bock1,2, Yeraldi Loera3, Thomas Rainwater4, Benjamin B. Parrott1,2 (1) Odum School of Ecology, University of Georgia (2) Savannah River Ecology Laboratory, University of Georgia (3) Department of Ecology & Evolutionary Biology, Princeton University (4) Belle W. Baruch Institute of Coastal Ecology & Forest Science, Clemson University Many ectotherms, including all crocodilians, rely on temperature cues experienced during development to determine offspring sex. Ever since the first descriptions of temperature-dependent sex determination (TSD) were made over 50 years ago, an understanding of its adaptive significance has remained elusive, especially in long-lived taxa. One novel hypothesis predicts that TSD should be evolutionarily favored when two criteria are met (1) incubation temperature influences juvenile survival and (2) sexes mature at different ages. Under these conditions, a sex-dependent effect of temperature on fitness arises through differences in age at sexual maturity, with the sex that matures later benefiting disproportionately from incubation temperatures that promote juvenile survival. Here, we test this hypothesis in the American alligator, a TSD species displaying a stark sex difference in age at first reproduction. By implementing a combination of artificial incubation experiments and mark-recapture methods, we disentangle the effects of incubation temperature and sex on annual survival in alligator hatchlings at two geographically distinct sites. Hatchlings incubated at male-promoting temperatures consistently exhibited higher survival compared to those incubated at female-promoting temperatures. Interestingly, this pattern appears independent of hatchling sex, as females incubated under male-promoting temperatures exhibited similar survival to their male counterparts. These findings support the hypothesis that TSD represents an adaptive sex-allocation strategy in this species. Ongoing work aims to understand the role of temperature-dependent hatchling phenotypes in mediating observed differences in early-life survival. Multivariate analyses of native and invasive plant community and the effects of deer exclusion in maritime forests Dessa L. Dunn1, Elizabeth G. King1,2, Nate P. Nibbelink2 (1) Odum School of Ecology, University of Georgia (2) Warnell School of Fore

History of the Graduate Student Symposium Year GSS Organizer ( s ) Keynote Speaker Affiliation at the time 1995

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Increasing the Pierre Shale Reservoir Volume Using Heat - Part I

History of the Graduate Student Symposium Year GSS Organizer ( s ) Keynote Speaker Affiliation at the time 1995