Theses and Dissertations at Montana State University (MSU)
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Item Crop damage by wheat stem sawfly as related to soil water holding properties(Montana State University - Bozeman, College of Agriculture, 1995) Heilig, Jeanne Ann KirchnerItem The impacts mountain pine beetle on forested snowpacks : accumulation and ablation(Montana State University - Bozeman, College of Agriculture, 2013) Welch, Christopher Michael; Chairperson, Graduate Committee: Paul C. StoyThe future of water resources in the west is tenuous, as climatic changes have resulted in earlier spring melts that have exacerbated summer droughts. Associated with climate changes to the physical environment are changes to the biological environment that may impact snow dynamics; namely via the massive outbreaks of Mountain Pine Beetle (MPB; Dendroctonus ponderosae) that have devastated several million hectares of Lodgepole Pine forests in the western U.S. and Canada. If snow accumulation and melt are determined by the physical environment of the snowpack, and forest canopies define in part this physical environment, how might recent insect outbreaks alter the timing and intensity of snowmelt? MPB often attack in large numbers, and within a few years, the canopy of an infected forest will turn from green but dying, to red, to grey. As needles fall, impacts on the snow pack include changes to wind driven transport, temperature gradients, and snow interception. Additionally, the shifting canopy alters the radiated physics of the canopy, specifically the shortwave/longwave flux density. Combined with a corresponding decrease of snow reflectance (albedo) from litter fall, the dying canopy will provide more energy available to the surface and likely drive snowpacks to melt more rapidly. Conversely, the diminished canopy cover will presumably decrease net longwave radiation of the snowpack. Canopy interception of snow is expected to decrease, and an increase in accumulation will result. I investigate the impacts of MPB disturbance on snow melt through modeling and micrometeorological measurements in intact lodgepole pine and mixed coniferous forests, a MPB-infested forest in the red stage, and a clearcut stand. Albedo at the homogenous intact stand is found to be 16 and 34% higher than the red stand during the melt periods of 2011 and 2012, but no significant difference is found between the red stand and the more heterogeneous 'healthy' stand. Modeled sensible heat over-predicts sensible heat by over 300% during the melt period of 2012. Results highlight the role of beetle-infested and mixed stands on altering snow albedo, and additionally suggest that model formulations for turbulent exchange between snow and atmosphere below forest canopies require improvement.Item Development of an environmental fate model for risk assessment of ultra-low-volume insecticides(Montana State University - Bozeman, College of Agriculture, 2012) Schleier, Jerome Joseph, III; Chairperson, Graduate Committee: Robert K. D. Peterson.One of the most effective ways of managing adult mosquitoes that vector human and animal pathogens is the use of ultra-low-volume (ULV) insecticides. The U.S. Environmental Protection Agency uses models that are not validated for ULV insecticide applications and exposure assumptions to perform their human and ecological risk assessments. Currently, there is no validated model that can accurately predict deposition of insecticides applied using ULV technology for adult mosquito management. In addition, little is known about the deposition and drift of small droplets like those used under conditions encountered during ULV applications. The objectives of my dissertation were to perform field studies to measure environmental concentrations of insecticides and to develop a validated model to predict the deposition of ULV insecticides, and use the data generated from the field study to perform refined human and aquatic ecological risk assessments. To model the field data collected during the summers of 2009-2011 a regression model selected by the Bayesian Information Criterion and k-fold cross validation was used to validate the selected model. k-fold cross validation demonstrated that the mean square error and mean square prediction error were similar indicating good predictive ability. The human-health risk assessment demonstrated that previous risk assessments used conservative exposure scenarios that overestimated risks, thus being conservative in protecting human health. Our results demonstrated a 10-fold reduction in the RQ estimates when comparing risk assessments using estimated environmental concentrations and actual environmental concentrations from the environmental fate model. Because I used a large data set to model concentrations deposited on surfaces, this variance in exposure is due to the inherent variability in deposition concentrations after ULV applications and, therefore, would not warrant further refinement to improve risk assessments. The aquatic risk assessment using actual environmental concentrations showed that the 95th percentile estimated concentration would result in less than 0.0001% of the potentially affected fraction of species reaching their respective LC50. Our results are supported by the weight of evidence that pyrethroids applied by ground-based ULV applications will not result in deleterious effects on aquatic organisms.