Acid mine drainage (AMD) is an acidic, iron-rich leachate that causes the dissolution of metals. It constitutes a worldwide problem of environmental contamination detrimental to aquatic life and water quality. AMD, however, is naturally attenuated at Davis Mine in Rowe, Massachusetts. We hypothesize that sulfate-reducing bacteria (SRB) are attenuating AMD. To elucidate the mechanisms by which SRB attenuate AMD, three research projects were conducted using a suite of molecular and geochemical techniques. First we established biological influence on the attenuation of AMD by comparing the microbial community and geochemical trends of microcosms of two contrasting areas within the site: AMD attenuating (AZ) and AMD generating (GZ) zones. The differences in geochemical trends between these zones were related to differences in microbial community membership. SRB were only detected in microcosms of the AZ, while iron oxidizers were only detected in the GZ. This study indicates that biological activity contributes to the attenuation of AMD and that SRB may have a role. To further describe the role of SRB, we determined the rates of sulfate reduction, the abundance, and membership of SRB in the second project. The sulfate reduction rate was weakly correlated with the abundance of SRB. This indicates that the SRB population may be utilizing another electron acceptor. One such electron acceptor would be iron, which was investigated in the third project. When SRB are inhibited, neither accumulation of reduced iron nor the formation of reduced iron sulfide precipitates occurred. Higher concentration of sulfide produced an increase in reduced iron and pH. Therefore, iron reduction mediated by reaction with biogenic sulfide contributes to the attenuation of AMD. This is the first report of the biological enhancement of iron reduction by acidotolerant SRB. The interdisciplinary research described in this dissertation provides evidence that SRB attenuate AMD through sulfate and iron reduction and a greater understanding of SRB in acidic environments. It also demonstrates how the biogeochemical cycling of sulfur is coupled to the iron cycle. Overall, the ubiquity and metabolic versatility of SRB offers boundless potential and exciting opportunities of study in the fields of bioremediation, geomicrobiology, and microbial ecology.

Surface sealing and hardpans in loam soils are problematic in the Mid-South U.S. because of intense tillage. Two experiments quantified the effects of soil management practices on infiltration and maize yield in loam soils. The first study measured the impacts of in-row subsoiling frequency × furrow irrigation frequency. In-row subsoiling significantly improved the infiltration of irrigation but not the infiltration of precipitation. In-row subsoiling with low irrigation frequency is optimal to achieve profitable maize yields while encouraging groundwater conservation. In the second study, six soil management treatments were imposed. For single-ring infiltrometer tests, infiltration rates were different between the two measurement dates but not between measured treatments. In 2022, neutron attenuation data indicated no differences in soil water content between measured treatments. Based on both studies, in-row subsoiling was proven to be an economically viable option in comparison to other Mississippi Delta on-farm conservation practices in the short term.

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In this study, the weather impact on lidar signals has been researched. A lidar system was placed with a target at approximately 90 m and has together with a weather station collected data for about a year before this study. By using the raw detector data from the lidar, the full waveform can be obtained and the amplitude of the return pulse can be calculated. Atmospheric attenuation of lidar signals is often modeled using the lidar equation, which predicts an exponential decrease in energy over the distance. The factor in the exponent is referred to as the extinction coefficient and it is the main property studied in this thesis. By utilizing models for the extinction coefficient under different weather conditions, it is possible to simulate the performance of the lidar.  The extinction coefficient was calculated using different empirical models. The empirical models investigated in this thesis are the Kim and Kruse models for known visibility, the Al Naboulsi model for different types of fog with known visibility, the Carbonneau model for known precipitation amount in rainy conditions, and a similar model for snowy conditions. For the case of rain, a physical model was also used, which is derived through Mie theory. The physical model requires a particle size distribution, which is the number of particles of a certain radius per unit volume. A particle size distribution for rain was generated using the Ulbrich raindrop size distribution, using the precipitation amount recorded by the weather station. Particle size distributions for radiation and advection fog were also simulated.  The measured attenuation in lidar signals was compared to the predicted attenuation that was calculated using different models for the extinction coefficient in the lidar equation. Generally, the models tend to underestimate the amplitude of the return pulse. This can partially be explained by the assumptions used to derive the lidar equation, which neglects all augmentation of the beam. The visibility models gave more accurate results compared to the precipitation models. This was expected, since visibility is defined as a measure of attenuation and precipitation amount is not.  When a lidar signal is emitted, the light will be reflected from optical surfaces within the lidar and cause a pulse to be detected. This pulse is referred to as the zeropulse. In the first couple of meters of the transmission, we expect to see some backscattered light from adverse weather, since the detector has a larger solid angle at shorter distances. This returned light will be combined with the zeropulse and cause it to expand in width. By examining the zeropulse, it was possible to observe a difference between the average zeropulse under some different weather conditions. This leads to the conclusion that it may be possible to extract some information about current weather conditions from the zeropulse data, given that there is little ambient light and snowy weather conditions.  By integrating the zeropulse, variations in the shape of the zeropulse could be described by a single value. Then by separating the data into low and high visibility populations, the zeropulse integral could be used to predict the visibility. The conclusion was that the zeropulse integral can accurately predict whether visibility is above or below a threshold value, given that there is little ambient light and the visibility is known to be below 19950 m.

Space equipment is often subjected to mechanical shocks. Some devices like electronics are sensitive to shocks, and they can easily be damaged. To protect these devices, it is important to study shock penetrations in space structures. The Finite Element Method is an effective tool to simulate response to transient excitations. Unlike Statistical Energy Analysis (SEA) which can ensure sufficient accuracy in high frequency range, Finite Element Analysis (FEA) is limited to low frequency range, but has no spatial restrictions. In this thesis, Tuma’s digital filter method and Irvine’s recursive digital method were combined to calculate the Shock Response Spectrum (SRS). FEA models based on a given experimental system, i.e., shock table were used to predict the structural response to Haversine shaped forces. The modal transient structural analysis in ANSYS Workbench was used as the solver. Transient analysis based on modal results neglects material and structural non-linearities, so it uses less memory and computation time. FEA and the Bernoulli beam equation were employed to simulate the shock response of cantilever beams and fixed-pinned beams to validate the FEA models. SRS calculated from FEA results were compared with those from the beam equation results. Almost no difference between Bernoulli beam equation results and FEA results for thin beams reveals that the FEA models were validated. The SRS of two beam models calculated from FEA using solid elements were compared with those using beam elements. The results from two different element types are almost consistent with each other. Response at different positions on the shock table were measured to predict the shock attenuation. The attenuation was described in the way of remaining percentage from shock source, and the curve from FEA simulation roughly agreed with the attenuation rule from the ESTEC database. / Rymdutrustning utsätts ofta för mekaniska stötar, s.k. mekanisk chock. Vissa enheter, som elektronik, är känsliga för stötar och de kan lätt skadas. För att skydda dessa enheter är det viktigt att studera chockdämpningen i rymdstrukturer. Finita elementmetoden är ett effektivt verktyg för att simulera responsen vid transienta excitationer. Till skillnad från statistisk energianalys (SEA) som kan säkerställa tillräcklig noggrannhet i högfrekvensintervall, är finit elementanalys (FEA) begränsad till lågt frekvensområde, men har inga rumsliga begränsningar. I detta examensarbete kombinerades Tumas digitala filtermetod och Irvines rekursiva digitala metod för att beräkna Chockresponsspektrum (SRS). FEA-modeller baserade på ett givet experimentellt system, d.v.s. chockbord, användes för att förutsäga den strukturella responsen på Haversine-formade krafter. Den modala transienta strukturanalysen genomfördes med ANSYS Workbench. Den transienta analysen baserad på modala resultat försummar icke-linjäriteter i material och struktur för att använda mindre minne och förkorta beräkningstiden. FEA och Bernoulli-balkekvationen användes för att simulera chockresponsen av konsolbalkar och balkar med fast inspänning i ena änden och fri uppläggning i den andra änden, för att validera FEA-modellerna. SRS beräknat från FEA-resultaten jämfördes med resultat från balkekvationen. Ingen avgörande skillnad noteras mellan Bernoullis balkekvationsresultat och FEA-resultat för tunna balkar, vilket validerar FEA-modellerna. SRS för två balkmodeller beräknade från FEA med solida element jämfördes med de som använde balkelement. Resultaten från de två olika elementtyperna överensstämmer mycket bra. Responsen vid olika positioner på chockbordet mättes för att förutsäga chockdämpningen. Chockdämpningen beskrivs som kvarvarande procent av responsen vid chockkällan och kurvan från FEA-simulering överensstämde ganska bra med tumregeln för chockdämpning från ESTEC-databasen.

Running popularity has led to a rise in chronic lower limb injuries resulting from cumulative loading. Many of these injuries are tibial stress fractures. Tibial accelerometers are commonly used to measure tibial stress and may even be predictive of injury at the distal limb. Lower body positive pressure (LBPP) treadmills have become increasingly popular amongst athletes and practitioners to prevent and treat lower limb injuries by reducing effective body weight (BW) through mechanical support. The purpose of this thesis is to investigate if BW unloading affects tibial acceleration (TA) and shock attenuation. Twelve trained distance runners (Sex: 6 males and 6 females; Age: 18-30 years) were recruited for this study. TA was measured through two Blue Trident, IMeasureU step units located at the distal tibiae. A STATSports Apex unit was also used to measure acceleration at the superior trunk and calculate shock attenuation for each limb. It was found that BW unloading had no discernable effect on mean peak TA and shock attenuation, bone stimulus, or contact time, regardless of running speed. However, a significant relationship was observed between running speed and both mean peak TA and bone stimulus where an increase in speed led to an increase in TA and bone stimulus. Furthermore, running speed did not affect shock attenuation or contact time. In conclusion, BW unloading did not alter gait kinematics in trained distance runners. / Master of Science / Running popularity has led to a rise in chronic lower limb injuries, particularly stress fractures at the shin or tibia bone, due to greater impact forces and "stiffer" landings. Tibial accelerometers are commonly used to measure these impact forces and may even be predictive of injury at the tibia bone near the ankle. The process of reducing these impact forces is called shock attenuation. Lower body positive pressure (LBPP) treadmills have become increasingly popular amongst athletes and practitioners to prevent and treat lower limb injuries by unloading body weight (BW) through mechanical support. The purpose of this thesis is to investigate if BW unloading affects tibial acceleration (TA) and shock attenuation. Twelve trained distance runners (Sex: 6 males and 6 females; Age: 18-30 years) were recruited for this study. TA was measured through two Blue Trident, IMeasureU step units located at the shin. A STATSports Apex unit was also used to measure impact at the upper trunk and calculate shock attenuation for each limb. It was found that BW unloading did not affect mean peak TA and shock attenuation, bone stimulus, or contact time, regardless of running speed. However, running speed significantly affected both mean peak TA and bone stimulus where an increase in speed led to an increase in TA and bone stimulus. Furthermore, running speed did not affect shock attenuation or contact time. In conclusion, BW unloading did not alter impact forces in trained distance runners. Caution is advised for individuals with injuries at the shin when using LBPP treadmills.

Reductive dechlorination is a significant natural attenuation process in chloroethene-contaminated aquifers where organic carbon combined with reducing redox conditions support active dechlorinating microorganisms. At sites where natural organic carbon (NOC) associated with the aquifer matrix provides fermentable organics, the ability to measure the NOC is needed to assess the potential for the long-term sustainability of reductive dechlorination. This study focused on developing a method to measure the potentially bioavailable organic carbon (PBOC) associated with aquifer sediment. To measure NOC and evaluate its biodegradability, liquid extraction techniques on aquifer sediment were investigated. Single extractions with different extracting solutions showed that extractable organic carbon associated with the sediment ranged from 1-38% of the total organic carbon content (TOCs). Bioassay experiments demonstrated that 30-60% of the extractable organic carbon can be utilized by a microbial consortium. Alternating between 0.1% pyrophosphate and base solutions over multiple extractions increased the rate of removal efficiency and targeted two organic carbon pools. The result of the investigation was a laboratory method to quantify organic carbon from the aquifer matrix in terms of the PBOC. In the second part, the extractable PBOC was shown to biodegrade under anaerobic conditions, to produce H2 at levels necessary to maintain reductive dechlorination, and to support reductive dechlorination in enrichment cultures. For the third part of the research, the difference in extractable organic carbon inside and outside of a chloroethene-contaminated plume was examined through the combination of PBOC laboratory data and field parameters. Supported by ground-water constituent data, the PBOC extraction and bioassay studies showed that less extractable organic carbon was present inside than outside of the chloroethene plume. The final part of the research investigated the distribution of PBOC extractions across six contaminated sites. PBOC extractions were directly correlated to the TOCs, soft carbon content, and level of reductive dechlorination activity at the sites. Based on these correlations, a range for organic carbon potentially available to subsurface microorganisms was proposed where the upper bound consisted of the soft carbon and the lower bound consisted of the PBOC. / Ph. D.