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Authors: Felice, M.L.; Advisor: -; Participants: Schmidt, R.; Peng, J.; de Sieyes, N.R.; Scow, K.M.; Mackay, D.M. (2018) - We established a densely monitored field site previously unexposed to high CH4 concentrations to allow the controlled release of CH4 into the vadose zone and monitoring of subsurface gas migration, surface efflux, and changes to MOB communities by quantitative polymerase chain reaction. During the initial stages of CH4 injection, soil conditions were very dry, and a large portion of the injected CH4 reached the ground surface as efflux. During this time, the composition of MOB remained similar to pre‐experimental conditions, with the Methylosinus group dominating. Following a period of rainfall and increased soil moisture conditions, efflux dropped, and only approximately 1% of injected CH4 was detected as efflux. The composition of the MOB community measured immediately following t...
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Authors: Oh, T.W.; Advisor: -; Participants: Vanapalli, S. (2018) - In geotechnical engineering practice, many projects such as stability analysis of slopes or trenches and pavement design involve soils in vadose zones at shallow depths, where soils are under unsaturated conditions. For these types of projects, undrained shear strength test results obtained under zero or low confining pressure can be effectively used to analyze the behaviors of unsaturated soils. Experimental procedures to determine the undrained shear strength for different soil suction values, however, is time consuming even under low confining pressure. For this reason, we attempted to develop a semi‐empirical model to predict the undrained shear strength of unsaturated soils at a shallow depth assuming zero confining pressure as a function of soil suction. In addition, existing ...
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Authors: Felice, M.; Advisor: -; Participants: de Sieyes, N.; Peng, J.; Schmidt, R.; Buelow, M.; Jourabchi, P.; Scow, K.; Mackay, D. (2018) - In this study, we simulated shallow CH4 generation with a controlled subsurface CH4 release from July 2014 to February 2015 to characterize subsurface CH4 migration and surface emissions and to determine environmental controls on CH4 fate and transport. July 2014 through November 2014 was an extended period of drought followed by precipitation during December 2014. Throughout the experiment, under varied CH4 injection rates, CH4 formed a radially symmetrical plume around the injection point. Surface efflux during the drought period of the experiment was relatively high and stable, with approximately 10 to 11 and 34 to 52% of injected CH4 reaching the ground surface during the low‐ and high‐rate injections, respectively. Following the period of precipitation and increased soil moistu...
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Authors: Forde, O.N. .; Advisor: -; Participants: Mayer, K.U.; Cahill, A.G; Mayer, B.; Cherry, J.A.; Parker, B.L. (2018) - This paper presents results from vadose zone gas and surface efflux monitoring during a natural gas release experiment at Canadian Forces Base Borden, Alliston, Ontario, Canada. Over 72 d, 51 m3 of natural gas (>93% CH4) was injected into a shallow, unconfined sand aquifer at depths of 4.5 and 9 m. Methane and CO2 effluxes in combination with soil gas concentrations and stable C isotopic signatures were used to quantify the spatiotemporal migration and fate of injected gas. Preferential gas migration pathways led to vadose zone hot spots, with CH4 concentrations exceeding the lower explosive limit (5% v/v). From these hot spots, episodic surface CH4 effluxes (temporally exceeding 2500 μmol m−2 s−1 [3465 g m−2 d−1]) occurred during active injection. Higher injection rates led to incr...
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Authors: Hruška, M; Advisor: -; Participants: Clauser, C.; De Doncker, R.W. (2018) - The critical isotherm is assessed by the temperature at which the steepest change occurs in the moisture content with temperature. We considered the impact of the properties of the surrounding medium and of the ambient temperature and moisture content on the dry‐out temperature. We found that seasonal variations in ambient conditions in a field in Italy have a greater impact on the critical temperature than the variations in soil properties in that field (under the assumption of a nearly uniform moisture content with depth). However, our analysis shows that, under certain conditions, a change in the van Genuchten parameter n and in a specific combination of parameters that we call a dynamic parameter can have as large an effect on the critical temperature. This suggests a direction ...
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Authors: Pütz, T.; Advisor: -; Participants: Fank, J.; Flury, M. (2018) - Lysimeters are methodological experimental tools to study the water and matter fluxes in the vadose zone, as well as the environmental fate of chemicals. Lysimeters are available in various types. The most sophisticated lysimeters are filled monolithically, are equipped with a pressure‐controlled lower boundary, and are weighable, allowing the measurement of hydraulic fluxes, i.e., rainfall, drainage, evapotranspiration, dew, and hoar frost with high precision. This special section of Vadose Zone Journal reports on current lysimeter research.
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Authors: Trost, J.J.; Advisor: -; Participants: Perkins, K.S.; Henson, W.; Mirus, B.B.; Nimmo, J.R.; Muñoz-Carpena, R. (2018) - We summarize key findings from 14 papers, several of which originated from a meeting convened by UZIG in 2017 at the University of Florida in Gainesville titled “Land‐Use Change, Climate Change, and Hydrologic Extremes: Unsaturated Zone Responses and Feedbacks.” This special section of Vadose Zone Journal contains multidisciplinary research in three general categories relevant to measuring and understanding unsaturated zone responses to changing land uses and climate: (i) unsaturated zone properties and processes; (ii) soil–plant–atmosphere interactions; and (iii) novel field sampling devices. A strong cross‐cutting theme in these papers is the value of continuous monitoring data and ways of utilizing them to discover novel hydrologic, biologic, and pedologic information. As climati...
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Authors: Stumpp, C.; Advisor: -; Participants: Brüggemann, N.; Wingate, L. (2018) - Recent developments in the measurement, modeling, and application of stable isotope tools to provide insights on water flow, transport, biogeochemical, and ecological processes in the vadose zone have motivated a special section in Vadose Zone Journal. We give an overview of recent advances and challenges in stable isotope approaches in the vadose zone and present the key findings from the five manuscripts in this special section. These five manuscripts advance our understanding of (i) analytical developments in water stable isotope analysis, (ii) modeling of water and transport within the soil matrix using water stable isotopes, and (iii) using compound‐specific isotope analysis for identifying the fate of nonaqueous‐phase liquids in the unsaturated zone.
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Authors: Dickinson, J.E.; Advisor: -; Participants: Ferré, T.P.A. (2018) - We have developed a screening tool to visualize and conceptualize the filtering properties of a layered vadose zone. Climate projections indicate that rainfall timing and magnitude may change and impact groundwater resources. This increases the importance of understanding how the vadose zone filters infiltration variability and ultimately affects recharge and groundwater resources. An approximate solution for the filtering of surface forcings through soil layers was developed previously, and the soil and conditions where its approximations are appropriate was evaluated. Here we present a screening tool based on the solution for estimating how periodic infiltration forcings filter in a layered vadose zone for different soil properties and surface flux conditions. The solutions identi...
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