Increasing atmospheric carbon dioxide (CO₂) leads to global warming. This can have several impacts on climate and on plant biodiversity, and has been the topic of many studies. The objective of this thesis was to understand the effects of higher atmospheric CO₂ on soil moisture dynamics in the grasslands of central Minnesota using detailed hydrologic modeling to explain previous experimental observations at the BioCON site, a free-air CO₂ enrichment experiment. The hydraulic properties and texture of soils collected from BioCON were determined in the laboratory through grainsize analysis and continuous evaporative drying to determine soil moisture retention curves and hydraulic conductivities. These results were used as input for numerical soil water flow and energy balance models. The models showed that vegetation presence and atmospheric CO₂ concentrations significantly affected the soil moisture dynamics. Summer evapotranspiration (ET) had a higher variation for bare plots than for vegetated plots. This likely occurred because the vegetation provided a buffer against the variations in weather conditions. Vegetation not only retains part of the precipitation on its leaves, it also retains water in its structure and transpires while carrying out photosynthesis. Higher water content was also seen for the bare plots than for the vegetated soils. For some vegetated plots, there were differences between simulated and observed soil moisture. This could have been caused by a difference in plant composition and could suggest that different plant species can respond differently to varying CO₂ atmospheric concentrations leading to different soil moisture dynamics. In addition to this, smaller ET values and higher soil water content values at vegetated elevated CO₂ conditions than at ambient CO₂ conditions were simulated. This was expected, as higher atmospheric CO₂ is linked to higher plant water efficiency and larger biomass. For the simulations, higher values for stomatal resistance and higher plant and plant residue biomass were used. If increasing CO₂ conditions in fact decreases ET, regional weather patterns could be affected as less ET could delay the speed that water flows through the water cycle. / text

No description available.

The dissertation deals with the experimental research that examines the effectiveness of the ESP e-learning course of Business English in comparison with the method of face-to-face instruction. The literature review has revealed the absence of scientific research in the field of our investigation. It has justified why our proposed research study should be conducted and led us to the rationale for our research. The main objective of this dissertation was to find out whether the e-learning method was as effective as the face-to-face instruction, i.e., whether there were no statistically significant differences between the results of the students who completed the e-learning course (experimental group) and those who completed the face-to-face course (control group). Simultaneously, we examined whether there were any statistically significant differences in the results of the students at the beginning of the course and at the end of the course within individual groups, i.e., whether the students improved their skills and vocabulary. The supplementary objective was to find out the students' opinions on the effectiveness of e- learning depending on the frequencies of their responses and on their qualitative signs. The practical outcome is the ESP e-learning course for the subject of Business English in...