>Magister Scientiae - MSc / The Namib Desert is a hyper-arid, coastal desert with limited bioavailable water and nutrients; characteristics which collectively impose constraints on edaphic microbial communities. Several studies in the Namib Desert have investigated changes in soil microbial communities across space. However, the temporal variation of edaphic bacterial community in response to seasonal microenvironmental variation in the Namib Desert gravel plains has never been investigated in situ.The edaphic bacterial community dynamics were evaluated over short (57 days) and long-term (1 year) sampling intervals using an extensive sampling strategy in combination with community fingerprinting by T-RFLP analyses and microenvironmental characterization. The short-term study was conducted on three distinct locations in the Namib Desert gravel plains. Soil bacterial communities were found to be more similar within habitats than between habitats, with the differences likely shaped by soil pH. These findings are consistent with the concept of habitat filtering.Investigation of edaphic bacterial communities over 1 year in an 8100 m2 sampling site revealed seasonal patterns of variation in community structure. Soil moisture,phosphorus, potassium and magnesium were identified as significant abiotic drivers of community temporal dynamics. β diversity was found to increase over time, while the environment remained relatively static. These findings support previous observations that desert communities are likely structured by stochastic and deterministic processes.Taken together, these findings advance understanding of temporal variation of edaphic communities in the Namib Desert.

With a precipitation falling to as low as 100 mm/yr, a high rate of non-renewable groundwater depletion, a growing population resulting in increased food demand and a lack of concern for water management, it is crucial to use all available tools to conserve water. One of the most important factors related to water management is crop evapotranspiration. This research examines five crop evapotranspiration models (one combination model, three radiation based models and one temperature based model) under hyper arid environment at practical field level. These models have been evaluated and calibrated using an alfalfa weekly water balance in 2010. The calibrated models have been evaluated and validated using wheat and potatoes on a weekly water balance, respectively. Based on the results and discussion, FAO-56 PM proved to be superior at estimating crop evapotranspiration while radiation and temperature based models underestimated evapotranspiration and would require subsequent local calibration. However, the drawback of FAO-56 PM is that it requires all weather data and is also significantly more complicated than other models. Important observations that were made are that calibrated Turc and Makkink models performed poorly even when they were calibrated while simple models such as calibrated Hargreaves-Samani (temperature-based) and Priestley–Taylor (radiation-based) can be adequately used for irrigation scheduling in a hyper arid environments. / Ministry of Higher Education, Saudi Cultural Bureau in Canada. Saudi Agricultural Development Company (INMA).

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Alluvial fan surfaces in the Atacama Desert of northern Chile preserve evidence of recent, precipitation-driven, surface flows. Determining the hydrologic characteristics of these flows is important for understanding the effects of rare yet significant storms in the region. Flow reconstruction, runoff analysis, and comparison with climatological data yield surface activation recurrence intervals of ~1-20 years for three small fans and associated catchments proximal to Iquique and Antofagasta. Relatively short-lived and intense precipitation events (1-3 hour, > 4 mm/hr) are required to mobilize and transport the largest surface grains. Modeled discharges provide minimum constraints on the rates of precipitation that yield surface-forming flows in the hyper-arid region. The results of this study aid in understanding the evolution of various surfaces in the region. In particular, results provide a clear indication of the ability of a particular storm event --i.e., precipitation rate to activate a surface. / Master of Science