Browsing by Subject "Soil Moisture"
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Item Long-Term Hydrologic Responses To Shrub Removal In A SW Texas Rangeland: Using Soil Chloride To Estimate Deep Drainage(2010-10-12) Barre, David AnthonyThe Carrizo-Wilcox aquifer is a valuable groundwater resource, situated in a semi-arid landscape of Southwest Texas, where over-use by dependent farming practices has lowered aquifer levels. In semi-arid regions, rates of groundwater recharge are predominantly low due to high potential evapotranspiration rates; however, least understood is the role that vegetation plays in soil-plant-water dynamics. Vegetation management potentially plays a major role in countering the loss to recharge because evapotranspiration (ET) varies with vegetation type and cover. The conversion from shrubland to grassland likely reduces rooting depths and total plant cover. Subsequently, deep drainage (percolation below the root zone) will likely increase and lead to groundwater recharge, at least temporarily. The primary aims of the study were to identify those biotic and abiotic factors facilitating deep drainage and to examine differences in recharge for the years following clearing of natural shrub vegetation. Soil chloride was examined to estimate long-term recharge rates, since its concentration in the soil is influenced by the movement of water. Short-term soil moisture trends were also monitored for any water movement deep in the soil profile in response to individual rain events. Rooting depths decreased following removal of vegetation; yet root biomass unexpectedly increased due to successful grass establishment during the first five years after treatment. Soil properties did not vary between treatments, indicating that the majority of chloride differences seen were a consequence of vegetation change. Peak and total soil chloride concentrations were expected to decrease and occur deeper in the soil profile 15-30 years following the clearing of woody vegetation. Total chloride decreased by up to 65% after 30 years and resulted in an estimated 14.9 mm/yr more recharge compared to adjacent untreated controls. Evidence in this study suggest that much of this chloride is leached during the first five years following treatment and that more leaching occurs in especially wet periods. During the wet 2007 growing season, soil moisture below the root zone increased by up to 17% after vegetation clearing. The results of this study indicate that hydrologic changes following brush removal were evident in this system and are likely to positively influence groundwater recharge in the long-term.Item Understanding Spatio-Temporal Variability and Associated Physical Controls of Near-Surface Soil Moisture in Different Hydro-Climates(2013-05-06) Joshi, ChampaNear-surface soil moisture is a key state variable of the hydrologic cycle and plays a significant role in the global water and energy balance by affecting several hydrological, ecological, meteorological, geomorphologic, and other natural processes in the land-atmosphere continuum. Presence of soil moisture in the root zone is vital for the crop and plant life cycle. Soil moisture distribution is highly non-linear across time and space. Various geophysical factors (e.g., soil properties, topography, vegetation, and weather/climate) and their interactions control the spatio-temporal evolution of soil moisture at various scales. Understanding these interactions is crucial for the characterization of soil moisture dynamics occurring in the vadose zone. This dissertation focuses on understanding the spatio-temporal variability of near-surface soil moisture and the associated physical control(s) across varying measurement support (point-scale and passive microwave airborne/satellite remote sensing footprint-scale), spatial extents (field-, watershed-, and regional-scale), and changing hydro-climates. Various analysis techniques (e.g., time stability, geostatistics, Empirical Orthogonal Function, and Singular Value Decomposition) have been employed to characterize near-surface soil moisture variability and the role of contributing physical control(s) across space and time. Findings of this study can be helpful in several hydrological research/applications, such as, validation/calibration and downscaling of remote sensing data products, planning and designing effective soil moisture monitoring networks and field campaigns, improving performance of soil moisture retrieval algorithm, flood/drought prediction, climate forecast modeling, and agricultural management practices.