Browsing by Subject "Evapotranspiration"
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Item Effect of nitrogen on the uptake of perchlorate by plants(Texas Tech University, 2004-08) Joseph, Preethi CPrevious studies have shown that plants were tolerant to perchlorate and will accumulate perchlorate in plant tissues. The objectives of this research were to determine the effect of nitrogen type (Ammonium or Nitrate) and concentration on the rate and extent of perchlorate uptake in lettuce and soybean plants. Studies were conducted in plant growth chambers and in greenhouses using sand as a support medium. Treatments included studies with defined laboratory fertilizer solutions at varying concentrations of nitrogen and constant concentrations of other ions, as well as with commercial NH4+ and NO3- based fertilizers at varying loading rates. The growth of plants was affected in response to varying nitrogen concentrations and sources. The perchlorate accumulation in plants was determined on a weekly basis by extracting the plant and sand samples and analyzing them for perchlorate levels using ion chromatography. In all experiments, plant growth was severely affected, and in most cases, plants did not proceed past the two leaf stage of growth. Perchlorate was detected in all plants with peak concentrations occurring between 3-6 weeks of growth and declining thereafter. The plant perchlorate concentrations were higher in plants fertilized with ammonium fertilizer than with the nitrate fertilizer although the difference in plant growth between treatments makes it difficult to say whether this would be observed under normal conditions. The perchlorate concentration also generally increased with an increase in nitrogen concentrations applied to the plants. Overall, the effects of source and nitrogen concentration are unlikely to have significant effects on perchlorate uptake in plants under normal environmental conditions.Item Estimating albedo for evapotranspiration models(Texas Tech University, 1989-05) Hannabas, Byron BSolar reflectance, or albedo, is one of the most critical factors affecting the prediction of evaporation and evapotranspiration. When evaporation or evapotranspiration is estimated from predictive models, and a poor selection of a value for albedo is made from that available in the published literature, significant errors become inherent in these estimations. A predictive, physically based model has been developed to substantially reduce and possibly eliminate the errors encountered in selecting values for albedo. A literature review concerning albedo is included in the text as well as justifications for the newly developed model.Item Estimating potential evapotranspiration over the Edwards Aquifer, utilizing the Priestley-Taylor equation(2011-12) Edwards, Carl Alexander; Groat, Charles G.; Kreitler, Charles W.; Quiñonez-Piñón, Rebeca; Scanlon, BridgetEstimating recharge is a critical aspect of groundwater management, when aquifer resources are constrained by multiple users. The Edwards Aquifer, an artesian aquifer underlying Austin and San Antonio, Texas, sustains municipalities, farmers and fragile habitats at discharge locations. Rising municipal demand for Edwards water supports the need for effective conservation over time to maintain the well-being of all users. Predicting recharge is a valuable tool for determining future available resources. Evapotranspiration (ET) accounts for a majority of water loss following precipitation, significantly affecting recharge. Developing a method for accurate regional estimates of ET is complicated by aquifer characteristics, expensive instrumentation, and a variable climate. This study investigates a specific method for estimating regional potential ET (ETp), by combining the Priestley-Taylor equation with data primarily retrieved from the Moderate-Resolution Imaging Spectroradiometer. Improved resolution and timing of satellite measurements provides greater regional specificity for variables related to ET calculations. ETp is then estimated for 2004 and 2005, utilizing data from MODIS, aboard NASA’s Aqua and Terra satellites. Land surface temperature, leaf area index and albedo retrieved from MODIS replace in situ measurements, which are often nonexistent in a regional context. Incoming radiation, a direct input in the Priestley-Taylor equation, is retrieved from the National Center for Environmental Prediction’s North American Regional Reanalysis Model (NARR). Results show methods overestimate ET between 400% to over 1000% when compared to actual ET (ETa) at two locations in the northeast portion of the aquifer. Correlation is improved when ETp is treated as an instantaneous rate rather than daily. During months of above average precipitation, which are more representative of potential conditions, instantaneous ETp exceeded ETa by an average of 81%, with a root mean squared error of 1.15 mm/30min and an average positive bias of 2.84 mm/30min. Considering the soil moisture limited conditions throughout Central Texas, a positive bias is not surprising. Incorporating a calibrated Priestly-Taylor could improve accuracy, but estimating regional ETp remains restricted by available daily data necessary for calculations and comparison.Item Evaluation of septic system drain fields(Texas Tech University, 2000-05) Ingram, Wesley WarrenAt the time of this thesis, the practice in Texas was to install absorptive drain fields in a septic system. The Texas On-Site Wastewater Treatment Research Council raised the question as to whether the combination of evapotranspiration and absorption in a septic system drain field in the arid and semi-arid regions of Texas could reduce the size of the drain field. As a result, a two-year study was undertaken in an attempt to answer that question. A field test facility was designed and installed at Reese Center near Lubbock, Texas. This facility consisted of septic tanks, header tanks, distribution system, and 18 drain fields. The 18 drain fields were divided evenly between wastewater and clean water. Three treatments were tested and include absorption (AB) fields, evapotranspiration (ET) fields, and combined evapotranspiration and absorption (ETA) fields. Each treatment and its control were installed in triplicate to enable statistical analyses of the results.Item Improved Modeling of Evapotranspiration using Satellite Remote Sensing at Varying Spatial and Temporal Scales(2012-10-19) Long, DiThe overall objective of the dissertation was to improve the spatial and temporal representation and retrieval accuracy of evapotranspiration (ET) using satellite imagery. Specifically, (1) aiming at improving the spatial representation of daily net radiation (Rn,24) under rugged terrains, a new algorithm, which accounts for terrain effects on available shortwave radiation throughout a day and utilizes four observations of Moderate-resolution Imaging Spectroradiometer (MODIS)-based land surface temperature retrievals to simulate daily net longwave radiation, was developed. The algorithm appears to be capable of capturing heterogeneity in Rn,24 at watershed scales. (2) Most satellite-based ET models are constrained to work under cloud-free conditions. To address this deficiency, an approach of integrating a satellite-based model with a large-scale feedback model was proposed to generate ET time series for all days. Results show that the ET time series estimates can exhibit complementary features between the potential ET and the actual ET at watershed scales. (3) For improving the operability of Two-source Energy Balance (TSEB) which requires computing resistance networks and tuning the Priestley-Taylor parameter involved, a new Two-source Trapezoid Model for ET (TTME) based on deriving theoretical boundaries of evaporative fraction (EF) and the concept of soil surface moisture availability isopleths was developed. It was applied to the Soil Moisture and Atmosphere Coupling Experiment (SMACEX) site in central Iowa, U.S., on three Landsat TM/ETM imagery acquisition dates in 2002. Results show the EF and latent heat flux (LE) estimates with a mean absolute percentage difference (MAPD) of 6.7 percent and 8.7 percent, respectively, relative to eddy covariance tower-based measurements after forcing closure by the Bowen ratio technique. (4) The domain and resolution dependencies of the Surface Energy Balance Algorithm for Land (SEBAL) and the triangle model were systematically investigated. Derivation of theoretical boundaries of EF for the two models could effectively constrain errors/uncertainties arising from these dependencies. (5) A Modified SEBAL (M-SEBAL) was consequently proposed, in which subjectivity involved in the selection of extreme pixels by the operator is eliminated. The performance of M-SEBAL at the SMACEX site is reasonably well, showing EF and LE estimates with an MAPD of 6.3 percent and 8.9 percent, respectively.Item Influence of varying replacement of potential evapotranspiration on water use efficiency and nutritive value of three Old World bluestems (Bothriochloa spp.)(Texas Tech University, 2004-05) Philipp, DirkForage systems offer alternatives to traditional cropping systems in the Texas High Plains, but information on water management is lacking. This research investigated whether differences in water use efficiency (WUE; kg total seasonal dry matter [DM] yield ha"' mm"' water [precipitation, irrigation, and soil water depletion]) existed among species of old world bluestems (Bothriochloa spp.). Additionally, effects of irrigation amounts on forage nutritive value and plant morphology were explored. Established stands of three Bothriochloa species ('Dahl' [bladhii]; 'Caucasian' [caucasica]; and 'Spar' [ischaemum]) were surface drip-irrigated weekly during the growing season to replace: 1) 0% (dryland); 2) 33% (low); 3) 66% (medium); and 4) 100% (high) of potential evapotranspiration minus precipitation during 2001,2002, and 2003. Soil organic carbon as influenced by irrigation level and optimum metabolic temperature for growth were investigated in 2003. Each species and water treatment was replicated three times in a complete randomized block design with a split plot treatment arrangement. In 2001 and 2002, no differences in water use efficiencies among species were found. Averaged across these 2 yr, WUE of 19.0, 19.3, and 15.3 kg ha"' mm"' were observed for Caucasian, Dahl, and Spar, respectively. In 2003, Caucasian produced 16.9 kg ha" mm', differing (P < 0.05) in slope fi-om Spar (7.4 kg ha"' mm"') but Dahl (12.4 kg ha"' mm"') was not different in slope from either Caucasian or Spar. Maximum seasonal DM yield was obtained with Caucasian under high irrigation (18.0 Mg ha"') vs. Dahl (15.2 Mg ha") and Spar (12.55 Mg ha"') averaged over all years. Percentage dry matter digestibility (DMD) was higher (P < 0.05) in all forage species irrigated at a low level (58% DMD) than for other water treatments (57, 56, and 55% DMD for dryland, medium, and high irrigation, respectively). Dahl generally averaged higher (P < 0.05) percentage crude protein (CP) than other species during the growing season. More differences in percentage CP were observed between dryland and irrigated forages than within the irrigated treatments but CP would have met nutritional needs of most livestock only in May. In all species, percentages total nonstructural carbohydrates (TNC) and DMD and leaf: stem ratio declined while percentage cell wall increased with increased irrigation amount in the first half of the growing season. Effects of irrigation on cell wall, TNC, and DMD appeared related to changes in plant morphology (leaf:stem) and to an increase in physiological age as indicated by growth stage (mean stage count and mean stage weight). Leaf:stem ratio following hay harvest in July showed fewer effects of irrigation treatments but ratios of live:dead plant material generally increased during the growing season in response to increased irrigation (linear effects; P < 0.05). Soil organic carbon was higher (P < 0.05) in all irrigated soils (5.5 g 100 g"') compared with dryland (4.6 g 100 g"') but did not differ among irrigation treatments. Optimum metabolic temperatures for growth of Caucasian, Spar, and Dahl old world bluestems were 24, 24, and 28°C, respectively. Our data suggest that differences in WUE among Bothriochloa species can be identified, and that yield, chemical composition, and morphology can be manipulated through irrigation management to optimize total nutrient yield and nutritive value.Item Using web services and remote sensing to visualize water balances in the San Marcos River Basin(2012-05) Siegel, Daniel Bandes, 1984-; Maidment, David R.; McKinney, Daene C.The water balance equation is one of the most fundamental concepts in hydrology. How much precipitation a river basin receives, and where that water goes, defines what flora, fauna, and industry the basin can support. Models for solving this equation originally relied only on precipitation, air temperature, and day length, but have adapted as new data becomes available. Recent advances in technology, especially remote sensing and web services, make it cheaper and easier than ever to obtain hydrological data, including many variables that were previously impossible to measure. This thesis will examine the water balance of the San Marcos River Basin and demonstrate how remote sensing and web services can improve our understanding of the basin's hydrology. It was found that 72% of precipitation in the San Marcos Basin is lost to evapotranspiration. This percentage varies from year to year as a function of precipitation, but the annual volume of evapotranspiration stays almost constant. It was only during the second consecutive year of drought that there was an appreciable change in evapotranspiration. This suggests that annual evapotranspiration can be thought of as a property inherent to a watershed's hydrology, and so long as there is enough stored water in the soil, that demand will be met. The water left over after ET takes its share can either flow out of the basin through a river channel or stay within the basin as storage. After examining methods for partitioning the available water between outflow and storage, it was found that lumped water balance models cannot be used in the San Marcos River Basin because of its complex interactions with the Edwards Aquifer. In order to better model soil moisture dynamics and groundwater infiltration, a distributed model will have to be developed that accounts for flow in and out of the aquifer.