Ziel dieses Projektes ist es, den Anbau von Energiepflanzen auf ertragsschwachen Standorten zu optimieren, wobei die Nutzung der Pflanzen zur Biogaserzeugung im Mittelpunkt steht. Als ertrags-schwache Standorte werden diluviale Böden, insbesondere Sandböden, in Trockengebieten Deutschlands in die Untersuchungen einbezogen. Im Vergleich zum Silomais, welcher zurzeit als nachwachsender Rohstoff am häufigsten in Biogasanlagen zum Einsatz kommt, werden Sorghum-hirsen (Zuckerhirse und Sudangras) hinsichtlich ihrer Eignung als Biogasrohstoff geprüft. Mit den Untersuchungen sollen für ertragsschwache Trockenstandorte Anbaualternativen aufgezeigt werden, die zu einem sicheren Ertrag und Einkommen in den entsprechenden Regionen führen.

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).

Bats inhabiting arid, subtropical environments face diverse challenges related to energy and water balance. First, they may have to conserve water and energy during cool, dry winters when water is scarce and insect availability reduced. Second, during hot summers when air temperature may routinely exceed body temperature, bats may need to avoid both hyperthermia and dehydration. A common response to the energetically challenging winter period in temperate, subtropical and tropical species is heterothermy (i.e. torpor and hibernation). Despite evidence suggesting that heterothermy is of major significance in the energy balance of tropical and subtropical bats, its occurrence in southern African species especially those in semi-arid subtropical regions have received relatively little attention. Moreover, the physiological and thermoregulatory responses of bats to high air temperatures (Ta) are relatively poorly known. The goal of my project was to investigate various seasonal physiological challenges imposed on bats in an arid, sub-tropical climate. I investigated the occurrence of winter heterothermy in Nycteris thebaica (Nycteridae) in the Limpopo Valley. Skin temperatures (Tskin) were measured using temperature-sensitive transmitters, and roost temperatures (Troost) were recorded using miniature temperature loggers. N. thebaica used multiple roosting sites, including a hollow baobab tree (Adansonia digitata) and several caves, and exhibited only moderate heterothermy. Tskin was maintained around normothermic levels, with differences of 3-9°C (7.5±1.7°C) between overall maximum and minimum Tbs. A minimum Tskin of 28.4°C occurred at Troost = 23.8°C, and patterns of thermoregulation did not appear to be influenced by prevailing weather conditions. Roost temperatures did not decrease below 10°C, and averaged 21.2±2.8°C and 23.3±2.9°C respectively. The lack of pronounced heterothermy in N. thebaica is surprising, particularly in view of the daily torpor cycles observed in many insectivorous bat species. I also investigated the physiological responses of three sympatric bat species during summer using an open-flow respirometry system to measure resting metabolic rates (RMR) and evaporative water loss (EWL) over a range of Tas ~ 10-42°C, with body temperatures (Tb) simultaneously recorded via temperature-sensitive passive integrated transponder (PIT) tags. Basal metabolic rates for Nycteris thebaica and Taphozous mauritianus were 8.9±2.7mW.g-1 and 6.6±2.2mW.g-1 respectively, falling within the 95% prediction intervals for bat BMR, whereas the value for Sauromys petrophilus (3.4±0.6mW.g-1) fell below the lower 95% prediction interval. Maximum EWL for N. thebaica, T. mauritianus and S. petrophilus were 18.6±2.1mg.g-1.h-1 (Ta=39.4°C), 14.7±3.1mg.g-1.h-1 (Ta=41.9°C) and 23.7±7.4mg.g-1.h-1 (Ta=41.7°C) respectively. Maximum individual Tbs recorded were 46.5°C in N. thebaica (Ta=39.3°C), 44.9°C in T. mauritianus (Ta=41.8°C) and 46.5°C in S. petrophilus (Ta=41.7°C). Overall, I found that N. thebaica was the least heat tolerant species, with T. mauritianus and S. petrophilus being more heat tolerant. In the face of climate change, heat tolerance together with specific thermal properties of a given roost may play a major role in the ability of a species to persist in a hot, arid environment. / Dissertation (MSc)--University of Pretoria, 2012. / Zoology and Entomology / unrestricted

Ziel dieses Projektes ist es, den Anbau von Energiepflanzen auf ertragsschwachen Standorten zu optimieren, wobei die Nutzung der Pflanzen zur Biogaserzeugung im Mittelpunkt steht. Als ertrags-schwache Standorte werden diluviale Böden, insbesondere Sandböden, in Trockengebieten Deutschlands in die Untersuchungen einbezogen. Im Vergleich zum Silomais, welcher zurzeit als nachwachsender Rohstoff am häufigsten in Biogasanlagen zum Einsatz kommt, werden Sorghum-hirsen (Zuckerhirse und Sudangras) hinsichtlich ihrer Eignung als Biogasrohstoff geprüft. Mit den Untersuchungen sollen für ertragsschwache Trockenstandorte Anbaualternativen aufgezeigt werden, die zu einem sicheren Ertrag und Einkommen in den entsprechenden Regionen führen.

nÃo hà / Um dos desafios centrais de investigadores e gestores de Ãgua em grandes bacias à avaliar, de modo confiÃvel, a disponibilidade de Ãgua em condiÃÃes reais. Em bacias do semi-Ãrido brasileiro, um dos principais desafios consiste em considerar os efeitos da proliferaÃÃo de pequenos aÃudes. Esta pesquisa tem como objetivo principal definir um arranjo Ãtimo para o sistema de acumulaÃÃo em grandes bacias no semi-Ãrido, denominado Ãtimo por corresponder ao melhor Ãndice de sustentabilidade (IS) da disponibilidade hidrolÃgica da bacia. Para atingir o objetivo proposto foi estudado o caso da bacia do aÃude OrÃs (CearÃ, 24 mil km2). A referida bacia conta atualmente com mais de quatro mil reservatÃrios de diversos tamanhos, sendo estratÃgica para o abastecimento do estado. O modelo WASA (Water Availability in Semi-Arid Environments) foi aplicado para o perÃodo entre 1961 e 2005 e sua validade comprovada para a Ãrea em estudo, comprovando a robustez do modelo para estimar a disponibilidade hÃdrica em grandes bacias hidrogrÃficas, mesmo considerando o efeito de milhares de pequenos reservatÃrios a montante. Usando-se o mÃtodo de otimizaÃÃo de busca direta Simplex-MSX, foram simulados cerca de 60 arranjos para a pequena aÃudagem na bacia. Para cada arranjo foi estimada a respectiva eficiÃncia hidrolÃgica atravÃs do Ãndice de sustentabilidade IS. O arranjo Ãtimo permitiu o estabelecimento de parÃmetros capazes de orientar a polÃtica para a pequena aÃudagem em grandes bacias semi-Ãridas. Os resultados da pesquisa indicam que a disponibilidade hÃdrica mÃxima pode ser obtida para a Ãrea mÃdia de captaÃÃo de 7 km2 por aÃude e para volume Ãtimo de armazenamento da bacia tal que seu tempo de residÃncia seja da ordem de 3 anos / One of the central challenges of researchers and water managers in large-scale watersheds is to evaluate the water availability in real conditions. In watersheds of the Brazilian semi-arid region, one of the main challenges consists of considering the effect of the proliferation of small reservoirs. This research has as the main objective to search the optimum arrangement for the system of accumulation in large watersheds in the semi-arid environment. The objective function to be optimized is the ASCE hydrological sustainability index (SI) of the watershed. In order to achieve the considered objective, the case of OrÃs dam (CearÃ, Brazil) watershed (ca. 24000 kmÂ) was studied. This watershed has presently more than four thousand small reservoirs, and it is strategic for the water supplying in the state. The WASA model (âWater Availability in Semi-Arid Environmentsâ) was applied to the watershed for the period from 1961 to 2005 for validation purposes. The robustness of the WASA model in predicting water availability in the large-scale watershed, considering the effect of thousands of small reservoirs, was proven. Using the optimization method of Simplex-MSX, 60 different arrangements for the small reservoirs in the watershed were simulated for a 45-year period with daily steps. For each arrangement the respective hydrological efficiency (assessed by the sustainability index) was estimated. The optimum arrangement allowed the establishment of parameters capable to guide the policy for small reservoirs in large semi-arid watersheds. The main results of the research showed that the maximum sustainability index was obtained for average contribution area of 7 km per dam; and storage volume of the basin such that its time of residence is in the order of 3 years

No description available.

Les environnements arides végétalisés seront parmi les environnements les plus impactés par la désertification dans le cadre du changement climatique. Ces environnements légèrement végétalisés sont caractérisés par une balance précaire entre un état de résilience et de vulnérabilité qui est intrinsèquement menacé par la désertification pouvant potentiellement mener à une augmentation du transport des sédiments éolien et une dégradation des environnements. Le nombre d’interactions présentes entre la végétation, la pluie, le transport des sédiments et la présence d’herbivore en milieu aride, ainsi que leur nature non-linéaire rend difficile de représenter ces interactions à l’aide de modèle physique et mathématique. La modélisation complexe est mieux adaptée à la représentation des interactions complexes entre la végétation, la pluie, le transport des sédiments et la présence d’herbivores dans les systèmes arides. Un nombre considérable d’études ont utilisées les modèles complexes pour étudier l’effet de la végétation sur le transport des sédiments ou l’effet de la présence d’herbivore sur la végétation, mais peu d’études ont utilisées une approche intégrant ces trois composantes en un même modèle. Un nouveau modèle d’herbivorie basé sur l’agent (GrAM) est présenté sous forme d’extension du modèle ViSTA_M17 et permet une meilleure représentation de l’impact des régimes de pâturage en environnement aride végétalisé. Cet ajout ayant un modèle complexe de transport des sédiments et de végétation déjà établit vise présenter un modèle hybride pouvant représenter l’impact de l’herbivorie sur la composition végétale et le transport des sédiments en environnement aride à l’échelle du paysage. Le développement du nouveau module à l’intérieur de la structure du modèle ViSTA original a souligné certaines limites de ce dernier, notamment une sensitivité importante de la végétation et de la force de cisaillement du vent. Le modèle ViSTA_GrAM répond à certaines limites du modèle original par l’intégration d’un nouveau module d’herbivorie et présente une avancée vers une modélisation environnementale englobante permettant une meilleure compréhension des dynamiques spatiales et temporelles des environnements arides. L’approche englobante utilisée par le modèle ViSTA_GrAM est bénéfique à la prise de décision, puisqu’elle offre un outil permettant d’explorer les réponses des environnements arides à un changement de leur végétation, leur régime de pluie, leur régime de transport des sédiments ou leur régime d’herbivorie. Les modèles complexes et l’exploration de scénarios futurs des environnements arides peuvent permettre d’améliorer la gestion de ces mêmes environnements. / Vegetated arid environments will be among one of the most affected by desertification as a result of climate change. These sparsely vegetated regions exhibit a delicate balance of resilience and vulnerability that are profoundly challenged by desertification, potentially producing an important positive feedback leading to increased aeolian activity and therefore land degradation. The high level of interaction between rainfall, vegetation, sediment transport and grazing in these arid environments and the non-linear nature of these interactions make them difficult to predict by traditional mathematical modeling mean. Complex modeling, on the other hand, offer better representation of the intricate relation between vegetation, rainfall, sediment transport and grazing in an arid environment system. A sizable amount of studies has been conducted with complex models to explore the effect of vegetation on sediment transport or grazing effect on vegetation, but few have used a truly integrative approach where all tree components were represented in a complex model. This research present a novel agent-based model (GrAM) integrated as an extension to already complete sediment transport-vegetation complex model (ViSTA) allowing a more refined representation of grazer’s impact in vegetated arid environments. This addition to the ViSTA model is aimed to combine a land management and systematic approach in a coupled model, to represent, at a landscape level, the impact of grazing on the composition of vegetation and sediment movement in arid environments. The development of this new module within the original ViSTA model, has highlighted some limitations of this model, most notably concerning its sensitivity to vegetation and wind shear. The ViSTA_GrAM model addresses these limitations through integrating a new module of grazing as the next step toward an integrated modelling effort that permits models to effectively increase our spatial and temporal understanding of arid environments vegetation, sediment transport and grazing dynamics. Integrative approach, like the one provided by the ViSTA_GrAM model, is beneficial to decision making by providing tools to investigate the response of an arid environment to different state of their vegetation, rainfall regime, wind stress and grazing regime. By developing complex modeling in arid environment and exploring various future scenarios for arid environment, we hope to lead to better management plan of those same environment.

Direct mountain front recharge (MFR), water table recharge at the base of the mountain front, was evaluated on the arid (<250 mm/yr precipitation) Silver Island Mountains by comparing mountain precipitation to groundwater response. Direct MFR contributions were assessed on two catchments, one bedrock (i.e., mountain block) dominated and the other alluvial fan (i.e., mountain front) dominated. Catchment precipitation and shallow groundwater levels at each catchment outlet were measured for a 24 month period beginning October 2005. This time period captured one complete hydrologic cycle (December 2005-February 2007) for which annual and seasonal direct MFR rates were calculated. Annual direct MFR was calculated using a modified version of the water table fluctuation (WTF) method as 0.015-0.016% of precipitation on both catchments, with seasonal variations of 0% in summer up to 0.023% in winter, spring and fall. Seasonal direct MFR contributions are similar on the bedrock and the alluvial fan dominated catchments, with a notable exception during fall 2006 when direct MFR was twice as effective on the bedrock dominated system than on the alluvial fan dominated system (0.022% and 0.011% of precipitation, respectively). Darcy's law calculations show similarly low annual direct MFR contributions (0.013-0.032% of precipitation) as those calculated by the WTF method. Calculated direct MFR is 10% or less than typical calculated combined MFR (near surface recharge and deep underflow from the mountain block) for similar terrains and climates, and is only 3.5% of the combined MFR for the Silver Island Mountains as calculated by the Maxey-Eakin model. However, based on total recharge to the adjacent playa, it is apparent that the Maxey-Eakin model overestimates combined MFR, and the small calculated direct MFR is at least 50% of combined MFR. Despite some uncertainty in the numerical results, several patterns are evident in the data. The data show that direct MFR occurs in response to small rainfall events throughout much of the year, and that snowmelt is not necessary to produce direct MFR. The data also show that direct MFR responds more quickly and flushes through the system faster on the alluvial fan catchment than on the bedrock catchment.

Over the past century, woody plants and shrubs have increased in abundance at the expense of grasslands in many semiarid regions. The availability and concentrations of nutrients influence the relative success of plants, but the effects of fire frequency on soil nutrients is unknown for semiarid grasslands. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established to examine the effects of fire frequency on soil biogeochemistry, plant biochemistry, and δ¹³C values in soil organic matter (SOM). The sites were on homogeneous granitic alluvium where wildfire frequency history is known from 1973 to present and no cattle grazing has occurred in recent decades. Subplots represent fire frequencies of no burns, 3 fires per decade, and 5 fires per decade. The "no burn" plot has abundant C₃ Prosopis veleruina (mesquite) trees, whereas the burned plots are open C₄-dominated grasslands with scattered mesquite trees. Prosopis trees have altered SOM pools by the concentration of plant nutrients and the addition of isotopically light shrub litter. Frequent fires have altered the basic geochemistry and nutrient availabilities of the soil, and the changes appear to be significant enough to affect plant growth. Soil pH increases with burning frequency, and TOC, total nitrogen, and plant -available phosphorus show significant increases on the infrequently burned plot. Burning is advantageous for preservation or restoration of grasslands, as total living grass biomass is greater on the two burned plots. Root biomass is significantly lower on the "frequently burned" plot. Concentrations of the key nutrients nitrogen and phosphorus are reduced in plants on the burned sites compared to plants on the unburned site. Fires help re-distribute nutrients but evidence of nutrient concentrations and δ¹³C values are retained in SOM for many decades. Estimates of bulk carbon turnover rates range from 112 to 504 years. Evidence for modern C₃ shrub expansion is found in the shift of SOM δ¹³C values from values characteristic of C₄ grasses to C₃ shrubs in surface soil layers. δ¹³C(SOM) values indicate that the Holocene and Late Pleistocene were dominated by C₄ grasslands, and the pre-Late Pleistocene vegetation was a C₄-grass savanna with abundant C₃ plants.