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Item Estimation of groundwater recharge along a precipitation gradient for Savannah aquifers in Namibia with special emphasis on the impact of vegetation(University of Namibia, 2022) Uugulu, ShoopalaThe quantification of groundwater resources is essential especially in water scarce countries like Namibia as well as the assessment of the influence of vegetation on groundwater recharge for a better management and sustainability of savannah aquifers. This study has two specific objectives which are firstly to identify groundwater recharge processes and quantify such along a precipitation gradient in Namibian savannah aquifers. Secondly, to determine the influence of savannah vegetation on groundwater recharge by determining the active root depth and source water sources for S. mellifera and B. albitrunca. The study was carried out along a precipitation gradient at three sites namely: Tsumeb; Waterberg and Kuzikus/Ebenhaezer. The chloride mass balance (CMB) method and water stable isotope methods were used in determining groundwater recharge rates at the three sites. Precipitation samples from Tsumeb and Waterberg were collected during the rainy season from 2017 to 2018, while Kuzikus/Ebenhaezer samples were collected between 2014 and 2015. Groundwater samples were collected before, during and after rainy seasons from 2016 to 2017. A deuterium tracer was inserted at different plots with varying depths in December 2016 in order to assess the active root depths for both S. mellifera and B. albitrunca at Ebenhaezer farm. Both woody plants were sampled for the xylem and transpired water. A scattered distribution of rain sample isotopic ratios along the global meteoric water line in the areas was attributed to a seasonal effect. Local meteoric water line equations for Tsumeb, Waterberg and Kuzikus/Ebenhaezer were obtained as: δ2H = 7.78 δ18O + 6.74, (R 2 = 0.95); δ2H = 7.37 δ18O + 5.77, R2 = (0.97); δ2H = 7.16 δ18O + ii 9.88, (R 2 = 0.96) respectively. All the slopes obtained from three study sites are all lower than that of a global meteoric water line equation. A lower slope indicates that the local precipitation has experienced some sub cloud evaporation, leading to enrichment of heavy isotopes. Waterberg groundwater plots on the GMWL which indicates little or absence of evaporation. Tsumeb groundwater plots on/close to the GMWL with an exception of groundwater from the karst Lake Otjikoto which is showing evaporation. Groundwater from Kuzikus/Ebenhaezer shows an evaporation effect. All groundwater isotopic values from three sites match those of precipitation depleted in heavy stable isotopes, which indicates that recharge only take place during January, February and March where the precipitation is highest and depleted in heavy stable isotopes. CMB method revealed that savannah aquifers are recharged at low rates, mostly below 10% of the annual precipitation The analysis of woody plant water isotopes at Ebenhaezer farm revealed their source water and the active root depth for S. mellifera. Of 49 transpired water samples, only one S. mellifera sample showed a high deuterium content of 515.9 ‰ where the tracer was inserted at 2.5 m soil depth. Elevated deuterium contents were observed in two S. mellifera xylem samples where the tracer was applied at 2.5 m and 3 m, a possible sign of the active root depth for S. mellifera. However, the active root depth of B. albitrunca could not be determined due to the absence of the tracer in the sampling depths used. S. mellifera δ 18O values indicate that it is using both groundwater and soil water while B. albitrunca δ 18O values show that it is mainly using groundwater. Groundwater recharge rates from this study can be used to guide policy makers on decisions regarding safe yields for the sustainability of the aquifers.Item Groundwater recharge of perched aquifers in the Cuvelai-Etosha basin, Namibia(University of Namibia, 2018) Hamutoko, Josefina TulimevavaThe United Nation predicted that by 2025, 1.8 billion people will be living in countries with absolute water scarcity and two-thirds of the world population could be under stress condition. In semi-arid regions, most communities depend on groundwater as the source of drinking water and thus with changes in global climatic conditions and increase in population, groundwater resources are facing challenges of both over-exploitation and contamination. Therefore, there is an urgent need to improve the understanding of existing groundwater resources in terms of aquifer distributions and interactions and process that control the groundwater dynamics, recharge and chemistry groundwater for an effective strategy to reduce the pressure on the hydrologic system. The main aim of this PhD is to contribute to knowledge about shallow groundwater in semi-arid environments by estimating groundwater recharge of perched aquifers in the Cuvelai-Etosha Basin (CEB). Four specific objectives were examined in this study; first, the study characterizes the groundwater chemistry and isotopic composition of oxygen (δ18O) and hydrogen (δ2H) in order to understand mechanisms of groundwater dynamics and quality of groundwater in perched aquifers, secondly, it analyses and understand the spatial and temporal variations of hydrochemical data and isotopic compositions of hand-dug wells in the CEB, with particular focus on water origin and recharge processes, thirdly, the study evaluates the relationship between the shallow (perched) aquifer and the deeper seated aquifers and finally develops a conceptual model for the perched aquifers. Methods employed in this research are based on isotopic and hydrochemical data to understand groundwater recharge mechanisms. Integrated isotopic and hydrochemical tracers along with standard hydrological data are used to understand complex dry land hydrological processes on different spatial and temporal scales. Different spatial and temporal scales are particularly important for arid environments due to high heterogeneity that are associated with these environments. Therefore in this study, water samples were collected from rain collectors, hand-dug wells and boreholes and analysed for major ions and stable isotopes (18O and 2H) for three years (2014-2017) in a total of 12 sampling campaigns. Chemical analyses were performed at the Analytical Laboratory Services in Windhoek, Namibia and at the hydrochemistry laboratory of BGR in Hanover, Germany using Titration, Ion Chromatography and ICP-OES. The reliability of the analyses was checked by an ion charge balance error on all samples. Stable isotopes were measured at the University of Namibia (UNAM) and BGR laboratories using an off-axis integrated cavity output spectroscope (OA-ICOS, Los Gatos DLT-100) and a cavity ring down spectrometer (CRDS, model L2120-i, Picarro Inc.) respectively. Results show that groundwater chemistry of perched aquifers is controlled mainly by strong evaporation, dissolution of carbonate minerals (calcite and dolomite) and evaporitic minerals (gypsum and halite) and silicate weathering and cation exchange. Stable isotope composition suggests that deep groundwater is recharged by high intensity/large rainfall events, whereas the shallow wells can be recharged by less intense/small rainfall events. Water in deep wells reflect mixture of water influenced by evaporation during or before infiltration and water that infiltrated through fast preferential pathways whereas shallow wells are strongly influenced by evaporation. The mean parent isotopic composition for shallow wells in the ephemeral river is -7.8 for δ18O and -51.8 for δ2H, for deep wells in the pans and depressions is -8.7 and -58.2 for δ18O and δ2H as well as - 8.6 and -57.5 for δ18O and δ2H for wells in Omusati region. Hydrochemical and isotopic data reflect spatial variability between samples from Omusati and Ohangwena regions. The spatial heterogeneity as shown by TDS can be attributed to lithological, climatic and anthropogenic factors. Furthermore, temporal variations indicate the timing of the groundwater recharge. Results also imply interaction between perched aquifer and regional aquifer in the pans and depressions while in the ephemeral river no relation could be established. High recharge rates are estimated for the pans and depressions (7.3 % to 25.5%) in comparison to the ephemeral river (7.9% to 17.8%). Therefore, it is recommended that groundwater management practices should be designed taking into account differences in perched aquifer characteristics. For example designing abstraction infrastructures which include treatment for natural contaminants i.e. fluoride and TDS. On the other hand contaminants from anthropogenic sources in the wells can be reduced or prevented by introducing protection zones. Education on basic water usage and protection will also be of an advantage. Furthermore, it could be shown that it is indeed essential to unravel the hydrogeological complexities of heterogeneous perched aquifers using isotopic and hydrochemical tracers at different spatial and temporal scales and thus more research is needed in this regard.Item Detektion eines mesozoischen Gangschwarmes in NW Namibia und rekonstruktion regionaler spannungszustände während der Südatlantiköffnung; XXX(2014) Hahne, KaiGangschwärme nehmen eine bedeutende Stellung im Verständnis zur kontinentalen Fragmentierung ein. Einerseits markieren sie das Paläo-Spannungsfeld und helfen bei der Rekonstruktion der strukturellen Entwicklung der gedehnten Lithosphäre, andererseits gibt ihre petrologische Beschaffenheit Aufschlußüber die Entstehung des Magmas, Aufstieg und Platznahme und schließlich erlaubt ihre Altersbestimmung die Rekonstruktion einer chronologischen Reihenfolge magmatischer und struktureller Ereignisse.<br><br>Das Arbeitsgebiet im namibianischen Henties Bay-Outjo Dike swarm (HOD) war zur Zeit der Unterkreide einem Rifting mit intensiver Platznahme von überwiegend mafischen Gängen unterworfen. Geochemische Signaturen weisen die Gänge als erodierte Förderkanäle der Etendeka Plateaubasalte aus.Durch den Einsatz von hochauflösenden Aeromagnetik- und Satellitendaten war es möglich, die Geometrie des Gangschwarmes erstmals detailliert synoptisch zu erfassen. V! iele zu den Schichten des Grundgebirges foliationsparallel verlaufende magnetische Anomalien können unaufgeschlossenen kretazischen Intrusionen zugeordnet werden.<br><br>Bei der nach Norden propagierenden Südatlantiköffnung spielte die unterschiedliche strukturelle Vorzeichnung durch die neoproterozoischen Faltengürtel sowie Lithologie und Spannungsfeld des Angola Kratons eine bedeutende Rolle. Im küstennahen zentralen Bereich war dank der Vorzeichnung des Nordost streichenden Damara-Faltengürtels ein Rifting in Nordwest-Südost-Richtung dominierend, bis das Angola Kraton ein weiteres Fortscheiten nach Nordosten hemmte und die Vorzeichnung des Nordwest streichenden Kaoko-Faltengürtels an der Westgrenze den weiteren Riftverlauf und die letztendlich erfolgreiche Öffnung des Südatlantiks bestimmte. Aus diesem Grund kann das Gebiet des HOD als ein failed rift betrachtet werden.<br><br>Die Entwicklung des Spannungsfeldes im HOD kann folgendermaß! en skizziert werden:<br><br>1. Platznahme von Gän! gen bei gleichzeitig hoher Dehnungsrate und hohem Magmenfluß.<br>2. Platznahme von Zentralvulkanen entlang reaktivierter paläozoischer Lineamente bei Abnahme der Dehnungsrate und fortbestehendem hohen Magmenfluß.<br>3. Abnahme/Versiegen des Magmenflusses und neotektonische Bewegungen führen zur Bildung von Halbgräben. Dike swarms play a fundamental role in understanding continental breakup. On the one hand they represent strain markers of the paleo-deformation field and help to reconstruct the structural evolution of the rifted lithosphere. On the other hand their magmatic infill contains information about the conditions of magma generation, ascent and emplacement. Finally, dating of dikes allows reconstructing a chronological order of magmatic and structural events. The study area of the Namibian Henties Bay-Outjo Dike swarm (HOD) underwent tectonic extension in the Lower Cretaceous associated with the widespread emplacement of predominantly mafic dikes and intrusive ring complexes representing the remnants of volcanic centres. Geochemical signatures of the dikes prove them to be the feeder structures of the Etendeka Plateau Basalts.The application of recent high resolution aeromagnetic surveys and satellite imaging revealed the dike swarm's extent and geometry for the first time.! The distribution and geometry of the dikes shown in the aeromagnetics reflect the propagation of the South Atlantic opening from south to north by their relative-ages.<br><br>Northwest-southeast-directed rifting was dominant in the central coastal area, due to the structural control of the northeast striking basement structures until further propagation was hampered by the Angola Craton. Subsequently the structural control of the coast-parallel Kaoko Belt became dominant and determined the successful opening of the South Atlantic. Hence, the area of the HOD can be considered as a failed rift.<br><br>The stress field evolution within the HOD can be outlined as follows:<br><br>1. Intrusion of dikes when extension rates as well as magma supply were high.<br>2. Intrusion of volcanic ring complexes along reactivated Panafrican lineaments when extension rates decreased and magma supply remained high.<br>3. Neotectonic movements create half-grabens after the termination of magmatismItem Tektonik und Metamorphose im Grenzbereich Damara-Prädamara, südwestlich Windhoek (Südwestafrika)(1973) Groote-Bidlingmaier, Michael