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Author |
Ammar, F.H.; Deschamps, P.; Chkir, N.; Zouari, K.; Agoune, A.; Hamelin, B. |
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Title |
Uranium isotopes as tracers of groundwater evolution in the Complexe Terminal aquifer of southern Tunisia |
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Journal Article |
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Year |
2020 |
Publication  |
Quaternary International |
Abbreviated Journal |
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Volume |
547 |
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33-49 |
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Keywords |
CT southern Tunisia, Holocene, Mixing, Radicarbon, Uranium isotopes, Water-rock interaction |
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Abstract |
The Complexe Terminal (CT) multi-layer aquifer is formed by Neogene/Paleogene sand deposits, Upper Senonian (Campanian-Maastrichtian limestones) and Turonian carbonates. The chemical composition and isotopes of carbon and uranium were investigated in groundwater sampled from the main hydrogeological units of the (CT) aquifer in southern Tunisia. We paid special attention to the variability of uranium contents and isotopes ratio (234U/238U) to provide a better understanding of the evolution of the groundwater system. Uranium concentrations range from 1.5 to 19.5 ppb, typical of oxic or mildly reducing conditions in groundwaters. The lowest concentrations are found southeast of the study area, where active recharge is supposed to take place. When looking at the isotope composition, it appears that all the samples, including those from carbonate levels, are in radioactive disequilibrium with significant 234U excess. A clear-cut distinction is observed between Turonian and Senonian carbonate aquifers on the one hand, with 234U/238U activity ratios between 1.1 and 1.8, and the sandy aquifer on the other hand, showing higher ratios from 1.8 to 3.2. The distribution of uranium in this complex aquifer system seems to be in agreement with the lithological variability and are ultimately a function of a number of physical and chemical factors including the uranium content of the hosting geological formation, water-rock interaction and mixing between waters having different isotopic signatures. Significant relationships also appear when comparing the uranium distribution with the major ions composition. It is noticeable that uranium is better correlated with sulfate, calcium and magnesium than with other major ions as chloride or bicarbonate. The 14C activities and δ13C values of DIC cover a wide range of values, from 1.1 pmc to 30.2 pmc and from −3.6‰ to −10.7‰, respectively. 14C model ages estimated by the Fontes and Garnier model are all younger than 22 Ka and indicate that the recharge of CT groundwater occurred mainly during the end of the last Glacial and throughout the Holocene. |
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1040-6182 |
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THL @ christoph.kuells @ ammar_uranium_2020 |
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119 |
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Author |
Gasse, F. |
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Title |
Hydrological changes in the African tropics since the Last Glacial Maximum |
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Journal Article |
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Year |
2000 |
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Quaternary Science Reviews |
Abbreviated Journal |
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19 |
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1 |
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189-211 |
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Paleohydrological data from the African tropics and subtropics, including lake, groundwater and speleothem records, are reviewed to show how environments and climates from both hemispheres are inter-related. Although orbitally induced changes in the monsoon strength account for a large part of long-term climatic changes in tropical Africa, the Late Pleistocene–Holocene hydrological fluctuations rather appear to have been a series of abrupt events that reflect complex interactions between orbital forcing, atmosphere, ocean and land surface conditions. During the Last Glacial Maximum (23–18ka BP), most records indicate that generally dry conditions have prevailed in both hemispheres, associated with lower tropical land- and sea-surface temperatures. This agrees with simulations using coupled ocean–atmosphere models, which predict cooling and reduced summer precipitation in tropical Africa; the global hydrological cycle was weaker than today when the extent of large polar ice-sheets and sea-ice was a prominent forcing factor of the Earth’s climate. Glacial-interglacial climatic changes started early: a first wetting/warming phase at ca. 17–16ka BP took place during a period of rapid temperature increase in Antarctica. Next, two drastic arid-humid transitions in equatorial and northern Africa occurred around 15–14.5ka BP and 11.5–11ka BP. Both are thought to match the major Greenland warming events, in concert with the switching of the oceanic thermohaline circulation to modern mode. However, part of the climatic signal after 15 ka BP also seems related to the Antarctica climate. During the Holocene, Africa has also experienced rapid hydrological fluctuations of dramatic magnitude compared to the climatic changes at high latitudes. In particular, major dry spells occurred around 8.4–8ka and 4.2–4ka BP in the northern monsoon domain. Comparison with other parts of the world indicates that these events have a worldwide distribution but different regional expressions. In the absence of large polar ice sheets, changes in the continental hydrological cycles in the tropics may have a significant impact on the global climate system. Climate information gathered here allows to identify geographical and methodological gaps, and raise some scientific questions that remain to be solved to better understand how the tropics respond to changes in major climate-forcing factors, and how they influence climate globally. |
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0277-3791 |
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THL @ christoph.kuells @ gasse_hydrological_2000 |
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96 |
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Author |
Röttcher, K. |
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Book Chapter |
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2018 |
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Risikomanagement und Nachhaltigkeit in der Wasserwirtschaft: Erfolgreiche Navigation durch die Komplexität und Dynamik des Risikos |
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165-174 |
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Im vorliegenden Beitrag werden beispielhaft unterschiedliche Ansätze des Risikomanagements und das Verständnis von Nachhaltigkeit in der Wasserwirtschaft dargelegt. Die Darstellung richtet sich insbesondere an Leser aus anderen Fachdisziplinen, wie das Rechts- und Finanzwesen, den Fahrzeug- und Maschinenbau oder auch die sozialen Berufe. Die Zusammenhänge werden überblicksartig mit einzelnen konkreten Beispielen dargestellt mit dem Fokus auf die grundsätzlichen Denk- und Vorgehensweisen. |
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Springer Fachmedien Wiesbaden |
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Wiesbaden |
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Michalke, A.; Rambke, M.; Zeranski, S. |
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978-3-658-19684-4 |
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THL @ christoph.kuells @ Röttcher2018 |
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90 |
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Pisa, P.F.; Nehren, U.; Sebesvari, Z.; Rai, S.; Wong, I. |
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Chapter 17 – Nature-based solutions to reduce risks and build resilience in mountain regions |
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2024 |
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Safeguarding Mountain Social-Ecological Systems |
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115-126 |
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Nature-based solutions, mountains, climate change adaptation, disaster risk reduction, ecosystem services, SDGs |
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Nature-based solutions (NbS) are increasingly recognized as effective environmental-management measures to address societal challenges such as climate change, water and food security, and disaster risk reduction, thus contributing to human well-being and protecting biodiversity. In addition to being particularly susceptible to these challenges, mountain areas are prone to multihazard conditions, due to their steep topography and particular climatic conditions. NbS can contribute greatly to the sustainable development of mountain ecosystems. This chapter presents examples of NbS in mountain areas around the globe that demonstrate how this approach contributes to achieving sustainable development. |
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Elsevier |
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Schneiderbauer, S.; Pisa, P.F.; Shroder, J.F.; Szarzynski, J. |
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978-0-12-822095-5 |
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THL @ christoph.kuells @ Fontanellapisa2024115 |
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263 |
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Post, V.E.A.; Vassolo, S.I.; Tiberghien, C.; Baranyikwa, D.; Miburo, D. |
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Title |
Weathering and evaporation controls on dissolved uranium concentrations in groundwater – A case study from northern Burundi |
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Journal Article |
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2017 |
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Science of The Total Environment |
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607-608 |
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281-293 |
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Geochemical modelling, Hydrochemistry, Lake Tshohoha South, Public health, Radionuclides, Water supply |
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The potential use of groundwater for potable water supply can be severely compromised by natural contaminants such as uranium. The environmental mobility of uranium depends on a suite of factors including aquifer lithology, redox conditions, complexing agents, and hydrological processes. Uranium concentrations of up to 734μg/L are found in groundwater in northern Burundi, and the objective of the present study was to identify the causes for these elevated concentrations. Based on a comprehensive data set of groundwater chemistry, geology, and hydrological measurements, it was found that the highest dissolved uranium concentrations in groundwater occur near the shores of Lake Tshohoha South and other smaller lakes nearby. A model is proposed in which weathering and evapotranspiration during groundwater recharge, flow and discharge exert the dominant controls on the groundwater chemical composition. Results of PHREEQC simulations quantitatively confirm this conceptual model and show that uranium mobilization followed by evapo-concentration is the most likely explanation for the high dissolved uranium concentrations observed. The uranium source is the granitic sand, which was found to have a mean elemental uranium content of 14ppm, but the exact mobilization process could not be established. Uranium concentrations may further be controlled by adsorption, especially where calcium-uranyl‑carbonate complexes are present. Water and uranium mass balance calculations for Lake Tshohoha South are consistent with the inferred fluxes and show that high‑uranium groundwater represents only a minor fraction of the overall water input to the lake. These findings highlight that the evaporation effects that cause radionuclide concentrations to rise to harmful levels in groundwater discharge areas are not only confined to arid regions, and that this should be considered when selecting suitable locations for water supply wells. |
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0048-9697 |
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THL @ christoph.kuells @ post_weathering_2017 |
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132 |
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