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Botha, R.; Lindsay, R.; Newman, R.T.; Maleka, P.P.; Chimba, G. |
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Title |
Radon in groundwater baseline study prior to unconventional shale gas development and hydraulic fracturing in the Karoo Basin (South Africa) |
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Journal Article |
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Year |
2019 |
Publication |
Applied Radiation and Isotopes |
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147 |
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7-13 |
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The prospect of unconventional shale gas development in the semi-arid Karoo Basin (South Africa) has created the prerequisite to temporally characterise the natural radioactivity in associated groundwater which is solely depended on for drinking and agriculture purposes. Radon (222Rn) was the primary natural radionuclide of interest in this study; however, supplementary radium (226Ra and 228Ra) in-water measurements were also conducted. A total of 53 aquifers spanning three provinces were studied during three separate measurement campaigns from 2014 to 2016. The Karoo Basin’s natural radon-in-water levels can be characterised by a minimum of 1 ± 1 Bq/L (consistent with zero or below LLD), a maximum of 183 ± 18 Bq/L and mean of 41 ± 5 Bq/L. The mean radon-in-water levels for shallow aquifers were systematically higher (55 ± 10 Bq/L) compared to deep (14 ± 3 Bq/L) or mixed aquifers (20 ± 6 Bq/L). Radon-in-water activity concentration fluctuations were predominantly observed from shallow aquifers compared to the generally steady levels of deep aquifers. A collective seasonal mean radon-in-water levels increase from the winter of 2014 (44 ± 8 Bq/L) to winter of 2016 (61 ± 16 Bq/L) was noticed which could be related to the extreme national drought experienced in 2015. Radium-in-water (228Ra and 226Ra) levels ranged from below detection level to a maximum of 0.008 Bq/L (226Ra) and 0.015 Bq/L (228Ra). The 228Ra/226Ra ratio was characterised by a minimum of 0.93, a maximum of 6.5 and a mean value of 3.3 ± 1.3. Developing and improving baseline naturally occurring radionuclide groundwater databases is vital to study potential radiological environmental impacts attributed to industrial processes such as hydraulic fracturing or mining. |
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0969-8043 |
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THL @ christoph.kuells @ botha_radon_2019 |
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169 |
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Borrego-Alonso, D.; Quintana-Arnés, B.; Lozano, J.C. |
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Title |
Natural radionuclides behaviour in drinking groundwaters from Castilla y León (Spain); radiological implications |
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Journal Article |
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Year |
2023 |
Publication |
Water Research |
Abbreviated Journal |
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245 |
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120616 |
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Drinking water, Environmental monitoring, Natural radioactivity, Public health, Radiological characterisation |
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Since the coming into force of the European Council Directive 51/2013 EURATOM and its transposition into the Spanish legislation, the presence of radioactive substances in drinking waters must be kept under surveillance to ensure that the health protection requirements are met. Driven by this regulatory framework, in an attempt to know the starting point from which to design surveillance plans, the groundwaters intended for human consumption of Castilla y León (Spain) have been radiologically characterised by using both low-level γ-ray and α-particle spectrometry to determine the activity concentration of the natural radionuclides needed to account for the indicative dose estimation. This extensive research has comprised the radiological characterisation of more than 400 drinking water samples from one of the European Union’s largest regions. Furthermore, the gross α and gross β activities have been analysed. Results showed a high geographical variability that can be related to the hydrogeological formations where the groundwaters come from. The uranium isotopes, 234U and 238U, are the main radionuclides present in the analysed drinking waters reaching values up to 2000 mBq/L, in the southwestern and western of Castilla y León, where U-rich minerals are part of the host rock. High 210Pb and 226,228Ra occurrences are found in the low permeability igneous and metasedimentary hydrogeological formations of Salamanca province. From a public health protection point of view, 4.4% of the total drinking water samples from intakes exceeded the Indicative Dose parametric value of 0.1 mSv, which is a not negligible number of samples, being very likely related to granitic and metamorphosed host rock under specific local conditions. This fact highlights the need for research and consideration of special surveillance of the groundwaters from these areas. |
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0043-1354 |
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THL @ christoph.kuells @ borrego-alonso_natural_2023 |
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157 |
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Bonnetti, C.; Zhou, L.; Riegler, T.; Brugger, J.; Fairclough, M. |
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Title |
Large S isotope and trace element fractionations in pyrite of uranium roll front systems result from internally-driven biogeochemical cycle |
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Journal Article |
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2020 |
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Geochimica et Cosmochimica Acta |
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282 |
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113-132 |
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Activity cycle, Pyrite composition, Roll front uranium deposits, S isotope and trace element fractionation |
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Complex pyrite textures associated with large changes in isotopic and trace element compositions are routinely assumed to be indicative of multi-faceted processes involving multiple fluid and sulfur sources. We propose that the features of ore-stage pyrite from roll front deposits across the world, revealed in exquisite detail via high-resolution trace element mapping by LA-ICP-MS, reflect the dynamic internal evolution of the biogeochemical processes responsible for sulfate reduction, rather than externally driven changes in fluid or sulfur sources through time. Upon percolation of oxidizing fluids into the reduced host-sandstones, roll front systems become self-organized, with a systematic reset of their activity cycle after each translation stage of the redox interface down dip of the aquifer. Dominantly reducing conditions at the redox interface favor the formation of biogenic framboidal pyrite (δ34S from −30.5 to −12.5‰) by bacterial sulfate reduction and the genesis of the U mineralization. As the oxidation front advances, oxidation of reduced sulfur minerals induces an increased supply of sulfate and metals in solution to the bacterial sulfate reduction zone that has similarly advanced down the flow gradient. Hence, this stage is marked by increased rates of the bacterial sulfate reduction associated with the crystallization of variably As-Co-Ni-Mo-enriched concentric pyrite (up to 10,000′s of ppm total trace contents) with moderately negative δ34S values (from −13.7 to −7.5‰). A final stage of pyrite cement with low trace element contents and heavier δ34S signature (from −6.9 to +18.8‰) marks the end of the roll front activity cycle and the transition from an open to a predominantly closed system behavior (negligible advection of fresh sulfate). Blocky pyrite cement is formed using the remaining sulfate, which now becomes quickly heavy according to a Rayleigh isotope fractionation process. This ends the cycle by depleting the nutrient supplies for the sulfate-reducing bacteria and cementing pore spaces within the host sandstone, effectively restricting fluid infiltration. This internally-driven roll front activity cycle results in systematic, large S isotope and trace element fractionation. Ultimately, the long-time evolution of the basin and fluid sources control the metal endowment and evolution of the system; these events, however, are unlikely to be preserved by the roll front, as a direct result of its hydrodynamic nature. |
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0016-7037 |
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THL @ christoph.kuells @ bonnetti_large_2020 |
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185 |
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Benito, G.; Rohde, R.; Seely, M.; Külls, C.; Dahan, O.; Enzel, Y.; Todd, S.; Botero, B.; Morin, E.; Grodek, T. |
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Title |
Management of alluvial aquifers in two southern African ephemeral rivers: implications for IWRM |
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2010 |
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Water Resources Management |
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24 |
Issue |
4 |
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641-667 |
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Springer Netherlands |
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THL @ christoph.kuells @ Benito2010management |
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25 |
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Belz, L.; Schüller, I.; Wehrmann, A.; Köster, J.; Wilkes, H. |
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Title |
The leaf wax biomarker record of a Namibian salt pan reveals enhanced summer rainfall during the Last Glacial-Interglacial Transition |
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Journal Article |
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2020 |
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Palaeogeography, Palaeoclimatology, Palaeoecology |
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543 |
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109561 |
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-Alkanes, -Alkanols, Late Quaternary, Organic geochemistry, Palaeohydrology, Southern Africa |
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Conventional continental geoarchives are rarely available in arid southern Africa. Therefore, palaeoclimate data in this area are still patchy and late Quaternary climate development is only poorly understood. In the western Kalahari, salt pans (playas, ephemeral lakes) are common and can feature quasi-continuous sedimentation. This study presents the first climate-related biomarker record using sediments from the Omongwa Pan, a Kalahari salt pan located in eastern Namibia. Our approach to reconstruct vegetation and hydrology focuses on biogeochemical bulk parameters and plant wax-derived lipid biomarkers (n-alkanes, n-alkanols, and fatty acids) and their compound-specific carbon and hydrogen isotopic compositions. The presented record reaches back to 27 ka. During the glacial, rather low δ2H values of n-alkanes and low sediment input exclude a strong influence of winter rainfall. n-Alkane and n-alkanol distributions and δ13C values of n-hentriacontane (n-C31) indicate a shift to a vegetation with a higher proportion of C4 plants at the end of the Last Glacial Maximum until the end of Heinrich Stadial I (ca. 18–14.8 ka), which we interpret to indicate an abrupt excursion to a short wetter period likely to be caused by a temporary southward shift of the Intertropical Convergence Zone. Shifts in δ2H values of n-C31 and plant wax parameters give evidence for changes to drier conditions during early Holocene. Comparison of this dataset with representative continental records from the region points to a major influence of summer rainfall at Omongwa Pan during the regarded time span and demonstrates the potential of southern African salt pans as archives for biomarker-based climate proxies. |
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0031-0182 |
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THL @ christoph.kuells @ belz_leaf_2020 |
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104 |
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