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Röttcher, K. (2018). In A. Michalke, M. Rambke, & S. Zeranski (Eds.), Risikomanagement und Nachhaltigkeit in der Wasserwirtschaft: Erfolgreiche Navigation durch die Komplexität und Dynamik des Risikos (pp. 165–174). Wiesbaden: Springer Fachmedien Wiesbaden.
Abstract: 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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Brook, G. A., Marais, E., Srivastava, P., & Jordan, T. (2007). Timing of lake-level changes in Etosha Pan, Namibia, since the middle Holocene from OSL ages of relict shorelines in the Okondeka region. Quaternary International, 175(1), 29–40.
Abstract: In 2003 examination of aerial photographs revealed a series of previously unknown relict shorelines on the arcuate ridge, possibly a clay lunette dune, that marks the western boundary of Etosha Pan in Namibia. The shorelines are 120–600m wide and the most prominent extend for tens of km around the lunette dune. The shorelines were examined on the ground in 2004 and an attempt was made to date the three lowest levels at ca. 5, 2.5 and 1m above the present pan surface. The OSL ages obtained indicate higher and more prolonged lake conditions than today at ca. 6.4, 4.0 and 2.1ka with the youngest shoreline sediments resting on an ancient pan surface dating to ca. 13ka. The evidence indicates dry conditions in the pan at ca. 13ka, wetter conditions and higher lake levels in the middle Holocene followed by a decline in lake levels to the present. Periods of inundation were of sufficient duration to produce shorelines at the southwestern end of the pan due to the prevailing northeasterly winds that would have maximized wave action along this section of the pan margin. The Etosha findings, together with other regional paleoclimate data, suggest four periods of increased wetness in SW Africa during the Holocene at 7–5, 4.5–3.5, 2.5–1.7 and ca. 1.0ka. There is widespread evidence for the oldest of these periods suggesting that it was a prominent and widespread interval of wetness. Prior to ca. 8.0ka the climate may have been drier than today.
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Boumaiza, L., Ammar, S. B., Chesnaux, R., Stotler, R. L., Mayer, B., Huneau, F., et al. (2023). Nitrate sources and transformation processes in groundwater of a coastal area experiencing various environmental stressors. Journal of Environmental Management, 345, 118803.
Abstract: In coastal salinized groundwater systems, contamination from various nitrate (NO3) inputs combined with complex hydrogeochemical processes make it difficult to distinguish NO3 sources and identify potential NO3 transformtation processes. Effective field-based NO3 studies in coastal areas are needed to improve the understanding of NO3 contamination dynamics in groundwater of such complex coastal systems. This study focuses on a typical Mediterranean coastal agricultural area, located in Tunisia, experiencing substantial NO3 contamination from multiple anthropogenic sources. Here, multiple isotopic tracers (δ18OH2O, δ2HH2O, δ15NNO3, δ18ONO3, and δ11B) combined with a Bayesian isotope MixSIAR model are used (i) to identify the major NO3 sources and their contributions, and (ii) to describe the potential NO3 transformation processes. The measured NO3 concentrations in groundwater are above the natural baseline threshold, suggesting anthropogenic influence. The measured isotopic composition of NO3 indicates that manure, soil organic matter, and sewage are the potential sources of NO3, while δ11B values constrain the NO3 contamination to manure; a finding that is supported by the results of MixSIAR model revealing that manure-derived NO3 dominates over other likely sources. Nitrate derived from manure in the study area is attributed to organic fertilizers used to promote crop growth, and livestock that deposit manure directly on the ground surface. Evidence for ongoing denitrification in groundwaters of the study area is supported by an enrichment in both 15N and 18O in the remaining NO3, although isotopic mass balances between the measured and the theoretical δ18ONO3 values also suggest the occurrence of nitrification. The simultaneous occurrence of these biogeochemical processes with heterogeneous distribution across the study area reflect the complexity of interactions within the investigated coastal aquifer. The multiple isotopic tracer approach used here can identify the effect of multiple NO3 anthropogenic activities in coastal environments, which is fundamental for sustainable groundwater resources management.
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Robin, V., Beaufort, D., Tertre, E., Reinholdt, M., Fromaget, M., Forestier, S., et al. (2020). Fate of dioctahedral smectites in uranium roll front deposits exploited by acidic In Situ Recovery (ISR) solutions. Applied Clay Science, 187, 105484.
Abstract: In Situ Recovery (ISR) is the most important process of uranium production in the world (50%). It consists of an injection of a leaching solution into a permeable mineralized aquifer (sandstone), pumping of the solution after dissolution of the ore minerals and recovery of the uranium from the pregnant solution in a surface plant. In this context, the fate of swelling clay minerals such as smectites is of main importance due to their role in the mobility of cationic elements by diverse geochemical processes such as ion-exchange reactions or dissolution. The present study details analysis of dioctahedral smectites before and after in-situ leaching by acidic (H2SO4) ISR solutions. Samples were collected from two sedimentary basins hosting some of the main uranium roll front deposits exploited by acidic ISR (Tortkuduk deposit, Shu-Saryssu basin, Kazakhstan, and Dulaan Uul and Zoovch Ovoo deposits, Sainshand basin, Mongolia). Scanning Electron Microscope and X-Ray Diffraction analysis revealed that dioctahedral smectite is a ubiquitous mineral in all analyzed samples, before and after acidification, and revealed a difference of crystal chemistry of the smectites between deposits of Kazakhstan (beidellite type) and Mongolia (montmorillonite type). Chemical analysis and semi-quantification of the smectites before and after acidification also revealed a difference in chemical reactivity, with a higher dissolution of montmorillonite layers compared to beidellite ones, and the importance of ion-exchange reactions. These findings are consistent with literature data obtained on model systems. The persistence of dioctahedral smectites after several years of acidification is crucial for the understanding of geochemical processes during uranium production or remediation of the aquifers. Finally, based on the analysis of samples from U-deposits hosted in both sedimentary basins, a schematic model of the impact of acid solutions on dioctahedral smectite was proposed.
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Schwiede, M., Duijnisveld, W. H. M., & Böttcher, J. (2005). Investigation of processes leading to nitrate enrichment in soils in the Kalahari Region, Botswana. Physics and Chemistry of the Earth, Parts A/B/C, 30(11), 712–716.
Abstract: In Southern Africa elevated nitrate concentrations are observed in mostly uninhabited semi-arid areas. In the Kalahari of Botswana groundwater locally exhibits concentrations up to 600mg/l. It is assumed, that nitrate found in the groundwater originates mainly from nitrogen input and transformations in the soils. Our investigations in the Kalahari between Serowe and Orapa show that cattle raising is an important source for enhanced nitrate concentrations in the soils (Arenosols). But also in termite mounds very high nitrate stocks were found, and under natural vegetation (acacia trees and shrubs) nitrate concentrations were mostly unexpectedly high. This nitrate enrichment in the soils poses a serious threat to the groundwater quality. However, calculated soil water age distributions in the unsaturated zone clearly show that today’s nitrate pollution of the groundwater below the investigation area could originate from natural sources, but cannot be caused by the current land use for cattle raising.
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