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  • Osenbruck, Karsten  (13)
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  • 1
    Language: English
    In: Journal of Hydrology, 27 November 2014, Vol.519, pp.3386-3399
    Description: The travel-time distribution between rivers and groundwater observation points and the mixing of freshly infiltrated river water with groundwater of other origin is of high relevance in riverbank filtration. These characteristics usually are inferred from the analysis of natural-tracer time series, typically relying on a stationary input–output relationship. However, non-stationarity is a significant feature of the riparian zone causing time-varying river-to-groundwater transfer functions. We present a non-stationary extension of nonparametric deconvolution by performing stationary deconvolution with windowed time series, enforcing smoothness of the determined transfer function in time and travel time. The nonparametric approach facilitates the identification of unconventional features in travel-time distributions, such as broad peaks, and the sliding-window approach is an easy way to accommodate the method to dynamic changes of the system under consideration. By this, we obtain time-varying signal-recovery rates and travel-time distributions, from which we derive the mean travel time and the spread of the distribution as function of time. We apply our method to electric-conductivity data collected at River Thur, Switzerland, and adjacent piezometers. The non-stationary approach reproduces the groundwater observations significantly better than the stationary one, both in terms of overall metrics and in matching individual peaks. We compare characteristics of the transient transfer function to base flow which indicates shorter travel times at higher river stages.
    Keywords: Travel-Time Distribution ; Bank Filtration ; Non-Stationarity ; Nonparametric Inference ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 2
    Language: English
    In: Journal of Hydrology, 2011, Vol.402(3), pp.274-289
    Description: ► Using multiple isotopes to study groundwater flow in active rifts. ► Hydrochemical and isotopic evolution from escarpments to Rift floor. ► Mantle CO influences groundwater hydrochemistry. ► Apparent C ages are similar in Rift floor groundwater. ► Groundwater flow paths occur both longitudinal and transversal to rift axis. This study aims to investigate groundwater recharge and flow patterns in tectonically active rift systems, exemplified by a case study in the Main Ethiopian Rift. The chosen approach includes the investigation of hydrochemical parameters and environmental isotopes ( H, δ H, δ O, δ C-DIC, C-DIC, Sr/ Sr). Apparent groundwater ages were determined by radiocarbon dating after correction of C-DIC using a modified δ C-mixing model and further validation using geochemical modelling with NETPATH. Hydrochemical and isotopic data indicate an evolutionary trend existing from the escarpments towards the Rift floor. Groundwater evolves from tritium-containing and hence recently recharged Ca–HCO -type water on the escarpments to tritium-free Na–HCO groundwater dominating deep Rift floor aquifers. Correspondingly, rising pH and values coupled with increasingly enriched δ C signatures point to hydrochemical evolution of DIC and beginning dilution of the carbon isotope signature by other carbon sources, related to a diffuse influx of mantle CO into the groundwater system. Especially thermal groundwater sampled near the most recent fault zones in the Fantale/Beseka region displays clear influence of mantle CO and increased water–rock interaction, indicated by a shift in δ C and Sr/ Sr signatures. The calculation of apparent groundwater ages revealed an age increase of deep groundwater from the escarpments to the Rift floor, complying with hydrochemical evolution. Within the Rift, samples show a relatively uniform distribution of apparent C ages of ∼1800 to ∼2800 years, with the expected down-gradient aging trend lacking, contradicting the predominant intra-rift groundwater flow described in existing transect-based models of groundwater flow. By combining hydrochemical and new isotopic data with knowledge of the structural geology of the Rift, we improve the existing groundwater flow model and propose a new conceptual model by identifying flow paths both transversal and longitudinal to the main Rift axis, the latter being strongly controlled by faulted and tilted blocks on the escarpment steps. The connection between groundwater flow and fault direction make this model applicable to other active rift systems with similar structural settings.
    Keywords: Rift Tectonics ; Hydrochemistry ; Isotope Hydrology ; Groundwater Cycle and Dating ; 87sr/ 86sr ; 14c ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Science of the Total Environment, 2008, Vol.398(1), pp.164-174
    Description: Seven years of monitoring groundwater in the Gaza Strip has shown that nitrate was and still is a major groundwater pollutant. The objectives of this research were to study the distribution of NO in the groundwater of the Gaza Strip and to identify the sources of NO in the Gaza aquifer system by assessing nitrogen and oxygen isotopes. The most recent samples collected in 2007 showed 90% of the wells having NO concentrations that are several times higher than the WHO standards of 50 mg/L. Potential NO source materials in Gaza are animal manure N, synthetic NH based fertilizers, and wastewater/sludge. The average concentrations of N in the sludge, manure and soil of Gaza were 2.9%, 1% and 0.08%, respectively. The range in N of solid manure samples was + 7.5 to + 11.9‰. The range in N of sludge samples was + 4.6 to + 7.4‰, while four brands of synthetic fertilizers commonly used in Gaza had N ranging from + 0.2 to + 1.0‰. Sludge amended soil had N ranging from + 2.0 to + 7.3‰. For both O and N, the ranges of groundwater NO were − 0.1 to + 9.3‰ and + 3.2 to 12.8‰, respectively. No significant bacterial denitrification is taking place in the Gaza Strip aquifer. Nitrate was predominantly derived from manure and, provided N of sludge represents the maximum N of human waste, to a lesser extent from septic effluents/sludge. Synthetic fertilizers were a minor source.
    Keywords: Gaza Strip ; Nitrate ; Nitrogen/Oxygen Isotopes ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 4
    Language: English
    In: Procedia Earth and Planetary Science, 2017, Vol.17, pp.574-577
    Description: Lithium and its isotopes has generally been used as a proxy for silicate weathering and only in a few case studies investigated the link between Lithium isotope systematics of surface and ground waters with respect to residence times in crustal reservoirs and aquifers. However, the processes controlling the Lithium isotope fractionation in such systems are not fully understood, yet. In order to gain a better understanding of how Lithium isotopes are fractionated in large catchments we analyzed Lithium concentrations and Lithium isotope compositions of different water reservoirs (rivers, groundwater, thermal water and lakes) of a high alpine granitic catchment in the Pamir Mountains. We also determined the Lithium concentration and Lithium isotope composition of the (granitic) basement as well as the suspended particulate matter (SPM) in the waters. We observe large isotopic variations in the water samples (from δ Li = +3 to +36‰) and light isotopic compositions for the bedrock and SPM (δ Li = -14 to +1.5‰). The wide span of Li isotope composition in the water samples reflects the weathering of silicate rock along the flow path of the (sub) surface water within the catchment.
    Keywords: Lithium Isotopes ; River Water ; Ground Water ; Granite ; Pamir ; Central Asia ; Geology
    ISSN: 1878-5220
    E-ISSN: 1878-5220
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  • 5
    In: Water Resources Research, June 2013, Vol.49(6), pp.3406-3422
    Description: Performing stream‐tracer experiments is an accepted technique to assess transport characteristics of streams undergoing hyporheic exchange. Recently, combining conservative and reactive tracers, in which the latter presumably undergoes degradation exclusively within the hyporheic zone, has been suggested to study in‐stream transport, hyporheic exchange, and the metabolic activity of the hyporheic zone. The combined quantitative analysis to adequately describe such tests, however, has been missing. In this paper, we present mathematical methods to jointly analyze breakthrough curves of a conservative tracer (fluorescein), a linearly degrading tracer (resazurin), and its daughter compound (resorufin), which are synchronously introduced into the stream as pulses. In‐stream transport is described by the one‐dimensional advection‐dispersion equation, amended with a convolution term to account for transient storage within the hyporheic zone over a distribution of travel times, transformation of the reactive tracer in the hyporheic zone, and two‐site sorption of the parent and daughter compounds therein. We use a shape‐free approach of describing the hyporheic travel‐time distribution, overcoming the difficulty of identifying the best functional parameterization for transient storage. We discuss how this model can be fitted to the breakthrough curves of all three compounds and demonstrate the method by an application to a tracer test in the third‐order stream Goldersbach in Southern Germany. The entire river water passes once through the hyporheic zone over a travel distance of about 200 m with mean hyporheic residence times ranging between 16 and 23 min. We also observed a secondary peak in the transfer functions at about 1 h indicating a second hyporheic flow path. We could jointly fit the breakthrough curves of all compounds in three monitoring stations and evaluated the parameter uncertainty of the individual and joint fits by a method based on conditional realizations of the hyporheic travel‐time distribution. The approach gives insight into in‐stream transport, hyporheic exchange, metabolic activity, and river‐bed sorption of the stream under investigation. joint analysis of fluorescein, resazurin and resorufin in streams shape‐free inference of hyporheic travel‐time distribution sorption of reactive tracers must not be neglected
    Keywords: Hyporheic Exchange ; Stream Tracer Experiments ; Resazurin ; Travel‐Time Distributions ; Shape‐Free Inference ; Stream‐Tracer Modeling
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 6
    Language: English
    In: Isotopes in Environmental and Health Studies, 01 September 2010, Vol.46(3), pp.257-258
    Keywords: Chemistry ; Physics
    ISSN: 1025-6016
    E-ISSN: 1477-2639
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  • 7
    In: Water Resources Research, May 2013, Vol.49(5), pp.3024-3037
    Description: concurrent tests of conservative and reactive tracers in streams joint analysis of the tracers improved the estimation of hyporheic parameters Markov chain Monte Carlo methods used to infer parameter distributions Knowledge about the strength and travel times of hyporheic exchange is vital to predict reactive transport and biogeochemical cycling in streams. In this study, we outline how to perform and analyze stream tracer tests using pulse injections of fluorescein as conservative and resazurin as reactive tracer, which is selectively transformed to resorufin when exposed to metabolically active zones, presumably located in the hyporheic zone. We present steps of preliminary data analysis and apply a conceptually simple mathematical model of the tracer tests to separate effects of in‐stream transport from hyporheic exchange processes. To overcome the dependence of common parameter estimation schemes on the initial guess, we derive posterior parameter probability density functions using an adaptive Markov chain Monte Carlo scheme. By this, we can identify maximum‐likelihood parameter values of in‐stream transport, strength of hyporheic exchange, distribution of hyporheic travel times as well as sorption and reactivity coefficients of the hyporheic zone. We demonstrate the approach by a tracer experiment at River Goldersbach in southern Germany (60 L/s discharge). In‐stream breakthrough curves were recorded with online fluorometers and jointly fitted to simulations of a one‐dimensional reactive transport model assuming an exponential hyporheic travel‐time distribution. The findings show that the additional analysis of resazurin not only improved the physical basis of the modeling, but was crucial to differentiate between surface transport and hyporheic transient storage of stream solutes. Parameter uncertainties were usually small and could not explain parameter variability between adjacent monitoring stations. The latter as well as a systematic underestimation of the tailing are due to structural errors of the model, particularly the exponential hyporheic travel‐time distribution. Mean hyporheic travel times were in the range of 12 min, suggesting that small streambed structures dominate hyporheic exchange at the study site.
    Keywords: Hyporheic Exchange ; Stream Tracer Experiments ; Travel‐Time Distributions ; Resazurin ; Resorufin
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 8
    Language: English
    In: Quaternary International, 04 August 2014, Vol.338, pp.59-70
    Description: Miocene–Pliocene and Upper Cretaceous formations in Tunisia contain one of the most productive artesian aquifers in the country. They consist of Mio-Pliocene sands and Senonian/Turonian carbonates. Intensive pumping in Kébili and Nefzaoua regions over the past decades resulted in gradual lowering of water table at the rate of approximately 0.85 m y . Forty-two groundwater samples have been collected from different sectors of the studied aquifers for chemical and isotopic analyses. The observed large spatial variability of chemical composition of groundwater in the study area is most probably linked to two processes: (i) dissolution of dolomite and gypsum, combined with calcite precipitation (dedolomitisation), and (ii) partial evaporation of water. The first process plays an important role in the study area due to abundance of evaporites. Partial evaporation occurs in the upper part of the unsaturated zone during infiltration, especially for groundwater sampled in the Kebili and Djerid regions. Apart from these processes, there are others which influence the salinity of the aquifers. In the Mio-Pliocene aquifer, which behaves as an open system to gases and which receives inputs of CO gas derived from intensive tectonic activity in the area, the interaction of carbon dioxide with carbonate matrix of the aquifer produces an increase in the alkalinity of water. In the Senonian and Turonian aquifers, the process of dedolomitisation evolves in a closed system with respect to CO gas. Ca /Na cation exchange and halite dissolution processes are also important. Stable isotope composition of water (δ O, δ H) indicates that the recharge occurs from the Dahar upland. The C activity varies between 89.5 (±1.5) and 3.7 (±2.1) pmc. The C content in the total dissolved inorganic carbon (TDIC) range between −13.9 and −3.6‰. The calculated concentrations of C in the CO gas in equilibrium with the TDIC vary between −22 and −11‰, indicating two sources of carbon in the solution: carbonate matrix (δ C = −2‰) and soil CO (δ C from −25 to −21‰ for the cultivated areas). Mean residence times of water have been determined after correction of the initial C activities for C-dilution processes including carbonate dissolution, calcite precipitation and cation-exchange. The dilution processes were quantified on the basis of geochemical and C mass balance equations. The calculated mean residence times of water confirm modern recharge from Dahar upland and the mountains surrounding depressions, and indicate the presence of paleowaters in the east and south-west region, and in the discharge zone.
    Keywords: Tunisia ; Dissolution ; Evaporation ; Dilution ; Residence Time ; Geology
    ISSN: 1040-6182
    E-ISSN: 1873-4553
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  • 9
    Language: English
    In: Isotopes in Environmental and Health Studies, 01 September 2010, Vol.46(3), pp.312-324
    Description: In the framework of the investigation of enrichment processes of nitrate in groundwater of the Kalahari of Botswana near Serowe, recharge processes were investigated. The thick unsaturated zone extending to up to 100 m of mostly unconsolidated sediments and very low recharge rates pose a serious...
    Keywords: Aquifer ; Botswana ; CFC ; Helium-3 ; Hydrogen-3 ; Infiltration ; Isotope Ecology ; Isotope Hydrology ; Kalahari ; Recharge ; Soil Water ; Sulphur Hexafluoride ; Chemistry ; Physics
    ISSN: 1025-6016
    E-ISSN: 1477-2639
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  • 10
    Language: English
    In: Isotopes in Environmental and Health Studies, 01 September 2010, Vol.46(3), pp.259-278
    Description: Many problems related to groundwater supply and quality, as well as groundwater-dependent ecosystems require some understanding of the timescales of flow and transport. For example, increased concern about the vulnerabilities of 'young' groundwaters...
    Keywords: Environmental Tracers ; Groundwater Dating ; Groundwater Age ; Isotope Tracer Techniques ; Isotope Measurements ; Methods and Equipment ; Residence Time ; Chemistry ; Physics
    ISSN: 1025-6016
    E-ISSN: 1477-2639
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