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  • 1
    Language: English
    In: Water Research, 15 October 2015, Vol.83, pp.205-216
    Description: Estimating respiration and photosynthesis rates in streams usually requires good knowledge of reaeration at the given locations. For this purpose, gas-tracer tests can be conducted, and reaeration rate coefficients are determined from the decrease in gas concentration along the river stretch. The typical procedure for analysis of such tests is based on simplifying assumptions, as it neglects dispersion altogether and does not consider possible fluctuations and trends in the input signal. We mathematically derive the influence of these non-idealities on estimated reaeration rates and how they are propagated onto the evaluation of aerobic respiration and photosynthesis rates from oxygen monitoring. We apply the approach to field data obtained from a gas-tracer test using propane in a second-order stream in Southwest Germany. We calculate the reaeration rate coefficients accounting for dispersion as well as trends and uncertainty in the input signals and compare them to the standard approach. We show that neglecting dispersion significantly underestimates reaeration, and results between sections cannot be compared if trends in the input signal of the gas tracer are disregarded. Using time series of dissolved oxygen and the various estimates of reaeration, we infer respiration and photosynthesis rates for the same stream section, demonstrating that the bias and uncertainty of reaeration using the different approaches significantly affects the calculation of metabolic rates.
    Keywords: Reaeration ; Gas-Tracer Tests ; Whole-Stream Metabolism ; Dispersion ; Oxygen Balance of Streams ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 2
    Language: English
    In: Hydrology Research, 11/2013, Vol.44(6), p.995
    Description: This study uses a high-frequency discharge and nitrate concentration dataset from the Weida catchment in Germany for the catchment scale hydrologic response analysis. Nitrate transport in the catchment is mostly conservative as indicated by the nitrate stable isotope ( delta 15N and delta 18O) analysis. Discharge-nitrate concentration data from the catchment show distinctive patterns, suggesting flushing and dilution response. A self-organizing feature map-based methodology was employed to identify such patterns or cluster in the datasets. Based on knowledge of the catchment conditions and prevailing understanding of discharge-nitrate concentration relationship, the clusters were characterized into five qualitative flow responses: (1) baseflow; (2) subsurface flow increase; (3) surface runoff increase; (4) surface runoff recession; and (5) subsurface flow decrease. Such qualitative flowpaths were used as soft data for a multi-objective calibration of a hydrological model (WaSiM-ETH). The calibration led to a reasonable simulation of overall discharge (Nash-Sutcliffe coefficient: 0.84) and qualitative flowpaths (76% agreement). A prerequisite for using such methodology is limited biogeochemical transformation of nitrate (such as denitrification).
    Keywords: Catchment Area ; Biogeochemistry ; Denitrification ; River Discharge ; Hydrology ; Nitrogen Isotopes ; Oxygen Isotope Ratio ; Runoff ; Response Analysis ; Oxygen Isotopes ; Hydrologic Analysis ; Nitrate Transport ; Numerical Simulations ; Catchment Basins ; Base Flow ; Surface Runoff ; Nitrogen Isotopes ; Subsurface Flow ; Isotopes ; Nitrates ; Biogeochemistry ; Denitrification ; Catchments ; Simulation ; Hydrology ; Hydrologic Models ; Assessments ; Surface Runoff ; Calibrations ; Nitrates ; Denitrification ; Catchment Areas ; Storm Seepage ; Hydrologic Data ; Hydrologic Models ; Assessments ; Surface Runoff ; Calibrations ; Nitrates ; Denitrification ; Catchment Areas ; Storm Seepage ; Hydrologic Data ; Germany ; Freshwater ; Identification of Pollutants ; Sewage ; General (556) ; General ; General ; Cluster Analysis ; Discharge-Nitrate Concentration Relationship ; Hydrological Flowpaths ; Model Calibration ; Nitrate Stable Isotopes ; Self-Organizing Feature Maps;
    ISSN: 0029-1277
    ISSN: 19989563
    E-ISSN: 22247955
    Source: CrossRef
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  • 3
    Language: English
    In: Environmental Earth Sciences, 2013, Vol.69(2), pp.381-393
    Description: In this study near-continuous time series of nitrate, electrical conductivity, and discharge were used to identify the dominating hydrological mechanisms that control nitrate export dynamics in two agricultural catchments. The main goal was to assess relationships between contrasting event based as well as long-term nitrate transport behaviour and catchment hydrology. Data records were obtained from online probes that allow field based high-frequency analyses over long time periods. The catchments of the Ammer River (southwestern Germany) and the Weida River (eastern Germany) are similar with respect to size (~100 km²), morphology, and climate and are dominated by agricultural use. Main differences are the stronger urbanization and the occurrence of karstic rocks in the Ammer catchment. Nitrate concentrations are high in water of both streams and range mostly between 20 and 50 mg l −1 . Nitrate export in the Ammer catchment is dominated by baseflow and a minor second, diluting runoff component generated in urbanized areas. In contrast, nitrate dynamics of the Weida catchment is governed by the interplay of at least three runoff components, while the largest amount of nitrate is mobilized intermittently by a delayed fast component generated in the catchment’s soils during wet conditions. These interpretations, derived with one online probe at the outlet of each catchment, are well in line with the former modeling results. This study shows that high-resolution data obtained by online techniques offers a large potential to improve the conceptualization of dominating flow and transport processes at catchment scales at relatively low costs and effort.
    Keywords: Nitrate export ; Catchment ; Hydrology ; High-frequency monitoring ; Online probe
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 4
    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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  • 5
    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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  • 6
    Language: English
    In: Geochimica et Cosmochimica Acta, 1998, Vol.62(18), pp.3041-3045
    Description: The {sup 4}He, {sup 40}Ar, and {sup 136}Xe content dissolved in the pore water of sedimentary rock samples was measured on samples from borehole cores near the repository for nuclear waste in Morsleben, Germany. Due to the very low permeabilities of the rock formations, conventional groundwater sampling was almost impossible. Hence, the authors developed a new sampling method for noble gases in the pore water of freshly drilled rock cores. This method provides vertical noble gas profiles in high depth resolution, even in impermeable rocks. By application of the new technique quantitative age information of groundwater and pore water have been derived. The authors find palaeowaters from the last glaciation depleted in {delta}D and {delta}{sup 18}O with a {sup 4}He age of about 55 kyr. The high saline pore solutions below are at least 6 Mio years old. This has been concluded from the profiles of radiogenic {sup 4}He and {sup 40}Ar close to diffusion in steady-state and from xenon isotopes produced by spontaneous fission of {sup 238}U in the rocks. A {sup 4}He flux of 2 {center_dot} 10{sup {minus}7} cc STP/cm{sup 2} yr is derived from the profile, which is due to local {sup 4}He production within the investigated sediments.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 7
    Language: English
    In: Environmental Earth Sciences, 2013, Vol.69(2), pp.359-372
    Description: First results of a multi-disciplinary hyporheic monitoring study are presented from the newly established Steinlach Test Site in Southern Germany. The site is located in a bend of the River Steinlach (mean discharge of 1.8 m³/s) underlain by an alluvial sandy gravel aquifer connected to the stream. The overall objective is a better understanding of hyporheic exchange processes at the site and their interrelations with microbial community dynamics and biochemical reactions at the stream–groundwater interface. The present paper focuses on the distribution of lateral hyporheic exchange fluxes and their associated travel times at the Steinlach Test Site. Water level dynamics in various piezometers correspond to the different domains of hydraulic conductivity in the shallow aquifer and confirms hyporheic exchange of infiltrated stream water across the test site. Hydrochemical compositions as well as increased damping of continuous time series of electrical conductivity (EC) and temperature at the respective piezometers confirmed the inferred distribution of hyporheic flowpaths. Mean travel times ranging from 0.5 days close to the stream to more than 8 days in the upstream part of the test site could be estimated from deconvolution of EC and δ 18 O–H 2 O data. The travel times agree well with the presumed flowpaths. Mg/Ca ratios as well as model fits to the EC and δ 18 O data indicate the presence of an additional water component in the western part of the test site which most likely consists of hillslope water or groundwater. Based on the mean travel times, the total lateral hyporheic exchange flux at the site was estimated to be of the order of 1–2 L/s.
    Keywords: Hyporheic zone ; Stream–groundwater interaction ; Travel time distribution ; Deconvolution ; Monitoring
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 8
    Language: English
    In: Water Research, 2007, Vol.41(15), pp.3259-3270
    Description: In this study, we used isotopic ( O, H, S-SO ) and chemical tracers (boron) to assess the sources and transport processes of the micropollutants carbamazepine, galaxolide, and bisphenol A in groundwater underlying the city of Halle (Saale), Germany. Their ubiquitous presence in urban groundwater results from a combination of local river water infiltration, sewer exfiltration, and urban stormwater recharge. Attenuation during transport with infiltrating river water increased from carbamazepine (0–60%) to galaxolide (60–80%) in accordance with their increasing sorption affinity and decreasing recalcitrance against biodegradation. Distinctly higher attenuation during transport was found for carbamazepine (85–100%) and galaxolide (95–100%) if micropollutants originated from sewer exfiltration. Most likely, this is related to higher contents of organic matter and higher transit times of the respective flow paths. Although attenuation undoubtedly also affects the transport of bisphenol A, quantification is limited due to additional contributions from the urban stormwater recharge. As a consequence, micropollutant loads in groundwater indicate that groundwater discharge may dominate the export of bisphenol A from urban areas.
    Keywords: Urban Groundwater ; Pharmaceuticals ; Personal Care Products ; Endocrine Disruptors ; Stable Isotopes ; Sewer Exfiltration ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 9
    Language: English
    In: Applied Geochemistry, 2008, Vol.23(10), pp.2945-2954
    Description: Naturally occurring stable and radioactive isotopes were used as environmental tracers to investigate contaminant metal mobilization processes in a metal smelter dump mainly consisting of slag. Water emerging from the dump at a spring is heavily contaminated by metals. The smelter dump contains minor amounts of flue dust, a material which shows a high potential for metal mobilization. Nearby dumps mainly consist of low-grade ore. Concentration patterns of U, Ra and Pb determined in sediment deposited close to the contaminated spring reveal the flue dust to be the major local metal source rather than the slag or the low-grade ore. Contamination pathways inside the dump were investigated using hydrological, chemical and isotopic data. Strong negative correlation between water discharge and metal concentration in the spring water suggests, besides short-term dilution of the metal concentration by direct rainwater runoff, distinct long-term dilution of the spring water by groundwater being discharged at a significantly increased rate as a result of heavy rains. δ O and δD signatures of rain, local groundwater and spring water confirm the importance of groundwater derived from the local aquifer. Another hydrological component with importance for metal mobilization was found to be water that is recharged in the dump itself. Tritium analysis allowed an assessment of the probable residence time of that water component in the smelter dump. Since that water component seems to represent a major local contamination pathway the findings of the study are of substantial importance for site remediation planning. As a primary result it could be stated that covering the dump would not result in any noteworthy short-term improvement of the spring water quality. First significant effects would only be visible after 2–3 decades at the earliest.
    Keywords: Geology
    ISSN: 0883-2927
    E-ISSN: 1872-9134
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  • 10
    Language: English
    In: Acta hydrochimica et hydrobiologica, September 2001, Vol.29(2‐3), pp.129-138
    Description: Flooding of uranium mines causes a release of considerable amounts of uranium, radium‐226, and arsenic into rivers and aquifers. Thus treatment is necessary in some cases. In order to evaluate alternative water treatment methods for mine water a research project was carried out by means of both laboratory experiments and small‐scale field tests in abundant mines of the Ore Mountains in East Germany. At two test sites columns filled with Fe, Fe/Mn containing waste sludge, and peat were installed for the duration of one year to investigate geochemical reactions and the fixation processes of relevant radionuclides and arsenic. While Fe is changing the geochemical conditions from oxidizing to reducing milieu, peat and Fe/Mn‐sludge have a significant sorption capacity. In addition, iron hydroxides coprecipitate residual contaminants. The fixation capacity of peat was found to be exhausted within half a year. The Fe/Mn‐sludge adsorbed 60% of radium and 70% of arsenic. The best results for uranium elimination of about 96% were obtained by means of Fe In‐situ‐Behandlung von radioaktiven Bergbauwässern mit reaktiven Materialien – Ergebnisse von Labor‐ und Feldversuchen in deutschen Uranbergwerken Bei der Flutung von Bergwerken sind die Metall‐ und Radionuklidgehalte der Wässer deutlich erhöht und müssen vielfach vor dem Eintritt in die Vorfluter behandelt werden. Als Alternative zu konventionellen Wasserreinigungsverfahren wurden neben Laborversuchen über ein Jahr Feldversuche mit reaktiven Materialien in Bergwerken im sächsischen Erzgebirge zur Eliminierung der Schadstoffe aus Flutungswässern durchgeführt. Als Materialien wurden Fe, Fe/Mn‐haltiger Wasserwerksschlamm (aus der Flockungsstufe) und Torf ausgewählt. Während die Fixierung des Urans mittels Fe auf einer geochemischen Milieuwandlung und Aus‐ bzw. Mitfällung an Eisenhydroxiden basiert, wird bei den übrigen Materialien die hohe Sorptionskapazität ausgenutzt. Wie die Ergebnisse zeigen, ist Fe gut für die alternative Behandlung von Flutungswässern geeignet. Die Sorptionskapazität von Torf war nach einem halben Jahr erschöpft. Mit Hilfe der Fe/Mn‐Verbindungen wurden im Mittel 60% Radium und 70% Arsen eliminiert. Die höchste Effektivität für Uran‐Spezies zeigten Eisenspäne mit einer Eliminierungsrate von bis zu 96%.
    Keywords: Mine Water Treatment ; Mine Flooding ; Zero‐Valent Iron ; Geochemical Barrier ; Radionuclide Fixation ; Wasserbehandlung ; Grubenflutung ; Nullwertiges Eisen ; Geochemische Barriere ; Radionuklidimmobilisierung
    ISSN: 0323-4320
    E-ISSN: 1521-401X
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