Adsorption as a cause for iron isotope fractionation in reduced groundwater     

Nadya Teutsch  Urs von Gunten  Olaf A. Cirpka 《Geochimica et cosmochimica acta》2005,69(17):4175-4185

Iron isotopes were used to investigate iron transformation processes during an in situ field experiment for removal of dissolved Fe from reduced groundwater. This experiment provided a unique setting for exploring Fe isotope fractionation in a natural system. Oxygen-containing water was injected at a test well into an aquifer containing Fe(II)-rich reduced water, leading to oxidation of Fe(II) and precipitation of Fe(III)(hydr)oxides. Subsequently, groundwater was extracted from the same well over a time period much longer than the injection time. Since the surrounding water is rich in Fe(II), the Fe(II) concentration in the extracted water increased over time. The increase was strongly retarded in comparison to a conservative tracer added to the injected solution, indicating that adsorption of Fe(II) onto the newly formed Fe(III)(hydr)oxides occurred. A series of injection-extraction (push-pull) cycles were performed at the same well. The δ⁵⁷Fe/⁵⁴Fe of pre-experiment background groundwater (−0.57 ± 0.17 ‰) was lighter than the sediment leach of Fe(III) (−0.24 ± 0.08 ‰), probably due to slight fractionation (only ∼0.3 ‰) during microbial mediated reductive dissolution of Fe(III)(hydr)oxides present in the aquifer. During the experiment, Fe(II) was adsorbed from native groundwater drawn into the oxidized zone and onto Fe(III)(hydr)oxides producing a very light groundwater component with δ⁵⁷Fe/⁵⁴Fe as low as −4 ‰, indicating that heavier Fe(II) is preferentially adsorbed to the newly formed Fe(III)(hydr)oxides surfaces. Iron concentrations increased with time of extraction, and δ⁵⁷Fe/⁵⁴Fe linearly correlated with Fe concentrations (R² = 0.95). This pattern was reproducible over five individual cycles, indicating that the same process occurs during repeated injection/extraction cycles. We present a reactive transport model to explain the observed abiotic fractionation due to adsorption of Fe(II) on Fe(III)(hydr)oxides. The fractionation is probably caused by isotopic differences in the equilibrium sorption constants of the various isotopes (K_ads) and not by sorption kinetics. A fractionation factor α_57/54 of 1.001 fits the observed fractionation.  相似文献   

Alteration of volcanic matter in deep sea sediments: evidence from the chemical composition of interstitial waters from deep sea drilling cores     

Joris M. Gieskes  James R. Lawrence 《Geochimica et cosmochimica acta》1981,45(10):1687-1703

Six Deep Sea Drilling Project (DSDP) Sites (252, 285, 315, 317, 336, 386) were examined for the chemical composition of the dissolved salts in interstitial waters, the oxygen isotopic composition of the interstitial waters, and the major ion composition of the bulk solid sediments. An examination of the concentration-depth profiles of dissolved calcium, magnesium, potassium, and H₂¹⁸O in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in DSDP pelagic drill sites concentration gradients in Ca. Mg. K, and H₂¹⁸O are largely due to alteration reactions occurring in the basalts of Layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column. Oxygen isotope mass balance calculations require substantial alteration of Layer 2 (up to 25% of the upper 1000 m). but only minor exchange of Ca, Mg, and K occurs with the overlying ocean. This implies that alteration reactions in Layer 2 are almost isochemical.  相似文献   

The Herschel-PACS photometer calibration     

Zoltan Balog  Thomas Müller  Markus Nielbock  Bruno Altieri  Ulrich Klaas  Joris Blommaert  Hendrik Linz  Dieter Lutz  Attila Moór  Nicolas Billot  Marc Sauvage  Koryo Okumura 《Experimental Astronomy》2014,37(2):129-160

This paper provides an overview of the PACS photometer flux calibration concept, in particular for the principal observation mode, the scan map. The absolute flux calibration is tied to the photospheric models of five fiducial stellar standards (α Boo, α Cet, α Tau, β And, γ Dra). The data processing steps to arrive at a consistent and homogeneous calibration are outlined. In the current state the relative photometric accuracy is ～2 % in all bands. Starting from the present calibration status, the characterization and correction for instrumental effects affecting the relative calibration accuracy is described and an outlook for the final achievable calibration numbers is given. After including all the correction for the instrumental effects, the relative photometric calibration accuracy (repeatability) will be as good as 0.5 % in the blue and green band and 2 % in the red band. This excellent calibration starts to reveal possible inconsistencies between the models of the K-type and the M-type stellar calibrators. The absolute calibration accuracy is therefore mainly limited by the 5 % uncertainty of the celestial standard models in all three bands. The PACS bolometer response was extremely stable over the entire Herschel mission and a single, time-independent response calibration file is sufficient for the processing and calibration of the science observations. The dedicated measurements of the internal calibration sources were needed only to characterize secondary effects. No aging effects of the bolometer or the filters have been found. Also, we found no signs of filter leaks. The PACS photometric system is very well characterized with a constant energy spectrum νF _ν = λF _λ = const as a reference. Colour corrections for a wide range of sources SEDs are determined and tabulated.  相似文献   

Determination of transverse dispersion coefficients from reactive plume lengths   总被引：3，自引：0，他引：3  

Cirpka OA  Olsson A  Ju Q  Rahman MA  Grathwohl P 《Ground water》2006,44(2):212-221

With most existing methods, transverse dispersion coefficients are difficult to determine. We present a new, simple, and robust approach based on steady-state transport of a reacting agent, introduced over a certain height into the porous medium of interest. The agent reacts with compounds in the ambient water. In our application, we use an alkaline solution injected into acidic ambient water. Threshold values of pH are visualized by adding standard pH indicators. Since aqueous-phase acid-base reactions can be considered practically instantaneous and the only process leading to mixing of the reactants is transverse dispersion, the length of the plume is controlled by the ratio of transverse dispersion to advection. We use existing closed-form expressions for multidimensional steady-state transport of conservative compounds in order to evaluate the concentration distributions of the reacting compounds. Based on these results, we derive an easy-to-use expression for the length of the reactive plume; it is proportional to the injection height squared, times the velocity, and inversely proportional to the transverse dispersion coefficient. Solving this expression for the transverse dispersion coefficient, we can estimate its value from the length of the alkaline plume. We apply the method to two experimental setups of different dimension. The computed transverse dispersion coefficients are rather small. We conclude that at slow but realistic ground water velocities, the contribution of effective molecular diffusion to transverse dispersion cannot be neglected. This results in plume lengths that increase with increasing velocity.  相似文献   

First U–Pb geochronology on detrital zircons from Early-Middle Cambrian strata of the Torgau-Doberlug Syncline (eastern Germany) and palaeogeographic implications     

Abubaker  Atnisha  Hofmann  Mandy  Gärtner  Andreas  Linnemann  Ulf  Elicki  Olaf 《International Journal of Earth Sciences》2017,106(7):2445-2459

International Journal of Earth Sciences - LA-ICP-MS U–Pb data from detrital zircons of the Ediacaran to Cambrian siliciclastic sequence of the Torgau-Doberlug Syncline (TDS, Saxo-Thuringia,...  相似文献   

Numerical modeling of early diagenetic processes in Haiyang 4 Area in the northern slope of the South China Sea     

Lihua Liu  Roger Luff  Haibing Shao  Olaf Kolditz  Nengyou Wu 《Environmental Earth Sciences》2017,76(13):453

Early diagenesis affects the distribution of solutes and minerals in unconsolidated sediments. The investigation of diagenesis is critical to understanding the geochemical transformation and benthic fluxes of elements. During the cruise mission SO-177 in 2004, gravity coring samples were recovered in the Haiyang 4 Area of the northern slope of the South China Sea (SCS). The geochemical concentrations in interstitial water were determined onboard. The 1D C.CANDI reactive transport software was used to model the early diagenesis processes at four sites: 56-GC-3, 70-GC-9, 94-GC-11, and 118-GC-13. All of the simulations reproduced concentration profiles that matched the measurements with the implemented geochemical reactions. The degradation of organic carbon and anaerobic oxidation of methane (AOM) primarily determine the distribution of solutes in the working area. The degradation is active in the top 150 cm, and AOM is vigorous at depths below 200 cm. The local advective flux, sediment rate, and kinetic reaction constants of organic matter, methane and sulfate were calibrated based on the existing concentrations of pore water solutes. Geochemical reactions in this area occur in considerably deeper layers compared to depths cited in the literature. The model results provide evidence for the existence of deep hydrocarbon reservoirs that provide methane to the upper sediments.  相似文献   

Mud dynamics in the Port of Zeebrugge     

Vanlede  Joris  Dujardin  Arvid  Fettweis  Michael  Van Hoestenberghe  Thomas  Martens  Chantal 《Ocean Dynamics》2019,69(9):1085-1099

Ocean Dynamics - This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea based on an analysis of field data. Mud is typically transported into and within the...  相似文献   

An Electron-Balance Based Approach to Predict the Decreasing Denitrification Potential of an Aquifer     

Matthias Loschko  Thomas Wöhling  David L. Rudolph  Olaf A. Cirpka 《Ground water》2019,57(6):925-939

Numerical models for reactive transport can be used to estimate the breakthrough of a contaminant in a pumping well or at other receptors. However, as natural aquifers are highly heterogeneous with unknown spatial details, reactive transport predictions on the aquifer scale require a stochastic framework for uncertainty analysis. The high computational demand of spatially explicit reactive-transport models hampers such analysis, thus motivating the search for simplified estimation tools. We suggest performing an electron balance between the reactants in the infiltrating solution and in the aquifer matrix to obtain the hypothetical time of dissolved-reactant breakthrough at a receptor if the reaction with the matrix was instantaneous. This time we denote as the advective breakthrough time for instantaneous reaction (τ_inst ). It depends on the amount of the reaction partner present in the matrix, the mass flux of the dissolved reactant, and the stoichiometry. While the shape of the reactive-species breakthrough curve depends on various kinetic parameters, the overall timing scales with τ_inst . We calculate the latter by particle tracking. The effort of computing τ_inst is so low that stochastic calculations become feasible. We apply the concept to a two-dimensional test case of aerobic respiration and denitrification. A detailed spatially explicit reactive-transport model includes microbial dynamics. Scaling the time of local breakthrough curves observed at individual points by τ_inst decreased the variability of electron-donor breakthrough curves significantly. We conclude that the advective breakthrough time for instantaneous reaction is efficient in estimating the time over which an aquifer retains its degradation potential.  相似文献   

The implications of bias correction methods and climate model ensembles on soil erosion projections under climate change     

Joris P. C. Eekhout  Joris de Vente 《地球表面变化过程与地形》2019,44(5):1137-1147

Climate change will most likely cause an increase in extreme precipitation and consequently an increase in soil erosion in many locations worldwide. In most cases, climate model output is used to assess the impact of climate change on soil erosion; however, there is little knowledge of the implications of bias correction methods and climate model ensembles on projected soil erosion rates. Using a soil erosion model, we evaluated the implications of three bias correction methods (delta change, quantile mapping and scaled distribution mapping) and climate model selection on regional soil erosion projections in two contrasting Mediterranean catchments. Depending on the bias correction method, soil erosion is projected to decrease or increase. Scaled distribution mapping best projects the changes in extreme precipitation. While an increase in extreme precipitation does not always result in increased soil loss, it is an important soil erosion indicator. We suggest first establishing the deviation of the bias-corrected climate signal with respect to the raw climate signal, in particular for extreme precipitation. Furthermore, individual climate models may project opposite changes with respect to the ensemble average; hence climate model ensembles are essential in soil erosion impact assessments to account for climate model uncertainty. We conclude that the impact of climate change on soil erosion can only accurately be assessed with a bias correction method that best reproduces the projected climate change signal, in combination with a representative ensemble of climate models. © 2018 John Wiley & Sons, Ltd.  相似文献