Evaluating Subsurface Parameterization to Simulate Hyporheic Exchange: The Steinlach River Test Site     

Reynold Chow  Jeremy Bennett  Jürnjakob Dugge  Thomas Wöhling  Wolfgang Nowak 《Ground water》2020,58(1):93-109

Hyporheic exchange is the interaction of river water and groundwater, and is difficult to predict. One of the largest contributions to predictive uncertainty for hyporheic exchange has been attributed to the representation of heterogeneous subsurface properties. Our study evaluates the trade-offs between intrinsic (irreducible) and epistemic (reducible) model errors when choosing between homogeneous and highly complex subsurface parameter structures. We modeled the Steinlach River Test Site in Southwest Germany using a fully coupled surface water-groundwater model to simulate hyporheic exchange and to assess the predictive errors and uncertainties of transit time distributions. A highly parameterized model was built, treated as a “virtual reality” and used as a reference. We found that if the parameter structure is too simple, it will be limited by intrinsic model errors. By increasing subsurface complexity through the addition of zones or heterogeneity, we can begin to exchange intrinsic for epistemic errors. Thus, the appropriate level of detail to represent the subsurface depends on the acceptable range of intrinsic structural errors for the given modeling objectives and the available site data. We found that a zonated model is capable of reproducing the transit time distributions of a more detailed model, but only if the geological structures are known. An interpolated heterogeneous parameter field (cf. pilot points) showed the best trade-offs between the two errors, indicating fitness for practical applications. Parameter fields generated by multiple-point geostatistics (MPS) produce transit time distributions with the largest uncertainties, however, these are reducible by additional hydrogeological data, particularly flux measurements.  相似文献   

Natural Radioactivity at the Sin Quyen Iron-Oxide-Copper-Gold Deposit in North Vietnam     

Dinh Chau Nguyen  Phon Le Khanh  Paweł Jodłowski  Jadwiga Pieczonka  Adam Piestrzyński  Hao Duong Van  Jakub Nowak 《Acta Geophysica》2016,64(6):2305-2321

The field radiometric and laboratory measurements were performed at the Sin Quyen copper deposit in North Vietnam. The field gamma-ray spectrometry indicated the concentration of uranium ranging from 5.5 to 87 ppm, thorium from 5.6 to 33.2 ppm, and potassium from 0.3 to 4.7%. The measured dose rates ranged from 115 to 582 nGy/h, the highest doses being at the copper ore. Concentrations in the solid samples were in the range of 20–1700 Bq/kg for uranium, 20–92.7 Bq/kg for thorium, and 7–1345 Bq/kg for potassium. The calculated doses were from 22 to 896 nGy/h; both measured and calculated dose rates are mostly related to uranium. Concentrations of radium in water samples were below 0.17 Bq/L. Uranium in water samples was significantly higher than the hydrogeological background; the maximum of 13 Bq/L was at the waste zone pool, but neither radium nor uranium were present in tap water. Radon concentration in the dwelling air was from 42 to 278 Bq/m³ for ²²²Rn and from 8 to 193 Bq/m³ for ²²⁰Rn. The estimated committed dose rates were principally related to ²²²Rn concentration and ranged from 1.1 to 8.1 mSv/y.  相似文献   

Analyses of pre-injection reservoir data for stable carbon isotope trend predictions in CO2 monitoring: preparing for CO2 injection     

A. Myrttinen  V. Becker  M. Nowak  M. Zimmer  P. Pilz  J. A. C. Barth 《Environmental Earth Sciences》2012,67(2):473-479

Baseline monitoring at the proposed enhanced gas recovery site in Altmark (Germany) was carried out in combination with theoretical and laboratory investigations to describe and predict the principles of expected stable carbon isotope and dissolved inorganic carbon (DIC) trends during CO₂ injection in reservoirs. This provides fundamental data for site-specific characterisation for monitoring purposes. Baseline ??¹³C values at the Altmark site ranged between ?1.8 and ?11.5??? and DIC values were about 2?mmol?L^?1. These baseline values form the basis for a theoretical study on the influences of the ambient reservoir conditions on the state of geochemical and isotope equilibrium of the reservoir fluids. Transferring this theoretical study to the Altmark site enables predictions on geochemical trends during potential injection. Assuming that CO₂ would be injected at the Altmark site to pCO₂?=?100?bar and with a ??¹³C of ?30???, at isotopic and geochemical equilibrium, ??¹³C_DIC values would approach this end-member, and DIC concentrations of 1,000?mmol L^?1 would be expected. Laboratory experiments were conducted at low pCO₂ levels (4?C35?bars) to mimic the approach of a CO₂ plume at a monitoring well. These results support field investigations from other sites: that ??¹³C_DIC is a sensitive tool for monitoring CO₂ migration in the subsurface and simultaneously allows quantification of geochemical trapping of CO₂.  相似文献   

Immune response of greenback flounder Rhombosolea tapirina after exposure to contaminated marine sediment and diet.     

J A Mondon  S Duda  B F Nowak 《Marine environmental research》2000,50(1-5):443-450

Non-specific immune response of greenback flounder, Rhombosolea tapirina, exposed to contaminated marine sediments was examined. Reference sediments from Port Sorell and contaminated sediments from Deceitful Cove, Tasmania, Australia were investigated. Hatchery-reared flounder were exposed to reference sediment, contaminated sediment or contaminated sediment and diet for 6 weeks. Phagocytic capacity and lysozyme response in flounder were examined on cessation of exposure trial. Significant differences were found in phagocytic capacity and lysozyme response between treatments. Exposure to contaminated sediment, irrespective of diet or benthic disturbance elicited inhibition of phagocytic efficiency in flounder. Disturbance of contaminated sediment stimulated lysozyme activity. The immune response in flounder indicates potential immunotoxicity of sediment from Deceitful Cove.  相似文献   

The mechanisms of water diffusion in polymerized silicate melts     

Harald Behrens  M. Nowak 《Contributions to Mineralogy and Petrology》1997,126(4):377-385

Diffusion of water was experimentally investigated for melts of albitic (Ab) and quartz-orthoclasic (Qz₂₉Or₇₁, in wt %) compositions with water contents in the range of 0 to 8.5 wt % at temperatures of 1100 to 1200 °C and at pressures of 1.0 and 5.0 kbar. Apparent chemical diffusion coefficients of water (D _water) were determined from concentration-distance profiles measured by FTIR microspectroscopy. Under the same P-T condition and water content the diffusivity of water in albitic, quartz-orthoclasic and haplogranitic (Qz₂₈Ab₃₈ Or₃₄, Nowak and Behrens, this issue) melts is identical within experimental error. Comparison to data published in literature indicates that anhydrous composition only has little influence on the mobility of water in polymerized melts but that the degree of polymerization has a large effect. For instance, D_water is almost identical for haplogranitic and rhyolitic melts with 0.5–3.5 wt % water at 850 °C but it is two orders of magnitude higher in basaltic than in haplogranitic melts with 0.2–0.5 wt % water at 1300 °C. Based on the new water diffusivity data, recently published in situ near-infrared spectroscopic data (Nowak 1995; Nowak and Behrens 1995), and viscosity data (Schulze et al. 1996) for hydrous haplogranitic melts current models for water diffusion in silicate melts are critically reviewed. The NIR spectroscopy has indicated isolated OH groups, pairs of OH groups and H₂O molecules as hydrous species in polymerized silicate melts. A significant contribution of isolated OH groups to the transport of water is excluded for water contents above 10 ppm by comparison of viscosity and water diffusion data and by inspection of concentration profiles from trace water diffusion. Spectroscopic measurements have indicated that the interconversion of H₂O molecules and OH pairs is relatively fast in silicate glasses and melts even at low temperature and it is inferred that this reaction is an active step for migration of water. However, direct jumps of H₂O molecules from one cavity within the silicate network to another one can not be excluded. Thus, we favour a model in which water migrates by the interconversion reaction and, possibly, small sequences of direct jumps of H₂O molecules. In this model, immobilization of water results from dissociation of the OH pairs. Assuming that the frequency of the interconversion reaction is faster than that of diffusive jumps, OH pairs and water molecules can be treated as a single diffusing species having an effective diffusion coefficient . The shape of curves of D_water versus water content implies that increases with water content. The change from linear to exponential dependence of D_water between 2 and 3 wt % water is attributed to the influence of the dissociation reaction at low water content and to the modification of the melt structure by incorporation of OH groups. Received: 26 March 1996 / Accepted: 23 August 1996  相似文献   

Glacial and periglacial floodplain sediments regulate hydrologic transfer of reactive iron to a high arctic fjord          下载免费PDF全文

Andrew Hodson  Aga Nowak  Hanne Christiansen 《水文研究》2016,30(8):1219-1229

The transport of reactive iron (i.e. colloidal and dissolved) by a glacier‐fed stream system draining a high relief periglacial landscape in the high Arctic archipelago of Svalbard is described. A negative, non‐linear relationship between discharge and iron concentration is found, indicative of increased iron acquisition along baseflow pathways. Because the glaciers are cold‐based and there are no intra‐ or sub‐permafrost groundwater springs, baseflow is principally supplied by the active layer and the colluvial and alluvial sediments in the lower valley. Collectively, these environments increase the flux of iron in the stream by 40% over a floodplain length of just 8 km, resulting in 6 kg Fe km^?2a^?1 of reactive iron export for a 20% glacierized watershed. We show that pyrite oxidation in shallow‐groundwater flowpaths of the floodplain is the most important source of reactive iron, although it is far less influential in the upper parts of the catchment where other sources are significant (including ironstone and secondary oxide coatings). Microbial catalysis of the pyrite oxidation occurs in the floodplain, enabling rapid, hyporheic water exchange to enhance the iron fluxes at high discharge and cause the non‐linear relationship between discharge and reactive iron concentrations. Furthermore, because the pyrite oxidation is tightly coupled to carbonate and silicate mineral weathering, other nutrients such as base cations and silica are also released to the stream system. Our work therefore shows that high Arctic floodplains should be regarded as critically important regulators of terrestrial nutrient fluxes to coastal ecosystems from glacial and periglacial sources. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Argon and CO₂ on the race track in silicate melts: A tool for the development of a CO₂ speciation and diffusion model     

Marcus Nowak  Dominik Schreen 《Geochimica et cosmochimica acta》2004,68(24):5127-5138

We have analysed the kinetics of Argon and CO₂ diffusion in simplified iron free rhyolitic to hawaiitic melts using the diffusion couple technique. The concentration distance profiles of Ar and CO₂ were measured with electron microprobe analysis and Fourier Transform Infrared Spectroscopy, respectively. Error functions were fitted to the symmetrical concentration distance profiles to extract the diffusion coefficients.In the temperature range 1373 to 1773 K the activation energies for Ar diffusion range from 169 ± 20 to 257 ± 62 kJ mol⁻¹. Ar diffusivity increases exponentially with the degree of depolymerisation. In contrast, the mobility of total CO₂, that is identical to Ar mobility in rhyolitic melt, keeps constant with changing bulk composition from rhyolite to hawaiite. CO₂ speciation at 1623 K and 500 MPa was modeled for the range of compositions studied using the diffusion data of Ar and total CO₂ in combination with network former diffusion calculated from viscosity data. Within error this model is in excellent agreement with CO₂ speciation data extrapolated from temperatures near the glass transition temperature for dacitic melt composition. This model shows that even in highly depolymerised hawaiitic and tholeiitic melts molecular CO₂ is a stable species and contributes 70 to 80% to the total CO₂ diffusion, respectively.  相似文献   

RXTE observation of Cygnus X-1 — I. Spectral analysis     

James B. Dove  Jo¨rn Wilms  Michael A. Nowak  Brian A. Vaughan  & Mitchell C. Begelman 《Monthly notices of the Royal Astronomical Society》1998,298(3):729-736

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Health of red morwong, Cheilodactylus fuscus, and rock cale, Crinodus lophodon, from Sydney cliff-face sewage outfalls     

Barbara F. Nowak 《Marine pollution bulletin》1996,33(7-12):281-292

Health of red morwong, Cheilodactylus fuscus and rock cale, Crinodus lophodon was assessed using histology to determine effects of the Sydney cliff outfalls on these two species. Ten individuals of each species were sampled from three outfall sites and three control sites. Benign epitheliocystis, presence of metazoan parasites, epithelial lifting, telangiectasis, haemorrhage and inflammation were found in the gills of some individuals. Hemosiderin was present in melanomacrophage aggregates in liver and spleen of some fish and also in kidneys of a few fish collected in Malabar outfall site. Hyaline droplets were present in tubular epithelium in kidney of some fish, particularly in the individuals collected from Malabar. Although for some changes there was a trend of greater prevalence at the outfall sites, there was no statistically significant difference between the fish from outfall sites and control sites. Most changes were species specific and the differences were statistically significant. This suggests problems with extrapolating results from one species to others. Greater replication, smaller range of size, chemical analysis of tissue residues as well as better knowledge of the fate of sewage and oceanographic processes would improve interpretation of any future surveys. A multidisciplinary approach would be most beneficial for pollution studies.  相似文献   

Sensitivity of Simulated Hyporheic Exchange to River Bathymetry: The Steinlach River Test Site     

Reynold Chow  Hao Wu  Jeremy P. Bennett  Jürnjakob Dugge  Thomas Wöhling  Wolfgang Nowak 《Ground water》2019,57(3):378-391

This study determines the aspects of river bathymetry that have the greatest influence on the predictive biases when simulating hyporheic exchange. To investigate this, we build a highly parameterized HydroGeoSphere model of the Steinlach River Test Site in southwest Germany as a reference. This model is then modified with simpler bathymetries, evaluating the changes to hyporheic exchange fluxes and transit time distributions. Results indicate that simulating hyporheic exchange with a high-resolution detailed bathymetry using a three-dimensional fully coupled model leads to nested multiscale hyporheic exchange systems. A poorly resolved bathymetry will underestimate the small-scale hyporheic exchange, biasing the simulated hyporheic exchange towards larger scales, thus leading to overestimates of hyporheic exchange residence times. This can lead to gross biases in the estimation of a catchment's capacity to attenuate pollutants when extrapolated to account for all meanders along an entire river within a watershed. The detailed river slope alone is not enough to accurately simulate the locations and magnitudes of losing and gaining river reaches. Thus, local bedforms in terms of bathymetric highs and lows within the river are required. Bathymetry surveying campaigns can be more effective by prioritizing bathymetry measurements along the thalweg and gegenweg of a meandering channel. We define the gegenweg as the line that connects the shallowest points in successive cross-sections along a river opposite to the thalweg under average flow conditions. Incorporating local bedforms will likely capture the nested nature of hyporheic exchange, leading to more physically meaningful simulations of hyporheic exchange fluxes and transit times.  相似文献