PHT3D‐UZF: A Reactive Transport Model for Variably‐Saturated Porous Media          下载免费PDF全文

Ming Zhi Wu  Vincent E.A. Post  S. Ursula Salmon  Eric D. Morway  Henning Prommer 《Ground water》2016,54(1):23-34

A modified version of the MODFLOW/MT3DMS‐based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably‐saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D‐UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated‐zone flow (UZF1) package. A volume‐averaged approach similar to the method used in UZF‐MT3DMS was adopted. The PHREEQC‐based computation of chemical processes within PHT3D‐UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional‐scale applications, UZF1 simulates downward‐only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably‐saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns.  相似文献   

GaBoDS: The Garching‐Bonn Deep Survey     

T. Erben  M. Schirmer  J. P. Dietrich  O. Cordes  L. Haberzettl  M. Hetterscheidt  H. Hildebrandt  O. Schmithuesen  P. Schneider  P. Simon  E. Deul  R. N. Hook  N. Kaiser  M. Radovich  C. Benoist  M. Nonino  L. F. Olsen  I. Prandoni  R. Wichmann  S. Zaggia  D. Bomans  R. J. Dettmar  J. M. Miralles 《Astronomische Nachrichten》2005,326(6):432-464

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Effects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean sea, is it an endocrine disruption?     

Schnitzler JG  Koutrakis E  Siebert U  Thomé JP  Das K 《Marine pollution bulletin》2008,56(10):1755-1764

We evaluated the alterations of organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) on the thyroid in wild and cultured sea bass (Dicentrarchus labrax) at environmental concentrations. These compounds influence the endocrine system of many fish species and are qualified as endocrine disruptors. The thyroid seems to be a target organ. Two alteration endpoints: the thyroid histology and the muscular thyroid hormone concentrations, were used simultaneously.High concentrations in PCBs and DDT were detected in muscles, supporting the idea that the Mediterranean fauna could be more polluted than the Atlantic fauna. The high abundance of DDE indicates a progressive degradation of remnant DDT load and the absence of new inputs in this area. Aquaculture sea bass shows a significant higher amount of pollutants on fresh weight basis (especially PCBs) in their muscles compared to the wild sea bass. Those differences may be related mainly to the contaminations of diet.Thyroid parameters vary between wild and aquaculture sea bass, wild sea bass were characterized by higher follicle diameters, epithelial cell heights and muscular T₄ concentrations. A significant relationship between persistent organic pollutants (muscular PCBs and DDT concentration) and the different thyroid parameters (diameters of follicles, epithelial cell heights and muscular T₄ levels) could be observed, which support the hypothesis that these compounds have an adverse impact on thyroid morphometry and function.  相似文献   

The Meteoritical Society and Meteoritics and Planetary Science: Past and future     

Ursula B. Marvin 《Meteoritics & planetary science》2000,35(1):4-4

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Pathline Density Distributions in a Null-Space Monte Carlo Approach to Assess Groundwater Pathways     

Christian Moeck  John Molson  Mario Schirmer 《Ground water》2020,58(2):189-207

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Assessing the Transport of Pharmaceutical Compounds in a Layered Aquifer Discharging to a Stream     

Nicola Balbarini  Majken Frederiksen  Vinni Rønde  Ingelise Møller  Anne T. Sonne  Ursula S. McKnight  Jørn K. Pedersen  Philip J. Binning  Poul L. Bjerg 《Ground water》2020,58(2):208-223

A groundwater plume containing high concentrations of pharmaceutical compounds, mainly sulfonamides, barbiturates, and ethyl urethane, in addition to chlorinated ethenes and benzene was investigated. The contamination originating from a former pharmaceutical industry discharges into a multilayered aquifer system and a downgradient stream. In this study, geological and hydrogeological data were integrated into a numerical flow model to examine identified trends using statistical approaches, including principal component analysis and hierarchal cluster analysis. A joint interpretation of the groundwater flow paths and contaminant concentrations in the different compartments (i.e., groundwater and hyporheic zone) provided insight on the transport processes of the different contaminant plumes to the stream. The analysis of historical groundwater concentrations of pharmaceutical compounds at the site suggested these compounds are slowly degrading. The pharmaceutical compounds migrate in both a deep semiconfined aquifer, as well as in the shallow unconfined aquifer, and enter the stream along a 2-km stretch. This contrasted with the chlorinated ethenes, which mainly discharge to the stream as a focused plume from the unconfined aquifer. The integrated approach developed here, combining groundwater flow modeling and statistical analyses of the contaminant concentration data collected in groundwater and the hyporheic zone, lead to an improved understanding of the observed distribution of contaminants in the unconfined and semiconfined aquifers, and thus to their discharge to the stream. This approach is particularly relevant for large and long-lasting contaminant sources and plumes, such as abandoned landfills and industrial production sites, where field investigations may be very expensive.  相似文献   

Flow dynamics at the continental scale: Streamflow correlation and hydrological similarity     

Andrea Betterle  Mario Schirmer  Gianluca Botter 《水文研究》2019,33(4):627-646

Streamflow variability in space and time critically affects anthropic water uses and ecosystem services. Unfortunately, spatiotemporal patterns of flow regimes are often unknown, as discharge measurements are usually recorded at a limited number of hydrometric stations unevenly distributed along river networks. Advances in understanding the physical processes that control the spatial patterns of river flows are therefore necessary to predict water availability at ungauged locations or to extrapolate pointwise streamflow observations. This work explores the use of the spatial correlation of river flows as a metric to quantify the similarity between hydrological responses of two catchments. Following a stochastic framework, 340,000 cross‐correlations between pairs of daily streamflows time series are predicted at a seasonal timescale across the contiguous United States using 413 catchments of the MOPEX dataset. Model predictions of streamflow correlation obtained in absence of run‐off information are successfully used to identify catchment outlets sharing similar discharge dynamics and flow regimes across a broad range of geomorphoclimatic conditions, without relying on calibration. The selection of reference streamgauges based on predicted streamflow correlation generally outperforms the selection based on spatial proximity, especially as the density of available gauged sections decreases. Interestingly, correlated outlets share a broad spectrum of hydrological signatures (mean discharge, flow variability, and recession properties), suggesting that catchments forced by analogous frequency and intensity of effective rainfall events might exhibit common geomorphoecological traits leading to similar hydrological responses. The proposed framework provides a physical basis to assist the regionalization of flow dynamics and to interpret the spatial variability of flow regimes along stream networks.  相似文献   

Paleoecology of mangroves along the Sibun River, Belize     

Natalie M. Monacci  Ursula Meier-Grünhagen  Bruce P. Finney  Hermann Behling  Matthew J. Wooller 《Quaternary Research》2011,76(2):220-228

This study examines a sediment core (SR-63) from a mangrove ecosystem along the Sibun River in Belize, which is subject to both changes in sea-level and in the characteristics of the river's drainage basin. Radiocarbon dates from the core show a decreased sedimentation rate from ~ 6 ka to 1 cal ka BP and a marked change in lithology from primarily mangrove peat to fluvial-derived material at ~ 2.5 cal ka BP. Changes in the sedimentation rates observed in mangrove ecosystems offshore have previously been attributed to changes in relative sea-level and the rate of sea-level rise. Pollen analyses show a decreased abundance of Rhizophora (red mangrove) pollen and an increased abundance of Avicennia (black mangrove) pollen and non-mangrove pollen coeval with the decreased sedimentation rates. Elemental ratios ([N:C]_a) and stable isotope analyses (δ¹⁵N and δ¹³C) show that changes in the composition of the organic material are also coeval with the change in lithology. The decrease in sedimentation rate at the site of core SR-63 and at offshore sites supports the idea that regional changes in hydrology occurred during the Holocene in Belize, influencing both mainland and offshore mangrove ecosystems.  相似文献   

Tunnel stability analysis during construction using a neuro‐fuzzy system     

Jos Luis Rangel  Ursula Iturrarn‐Viveros  A. Gustavo Ayala  Francisco Cervantes 《国际地质力学数值与分析法杂志》2005,29(15):1433-1456

This paper presents an alternative strategy to evaluate the stability of tunnels during the design and construction stages based on a hybrid system, composed by neural, neuro‐fuzzy and analytical solutions. A prototype of this system is designed using a database formed by 261 cases, 45 real and the rest synthetic. This system is capable of reproducing the displacements induced at the periphery of the tunnel before and after support installation. The stability of the excavation process is evaluated using a criterion that considers dimensionless parameters based on the shear strength of the media, the induced deformation level in the ground, the plastic radii and the advance of excavation without support. The efficiency and validity of the prototype is verified with two examples of actual tunnels, one included in the database used to train the system and the other not included. The results of both examples show a better approximation than other commonly used techniques. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

软性海洋沉积物中水含量对XRF测试的影响     

Rik Tjallingii  Ursula R 《海洋地质前沿》2008,24(3):24-26

Avaatech型X荧光扫描仪是由计算机控制的柱状样扫描装置，可以从剖开样品表面直接获得沉积物的化学组成，无需破坏样品的整体性。能够实现几乎连续的测试，快速地得到从Al到u的所有元素的相对含量。XRF扫描仪已经成功地应用于高分辨率、不同时间序列和时间尺度的地层对比以及沉积相和古气候重建。  相似文献