ISSN:1025-6016    

DOI:10.1080/10256010008036380

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In Germany, geochemical modelling takes a strong position in two aspects of broader public interest. The first aspect is the safety assessment of a nuclear waste repository, the second is remediation of uranium mining areas. In both aspects, the application of geochemical modelling is stipulated by authorities. This situation results from the possibility to model highly complex situations by computers. The increase in computing power experienced in recent times now offers techniques to assess the sensitivity of modelling results to uncertain input data both in the thermodynamic data base and the site-specific field data. Both aspects are investigated by using Monte Carlo methods in combination with non-parametric statistics. A probabilistic geochemical modelling of uranium mill tailings leaching is demonstrated by application of TReaC modelling code using a simplified site model.

ISSN:1025-6016    

DOI:10.1080/10256010008036381

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Groundwaters in the area of a mixed landfill (domestic waste above uranium mill tailings) in Dresden (Saxony, Germany) were investigated for their isotope signatures to distinguish between different groundwater types. To determine between the two contamination sources (waste and uranium mill tailings) a multi parameter interpretation was done using both, the main hydrochemical parameters the radionuclides234U,238U,226Ra and222Rn as well as the environmental isotopes of the elements hydrogen, oxygen, sulphur and carbon.

ISSN:1025-6016    

DOI:10.1080/10256010008036382

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The modeling of geo-chemical processes needs the detailed and comprehensive knowledge of all chemical interactions existing in the flow path of waste dumps, subsoil and aquifer. This includes the adsorption, displacement and transport of heavy metal species of fulvic and humic acids, which represent the main amount of DOC in the liquid/solid system of the flow path. Comparative measurements of DOC concentrations in the input and output flow at the three waste dumps in the district Schlema/Alberoda indicated that DOC is produced and/or supplied within the waste dumps. The speciation of heavy metal compounds of fulvic and humic acids was achieved by means of sequential chromatographic analysis SCA and isoelectric focusing IEF. Between 5% and 20% of uranium exist in the flow path in the form of stable fulvic and humic acid species. Their distribution coefficients are strongly correlated with the pH values of the geo-chemical system.

ISSN:1025-6016    

DOI:10.1080/10256010008036383

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The mechanism of detection of chemical vapors in air by an ionization chamber supplied by DC and AC voltage has been described. The theoretical explanation is based on numerical solutions of the differential equations of the cylindrical ionization chamber. The current of the ionization chamber operating in the AC regime has two components: aconductive component, caused by the ions drifts, and acapacitive component, caused by the distortion of the electric field. The ionization chamber operating in the DC regime has only the first component; hence the AC supplied chamber has larger response than the DC supplied chamber.

ISSN:1025-6016    

DOI:10.1080/10256010008036384

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1025-6016    

DOI:10.1080/10256010008036385

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Nitrogen and carbon stable isotope ratios and uric acid concentrations in termites sampled from a dry evergreen forest in Thailand, were determined across three kinds of feeding habits. Feeding habits ofMicrocerotermes crassus, which is an abundant woodfeeder, andDicuspiditermes makhamensis, a common soil-feeding termite, were confirmed by isotopic signatures. Lichen feeding termites (Hospitalitermes birmanicus, H. bicolorandH. ataramensis) were characterized by low δ15N values, suggesting that they assimilated nitrogen deposited from the atmosphere. There was also a significant difference in uric acid concentrations between termites representing different feeding habits. No significant relationships were found between uric acid concentrations and δ15N or δ13C inHospitalitermes. However, δ15N values were correlated with C/N ratios inH. birmanicus, except in one colony ofH. ataramensis. δ13C values in both species were negatively correlated with C/N ratios.

ISSN:1025-6016    

DOI:10.1080/10256010008036386

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In estuarine ecosystems, large spatial and seasonal variations in δ13C values of primary producers can occur, and knowledge of these variations may be crucial when interpreting stable isotope data of higher trophic levels. Obtaining clean phytoplankton samples for isotope analysis is usually impossible in such systems, and analysis of total suspended matter is not a simple proxy for phytoplankton δ13C variations. Based on a few simple assumptions regarding the C and N content of the two end-members (terrestrial detritus and phytoplankton) and the δ13C of the terrestrial component, we here present a simple model to estimate the phytoplankton δ13C variations using an existing dataset on the δ13C and elemental (C:N) composition of suspended organic matter from an estuarine mangrove ecosystem in southeast India.

ISSN:1025-6016    

DOI:10.1080/10256010008036387

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We evaluated the use of δ15N- and δ13C-values to monitor the development of food web complexity and biodiversity in a regenerating ecosystem. Therefore a model food chain was established feeding cultivated woodlice (Porcellio dilatatus) on a cellulolytic fungus (Chaetomium globosum) grown on cellulose paper. Two diets of different quality (C:N ratios of 54vs.200) with different δ15N- (1.3‰vs.3.1‰) but identical δ13C-values caused low and high dietary stress in animals of treatmentAandB, respectively. After an incubation time of 7 weeks amount, elemental and isotopic composition of collected faeces and exuviae as well as woodlice and remaining food were determined.

ISSN:1025-6016    

DOI:10.1080/10256010008036388

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The isotopic composition of tree-ring cellulose was obtained over a two-year period from small diameter, riparian zone trees along an elevational transect in Big Cottonwood Canyon, Utah, USA to test for a possible temperature dependence of net biological fractionation during cellulose synthesis. The isotope ratios of stream water varied by only 3.6‰ and 0.2‰ in δD and δ18O, respectively, over an elevation change of 810m. The similarity in stream water and macroenvironment over the short (13km) transect produced nearly constant stem and leaf water δD and δ18O values. In addition, what few seasonal variations observed in the isotopic composition of source water and atmospheric water vapor or in leaf water evaporative enrichment were experienced equally by all sites along the elevational transect. The temperature at each site along the transect spanned a range of ≥ 5°C as calculated using the adiabatic lapse rate. Since the δD and δ18O values of stem and leaf water varied little for these trees over this elevation/ temperature transect, any differences in tree-ring cellulose δD and δ18O values should have been associated with temperature effects on net biological fractionation. However, the slopes of the regressions of elevationversusthe δD and δ18O values of tree-ring cellulose were not significantly different from zero indicating little or no temperature dependence of net biological fractionation. Therefore, cross-site climatic reconstruction studies using the isotope ratios of cellulose need not be concerned that temperatures during the growing season have influenced results.

ISSN:1025-6016    

DOI:10.1080/10256010008036389

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor