摘要:

One general problem of the15N dilution technique for determining symbiotic biological nitrogen fixation (BNF) by legumes is deciding on a suitable reference crop. The reference crop must exhibit a similar temporal and spatial pattern of N uptake and must take up nitrogen from the same soil layers as the N-fixing plant being investigated. To verify these presumptions, mixtures of red clover (Trifolium pratenseL.) and ryegrass (Lolium perenneL.) were cultivated on different soils in lysimeters. The organic matter of these lysimeter soils was nearly homogeneously labeled with15N by long-term15N fertilization. The15N abundance of the potentially plant-available nitrogen was investigated via mineralization experiments after Stanford and by hot water extraction. The land-use system on the lysimeter soils had been switched from intensive to ecological farming and no N fertilizer had been administered during the last two years before the clover-ryegrass mixtures were sown. It was found that 80–93% of the plant nitrogen originates from the atmosphere. The impact of different reference crops (Lolium perenneL.,Apera spica-ventiL.,Atriplex patulaL.) on the calculated biological N fixation is minor. Taking into account the15N abundance of the plant-available inorganic nitrogen determined by mineralization after Standford and by hot water extraction, similar results are obtained for biological N fixation.

ISSN:1025-6016    

DOI:10.1080/10256019708234046

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The river Nile has been used as an example to study the evolution of the Sr content and the Sr isotope ratios in rivers in dependence on rock types of the catchment areas, the mixing of the waters from tributaries, the levelling out in a reservoir and evaporation losses.

ISSN:1025-6016    

DOI:10.1080/10256019708234047

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Groundwaters in the area of a mixed landfill (domestic waste above uranium mill tailings) in the Erzgebirge (Saxony, Germany) were investigated for their isotope signatures to distinguish between different groundwater types. The seepage water from the landfill shows higher δ34S values as the inflow whereas the parameters tritium and δ18O do not significantly vary. Uranium values are lower than at other comparable sites, The maximum of 0.7 mg/l Unatwas measured in the geological underground of the landfill. Significant radium concentrations occur in the geological background and are due to former mining activities. The landfill does not produce increased radium values in the water.

ISSN:1025-6016    

DOI:10.1080/10256019708234048

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A sediment core from Lake Trenntsee in northeastern Germany was dated radiometrically to gain a chronology of the observed depth profiles of heavy metal concentration. The chronology was based on gammaspectrometric measurements of fallout nuclides and210Pb dating. Fallout from the Chernobyl reactor accident could be distinguished from the one of nuclear bomb testing by means of134Cs data and published ratios of137Cs/134Cs in fallout. The detection of241Am, resulting only from nuclear weapon testing, confirmed this position of bomb fallout. Using the common dating models computed210Pb ages agreed within the errors with each other and with the time markers from anthropogenic fallout. The resulting mean sedimentation rate ranges from 5.8 to 8 mm/a (0.07 to 0.1 g/(cm2a)), depending on the dating model used. Elevated Pb and Zn concentrations in the upper part of the sediment core are attributed to elevated anthropogenic emissions reaching the environment after World War II.

ISSN:1025-6016    

DOI:10.1080/10256019708234049

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This study aims to identify the recharge sources of the Pleistocene groundwater aquifer East of Sadat city and evaluation of its water quality for different uses. The isotopic data of the investigated groundwater points to the presence of three different recharging sources to the Pleistocene aquifer:1.Seepage of irrigation and drainage watersOld Nile water percolate to the aquifer prior the completion of the high Aswan dam andWestern Desert palaeowater. The variation in the chemical composition of groundwaters in the study area is due to extensive use of nitrate-fertilizers, leaching of terrestrial salts and ion exchange between soil's minerals and water. The examined groundwater quality is fairly suitable for domestic and irrigation uses.

ISSN:1025-6016    

DOI:10.1080/10256019708234050

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The aim of this paper is to rehabilitate informative potential of using deuterium as a natural tracer in geofluids investigations and to illustrate how the deuterium concentration from geological fluid links the micro-scale effects to the macro-scale processes.

ISSN:1025-6016    

DOI:10.1080/10256019708234051

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Results of two routine40Ar/39Ar stepwise heating experiments on a biotite and a basanite are interpreted in terms of Fick's and Arrhenius' laws. Both patterns represent a saddle-shaped39Ar release. Argon isotope spectra are suggested to be controlled by the activation energy of diffusionEand the frequency factorDo. The activation energy of39Ar is lower than the one of40Ar. This results in a preferable release of40Ar relatively to39Ar at high-temperature steps and an increasing high-temperature wing in the saddle-shaped age spectrum. At low temperatures, considerable losses and irregularities in release of mainly39Ar are observed, which cause the decreasing low-temperature wing in the “saddle”. The suggestion of argon losses (mainly of39Ar) from a loose, “unstable” zone of the mineral structures becomes justified. Then-irradiation of the samples and the shift ofEof39Ar towards lower values seems to explain the saddle-shaped age-spectra often encountered in40Ar/39Ar-geochronometry.

ISSN:1025-6016    

DOI:10.1080/10256019708234052

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1025-6016    

DOI:10.1080/10256019708234053

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Proceedings of an International Symposium on the Use of Nuclear and Related Techniques for Studying Environmental Behaviour of Crop Protection Chemicals Jointly Organized by the International Atomic Energy Agency and the Food and Agriculture Organization of the United Nations and held in Vienna, 1–5 July 1996. IAEA Vienna 1997, 519 pp.

ISSN:1025-6016    

DOI:10.1080/10256019708234054

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:1025-6016    

DOI:10.1080/10256019708234045

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor