Travel time based approach for the assessment of vulnerability of karst groundwater: the Transit Time Method     

Karolin Brosig  Tobias Geyer  Ali Subah  Martin Sauter 《Environmental Geology》2008,54(5):905-911

Karst aquifers represent important water resources in many parts of the world. Unfortunately, karst aquifers are characterised by high contamination risks. This paper presents a travel time based method for the estimation of karst groundwater vulnerability. It considers (1) physics-based lateral flow within the uppermost weathered zone (epikarst) in a limestone-dominated region and (2) high velocities of vertical infiltration at discrete infiltration points (e.g. sinkholes) or lines (e.g. dry valleys, faults). Consequently, the Transit Time Method honours the actual flow path within the unsaturated zone of a karst aquifer system. A test site in Northern Jordan was chosen for the demonstration of the assessment technique, i.e. the catchment area of the Qunayyah Spring north of the capital Amman. The results demonstrate that zones of highest vulnerability lie within valleys and nearby main fault zones. It also reveals that regions, categorised as protected areas by other methods due to thick unsaturated zones, contribute to a major degree to the total risk.  相似文献   

How a court, a commissioner and a lobby group brought European transport policy to life in 1985     

Marco te Brömmelstroet  Tobias Nowak 《GeoJournal》2008,72(1-2):33-44

Until the mid-1980s, transport policy was considered by many as one of the least successful domains of the European integration project. However, from the early 1990s onwards, there are clear signs of a single European transport policy, along with the accompanying implementation of infrastructure projects. What is the explanation for such a change in pace? This paper aims to offer insight in these processes by looking at the mechanisms which form and transform this policy domain. To understand the state of a policy domain and its dynamics over time an institutional approach is taken. Two concepts in political science, ‘policy arrangements’ and ‘supranational governance’ are combined and used as a framework to analyse the European transport policy domain. This analysis describes the development of several elements: organisations, rules, the transnational society, power, resources, and the central transport discourse. It demonstrates that all of these elements have developed from an intergovernmental setting towards a more supranational one. This development was slow in the first decennia when European transport policy was rather passive, but it picked up speed in the 1980s and 1990s. In the pivotal year of 1985, pressure from the transnational society resulted in a rapid change of the rules, the resources and the discourse.  相似文献   

Vertical migration and mortality of benthos in dredged material: Part III—polychaeta     

Don Maurer  Richard T Keck  Jeff C Tinsman  Wayne A Leathem 《Marine environmental research》1982,6(1):49-68

The survival of benthic invertebrates from dredging and disposal activities is a major environmental concern in such projects. The purpose of the research described in this paper was to determine the ability of benthos (polychaetes, Scoloplos fragilis and Nereis succinea) to migrate vertically in natural and exotic sediments and to determine the survival of benthos when exposed to particular amounts of simulated dredged material.Mortalities generally increased with increased sediment depth, exotic sediment and burial time. Temperature also affected vertical migration and mortalities. These experiments, together with other experiments conducted by us and other workers, indicate that polychaetes in particular, and benthos in general, can survive dredging and disposal projects. Under certain conditions several major taxa (polychaetes, molluscs, crustaceans) can be expected to successfully recolonise disposal sites by vertical migration.  相似文献   

Research challenges at the land–sea interface     

Drew M. Talley  Elizabeth W. North  Andrew R. Juhl  David A. Timothy  Daniel Conde  Jody F. C. deBrouwer  Cheryl A. Brown  Linda M. Campbell  Tobias Garstecki  Catherine J. Hall  Filip J. R. Meysman  David M. Nemerson  Pedro W. Souza Filho  Robert J. Wood 《Estuarine, Coastal and Shelf Science》2003,58(4):699

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Vertical migration and mortality of benthos in dredged material: Part II—crustacea     

Don Maurer  Richard T. Keck  Jeff C. Tinsman  Wayne A. Leathem 《Marine environmental research》1981,5(4):301-317

Benthic invertebrates have many characteristics which make them prime candidates for burial studies in dredged material. A major concern in dredging and disposal projects is the effect of burial on the survival of benthic invertebrates. The purpose of the research reported in this paper was to determine the ability of estuarine benthos—in particular three species of molluscs (Mercenaria mercenaria, Nucula proxima and Ilyanassa obsoleta)—to migrate vertically in natural and exotic sediments and to determine the survival of benthos when exposed to particular amounts of simulated dredged material.Mortalities generally increased with increased sediment depth, with increased burial time and with overlying sediments whose particle size distribution differed from that of the species native sediment. Temperature affected mortalities and vertical migration. It was concluded that vertical migration is a viable process which can significantly affect rehabilitation of a dredged disposal area. Under certain conditions, vertical migration should be considered, together with larval settling and immigration from outside impacted areas, as a mechanism of recruiting a dredgedump site.  相似文献   

Zircon M257 ‐ a Homogeneous Natural Reference Material for the Ion Microprobe U‐Pb Analysis of Zircon     

Lutz Nasdala  Wolfgang Hofmeister  Nicholas Norberg  James M. Martinson  Fernando Corfu  Wolfgang Dörr  Sandra L. Kamo  Allen K. Kennedy  Andreas Kronz  Peter W. Reiners  Dirk Frei  Jan Kosler  Yusheng Wan  Jens Götze  Tobias Häger  Alfred Kröner  John W. Valley 《Geostandards and Geoanalytical Research》2008,32(3):247-265

We introduce and propose zircon M257 as a future reference material for the determination of zircon U‐Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS‐determined, mean isotopic ratios (2s uncertainties) of 0.09100 ± 0.00003 for ²⁰⁶pb/²³⁸U and 0.7392 ± 0.0003 for ²⁰⁷pb/²³⁵U. Its ²⁰⁶pb/²³⁸U age is 561.3 ± 0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U‐Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ～ 840 μg g^?1 U (Th/U ～ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit‐cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the “Sri Lankan trends”, with actinide concentrations, U‐Pb age, and the calculated alpha fluence of 1.66 × 10¹⁸ g^?1. This, and a (U+Th)/He age of 419 ± 9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc‐silicate skarn.  相似文献   

The Martian paleoclimate and enhanced atmospheric carbon dioxide     

R.D. Cess  V. Ramanathan  Tobias Owen 《Icarus》1980,41(1):159-165

Current evidence indicates that the Martian surface is abundant with water presently in the form of ice, while the atmosphere was at one time more massive with a past surface pressure of as much as 1 atm of CO₂. In an attempt to understand the Martian paleoclimate, we have modeled a past CO₂H₂O greenhouse and find global temperatures which are consistent with an earlier presence of liquid surface water, a finding which agrees with the extensive evidence for past fluvial erosion. An important aspect of the CO₂H₂O greenhouse model is the detailed inclusion of CO₂ hot bands. For a surface pressure of 1 atm of CO₂, the present greenhouse model predicts a global mean surface temperature of 294°K, but if the hot bands are excluded, a surface temperature of only 250°K is achieved.  相似文献   

The abundances of ammonia in the atmospheres of Jupiter,Saturn, and Titan     

Jerry H. Woodman  L. Trafton  Tobias Owen 《Icarus》1977,32(3):314-320

An investigation of low-resolution ratio spectra of Jupiter, Saturn, and Titan in the region 5400–6500 Å has permitted new evaluations of ammonia absorption bands. The distribution of ammonia over the disk of Jupiter is very inhomogeneous. The carbon-to-nitrogen ratio is distinctly different from the solar value, but this is probably a result of uneven mixing of methane and ammonia, as suggested previously by Kuiper, rather than a compositional anomaly. The abundance of ammonia on Saturn also shows spatial variations, but appears constant in time over a 3-yr period. Two weak, unidentified absorptions were discovered in the red region of Titan's spectrum, in the absence of any detectable ammonia. The new upper limit is ηN < 120 cm-am.  相似文献   

Abundances of isotopes in planetary atmospheres     

Tobias Owen 《Earth, Moon, and Planets》1978,19(2):297-303

Carbon and oxygen isotopes show no large anomalies on Venus (10–15%) or Mars (<5%); the high value of¹⁵N/¹⁴N found on Mars is explained by non-thermal escape of nitrogen. The isotopes of non-radiogenic noble gases in the atmosphere of Mars exhibit abundance patterns similar to those in the primordial component of meteoritic gases and in the Earth's atmosphere. This implies that gas fractionation took place in the inner solar nebula prior to planet formation. The relatively high value of¹²⁹Xe on Mars emphasizes its deficiency on Earth, implying a difference in accretion histories of volatiles for the two planets. In the outer solar system, we find normal isotope ratios for nitrogen and carbon on Jupiter, and for carbon on Saturn, but precision is low (±15% at best). Controversy exists about the correct value of D/H, with current estimates ranging from 2.3±1.1 to 5.1±0.7×10^–5. Planetary missions planned for the next few years should add considerably to the quantity and quality of these data.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.  相似文献   

Production of organic molecules in the outer solar system by proton irradiation: Laboratory simulations     

Thomas Scattergood  Peter Lesser  Tobias Owen 《Icarus》1975,24(4):465-471

In the past few years considerable attention has been given to the determination of likely compounds that could account for the various colors observed in the outer solar system: and to possible formation mechanisms for these compounds. Many experiments have been done using electrical discharges (Chadha, M. S., et al., 1971, Icarus15, 39) and ultraviolet light (Khare, B. N., and Sagan, C., 1973, Icarus20, 311) on mixtures of CH₄, NH₃, and H₂S, which are most likely the dominant minor constituents of the atmospheres of Jupiter, Saturn, Titan, and possibly the other satellites early in their histories. Colored polymers, usually brownish-red, have been produced in these experiments. With the passage of Pioneer 10 around Jupiter, there is another source of energy worthy of consideration, energetic protons (and electrons). Preliminary experiments to investigate the formation of colored polymers and other interesting molecules by the irradiation of gas mixtures by protons are discussed. Two to four Mev protons were used, with corresponding beam fluxes (as measured at 6R_J from the planet) equivalent to approximately 80 Earth years at Jupiter per hour of exposure. As in the other types of experiments, colored polymers have been produced. An important feature of this work is the presence or absence of absorption at 5 μm in the different materials produced; Titan is quite dark at this wavelength and Io is fairly bright. Such features may provide criteria for accepting or rejecting various materials produced in these experiments as reasonable coloring agents for the outer solar system.  相似文献