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

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.     

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

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.     

Abundances of isotopes in planetary atmospheres

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.     

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

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.     

The BEAM-project: prediction and assessment of mixture toxicities in the aquatic environment

Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined.     

Zircon M127 – A Homogeneous Reference Material for SIMS U–Pb Geochronology Combined with Hafnium,Oxygen and,Potentially, Lithium Isotope Analysis

In this article, we document a detailed analytical characterisation of zircon M127, a homogeneous 12.7 carat gemstone from Ratnapura, Sri Lanka. Zircon M127 has TIMS‐determined mean U–Pb radiogenic isotopic ratios of 0.084743 ± 0.000027 for ²⁰⁶Pb/²³⁸U and 0.67676 ± 0.00023 for ²⁰⁷Pb/²³⁵U (weighted means, 2s uncertainties). Its ²⁰⁶Pb/²³⁸U age of 524.36 ± 0.16 Ma (95% confidence uncertainty) is concordant within the uncertainties of decay constants. The δ¹⁸O value (determined by laser fluorination) is 8.26 ± 0.06‰ VSMOW (2s), and the mean ¹⁷⁶Hf/¹⁷⁷Hf ratio (determined by solution ICP‐MS) is 0.282396 ± 0.000004 (2s). The SIMS‐determined δ⁷Li value is ?0.6 ± 0.9‰ (2s), with a mean mass fraction of 1.0 ± 0.1 μg g^?1 Li (2s). Zircon M127 contains ~ 923 μg g^?1 U. The moderate degree of radiation damage corresponds well with the time‐integrated self‐irradiation dose of 1.82 × 10¹⁸ alpha events per gram. This observation, and the (U–Th)/He age of 426 ± 7 Ma (2s), which is typical of unheated Sri Lankan zircon, enable us to exclude any thermal treatment. Zircon M127 is proposed as a reference material for the determination of zircon U–Pb ages by means of SIMS in combination with hafnium and stable isotope (oxygen and potentially also lithium) determination.     

The eastward shift of the Walker Circulation in response to global warming and its relationship to ENSO variability

This study investigates the global warming response of the Walker Circulation and the other zonal circulation cells (represented by the zonal stream function), in CMIP3 and CMIP5 climate models. The changes in the mean state are presented as well as the changes in the modes of variability. The mean zonal circulation weakens in the multi model ensembles nearly everywhere along the equator under both the RCP4.5 and SRES A1B scenarios. Over the Pacific the Walker Circulation also shows a significant eastward shift. These changes in the mean circulation are very similar to the leading mode of interannual variability in the tropical zonal circulation cells, which is dominated by El Niño Southern Oscillation variability. During an El Niño event the circulation weakens and the rising branch over the Maritime Continent shifts to the east in comparison to neutral conditions (vice versa for a La Niña event). Two-thirds of the global warming forced trend of the Walker Circulation can be explained by a long-term trend in this interannual variability pattern, i.e. a shift towards more El Niño-like conditions in the multi-model mean under global warming. Further, interannual variability in the zonal circulation exhibits an asymmetry between El Niño and La Niña events. El Niño anomalies are located more to the east compared with La Niña anomalies. Consistent with this asymmetry we find a shift to the east of the dominant mode of variability of zonal stream function under global warming. All these results vary among the individual models, but the multi model ensembles of CMIP3 and CMIP5 show in nearly all aspects very similar results, which underline the robustness of these results. The observed data (ERA Interim reanalysis) from 1979 to 2012 shows a westward shift and strengthening of the Walker Circulation. This is opposite to what the results in the CMIP models reveal. However, 75 % of the trend of the Walker Circulation can again be explained by a shift of the dominant mode of variability, but here towards more La Niña-like conditions. Thus in both climate change projections and observations the long-term trends of the Walker Circulation seem to follow to a large part the pre-existing dominant mode of internal variability.     

Is there a superior conceptual groundwater model structure for baseflow simulation?

Previous work has shown that streamflow response during baseflow conditions is a function of storage, but also that this functional relationship varies among seasons and catchments. Traditionally, hydrological models incorporate conceptual groundwater models consisting of linear or non‐linear storage–outflow functions. Identification of the right model structure and model parameterization however is challenging. The aim of this paper is to systematically test different model structures in a set of catchments where different aquifer types govern baseflow generation processes. Nine different two‐parameter conceptual groundwater models are applied with multi‐objective calibration to transform two different groundwater recharge series derived from a soil‐atmosphere‐vegetation transfer model into baseflow separated from streamflow data. The relative performance differences of the model structures allow to systematically improve the understanding of baseflow generation processes and to identify most appropriate model structures for different aquifer types. We found more versatile and more aquifer‐specific optimal model structures and elucidate the role of interflow, flow paths, recharge regimes and partially contributing storages. Aquifer‐specific recommendations of storage models were found for fractured and karstic aquifers, whereas large storage capacities blur the identification of superior model structures for complex and porous aquifers. A model performance matrix is presented, which highlights the joint effects of different recharge inputs, calibration criteria, model structures and aquifer types. The matrix is a guidance to improve groundwater model structures towards their representation of the dominant baseflow generation processes of specific aquifer types. Copyright © 2014 John Wiley & Sons, Ltd.