Dealing with contaminated dredged materials with reference to the Oslo Convention 1972 and the new Paris Convention 1992

Protection of the sea has received much political attention—for example, at successive North Sea Conferences environmental ministers have formulated a stringent policy with the aim of reducing pollution in the north-east Atlantic. In the past this area received many substances from many sources, but gradually intergovernmental action since 1972 in the Oslo and Paris Conventions has succeeded in tracing the major sources and understanding the effects of these inputs on the marine environment. After long discussion, many dumpings and discharges have been ended because they were considered harmful to the marine environment. Dredging activities were included in the discussions but they may be regarded as being a special case compared with many other disposals.

In general, clean dredged material for sea disposal offers no problems, although restrictions may be caused by physical impacts, mainly to habitats for living organisms. However, this material also has positive, often even beneficial uses. In contrast, contaminated material disposal is restricted and the internationally accepted rule is that the material should not create hazards to human health, harm living resources and marine life or damage amenities or interfere with other legitimate uses of the sea. There are in principle three options for dealing with polluted sediments: doing nothing, remedial action in situ, removal of the contaminated material; occasionally treatment is a possibility. The distinction has been made between the disposal of industrial waste, sewage sludge or dredged material. Industrial waste disposal is now prohibited; sewage sludge may be dumped until 31 December 1998, although dredged material may still be stored at sea under certain conditions. The Oslo Convention 1972 decided with regard to dredged material: that pollution has to be tackled at the source; dumping at sea is forbidden, although dredged materials may be excluded from this; land disposal prevails, although in several countries there is a growing resistance to disposal on land; there should be a precautionary approach against marine disposal; a stand-still principle should be followed where the quantities disposed in a certain year should not be exceeded nor should the quality of the receiving water be reduced; marine disposal should be phased out and, where appropriate, time-limits set; and the polluter pays.

Dredged material is regarded as polluted and as a consequence may in general not be disposed of at sea when it contains substances listed in the Annexes of the Convention. Exceptions to this are indicated by the terms ‘a trace contaminant’, ‘rapidly rendered harmless’ or ‘significant amounts’. Therefore, to achieve uniformity in the application of the Convention, guidelines have been prepared by a joint London Dumping Convention/Oslo Commission working group of experts on dredged material. Several characteristics must be considered when choosing a site for marine disposal and interests such as beach recreation, sport and commercial fishing, nature, cultural or historical interests, navigation, military interests and cables and pipelines should be taken into account. Also the capacity of the area to assimilate disposed matter per time unit must not be exceeded, especially in low energy areas. It is considered that in discussions of the environmental aspects of dredging it is important that associations such as PIANC argue for safe and economic navigation.     

Spatial, temporal and geochemical characteristics of Silurian collision-zone magmatism, Newfoundland Appalachians: An example of a rapidly evolving magmatic system related to slab break-off

Silurian plutonic suites in the Newfoundland Appalachians include abundant gabbro, monzogabbro and granite to granodiorite and lesser quartz diorite and tonalite. Most are medium- to high-K, but included are some low-K and shoshonitic mafic compositions. Felsic rocks are of both alkaline (A-type or within-plate granite (WPG)) and calc-alkaline volcanic arc granite (VAG) affinity. Mafic rocks include both arc-like (Nb/Th < 3) calc-alkaline and non-arc-like (Nb/Th > 3) transitional calc-alkaline basalt to continental tholeiitic affinity compositions. ε_Nd(T) values range from − 9.6 to + 5.4 and δ¹⁸O (VSMOW) values range from + 3.1 to + 13.2‰.

A rapid progression from exclusively arc-type to non-arc-like mafic and then contemporaneous WPG plus VAG magmatism has been documented using precise U–Pb zircon dating. Earlier arc-like plutonism indicates subduction, while asthenosphere-derived mafic magmas support slab break-off, due to subduction of a young, warm back-arc basin. Contemporaneous mafic magmas with arc and non-arc geochemical signatures may reflect tapping of asthenospheric and subcontinental lithospheric mantle (SCLM) sources and/or contamination of asthenosphere-derived magmas by SCLM or crust.

The brevity (< 5 Ma) of the mafic magmatic pulse agrees with the transient nature of magmatism associated with slab break-off. The subsequent ca. 1 to 2 m.y. period of voluminous WPG and VAG plutonism likely reflects mafic magma-driven partial melting of both SCLM and crustal sources, respectively. Continuation of VAG-like magmatism for an additional 2 to 5 m.y. may reflect lower solidus temperatures of crustal materials, enabling anatexis to continue after mantle melting ceased. East to west spatial variation of ε_Nd and (La/Yb)_CN in Silurian plutons suggests a transition from shallow melting of juvenile sources proximal to the collision zone to deeper melting of old source materials in the garnet-stability field further inboard.

Previous work has demonstrated that geochemical discriminaton of post-collisional granitoid magmatism (PCGM) is difficult in the absence of other constraints. Our example should contribute to the understanding and identification of PCGM if it can be employed as a ‘fingerprint’ for slab break-off-related PCGM within the Paleozoic geological record.     

Study on collision avoidance in busy waterways by using AIS data

Due to high density of vessel traffic, busy waterways are water areas with high potential for collisions. The application of AIS makes it possible to investigate accurate and actual behavior of collision-involved ships, and benefits vessel traffic management and waterways design for these areas. As a case study, the authors focus on a Traffic Separation Scheme (TSS) off Rotterdam Port in Europe, and using AIS data, statistical analysis is made for collision involved ships. In order to identify the correlation of CPA, which is a key indicator for collision avoidance, with ship's size, speed, and course, linear regression models are developed. To assess risks, a dynamic method based on SAMSON is presented.     

Assessing landslide exposure in areas with limited landslide information

Landslide risk assessment is often a difficult task due to the lack of temporal data on landslides and triggering events (frequency), run-out distance, landslide magnitude and vulnerability. The probability of occurrence of landslides is often very difficult to predict, as well as the expected magnitude of events, due to the limited data availability on past landslide activity. In this paper, a qualitative procedure for assessing the exposure of elements at risk is presented for an area of the Apulia region (Italy) where no temporal information on landslide occurrence is available. Given these limitations in data availability, it was not possible to produce a reliable landslide hazard map and, consequently, a risk map. The qualitative analysis was carried out using the spatial multi-criteria evaluation method in a global information system. A landslide susceptibility composite index map and four asset index maps (physical, social, economic and environmental) were generated separately through a hierarchical procedure of standardising and weighting. The four asset index maps were combined in order to obtain a qualitative weighted assets map, which, combined with the landslide susceptibility composite index map, has provided the final qualitative landslide exposure map. The resulting map represents the spatial distribution of the exposure level in the study area; this information could be used in a preliminary stage of regional planning. In order to demonstrate how such an exposure map could be used in a basic risk assessment, a quantification of the economic losses at municipal level was carried out, and the temporal probability of landslides was estimated, on the basis of the expert knowledge. Although the proposed methodology for the exposure assessment did not consider the landslide run-out and vulnerability quantification, the results obtained allow to rank the municipalities in terms of increasing exposure and risk level and, consequently, to identify the priorities for designing appropriate landslide risk mitigation plans.     

Limits on the X-ray and optical luminosity of the progenitor of the Type Ia supernova 2007sr

We present Hubble Space Telescope ( HST )/Wide Field Planetary Camera 2 (WFPC2), Galaxy Evolution Explorer ( GALEX ) and Chandra observations of the position of the Type Ia supernova 2007sr in the Antennae galaxy, taken before the explosion. No source is found in any of the observations, allowing us to put interesting constraints on the progenitor luminosity. In total there is about 450 ks of Chandra data, spread over seven different observations. Limiting magnitudes of far-ultraviolet (FUV) (23.7 AB mag), near-ultraviolet (NUV) (23.8 AB mag), F555W (26.5 Vega mag) and F814W (24.5–25 Vega mag) are derived. The distance to the Antennae galaxy is surprisingly poorly known, with almost a factor of 2 difference between the latest distance based on the tip of the red giant branch (13.3 Mpc) and the distance derived from the 2007sr light curve (25 Mpc). Using these distances we derive limits on absolute optical and UV magnitudes of any progenitor but these are still above the brightest (symbiotic) proposed progenitors. From the Chandra data a 3σ upper limit to the X-ray luminosity of  0.5–8.0 × 10³⁷ erg s⁻¹  in the 0.3–1 keV range is found. This is below the X-ray luminosity of the potential progenitor of the Type Ia supernova 2007on that we recently discovered and for which we report a corrected X-ray luminosity. If that progenitor is confirmed it suggests the two supernovae have different progenitors. The X-ray limit is comparable to the brightest supersoft X-ray sources in the Galaxy, the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) and significantly below the luminosities of the brightest supersoft and quasi-soft X-ray sources found in nearby galaxies, ruling out such sources as progenitors of this Type Ia supernova.     

Digital mapping in structural geology — Examples from Namibia and Greece

Many problems in geology, especially structural geology, can only be solved by detailed mapping. Presently, mapping is still mainly carried out on paper using techniques from the 19^th Century. However, tools are now available to carry out most mapping tasks on microcomputers in the field without any need of paper. This speeds up geological mapping and reduces the errors involved in the mapping process. Digital mapping also allows work in featureless areas and areas of great structural complexity that would not be possible using paper maps. We present two practical examples of the new technology of digital mapping using microcomputers, from Namibia and Greece.     

Magmatic versus metamorphic origin of olivine-plagioclase coronas

An SEM, REE, and mineral Sm-Nd isotope study on olivine-plagioclase coronas in the Vestre Dale gabbro, Norway, was carried out in order to solve the temporal relationships within these coronas. It is demonstrated that in contrast to common models, corona formation is a multistage, late-magmatic process, starting with the formation of orthopyroxene by (partial) dissolution of olivine, followed by the nucleation and rapid outward growth of orthopyroxene+spinel symplectites at its outer margin, and concluded by replacement of this precursory outer shell by calcic amphibole. Isotopic equilibrium between inner shell orthopyroxene and the magmatic assemblage, and the REE contents of orthopyroxene and outer shell amphibole also provide strong arguments for a magmatic origin, with the local availability of fractionated magma acting as a limiting factor. The absence of replacement of intercumulus clinopyroxene by amphibole also favours a late stage magmatic rather than a metamorphic origin for corona amphibole.