A New Method for Low‐Temperature Decomposition of Chromites and Dichromium Trioxide using Bromic Acid Evaluated by Chromium Isotope Measurements

In recent years, routine application of the stable isotope determination of chromium (Cr) in environmental and health protection research has led to the search for simpler chromite decomposition techniques. As the range of Cr isotope abundance ratios in nature is very narrow, conventional chromite decomposition techniques are no longer suitable, due to the relatively high risk of contamination during laboratory procedures. We have developed a protocol for the decomposition of chromites based on oxidation by bromic acid at room temperature. The procedure takes 15 d and requires two doses of bromic acid during the reaction period (day 1 and 8), due to the limited stability of the reagent. Chromium extracted by alkaline oxidative fusion and by bromic acid decomposition yielded statistically indistinguishable δ⁵³Cr values, measured by multi‐collector inductively coupled plasma‐mass spectrometry following addition of a ⁵⁰Cr‐⁵⁴Cr double‐spike.     

Skin toxins in coral‐associated Gobiodon species (Teleostei: Gobiidae) affect predator preference and prey survival

Predation risk is high for the many small coral reef fishes, requiring successful sheltering or other predator defence mechanisms. Coral‐dwelling gobies of the genus Gobiodon live in close association with scleractinian corals of the genus Acropora. Earlier studies indicated that the low movement frequency of adult fishes and the development of skin toxins (crinotoxicity) are predation avoidance mechanisms. Although past experiments showed that predators refuse food prepared with goby skin mucus, direct predator–prey interactions have not been studied. The present study compares the toxicity levels of two crinotoxic coral gobies – Gobiodon histrio, representative of a conspicuously coloured species, and Gobiodon sp.3 with cryptic coloration – using a standard bioassay method. The results show that toxin levels of both species differ significantly shortly after mucus release but become similar over time. Predator preferences were tested experimentally in an aquarium in which the two gobies and a juvenile damselfish Chromis viridis were exposed to the small grouper Epinephelus fasciatus. Video‐analysis revealed that although coral gobies are potential prey, E. fasciatus clearly preferred the non‐toxic control fish (C. viridis) over Gobiodon. When targeting a goby, the predator did not prefer one species over the other. Contrary to our expectations that toxic gobies are generally avoided, gobies were often captured, but they were expelled quickly, repeatedly and alive. This unusual post‐capture avoidance confirms that these gobies have a very good chance of surviving attacks in the field due to their skin toxins. Nonetheless, some gobies were consumed: the coral shelter may therefore also provide additional protection, with toxins protecting them mainly during movement between corals. In summary, chemical deterrence by crinotoxic fishes seems to be far more efficient in predation avoidance than in physical deterrence involving body squamation and/or strong fin spines.     

Seismic hazard in the Northwestern Apennines

A study of the seismic hazard for the Northwestern Apennines, based on seismotectonic and seismicity data, is presented. Starting from a seismotectonic analysis, showing the complex structural evolution of the region, the seismic activity in the period 1000–1975 has been modeled by some seismic source zones justified by geostructural and seismological considerations. The recurrence statistical parameters and the attenuation laws have been determined for all these sources. With an appropriate analysis method, maps of seismic hazard for return periods of 50, 200, and 500 years were elaborated. Finally, a comparison with the map of maximum felt intensity and with hazard values calculated by a different approach is presented.     

The 8.2 ka event: Evidence for seasonal differences and the rate of climate change in western Europe

Recent studies have drawn attention to differences in the seasonal impact of the 8.2 ka event, with longer cooler summers and shorter cooler/drier winters. However, there are no data available on the simultaneity or the rate of onset of the seasonal changes in Europe. Based on the microfacies and geochemical analyses of seasonally laminated varved sediments from Holzmaar, we present evidence of differences in duration and onset time of changes in summer temperature and winter rainfall during the 8.2 ka event. Since both summer and winter climate signals are co-registered within a single varve, there can be no ambiguity about the phasing and duration of the signals. Our data show that the onset and withdrawal of the 8.2 ka summer cooling occurred within a year, and that summer rains were reduced or absent during the investigated period. The onset of cooler summers preceded the onset of winter dryness by ca. 28 years. In view of the differences in nature and duration of the impact of the 8.2 ka event we suggest that a clearer definition of the 8.2 ka event (summer cooling or winter cooling/dryness) needs to be developed. Based on regional comparison and available modelling studies we also discuss the roles of solar variability, changes in North Atlantic Thermohaline circulation, and North Atlantic Circulation (NAO) during the period under consideration. Wavelet analyses of seasonal laminae indicates that the longer NAO cycles, linked to changes in the N. Atlantic temperatures, were more frequent during the drier periods.     

Climatic and oceanographic changes in the Northeast Atlantic reflected by magnetic properties of sediments deposited on the Portuguese Margin during the last 340 ka

Rock magnetic parameters measured along two giant piston cores MD95-2040 (40°34′N, 9°51′W) and MD95-2042 (37°47′N, 10°09′W) collected off the Portuguese Margin, related to other proxy-climatic data, have been used to reconstruct magnetic mineralogical changes of, in relation to environmental and climatic conditions over the North Atlantic, Western Europe and Northwest Africa during the last three climatic cycles (since isotope stage 10). Thin discrete layers containing coarse grains of titano-magnetite are associated with events of iceberg discharge during Heinrich events 1-6 [Heinrich, Quat. Res. 29 (1988) 142] that have equivalent events in isotope stages 5-8. Concentrations of fine-grained (Ti-) magnetite and hematite/goethite, varying in phase opposition, are directly linked with alternations of cold and warm climatic periods. Spectral analyses of the rock magnetic signals reveal Milankovitch periods at 100 and 41 ka, confirming the relationship with long-term climatic changes at high latitudes. The nature (Ti-magnetite) and size range of the finest ferrimagnetic fraction as well as its variation, suggest a control by deep currents carrying a colloidal/clayey fraction from remote sources (Iceland, Faeroes, mid-Atlantic Ridge). Variation of hematite/goethite contents is linked with transport by rivers and winds from the neighbouring continent. A tight correlation with the D-O cycles in Greenland ice records confirms that North Atlantic oceanic regimes and continental wind regimes were strongly influenced by millennial scale climatic changes throughout the last 350 ka.     

Coupling of a Column System with ICP‐MS for the Characterisation of Colloid‐mediated Metal(loid) Transport in Porous Media

In this work a coupling method for the characterisation of colloid‐mediated transport of the metal(loid) species in porous media was developed. For this transport experiments quartz sand was used as column packing material and the synthetic three‐layer clay mineral laponite as model colloid. The determination of colloids was conducted by means of UV detection. The quantification of the metal(loid) ions was carried out in two different ways: (1) The fractions collected at the column outlet were analysed with an inductively coupled plasma mass spectrometer (ICP‐MS) (offline measurements); (2) the column system was directly coupled with ICP‐MS (online measurements). In the column experiments the influence of laponite colloids on the transport of Cu, Pb, Zn, Pt and As species was investigated. In the offline experiments as a consequence of dilution during sample preparation no metal(loid) species at the column outlet could be found. Unlike this the breakthrough of all metal(loid)s could be detected under the same experimental column conditions in the coupling experiments. This coupling technique offers the online detection of the metal species and colloidal particles with high resolution even at low concentrations and without any time‐consuming preparation. The coupling experiments have shown that the laponite particles accelerate the transport of the cationic metals. For anionic metal(loid) species no influence of laponite on their transport behaviour was found.     

A transport‐distance approach to scaling erosion rates: 3. Evaluating scaling characteristics of Mahleran

In the two previous papers of this series, we demonstrated how a novel approach to erosion modelling (Mahleran – Model for Assessing Hillslope‐Landscape Erosion, Runoff And Nutrients) provided distinct advantages in terms of process representation and explicit scaling characteristics when compared with existing models. A first evaluation furthermore demonstrated the ability of the model to reproduce spatial and temporal patterns of erosion and their particle‐size characteristics on a large rainfall‐simulation plot. In this paper, we carry out a more detailed evaluation of the model using monitored erosion events on plots of different size. The evaluation uses four plots of 21·01, 115·94, 56·84 and 302·19 m², with lengths of 4·12, 14·48, 18·95 and 27·78 m, respectively, on similar soils to the rainfall‐simulation plot, for which runoff and erosion were monitored under natural rainfall. Although the model produces the correct ranking of the magnitude of erosion events, it performs less well in reproducing the absolute values and particle‐size distributions of the eroded sediment. The implications of these results are evaluated in terms of requirements for process understanding and data for parameterization of improved soil‐erosion models. We suggest that there are major weaknesses in the current understanding and data underpinning existing models. Consequently, a more holistic re‐evaluation is required that produces functional relationships for different processes that are mutually consistent, and that have appropriate parameterization data to support their use in a wide range of environmental conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Flow cytometry and conventional enumeration of microorganisms in ships' ballast water and marine samples

Conventional methods for bacteriological testing of water quality take long periods of time to complete. This makes them inappropriate for a shipping industry that is attempting to comply with the International Maritime Organization's anticipated regulations for ballast water discharge. Flow cytometry for the analysis of marine and ship's ballast water is a comparatively fast and accurate method. Compared to a 5% standard error for flow cytometry analysis the standard methods of culturing and epifluorescence analysis have errors of 2-58% and 10-30%, respectively. Also, unlike culturing methods, flow cytometry is capable of detecting both non-viable and viable but non-culturable microorganisms which can still pose health risks. The great variability in both cell concentrations and microbial content for the samples tested is an indication of the difficulties facing microbial monitoring programmes. The concentration of microorganisms in the ballast tank was generally lower than in local seawater. The proportion of aerobic, microaerophilic, and facultative anaerobic microorganisms present appeared to be influenced by conditions in the ballast tank. The gradual creation of anaerobic conditions in a ballast tank could lead to the accumulation of facultative anaerobic microorganisms, which might represent a potential source of pathogenic species.