Assessing degradation capability of aerobic indigenous microflora in PAH-contaminated brackish sediments

A study was conducted to determine polycyclic aromatic hydrocarbons (PAHs) distribution and microbial population changes in brackish sediments from an Italian lagoon included in the Ramsar List of Wetlands of International Importance. The presence and level of PAH-degrading bacteria were estimated by the most probable number (MPN) enumeration technique, whereas degradation capability towards target compounds was checked against loss of spiked PAHs (Phenanthrene, Anthracene and Fluoranthene) in MPN tubes after incubation in optimal conditions. Chemical analyses and microbiological counts suggested a potential for PAHs biodegradation by natural occurring populations of sediment microorganisms, thus indicating an "optimal range" in sediment PAHs concentrations, outside of which the natural selection of the indigenous microflora did not occur. The MPN procedure here described, provided an effective and reliable way to simultaneously determine microbial population densities and subsequent confirmation of the biodegradation capability of sediment indigenous microflora when exposed to laboratory and environmental concentrations of PAHs.     

Microhabitat preferences and depth distribution of combtooth blennies (Blenniidae) in the Gulf of Trieste (North Adriatic Sea)

The microhabitat preferences and depth distribution of blenniid species (Blenniidae) in the Gulf of Trieste (North Adriatic Sea) were surveyed using the all‐occurrence sampling method, a non‐destructive visual census method, aided by SCUBA diving. Fourteen species were identified during the entire survey. Four species showed to be indiscriminate in their microhabitat choice while 10 species were classified as infrequent in the surveyed coastal area. A statistically significant correlation was found between the blenniid assemblage and nine microhabitat variables. The blenniid assemblage was divided in two main groups, by the use of canonical correspondence analysis, electivity index, and the depth distribution analysis. The first group comprises species that dwell in surface waters and show a high positive correlation with boulders, the presence of Mytilus galloprovincialis, cirripeds and empty holes bored by Lithophaga lithophaga. The second group includes species that mostly inhabit deeper waters and show a high positive correlation with rocks covered by precoralligenous bioformations.     

Sources and biogeochemical cycling of particulate selenium in the San Francisco Bay estuary

As part of a study of estuarine selenium cycling, we measured the concentration, chemical form (speciation), and distribution of particulate selenium under various river flow conditions in the North San Francisco Bay (from the Golden Gate to the Sacramento and San Joaquin Rivers). We also conducted laboratory studies on the accumulation of selenium by phytoplankton, the critical first step in the transformation of dissolved to particulate selenium. Total particulate selenium concentration in the North SF Bay was relatively constant between high and low flow periods, ranging spatially from 0.05 to 0.35 nmol l⁻¹ and comprising between 5 and 12% of the total water column selenium inventory. Mean concentrations were generally highest in the Carquinez Strait–Suisun Bay region (salinity 0–17) and lowest in Central Bay. However, selenium content of suspended particles varied with river flow, with higher content during low flow (9.76 ± 4.17 nmol g⁻¹; mean ± sd; n = 67) compared to high flow (7.10 ± 4.24 nmol g⁻¹; n = 39). Speciation analyses showed that most particulate selenium is organic selenide (45 ± 27%), with a smaller proportion (typically <30%) of adsorbed selenite + selenate and a varying proportion (35 ± 28%) of elemental selenium. Based on the amount of elemental selenium in the seston (total suspended material), we calculate that resuspension of estuarine sediments could contribute 29–100% of particulate selenium in the water column. While selenium content of SF Bay seston (>0.4 μm) is relatively unenriched compared to phytoplankton (13.6–155 nmol g⁻¹ dry weight) on a mass basis, when normalized to carbon or nitrogen, seston contains a similar selenium concentration to SF Bay sediments or phytoplankton cultures. SF Bay seston is thus comprised of selenium-rich phytoplankton and phyto-detritus, but also inorganic clay mineral particles that effectively “dilute” total particulate selenium. Selenium concentrations in algal cultures (11 species) exposed to 90 nmol l⁻¹ selenite show relatively large differences in selenium accumulation, with the diatoms, chlorophytes and cryptophytes generally having lower selenium cell content (3.8 ± 2.7 × 10⁻⁹ nmol selenium cell⁻¹) compared to the dinoflagellates (193 ± 73 × 10⁻⁹ nmol selenium cell⁻¹). Because phytoplankton are such a rich (but variable) source of selenium, their dynamics could have a profound effect on the particulate selenium inventory in the North SF Bay.     

Détection des cavités à l'aide de mesures électriques et du géoradar dans une galerie d'amenée d'eau

Old water-delivery tunnels can become leaky and produce water losses of some economic importance. The detection of solution cavities behind the concrete lining was the purpose of an investigation in a 2 km long part of a water-delivery tunnel in Switzerland. A gypsum zone of about 700 m length was considered to be especially critical. Two geophysical methods were used at the same time: resistivity profiling with three different array lengths, and ground-penetrating radar. The cavities were characterized by higher electrical resistivity, principally for the short array (AB = 3 m). Detailed measurements with a pole-dipole array were made for a better depth interpretation of anomalies in some critical zones. The GPR investigations were made with an antenna of 500 MHz. Some transverse profiles were carried out with GPR in order to better delineate the discovered cavernous or weathered zones. GPR located cavities up to a few meters in length, at depths between 0 and 4 m behind the lining. Anomalies found by one investigation method were often confirmed by the other one. Their complementarity thus allowed a more reliable interpretation of the gathered data. Verifying drillholes have mostly confirmed the good correlation between geophysical interpretation and drilling results. Endoscopic investigations in the drillholes enabled us to have a real vision of discovered cavities.Although GPR-profiling has the advantage of a continuous underground imaging and of greater efficiency during data acquisition (investigation speed) we consider the combination of both methods in the present study as a good example of an integrated geophysical survey, which enables a more reliable interpretation of the gathered data.

Résumé

Les galeries d'amenée d'eau d'un certain âge peuvent poser des problèmes à cause de pertes d'eau parfois importantes. L'objectif de cette étude a été la mise en évidence et le positionnement de cavités derrière le revêtement d'une galerie en Suisse, sur une longueur de 2 km. Une zone de gypse longue de 700 m était considérée comme particulièrement critique. Deux méthodes géophysiques ont été conjointement utilisées: le traîné électrique multiple avec trois longueurs de ligne d'envoi de courant et le géoradar. Les cavités, caractérisées par des résistivités élevées, ont surtout été mises en évidence par le dispositif le plus court (AB = 3 m). Des mesures de détail ont été réalisées dans les zones critiques avec un dispositif pôle-dipôle en vue d'une meilleure interprétation des anomalies en profondeur. Les mesures de géoradar ont été exécutées avec une antenne de 500 MHz. Quelques profils transversaux ont été effectués pour vérifier l'extension des zones d'altérations ou des cavités. Le géoradar a pu localiser des cavités mesurant jusqu'à plusieurs mètres en longueur à des profondeurs variant entre 0 et 4 m derrière le revêtement de la galerie. Les anomalies décelées par une méthode ont souvent pu être confirmées par l'autre et leur complémentarité a permis une interprétation plus sûre. Des forages carottés ont montré une bonne corrélation entre les anomalies géophysiques et la réalité. Des mesures de fibroscopie dans les forages nous ont permis de déterminer la géométrie des cavités.Le géoradar possède des avantages certains: imagerie continue du massif rocheux et grande rapidité dans l'acquisition des données. Néanmoins, nous considérons la combinaison des deux méthodes utilisées dans cette étude comme le bon exemple d'une investigation géophysique combinée permettant une interprétation optimale de tous les résultats.     

A rationale for beach selection by the public on the coast of Wales, UK

Questionnaires were completed by 2306 beach users at 19 Welsh beaches with respect to beach selection parameters. The modal group of respondents was female aged 30–39. Beach choice was primarily determined by clean litter-free sand and seawater, followed by safety. Refreshment facilities and beach awards were deemed minor considerations by the public when choosing a beach to visit. Approximately 58 per cent of respondents were aware of beach award and rating schemes. Of coastal visitors interviewed for this paper, 67 per cent rated a beach as 'important' or 'very important' to their holiday, with just 2 per cent replying that they were unimportant.     

Argon isotope fractionation induced by stepwise heating

Noble gas isotopes are widely used to elucidate the history of the rocks in which they have been trapped, either from distinct reservoirs or by accumulation following radioactive decay. To extract noble gases from their host rocks, stepwise heating is the most commonly used technique to deconvolve isotopically different components, e.g., atmospheric, in situ radiogenic, or excess radiogenic from mantle or crustal reservoirs. The accurate determination of the isotopic composition of these different components is of crucial importance, e.g., for ages obtained by ⁴⁰Ar-³⁹Ar stepheating plateaus. However, diffusion theory-based model calculations predict that the stepwise thermal extraction process from mineral phases induces isotope fractionation and, hence, adulterates the original composition. Such effects are largely unconsidered, as they are small and a compelling experimental observation is lacking. We report the first unequivocal evidence for significant mass fractionation of argon isotopes during thermal extraction, observed on shungite, a carbon-rich Precambrian sedimentary rock. The degree of fractionation, as monitored by ³⁸Ar/³⁶Ar and ⁴⁰Ar/³⁶Ar ratios, very well agrees with theoretical predictions assuming an inverse square root dependence of diffusion coefficient and atomic mass, resulting in easier extraction of lighter isotopes. Hence, subatmospheric ⁴⁰Ar/³⁶Ar ratios obtained for argon extracted at low temperatures may not represent paleoatmospheric argon. Shungite argon resembles modern atmospheric composition, but constraints on the timing of trapping appear difficult to obtain, as shungites are multicomponent systems.In ⁴⁰Ar-³⁹Ar stepwise heating, the isotope fractionation effect could cause systematic underestimations of plateau ages, between 0.15 and 0.4% depending on age, or considerably higher if samples contain appreciable atmospheric Ar. The magnitude of this effect is similar to the presently achieved uncertainties of this increasingly precise dating technique. Our results also indicate the importance of thermally activated diffusion as a possible fractionation mechanism, e.g., for hydrothermal gas exhalations, or for carbonaceous carrier phases such as “Q” in meteorites that have been suggested as carriers of highly fractionated noble gas residues from the early solar nebula.     

Forecasting rock slope failure: how reliable and effective are warning systems?

Warning systems are increasingly applied to reduce damage caused by different magnitudes of rockslides and rockfalls. In an integrated risk-management approach, the optimal risk mitigation strategy is identified by comparing the achieved effectiveness and cost; estimating the reliability of the warning system is the basis for such considerations. Here, we calculate the reliability and effectiveness of the warning system installed in Preonzo prior to a major rockfall in May 2012. “Reliability” is defined as the ability of the warning system to forecast the hazard event and to prevent damage. To be cost-effective, the warning system should forecast an event with a limited number of false alarms to avoid unnecessary costs for intervention measures. The analysis shows that to be reliable, warning systems should be designed as fail-safe constructions. They should incorporate components with low failure probabilities, high redundancy, have low warning thresholds, and additional control systems. In addition, the experts operating the warning system should have limited risk tolerance. In an additional hypothetical probabilistic analysis, we investigate the effect of the risk attitude of the decision makers and of the number of sensors on the probability of detecting the event and initiating a timely evacuation, as well as on the related intervention cost. The analysis demonstrates that quantitative assessments can support the identification of optimal warning system designs and decision criteria.     

Towards new applications of underwater photogrammetry for investigating coral reef morphology and habitat complexity in the Myeik Archipelago,Myanmar

Photogrammetry represents a non-destructive, cost-effective tool for coral reef monitoring, able to integrate traditional remote sensing techniques and support researchers’ work. However, its application to submerged habitats is still in early stage. We present new ways to employ Structure from Motion techniques to infer properties of reef habitats. In particular, we propose the use of Digital Surface Models and Digital Terrain Models for assessing coral colonies extension and height and discriminating between seabed and coral cover. Such information can be coupled with digital rugosity estimates to improve habitat characterization. DTM, DSM and orthophotos were derived and used to compute a series of metrics like coral morphologies, reef topography, coral cover and structural complexity. We show the potentialities offered by underwater photogrammetry and derived products to provide useful basic information for marine habitat mapping, opening the possibility to extend these methods for large-scale assessment and monitoring of coral reefs.     

Using Clustered Heat Maps in Mineral Exploration to Visualize Volcanic-Hosted Massive Sulfide Alteration and Mineralization

Natural Resources Research - This study proposes an extension of a visualization approach common in biochemistry (the clustered heat maps—CHMs) to geochemical data with the main objective of...