Spatial distribution and content of soil organic matter in an agricultural field in eastern Canada,as estimated from geostatistical tools

Soil erosion induces soil redistribution within the landscape and thus contributes to the spatial variability of soil quality. This study complements a previous experimentation initiated by the authors focusing on soil redistribution as a result of soil erosion, as indicated by caesium‐137 (¹³⁷Cs) measurements, in a small agricultural field in Canada. The spatial variability of soil organic matter (SOM) was characterized using geostatistics, which consider the randomized and structured nature of spatial variables and the spatial distribution of the samples. The spatial correlation of SOM (in percentages) patterns in the topsoil was established taking into account the spatial structure present in the data. A significant autocorrelation and reliable variograms were found with a R² ≥ 0·9, thus demonstrating a strong spatial dependence. Ordinary Kriging (OK) interpolation provided the best cross validation (r² = 0·35). OK and inverse distance weighting power two (IDW2) interpolation approaches produced similar estimates of the total SOM content of the topsoil (0–20 cm) of the experimental field, i.e. 211 and 213 tonnes, respectively. However, the two approaches produced differences in the spatial distribution patterns and the relative magnitude of some SOM content classes. The spatialization of SOM and soil redistribution variability – as evidenced by ¹³⁷Cs measurements – is a first step towards the assessment of the impact of soil erosion on SOM losses to recommend conservation measures. Copyright © 2009 John Wiley & Sons, Ltd.     

Factors controlling the lengths of channel-fed lava flows

Factors which control lava flow length are still not fully understood. The assumption that flow length as mainly influenced by viscosity was contested by Walker (1973) who proposed that the length of a lava flow was dependent on the mean effusion rate, and by Malin (1980) who concluded that flow length was dependent on erupted volume. Our reanalysis of Malin's data shows that, if short duration and tube-fed flows are eliminated, Malin's Hawaiian flow data are consistent with Walker's assertion. However, the length of a flow can vary, for a given effusion rate, by a factor of 7, and by up to 10 for a given volume. Factors other than effusion rate and volume are therefore clearly important in controlling the lengths of lava flows. We establish the relative importance of the other factors by performing a multivariate analysis of data for recent Hawaiian lava flows. In addition to generating empirical equations relating flow length to other variables, we have developed a non-isothermal Bingham flow model. This computes the channel and levee width of a flow and hence permits the advance rates of flows and their maximum cooling-limited lengths for different gradients and effusion rates to be calculated. Changing rheological properties are taken into account using the ratio of yield strength to viscosity; available field measurements show that this varies systematically from the vent to the front of a lava flow. The model gives reasonable agreement with data from the 1983–1986 Pu'u Oo eruptions and the 1984 eruption of Mauna Loa. The method has also been applied to andesitic and rhyolitic lava flows. It predicts that, while the more silicic lava flows advance at generally slower rates than basaltic flows, their maximum flow lengths, for a given effusion rate, will be greater than for basaltic lava flows.     

Which variables are essential for renewable energies?

ABSTRACT

Essential Variables are defined as a minimal set of variables that explain the state of the system. They are crucial for predicting its developments, and support metrics that measure its evolution. The variables should be relevant to meet requirements of stakeholders and be technically and economically feasible for systematic observation. A definition of Essential Renewable Energies Variables is proposed linked with their identification in several domains in renewable energy using a bottom-up and user-driven approach, and spanning over several years of documented interaction with stakeholders. Lists of variables are proposed in hydropower, solar, wind, and marine energies. It does not comprise the variables relating to social and economic aspects supporting decision making in investment nor those relating to civil engineering that are needed to erect a plant or farm.     

Cellular energy allocation in the Arctic sea ice amphipod Gammarus wilkitzkii exposed to the water soluble fractions of oil

Increasing offshore oil and gas activities in the European Arctic has raised concerns of the potential anthropogenic impact of oil-related compounds on the polar marine ecosystem. We measured cellular energy allocation (CEA) in the sea ice amphipod Gammarus wilkitzkii after exposure for one month to the water soluble fraction (WSF) of oil. The CEA biomarker measures the energy budget of organisms by biochemically assessing changes in carbohydrates, protein and lipid content as well as the electron transport system activity. A significantly higher protein content was observed in the medium dose compared to controls, while the total energy budget was not affected in G. wilkitzkii. This indicates that parts of the energy budget of G. wilkitzkii, which is a key species in the Arctic ecosystem, is affected by a WSF of oil.     

Stability of lysosomal and cell membranes in haemocytes of the common mussel (Mytilus edulis): effect of low temperatures.

Expanding industrial activities in the Arctic require an urgent assessment of the toxicity of chemicals at low temperatures. Organisms acclimatized to low temperature exhibit specific adaptations. For example, the amount of unsaturated lipids is increased to maintain the fluidity of the cell membranes. It has been hypothesized that such temperature-induced alterations in membrane lipid composition may affect the stability of lysosomal and cell membranes in the common mussel, Mytilus edulis, an organism exposed to seasonal temperature extremes. As mussels may be exposed to petroleum compounds along industrialized coastlines, we tested the combined effects of exposure to low temperature and the petroleum compound, phenanthrene, on haemocyte membrane stability. Test animals, acclimated to either 0 or 10 degrees C, were exposed to phenanthrene (0 = control or 500 micrograms l-1) and haemocytes were examined using the neutral red retention assay (lysosomal stability) and a fluorescence assay (cell membrane stability). At 0 degree C, lysosomal and cell membranes from uncontaminated mussels were destabilized compared with 10 degrees C (P = 0.0005). No significant effects (P > 0.05) of phenanthrene were detected at either temperature. Possible mechanisms underlying membrane destabilization include a weaker physical resistance of the membrane due to a higher amount of unsaturated lipids, a potentially higher level of reactive oxygen radicals at low temperature and the higher susceptibility of unsaturated lipids to oxidative stress. More work is required to better understand the consequences of this membrane destabilization at low temperature on the susceptibility of the organism to pollutants.     

Chronological and geochemical study of lavas from the Chaîne des Puys,Massif Central,France: Evidence for crustal contamination

Datations of ancient lavas from the Chaîne des Puys through the ²³⁰Th-²³⁸U radioactive disequilibrium method confirm the eruption of several basaltic or slightly differentiated lavas around 40,000 years ago. The study of (²³⁰Th/²³²Th)₀ initial ratios of these lava flows clearly demonstrates the influence of a crustal contamination of magmas superimposed to crystal fractionation. This contamination probably affects many trace elements, in particular, U, Th and Sr. A model based on the (²³⁰Th/²³²Th)₀ initial ratio variations of non-contaminated lavas permits to consider that the first eruptions in the Chaîne des Puys could have occurred about 100,000 years ago.     

Igneous scapolite-bearing associations in the Chaîne des Puys,Massif Central (France) and Atakor (Hoggar,Algeria)

A scapolite+amphibole+clinopyroxene+Fe-Ti oxide+apatite association has been found as megacrysts in tephra from the Enval-Volvic volcanic line, east of the Chaîne des Puys (Massif Central, France) and in the cinder cone of the Segueïka volcano (Atakor, Algeria). In both kinds, lavahosts are basanites. Although never seen together in a single xenolith, a study of their inclusions indicates close genetic relationship between all 5 phases. This association must be considered as a paragenesis that crystallized within a narrow PT range. Volcanological, petrological and geochemical data suggest that these megacrysts are high-pressure phenocrysts rather than mechanically desintegrated fragments derived from coarse rocks. The composition of the amphibole suggests a pressure between 5 and 15 kb; Fe-Ti oxides imply a temperature close to 1,100° C.Crystallization of sulfur-rich scapolite involves a high fSO₃, and therefore a high fO₂, remarkable for such relatively undifferenciated alkalic magmas. Coexisting Fe-Ti oxides indicate a fO₂ close to 10^–6 bar. Such conditions imply that H₂O was a major component of the gaseous phase. This high water content can be explained in terms of derivation from an hydrated upper mantle source. This is in agreement with other petrological evidences indicating that the basic magmas of the Massif Central crystallized under high fSO₃ conditions.     

Effects of industrial outfalls on tropical macrobenthic sediment communities in Reunion Island (Southwest Indian Ocean)

Temporal changes in the composition of soft bottom macrobenthic assemblages at Reunion Island (Southwest Indian Ocean) were studied in the context of a long-term environmental monitoring programme studying the impacts of effluents of industrial sugar cane refineries that are transferred to shallow and deep coastal environments by different pathways: surface discharge and deep underground injection. Seven stations (between 20 and 160 m depth) were surveyed between 1994 and 2003 on the industrial zone. One additional station was surveyed on a reference site. Spatio-temporal changes in the composition of macrobenthic communities were assessed using several diversity indices, ABC curves, MDS and associated ANOSIM tests and biotic indices. Among the 171 taxa recorded, polychaetes were dominant (89 species), followed by crustaceans and molluscs. The analysis of spatial changes in the composition of macrobenthos showed the existence of distinct benthic communities along the depth gradient. Temporal changes in macrobenthos composition were most prominent at the shallowest station. They mainly corresponded to the decline of several initially dominant taxa and the increase of the Eunicid polychaete Diopatra cuprea. This station further showed increasing macrofaunal abundance, biomass and sediment organic content over time, concomitant with decreasing sediment grain sizes. In deeper environments, temporal changes were much smaller. Macrofaunal abundance and species richness increased progressively, suggesting a moderate impact on benthic ecosystems resulting from slight enrichments due to effluents rich in organic matter. Our results highlight an original response to disturbance pattern involving opportunistic Eunicidae species (D. cuprea) not previously described. Moreover, they allow for the comparison of the impact on macrofauna caused by industrial effluents exported by two distinct and different pathways in a tropical coastal high-energy marine environment.     

Pyroclast loss or retention during explosive volcanism on asteroids: Influence of asteroid size and gas content of melt

Abstract– We review the conditions under which explosive volcanism took place on early‐forming differentiated asteroids. The pressure‐dependent solubility of typical asteroid volatiles in melts implies that the gas driving explosive volcanism on asteroids less than approximately 100 km in diameter was probably present mainly as a free phase capable of accumulating into large gas bodies and, thus, causing slug flow in melts approaching the surface. In contrast, in asteroids larger than approximately 100 km the gas was probably present largely as a dispersion of small bubbles. We show that these gas distributions have implications for the size distribution of the pyroclastic droplets produced in explosive eruptions at the surface. All pyroclastic melt droplets are accelerated by the expanding gases, but their speeds lag the gas speed by a finite amount that is a function of the droplet size and density and the asteroid size and, hence, acceleration due to gravity. We compute pyroclast speeds and, by comparing them with escape velocities, we identify the critical pyroclast diameter on a given‐size asteroid that distinguishes droplets lost to space from droplets that return to the surface. Identification of asteroidal pyroclasts and measurements of their sizes could throw light on the amounts of gas driving eruptions.     

Relationships between pressure, volatile content and ejecta velocity in three types of volcanic explosion

Consideration of the energy equation for a flowing compressible fluid shows that the so-called modified Bernoulli equation, commonly used to relate ejects velocity to pre-explosion pressure in vulcanian-style volcanic explosions, is inadequate in almost all circumstances because of its neglect of the detailed role of volatiles in explosive eruptions.The physical differences between three common types of explosive volcanic activity, typified by plinian, strombolian and vulcanian events, are reviewed and simple mathematical models are proposed for them. The models relate velocities of ejects to initial pressures at the start of an explosive phase and to mass fractions of volatiles (generally taken to be water) in the explosion products. When fitted to observed ejects velocities (or velocities deduced from the dispersal of debris) up to 500 m/s the models predict pressures up to 300 bars — almost always much lower than those deduced in earlier treatments.