Effect of Bioremediation on the Microbial Community in Oiled Mangrove Sediments

Bioremediation was conducted in the field on a mature Rhizophora stylosa mangrove stand on land to be reclaimed near Fisherman’s Landing Wharf, Gladstone Australia. Gippsland crude oil was added to six large plots (>40 m²) and three plots were left untreated as controls. Bioremediation was used to treat three oiled plots and the remaining three were maintained as oiled only plots. The bioremediation strategy consisted of actively aerating the sediment and adding a slow-release fertilizer in order to promote oil biodegradation by indigenous micro-organisms. Oil addition stimulated the numbers of alkane-degrading bacteria slightly to levels of 10⁴–10⁵/g sediment. Bioremediation of the oiled sediment had a marked effect on the alkane-degrading population, increasing the population size by three orders of magnitude from 10⁵ to 10⁸ cells/g of sediment. An effect of bioremediation on the growth of aromatic-degraders was detected with numbers of aromatic-degraders increasing from 10⁴ to 10⁶ cells/g of sediment. Active aeration and nutrient addition significantly stimulated the growth of hydrocarbon-degraders in oiled mangrove sediment in the field.     

The global oscillation network group site survey

The Global Oscillation Network Group (GONG) Project is planning to place a set of instruments around the world to observe solar oscillations as continuously as possible for at last three years. The Project has now chosen the sites that will comprise the network. This paper describes the methods of data collection and analysis that were used to make this decision.Solar irradiance data were collected with a one-minute cadence at fifteen sites around the world and analyzed to produce statistics of cloud cover, atmospheric extinction, and transparency power spectra at the individual sites. Nearly 200 reasonable six-site networks were assembled from the individual stations, and a set of statistical measures of the performance of the networks was analyzed using a principal component analysis. An accompanying paper presents the results of the survey.     

Silica-rich orthopyroxenite in the Bovedy chondrite

Abstract— A large (≥4.5 × 7 × 4 mm), igneous-textured clast in the Bovedy (L3) chondrite is notable for its high bulk SiO₂ content (57.5 wt%). The clast consists of normally zoned orthopyroxene (83.8 vol%), tridymite (6.2 %), an intergrowth of feldspar (5.8 %) and sodic glass (3.1 %), pigeonite (1.0 %), and small amounts of chromite (0.2 %), augite, and Fe, Ni-metal; it is best described as a silica-rich orthopyroxenite. The oxygen-isotopic composition of the clast is similar, but not identical, to Bovedy and other ordinary chondrites. The clast has a superchondritic Si/Mg ratio, but has Mg/(Mg + Fe) and Fe/Mn ratios that are similar to ordinary chondrite silicate. The closest chemical analogues to the clast are radial-pyroxene chondrules, diogenites, pyroxene-silica objects in ordinary chondrites, and silicates in the IIE iron meteorite Weekeroo Station. The clast crystallized from a siliceous melt that cooled fast enough to prevent complete attainment of equilibrium but slow enough to allow nearly complete crystallization. The texture, form, size and composition of the clast suggest that it is an igneous differentiate from an asteroid or planetesimal that formed in the vicinity of ordinary chondrites. The melt probably cooled in the near-surface region of the parent object. It appears that in the source region of the clast, metallic and silicate partial melt were largely-to-completely lost during a relatively low degree of melting, and that during a higher degree of melting, olivine and low-Ca pyroxene separated from the remaining liquid, which ultimately solidified to form the clast. While these fractionation steps could not have all occurred at the same temperature, they could have been accomplished in a single melting episode, possibly as a result of heating by radionuclides or by electromagnetic induction. Fractionated magmas can also account for other Si-rich objects in chondrites.     

Charged dust in the outer planetary magnetospheres

In this paper we consider the dynamics of the electrostatic disruption products of fragile interplanetary dust aggregates which are initially electrically charged on entering the Jovian plasmasphere. On account of their large specific charges, these small dust fragments are strongly effected both by the Lorentz electric force as well as by the polarization electric force resulting from the corotation of the Jovian plasmasphere. The detailed orbits of these charged dust fragments, which are shown to be confined to the equatorial plane, are computed for various launch angles. It is established that the fragments with radii typically around 1 are magneto-gravitationally trapped within the plasma sphere due to the velocity induced oscillation of their surface potentials. The spatial distribution of these fragments are evaluated and the time evolution of the distributions followed. On this basis it is argued that the distribution of micrometeoroid dust within the Jovian magnetospheres, observed by the Pioneer 10 and the recent Voyager spacecraft, is a result of this magneto-gravitational trapping and subsequent orbital evolution of these charged dust fragments. Our discussion includes both the sudden increase, by over an order of magnitude, of the micrometeoroid dust flux at about 30R _J observed by Pioneer 10, and the thin inner dust ring recently observed by the Voyaer spacecraft. The observed brightness asymmetries between the leading and trailing sides of the Galilean satellites appears to be a natural consequence of the impact geometries of these charged dust grains with the satellite surfaces.     

SiO and GeO bonded interactions as inferred from the bond critical point properties of electron density distributions

The topological properties of the electron density distributions for more than 20 hydroxyacid, geometry optimized molecules with SiO and GeO bonds with 3-, 4-, 6- and 8-coordinate Si and Ge cations were calculated. Electronegativities calculated with the bond critical point (bcp) properties of the distributions indicate, for a given coordination number, that the electronegativity of Ge (∼1.85) is slightly larger than that of Si (∼1.80) with the electronegativities of both atoms increasing with decreasing bond length. With an increase in the electron density, the curvatures and the Laplacian of the electron density at the critical point of each bond increase with decreasing bond length. The covalent character of the bonds are assessed, using bond critical point properties and electronegativity values calculated from the electron density distributions. A mapping of the (3, −3) critical points of the valence shell concentrations of the oxide anions for bridging SiOSi and GeOGe dimers reveals a location and disposition of localized nonbonding electron pairs that is consistent with the bridging angles observed for silicates and germanates. The bcp properties of electron density distributions of the SiO bonds calculated for representative molecular models of the coesite structure agree with average values obtained in X-ray diffraction studies of coesite and danburite to within ∼5%. Received: 18 August 1997 / Revised, accepted: 19 February 1998     

A map of the horizontal flows in the solar convection zone

The first map of the horizontal flows as a function of depth and heliocentric position in the solar convection zone is presented. The map is inferred from a least-squares smoothness-constrained inversion of velocities measured from ring diagrams of the solar p-mode oscillations. The data provide information in four longitude regions at a latitude just south of the solar equator. The presence of several features is suggested by the results: