A Donnan potential model for metal sorption onto Bacillus subtilis

In this study, we conducted electrophoretic mobility, potentiometric titration, and metal sorption experiments to investigate the surface charge characteristics of Bacillus subtilis and the electrostatic interactions between metal cations and the cell surface electric field. Electrophoretic mobility experiments performed as a function of pH and ionic strength show an isoelectric point of pH 2.4, with the magnitude of the electrokinetic potential increasing with increasing pH, and decreasing with increasing ionic strength. Potentiometric titration experiments conducted from pH 2.4 to 9 yield an average surface charge excess of 1.6 μmol/mg (dry mass). Corresponding cell wall charge density values were used to calculate the Donnan potential (Ψ_DON) as function of pH and ionic strength. Metal sorption experiments conducted with Ca(II), Sr(II), and Ba(II) exhibit strong ionic strength dependence, suggesting that the metal ions are bound to the bacterial cell wall via an outer-sphere complexation mechanism. Intrinsic metal sorption constants for the sorption reactions were determined by correcting the apparent sorption constant with the Boltzmann factor. A 1:2 metal-ligand stoichiometry provides the best fit to the experimental data with log K₂^int values of 5.9 ± 0.3, 6.0 ± 0.2, 6.2 ± 0.2 for Ca(II), Sr(II), and Ba(II) respectively. Electrophoretic mobility measurements of cells sorbed with Ca(II), Sr(II), and Ba(II) support the 1:2 sorption stoichiometry. These results indicate that electrical potential parameters derived from the Donnan model can be applied to predict metal binding onto bacterial surfaces over a wide range of pH and ionic strength conditions.     

Effects of sediment slurry enrichment on salt marsh rehabilitation: Plant and soil responses over seven years

In deltaic marshes, mineral sediment promotes positive elevation change and counters subsidence and sea level rise. In many such marshes sediment deficits result in wetland loss. One new way to address sediment deficiency is to supply marshes with sediments in a slurry that deposits the sediment in a thin layer over a large area. The long-term effects of this strategy are poorly understood. In a rapidly submerging,Spartina alterniflora salt marsh, we tested how different amounts of sediment ameliorated the effects of sea level rise and subsidence over 7 yr (1992–1998). Sediment slurry enrichment likely affected plants and soils by two mechanisms. It increased elevation and soil bulk density, leading to increased plant vigor and soil condition. These effects were long lasting, such that by 1998 areas receiving moderate amounts of sediment (5–12 cm relative elevation) had better plant vigor and soil condition compared to areas not receiving sediment (55% cover versus 20%; bulk densities of 0.4–1.0 g cm⁻³ versus 0.2 g cm⁻³; 0 mM hydrogen sulfide versus > 1.0 mM). The sediment slurry also had high nutrient content, which resulted in a pulse of growth, especially in areas receiving the most sediment (areas > 12 cm relative elevation initially had >90% cover and canopy heights >1.6 m). This nutrient-induced growth spurt was short lived and faded after 3 yr, at which point the long lasting effects of increased elevation probably became the dominant factor promoting plant vigor and soil condition. Moderate levels of sediment generated the most beneficial and long lasting effects to the vegetation and soils. This degree of sediment slurry addition countered the effects of subsidence and sea level rise, but not so much as to surpass the intertidal position to whichS. alterniflora is best adapted.     

The northern New Hebrides back-arc troughs: history and relation with the North Fiji basin

The New Hebrides back-arc troughs (southwest Pacific) are located between the New Hebrides trench-arc system and the active North Fiji marginal basin. They are restricted to the southern and northern segments of the arc and were generally related to effects of the Indo-Australian subducting plate (rolling-back and/or subduction of the d'Entrecasteaux ridge). A detailed bathymetric and magnetic survey over the northern back-arc troughs is used to propose a new model for the origin of the New Hebrides back-arc troughs. The northern troughs extend over a width of 60 km and are composed of N-S trending grabens and horsts, discontinuous along strike and associated with volcanism. The troughs are disrupted southward at 13° 30′S, where the Hazel Holme fracture zone intercepts the New Hebrides island arc. The E-W trending Hazel Holme fracture zone is an extensional feature bisecting the North Fiji basin. In its western end, the Hazel Hohne fracture zone is composed of a succession of horsts and grabens striking N90 ° –N100 ° E. Geometrical and structural relationships between the back-arc troughs and the Hazel Holme fracture zone suggest that both these extensional features result from the same process and are closely linked. The northern troughs-western end of the Hazel Holme fracture zone region is dominated by N130°–135°E trending magnetic lineations typical of oceanic crust. These lineations are oblique to the horsts and grabens systems, and are characteristic of the old North Fiji basin oceanic crust. Consequently we conclude that the northern back-arc troughs are partly developed on the North Fiji basin oceanic basement and that extensional tectonic processes postdate the oldest North Fiji basin oceanic crust. Morphological and structural evidence suggests that both the back-arc troughs and the Hazel Holme fracture zone are recent, still active and result from NE-SW extensional tectonics. Because other tectonic features throughout the North Fiji basin are related to the same stress field, it is inferred that such a NE-SW extension could be a large-scale deformation affecting the North Fiji basin. It is proposed that the back-arc troughs are primarily related to this recent extension within the North Fiji basin, but their locations along the arc are also influenced by the subduction of the d'Entrecasteaux ridge which produces, south of 13°30′S, nearly E-W trending compression and prevents the formation of troughs. Possibly, these recent extensional tectonic processes result from a major reorganization in the spreading process of the North Fiji basin, and could be as young as 0.6–0.7 Ma.     

Excrétion de carbone organique par le phytoplancton lémanique

The release of soluble organic carbon by the phytoplankton in the trophogenic layer of Lake Geneva has been investigated by¹⁴C method from March to November 1984. The carbon excretion rate varied from 0.01 to 0.5 mg C·m⁻³·h⁻¹ and depended primarily upon the rate of its photosynthetic assimilation. The carbon excretion rate varied generally between 2 and 5% of photoassimilated carbon and exceptionally exceeded 6%. These values were underestimated from part of heterotrophic reassimilation. The study of the carbon balance over 24 hours has shown that night excretion represents less than 10% of losses due to respiration. Heterotrophic activity measured by¹⁴C glucose assimilation exhibited seasonal variations following the same general pattern as excretion. The quantity of phytoplankton excretion products appeared to be superior to the needs in organic compounds of heterotrophic organisms in the trophogenic layer.      

Simple Spectrophotometric Determination of Ferrous Iron in Twelve French Geochemical Reference Standards

Iron (II) oxide in silicate rocks can readily be measured after digestion with HF and HCl by reaction with KI and KIO₃. The iodine produced during the digestion is trapped in CCl₄ and measured at 512 nm spectrophotometrically. Results for ten accepted and two new geochemical reference standards are presented.     

Dauphiné twinning and texture memory in polycrystalline quartz. Part 1: Experimental deformation of novaculite

Mechanical Dauphiné twinning in quartz has been of long-standing interest, both in single crystals and polycrystalline aggregates. This study investigates texture development in fine-grained quartz rock novaculite with no initial texture using compression experiments conducted in the Paterson gas apparatus to explore the influence of stress and temperature. Texture patterns are measured with time-of-flight neutron diffraction and hard synchrotron X-rays, analyzing diffraction data with the Rietveld method. Similar texture patterns are observed as described previously but the new results establish a profound influence of temperature and document that twinning initiates at stresses less than 50 MPa. Possibilities of using Dauphiné twinning as a paleopiezometer in quartz-bearing rocks are discussed.     

Characterization and Quantification of Uncertainty in?Coregionalization Analysis

Coregionalization analysis has been presented as a method of multi-scale analysis for multivariate spatial data. Despite an increasing use of this method in environmental and earth sciences, the uncertainty associated with the estimation of parameters in coregionalization analysis (e.g., sills and functions of sills) is potentially high and has not yet been characterized. This article aims to discuss the theory underlying coregionalization analysis and assess the robustness and limits of the method. A theoretical framework is developed to calculate the ergodic and fluctuation variance-covariance matrices of least-squares estimators of sills in the linear model of coregionalization. To adjust for the positive semidefiniteness constraint on estimated coregionalization matrices, a confidence interval estimation procedure for sills and functions of sills is presented. Thereafter, the relative importance of uncertainty measures (bias and variance) for sills and structural coefficients of correlation and determination is assessed under different scenarios to identify factors controlling their uncertainty. Our results show that the sampling grid density, the choice of the least-squares estimator of sills, the positive semidefiniteness constraint, the presence of scale dependence in the correlations, and the number and range of variogram models, all affect the level of uncertainty, sometimes through multiple interactions. The asymptotic properties of variogram model parameter estimators in a bounded sampling domain impose a theoretical limit to their accuracy and precision. Because of this limit, the uncertainty was found to be high for several scenarios, especially with three variogram models, and was often more dependent on the ratio of variogram range to domain extent than on the sampling grid density. In practice, in the coregionalization analysis of a real dataset, the circular requirement for sill estimates in the calculation of uncertainty measures makes the quantification of uncertainty very problematic, if not impossible. The use of coregionalization analysis must be made with due knowledge of the uncertainty levels and limits of the method.