Sorption-desorption kinetics and toxic cell concentration in marine phytoplankton microalgae exposed to Linear Alkylbenzene Sulfonate

Linear Alkylbenzene Sulfonates (LAS) are ubiquitous surfactants. Traces can be found in coastal environments. Sorption and toxicity of C₁₂-LAS congeners were studied in controlled conditions (2-3500 μg C₁₂LAS/L) in five marine phytoplanktonic species, using standardized methods. IC₅₀ values ranged from 0.5 to 2 mg LAS/L. Sorption of ¹⁴C₁₂-6 LAS isomer was measured at environmentally relevant trace levels (4 μg/L) using liquid scintillation counting. Steady-state sorption on algae was reached within 5 h in the order dinoflagellate > diatoms > green algae. The sorption data, fitted a L-type Freundlich isotherm, indicating saturation. Desorption was rapid but a low LAS fraction was still sorbed after 24 h. Toxic cell concentration was 0.38 ± 0.09 mg/g for the studied species. LAS toxicity results from sorption on biological membranes leading to non-specific disturbance of algal growth. Results indicate that LAS concentrations in coastal environments do not represent a risk for these organisms.     

Towards a comprehensive approach to parameter estimation in land surface parameterization schemes

In climate models, the land–atmosphere interactions are described numerically by land surface parameterization (LSP) schemes. The continuing improvement in realism in these schemes comes at the expense of the need to specify a large number of parameters that are either directly measured or estimated. Also, an emerging problem is whether the relationships used in LSPs are universal and globally applicable. One plausible approach to evaluate this is to first minimize uncertainty in model parameters by calibration. In this paper, we conduct a comprehensive analysis of some model diagnostics using a slightly modified version of the Simple Biosphere 3 model for a variety of biomes located mainly in the Amazon. First, the degree of influence of each individual parameter in simulating surface fluxes is identified. Next, we estimate parameters using a multi‐operator genetic algorithm applied in a multi‐objective context and evaluate simulations of energy and carbon fluxes against observations. Compared with the default parameter sets, these parameter estimates improve the partitioning of energy fluxes in forest and cropland sites and provide better simulations of daytime increases in assimilation of net carbon during the dry season at forest sites. Finally, a detailed assessment of the parameter estimation problem was performed by accounting for the decomposition of the mean squared error to the total model uncertainty. Analysis of the total prediction uncertainty reveals that the parameter adjustments significantly improve reproduction of the mean and variability of the flux time series at all sites and generally remove seasonality of the errors but do not improve dynamical properties. Our results demonstrate that error decomposition provides a meaningful and intuitive way to understand differences in model performance. To make further advancements in the knowledge of these models, we encourage the LSP community to adopt similar approaches in the future. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydrological response characteristics of Mediterranean catchments at different time scales: a meta-analysis

ABSTRACT

This work examines 140 hydrological studies conducted in the Mediterranean region. It identifies key characteristics of the hydrological responses of Mediterranean catchments at various time scales and compares different methods and modelling approaches used for individual-catchment studies. The study area is divided into the northwestern (NWM), eastern (EM) and southern (SM) Mediterranean. The analysis indicates regional discrepancies in which the NWM shows the most extreme rainfall regime. A tendency for reduced water resources driven by both anthropogenic and climatic pressures and a more extreme rainfall regime are also noticeable. Catchments show very heterogeneous responses over time and space, resulting in limitations in hydrological modelling and large uncertainties in predictions. However, few models have been developed to address these issues. Additional studies are necessary to improve the knowledge of Mediterranean hydrological features and to account for regional specificities.

Editor D. Koutsoyiannis Associate editor A. Efstratiadis     

Energetic Charged Particles Above Thunderclouds

The French government has committed to launch the satellite TARANIS to study transient coupling processes between the Earth’s atmosphere and near-Earth space. The prime objective of TARANIS is to detect energetic charged particles and hard radiation emanating from thunderclouds. The British Nobel prize winner C.T.R. Wilson predicted lightning discharges from the top of thunderclouds into space almost a century ago. However, new experiments have only recently confirmed energetic discharge processes which transfer energy from the top of thunderclouds into the upper atmosphere and near-Earth space; they are now denoted as transient luminous events, terrestrial gamma-ray flashes and relativistic electron beams. This meeting report builds on the current state of scientific knowledge on the physics of plasmas in the laboratory and naturally occurring plasmas in the Earth’s atmosphere to propose areas of future research. The report specifically reflects presentations delivered by the members of a novel Franco-British collaboration during a meeting at the French Embassy in London held in November 2011. The scientific subjects of the report tackle ionization processes leading to electrical discharge processes, observations of transient luminous events, electromagnetic emissions, energetic charged particles and their impact on the Earth’s atmosphere. The importance of future research in this area for science and society, and towards spacecraft protection, is emphasized.     

Experimental investigation on the seismic performance of masonry buildings using shaking table testing

Masonry buildings worldwide exhibited severe damage and collapse in recent strong earthquake events. It is known that their brittle behavior, which is mainly due to the combination of low tensile strength, large mass and insufficient connection between structural elements, is the main limitation for their structural implementation in residential buildings. A new construction system for masonry buildings using concrete blocks units and trussed reinforcement is presented here and its seismic behavior is validated through shaking table tests. Dynamic tests of two geometrically identical two-story reduced scale (1:2) models have been carried out, considering artificial accelerograms compatible with the elastic response spectrum defined by the Eurocode 8. The first model was reinforced with the new proposed system while the second model was built with unreinforced masonry. The experimental analysis encompasses local and global parameters such as cracking patterns, failure mechanisms, and in-plane and out-of-plane behavior in terms of displacements and lateral drifts from where the global dynamic behavior of the two buildings is analyzed comparatively. Finally, behavior factors for the design recommendations in case of unreinforced masonry are also evaluated.     

Sampling strategy and climatic implications of tree-ring stable isotopes on the southeast Tibetan Plateau

We explore the potential of tree-ring cellulose δ¹⁸O and δ¹³C records for reconstructing climate variability in the southeast Tibetan Plateau. Our sampling strategy was designed to investigate intra and inter-tree variability, and the effects of the age of tree on δ¹⁸O variation. We show that intra-tree δ¹³C and δ¹⁸O variability is negligible, and inter-tree coherence is sufficient to build robust tree-ring δ¹⁸O or δ¹³C chronologies based on only four trees. There is no evidence of an age effect regarding δ¹⁸O, in contrast with tree-ring width. In our warm and moist sampling site, young tree δ¹³C is not clearly correlated with monthly mean meteorological data. Tree-ring δ¹⁸O appears significantly anti-correlated with summer precipitation amount, regional cloud cover, and relative humidity. Simulations conducted with the ORCHIDEE land surface model confirm the observed contribution of relative humidity to tree cellulose δ¹⁸O, and explain the weak correlation of δ¹³C with climate by the non-linear integration linked with photosynthesis. Altogether, the tree-ring cellulose δ¹⁸O is shown to be a promising proxy to reconstruct regional summer moisture variability prior to the instrumental period.     

Long-term and transient time variation of cosmic ray fluxes detected in Argentina by CARPET cosmic ray detector

We present results obtained at El Leoncito (CASLEO, San Juan, Argentina) with the CARPET charged particles detector installed in April 2006. The observed modulation of the cosmic ray flux is discussed as a function of its time variability and it is related to longer solar activity variations and to shorter variations during solar and geomagnetic transient activity. Short period (few minutes, few hours) cosmic ray modulation events are observed during rain time (precipitation) and significant variations of the atmospheric electric field. Complementary observations of the atmospheric electric field indicate that its time variations play an important role in the detected cosmic ray event.     

A Multi‐Element Ion‐Pair Extraction for Trace Metals Determination in Environmental Samples

A multi‐element ion‐pair extraction method was described for the preconcentration of Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), and Zn(II) ions in environmental samples prior to their determinations by flame atomic absorption spectrometry (FAAS). As an ion‐pair ligand 2‐(4‐methoxybenzoyl)‐N′‐benzylidene‐3‐(4‐methoxyphenyl)‐3‐oxo‐N‐phenyl‐propono hydrazide (MBMP) was used. Some analytical parameters such as pH of sample solution, amount of MBMP, shaking time, sample volume, and type of counter ion were investigated to establish optimum experimental conditions. No interferences due to major components and some metal ions of the samples were observed. The detection limits of the proposed method were found in the range of 0.33–0.9 µg L^?1 for the analyte ions. Recoveries were found to be higher than 95% and the relative standard deviation (RSD) was less than 4%. The accuracy of the procedure was estimated by analyzing the two certified reference materials, LGC6019 river water and RTC‐CRM044 soil. The developed method was applied to several matrices such as water, hair, and food samples.