Radial distribution of lead and lead isotopes in stem wood of Norway spruce: A reliable archive of pollution trends in Central Europe

Annual growth rings of a common hardwood species, Picea abies L., were investigated as a potential archive of past atmospheric Pb pollution. Wide distribution of trees in terrestrial settings and straightforward chronology are two advantages of this potential geochemical archive, but several processes described in the literature may obscure the trends in past Pb deposition. These confounding factors include, e.g., radial post-depositional mobility of Pb in xylem, and ecosystem acidification leading to higher bioavailability of Pb. One- to five-year annual wood increments were analyzed for Pb concentrations and ²⁰⁶Pb/²⁰⁷Pb ratios at Jezeri (JEZ), Uhlirska (UHL) and Na Lizu (LIZ), three sites in the Czech Republic, differing in atmospheric Pb loads. Three to four trees per site were included in the study. Distinct Pb concentration maxima between 1960 and 1990 at the two heavily polluted sites (JEZ and UHL) coincided with historical Pb emissions known from inventories of industrial production. No Pb concentration maxima were found at one site, LIZ, situated in a national park 150 km from major pollution sources. Spruce tree rings from JEZ, located just 5 km from coal-burning power stations, contained a large proportion of coal-derived Pb (a high-²⁰⁶Pb/²⁰⁷Pb ratio of 1.19). A coal-related maximum in ²⁰⁶Pb/²⁰⁷Pb in JEZ tree rings was found using two different analytical techniques, laser-ablation multi-collector ICP MS, and single-collector sector-field ICP MS. In a three-isotope graph (²⁰⁶Pb/²⁰⁷Pb vs. ²⁰⁸Pb/²⁰⁷Pb), tree-ring data plotted into the field of ombrotrophic (i.e., rain-fed) peat bogs, suggesting negligible contribution of bedrock-derived Pb in the xylem. We concluded that none of the potential confounding factors played a major role at our sites. Annual growth rings of P. abies in Central Europe faithfully recorded historical changes in atmospheric Pb depositions.     

Phylogeography of Ophryotrocha labronica (Polychaeta,Dorvilleidae) along the Italian coasts

Species of the genus Ophryotrocha are a well‐studied group of organisms but, despite the relatively large body of biological studies, little is known about their intra‐specific patterns of genetic diversity. In the present study, we analysed the patterns of genetic variation in samples of Ophryotrocha labronica (Polychaeta, Dorvilleidae) collected along the Italian coasts within three regions with different thermal regimes: the Northern Adriatic Sea (NAS), the Ligurian Sea (LS), and the South/Southeast Sicilian Sea (SS). A partial sequence of the cytochrome c oxidase subunit I (COI) gene was used as a genetic marker. An analysis of molecular variance (AMOVA) showed significant genetic differentiation between the NAS and the other regions. Conversely, little or no genetic structuring was found between the LS and the SS or amongst locations within a given region. A Bayesian phylogenetic tree and a median‐joining network provided evidence for the occurrence of two highly divergent genetic lineages characterized by a high average sequence divergence (17.2%, Kimura two‐parameter distance). The spatial patterns of genetic variation found in O. labronica may reflect the signature of past expansion events of the two genetic lineages. Although the high sequence divergence suggested that cryptic speciation within O. labronica may have occurred, other traits such as the absence of reproductive isolation, pattern of phenotypic variation and habitat specificity prompted us to regard the two groups as distinct COI lineages of O. labronica.     

Mud volcanoes in the Mediterranean Sea are hot spots of exclusive meiobenthic species

Mud volcanoes are cold seeps, in which the escape of gas and fluids associated with mud creates 3-D bottom structures that enhance the spatial heterogeneity and potentially alter the functioning of the benthic ecosystems. We investigated a complex system of mud volcanoes of the Mediterranean Sea characterised by the presence of different structures (i.e., isolated domes, domes surrounded by moats, clustered domes, and ridges) displaying different levels of seepage. We hypothesize that the combined effects of seafloor heterogeneity (i.e., different 3-D structures as revealed by detailed topographic analysis), fluid emissions and trophic characteristics of these systems can influence the structural and functional biodiversity of meiofauna (with special focus on the nematodes). We found that sediments affected by intensive seepage displayed the lowest faunal abundances and number of higher taxa. However, mud volcanoes without emissions, but characterized by a high structural complexity (such as the ridges), were associated with the highest meiofaunal abundances and number of higher taxa. Mud volcanoes hosted also a remarkable abundance of rare taxa specifically associated with these structures (e.g., acarians, cumaceans, tanaids, cladocerans and hydroids) and absent in slope sediments (used as a control). Each mud-volcano area displayed a different nematode species composition. Overall 76 nematode species (from a total of 235) were exclusively associated with mud-volcano structures, whilst 29 were exclusively encountered in slope sediments. We conclude that the presence of mud volcanoes, for their contribution to increase spatial heterogeneity and for the extreme conditions associated with gas emissions, promotes higher levels of beta diversity, thus enhancing the regional (gamma) benthic diversity. These findings provide new insights on the factors controlling meiobenthic biodiversity in mud volcanoes and clues for future action of conservation of the biodiversity specifically associated with these habitats.     

New insights into aggregation and conformational behaviour of humic substances: Application of high resolution ultrasonic spectroscopy

The potential of high resolution ultrasonic analysis (HRUS) in humic acid colloidal properties research has been demonstrated. Sodium salts of humic acids from soil and lignite showed similar behaviour, supporting the hypothesis that, at both neutral and alkaline pH, they aggregate from very low concentration. The same conclusion can be reached for solutions at high ionic strength. We tried to apply the same procedure as used for the study of micellization and determination of critical micelle concentration of common surfactants. As expected, our experiments did not show the same break as demonstrated on the HRUS records for sodium dodecyl sulfate, at least in the range of measured concentration (i.e. from 0.001 up to 10 g L⁻¹). The colloidal state of humic acids in aqueous solution is very sensitive to the presence of other, both charged and neutral, molecules. Aggregation of humic acids can be disturbed or promoted, depending on the concentration, by electrostatic or other weak interactions with extraneous molecules. Structures of varying mechanical strength (rigidity) can be formed in solutions of the same components but at different concentration. Such behaviour reflects mechanisms which occur during the sequestration of hydrophobic organic compounds and has several implications for the protection/transportation of labile structures and contaminants which are hypothesized to be encapsulated within hydrophobic pockets of soluble humic aggregates.     

Leucogranite intruding the South Tibetan Detachment in western Nepal: implications for exhumation models in the Himalayas

The most popular models regarding the exhumation of the Greater Himalayan Sequence (GHS), such as extrusion, channel flow, critical taper and wedge extrusion, require prolonged activity of the two bounding shear zones and faults, the Main Central Thrust (MCT) and the South Tibetan Detachment (STD). We present the crystallization age of an undeformed leucogranite that intrudes both the GHS and the Tethyan Himalaya Sequence (THS). Zircon and monazite U‐Pb ages in the leucogranite give ages between 23 and 25 Ma constraining, at that time, the end of shearing along the STD. Our results limit the contemporaneous activity of the MCT and STD to a short period of time (~1–2 Ma) and thus argue against exhumation models requiring prolonged contemporaneous activity of the MCT and STD.     

A new versatile constitutive law for modelling the monotonic response of soft rocks and structured fine-grained soils

This paper deals with a new critical state–based constitutive model for soft rocks and fine-grained soils. The model, formulated in the single-surface plasticity framework, is characterised by the following main features: (i) a generalised three-invariant yield surface capable of reproducing a wide set of well-known criteria, (ii) the dependency of the elastic stiffness on the current stress state by means of a hyperelastic formulation, (iii) the ability of simulating the plastic strain–driven structure degradation processes by a set of appropriate isotropic hardening laws, and (iv) a nonassociate flow rule in the meridian plane. The adopted formulation is hierarchical, such that the various features of the model can be activated or excluded depending on the specific kind of geomaterial to be modelled and on the quality and quantity of the related available experimental results. The constitutive model was implemented in a commercial finite element code by means of an explicit modified Euler scheme with automatic substepping and error control. The procedure does not require any form of stress correction to prevent drift from the yield surface. The performance of the model is first analysed by means of a wide set of parametric analyses, in order to highlight the main features and to evaluate the sensitivity of the formulation with reference to the input parameters. The model is then adopted to simulate the experimental response observed on three different geomaterials, ranging from soft clays to soft rocks.     

Geochemical mobility of arsenic in the surficial waters from Argentina

The presence of arsenic (As) in surface water constitutes an important environmental risk, where mobility and adsorption processes are responsible for its behavior in the sediment–water interface. Therefore, the assessment of adsorption, mobility and water availability of arsenic in freshwater sediments, with agricultural, livestock and urban soil uses was performed. Arsenic concentrations in sediments ranged from 5.4 to 15.9 mg kg^?1 (total) and 2.8 to 6.5 mg kg^?1 (labile), and those of iron and manganese were 11,563–23,500 and 140.6–662.1 mg kg^?1, respectively. The As levels in water were significantly lower than those of sediments. Results would suggest that As co-precipitation and adsorption on Fe oxides are probably the major route of immobilization, determining its low lability. Manganese did not present an outstanding contribution to the retention, and cation-exchange capacity, pH and organic matter of sediments did not show an influence on the mobility of As.