Distribution of trace elements in waters and sediments of the Seversky Donets transboundary watershed (Kharkiv region,Eastern Ukraine)

This paper reports on the aquatic chemistry of trace elements in terms of spatial and temporal distribution, but also pollution sources in the transboundary watershed of the Seversky Donets River (Ukraine/Russia). Bed sediments and filtered water were collected from the Udy and Lopan Rivers at sites from the river source in the Belgorod region (Russia) to rural and urban areas in the Kharkiv region (Ukraine) in May and August 2009. Priority trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn), an urban tracer (Ag) and additional metals (Co, Mo, V) and Th were measured in stream water and sediments. The low levels and variability of Th-normalized concentrations indicated the absence of geochemical anomalies in the upstream part of the rivers and suggested that these data represent a regional baseline for trace elements in bed sediments. In contrast, water and sediments within the city of Kharkiv were contaminated by Ag, Pb, Cd, Cu, Cr and Zn, which are mainly attributed to municipal wastewater inputs and urban run-off. Results of the environmental quality assessment showed that element concentrations in the sediments can be considered as potentially toxic to aquatic organisms in sites downstream of the wastewater discharges.     

The opening of the Plio-Quaternary Gibraltar Strait: assessing the size of a cataclysm

Abstract

The widespread Lago-Mare facies show that the Mediterranean was fully isolated from the World Ocean at the end of the Messinian salinity crisis (MSC): the Plio-Quaternary Gibraltar Strait has no geographical feature in common with the Miocene Portals, which were continentalised before the end of the MSC. A copy of a budget model has been modified to study the infilling of the Mediterranean. The yearly Atlantic water supply follows an exponential increase law. The level of the basins does not change significantly during the 26 early years, but the refill of the Mediterranean basins is completed within the next 10–11 years. The high velocity of the flow of Atlantic water can be reconfirmed by hydraulic calculations. The morphological study of the area suggests that the Gibraltar Strait originates from an eastwards flowing stream, which drained the eastern slope of an emergent Gibraltar Isthmus to the Mediterranean Basins at the end of the Messinian. Similar canyons are still found in the marine topography towards the Alboran Sea. The present Spartel and Camarinal Sills both originate from the coeval mass sliding of the northern bank of the strait. The strait of Gibraltar results from the work of a stream, which managed water-piracy from an Ocean. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

Contourites in the Gulf of Cadiz: a cautionary note on potentially ambiguous indicators of bottom current velocity

Facies associations in cores collected in the deep part of the Gulf of Cadiz, which is under the influence of the lower branch of the Mediterranean Outflow Water, are investigated in terms of the classical contourite model using grain-size analyses and thin sections of indurated sediment. Cores include both low-energy (contourite drift) and high-energy (channel) environments. The thin sections and grain-size distributions show that clayey fine silts and sandy coarse silts are the most common facies associations in the studied contourite sequences, while coarse-grained, gravelly contourites are less common. Grain-size distributions are unimodal in the fine-grained and bi- or trimodal in the coarser-grained contourites. This change in grain-size composition is related both to the partial removal of the fine-grained fraction and to the replenishment of the coarser-grained one. In addition, most of the contacts between individual facies are sharp rather than transitional. This suggests that the contourite sequence is only in part related to changes in bottom current velocity and flow competency, but may also be related to the supply of a coarser terrigeneous particle stock, provided by either increased erosion of indurated mud along the flanks of confined contourite channels (mud clasts), or by increased sediment supply by rivers (quartz grains) and downslope mass transport on the continental shelf and upper slope. The classical contourite facies association may therefore not be solely controlled by current velocity, but may be the product of a variety of depositional histories. The classical contourite depositional sequence should therefore be interpreted with greater care and in the light of the regional sedimentological background. In addition, the wisdom of exclusively using mean or modal particle size for the interpretation of depositional contourite processes is questioned. Instead, it is proposed that the vertical evolution of grain-size populations in the facies successions forming contourite sequences be assessed.     

Thermodynamic properties of chlorite CCa-2. Heat capacities, heat contents and entropies

The heat capacities of the international reference clay mineral chlorite CCa-2 from Flagstaff Hill, California, were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 5 to 520 K (at 1 bar). The studied chlorite is a Fe-bearing trioctahedral chlorite with an intermediary composition between ideal clinochlore (Si₃Al)(Mg₅Al)O₁₀(OH)₈ and chamosite (Si₃Al)(Fe₅Al)O₁₀(OH)₈. Only few TiO₂ impurities were detected in the natural chlorite sample CCa-2. Its structural formula, obtained after subtracting the remaining TiO₂ impurities, is (Si_2.633Al_1.367)(Al_1.116Mg_2.952Mn_0.012Ca_0.011)O₁₀(OH)₈. From the heat capacity results, the entropy, standard entropy of formation and heat content of the chlorite were deduced. At 298.15 K, the heat capacity of the chlorite is 547.02 (±0.27) J mol⁻¹ K⁻¹ and the molar entropy is 469.4 (±2.9) J mol⁻¹ K⁻¹. The standard molar entropy of formation of the clay mineral from the elements is −2169.4 (±4.0) J mol⁻¹ K⁻¹.     

Provision,transport and deposition of debris in urban waterways

The transport of woody debris from urban surfaces,through local urban waterways,to constriction and blockage risk locations is not well understood.Flume trials have identified debris and watercourse dimensions as influential factors on debris movement,and large woody debris movement has been traced in the natural rural environment using time series photography,active transponders,and field surveys.Using novel passive transponder technology,small woody debris has been traced through an urban case study watercourse to establish key influential factors on urban debris transport.Through incorporating urban debris transport detail into the source and deposition process,a complete picture of urban debris transport can be created,supporting effective culvert and trash screen design,watercourse maintenance and blockage risk assessment.This case study highlights that factors beyond watercourse depth and velocity are influential in debris movement within an urban watercourse.Debris dimension and source location upstream are shown to significantly affect the potential for debris to reach a downstream constriction,illustrating a possible distance limitation in nuisance flow debris blockage risk.     

Thermal decomposition process in algaenan of Botryococcus braunii race L. Part 2: Molecular dynamics simulations using the ReaxFF reactive force field

This paper reports ReaxFF MD simulation results on pyrolysis of a molecular model of the algaenan Botryococcus braunii race L biopolymer, specifically, ReaxFF predictions on the pyrolysis of prototypical chemical structures involving aliphatic chain esters and aldehydes. These preliminary computational experiments are then used to analyze the thermal cracking process within algaenan race L biopolymers. The simulations indicate that the thermal decomposition of the algaenan biopolymer is initiated by the cleavage of a C–O bond in the ester group, followed by the release of carbon dioxide. We also observe a significant, strongly temperature dependent, release of ethylene. This degradation mechanism leads to products similar to those observed in pyrolysis experiments, validating this computational approach.     

Early maturation processes in coal. Part 1: Pyrolysis mass balance and structural evolution of coalified wood from the Morwell Brown Coal seam

We have developed a theoretical approach for evaluating the maturation of kerogen-like material, involving molecular dynamic reactive modelling with a reactive force field to simulate thermal stress. Morwell Brown Coal was selected to study the thermal evolution of terrestrial organic matter (OM). To achieve this, a structural model is first constructed on the basis of literature models and analytical characterization of our samples using modern 1and 2D nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and elemental analysis. Then, artificial maturation of the coal is performed at low conversion in order to obtain quantitative and qualitative detailed evidence for the structural evolution of the kerogen upon maturation. The chemical changes include defunctionalization of carboxyl, carbonyl and methoxy functional groups, coupled with an increase in cross linking in the residual matured kerogen. Gaseous and liquid hydrocarbons, essentially CH₄, C₄H₈ and C₁₄₊ hydrocarbons, are generated in low amount, merely via cleavage of the lignin side chain.     

Thermal decomposition processes in algaenan of Botryococcus braunii race L. Part 1: Experimental data and structural evolution

The thermal reactivity of organic matter in source rocks is usually kinetically represented by a set of parallel and independent first order reactions. The approach assumes that only defunctionalisation reactions take place upon thermal decomposition, regardless of the chemical nature of kerogen. We have developed a new method for evaluating maturation pathways for an important kerogen-forming geopolymer, algaenan from the alga Botryococcus braunii (B. braunii), involving molecular dynamic reactive modelling based on quantum mechanics to reproduce maturation. To achieve this, a structural model is first constructed on the basis of models from the literature and analytical characterization of our samples using modern 1D and 2D nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) and elemental analysis (EA). Then, thermal decomposition of the algaenan is performed at low conversion in order to describe the initial transformations analytically. In an additional step, the observed chemical changes are quantitatively and qualitatively compared to simulated maturation from the molecular models. From this simulated maturation detailed reaction schemes are extracted for primary cracking mechanisms.     

Mapping the sedimentary basins of the Barents and Kara Seas using ERS-1 altimetry-geodetic mission

The continental shelf in the Arctic north of Russia consists of a series of epicontinental seas, which are the offshore continuation of potentially oil and gas basins on land. The geology of all these epicontinental seas is poorly known, due to the remoteness, the extreme climatic conditions and the extensive costs associated with seismic exploration. Radar altimeter sensors thus provide an invaluable tool for studying the geological structures off the coast. The unique ERS-1 contribution comes from its high latitude coverage (81.5 deg south to north), and the space and time density of its measurements (168-day repeat-orbit).The gravity anomaly field is derived from the geoid height measurements by computing the deflections of the vertical in the north-south and east-west directions and transforming these deflections into gravity anomalies. The gravimetry reveals interesting features of the basement of the Barents and Kara Seas which have not been chartered in recent, previous compilation maps of sedimentary thickness in the Arctic Ocean (Jackson and Oakey, 1988; Gramberg and Puscharovski, 1989). We obtain no indication of the SE-NW offshore Baikalian trend described by Fichler et al (1997) using ERS-1 gravimetry. Instead, the data indicate the presence of a north-south trending gravity high associated with the maximum sediment thickness within the South Barents Sea and the North Barents Sea Basins. Further geological studies are needed to interpret the gravimetric data, which directly addresses the problem of understanding the gravity signature of deep, old, sedimentary basins.