Sources of organic carbon in the Portuguese continental shelf sediments during the Holocene period

Organic C (OC) and total N (TN) concentrations, and stable isotope ratios (δ¹³C) in muddy deposit sediments of the Northern and Southern Portuguese continental shelf were used to identify sources of fine-sized organic matter (<63 μm) during the Holocene period. Sedimentary columns off the Guadiana (core CRIDA 05), Tagus (core MD 992332) and Douro (core KSGX 57) estuaries are characterised by elemental and isotopic values that reflect distinct sources of organic matter (OC/TN and δ¹³C ranging, respectively, from 8.5 to 21 and from −22.4‰ to −27‰). Intense supplies to the Guadiana continental shelf of fine terrigenous particles during the Younger-Dryas Event are closely linked with higher OC/TN values and lower δ¹³C ratios. During the postglacial transgression phase, an increasing contribution of marine supplies (up to 80%) occurred. Higher δ¹³C (up to −22.4‰) values and low OC/TN ratios (down to 8.5) are found as the sea level approaches the current one. The Upper Holocene records emphasize the return to enhanced terrestrial supplies except for the Little Climatic Optimum between the 11th and 15th centuries AD. This climatic event is especially obvious in the three cores as a return to marine production and a decrease in terrestrial sediment supply to the continental shelf. The return to a cooling event, the Little Ice Age, between the 15th and 19th centuries AD, is mirrored by decreased terrigenous supplies in core KSGX 57. Gradually increasing sedimentation in estuaries, as well as formation of coastal dune fields, have been hypothesized on the basis of increasing δ¹³C and decreasing OC, TN and OC/TN values.     

Determination of reaeration‐rate coefficient by modified tracer gas technique

The modified tracer gas technique is used to determine the reaeration coefficient in six different water bodies of the Itajaí River basin, three with rural land use and three in urban areas. Propane was used as the tracer gas and Rhodamine WT as the conservative tracer, providing information on dilution, mixing and dispersion. Liquefied petroleum gas was used instead of high purity propane, aimed at reducing the costs associated with the field trials. Reaeration‐rate coefficients observed in the field ranged from 25.8 to 367.7 d^?1. Two data sets could be observed where smaller streams had substantially larger coefficients of between 133.1 and 367.7 d^?1, while the larger streams had values ??ranging from 25.8 to 54.5 d^?1. Five empirical equations were evaluated by comparing the values ??obtained in the field. The equations proposed by Tsivolgou and Wallace and Tsivoglou and Neal showed greater adherence to the values ??determined in the tests. Reaeration‐rate coefficients obtained in the field were correlated with the hydrodynamic characteristics of the watercourses, thus establishing a mathematical function through which to obtain estimates for future evaluations. The R² value obtained using this equation was 0.959, indicating a high correlation between the calculated values ??and those estimated in the field. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling of coupled fluid‐mechanical problems in fractured geological media using enriched finite elements

Geological environments, such as petroleum reservoirs, normally exhibit physical discontinuities, for example, fractures and faults. Because of the reduced thickness of these discontinuities, finite element formulations with strong discontinuity have been applied to the numerical modelling of geological environments. Until now, two relevant characteristics of petroleum reservoirs have not been addressed by these formulations. The first is the pore pressure jump in the direction normal to a discontinuity in a fluid‐mechanical coupling condition, which is present primarily in sealing faults owing to the contrast of permeability with the porous medium. The absence of this jump can affect the prediction of the deformability of a physical discontinuity. Furthermore, reservoir models frequently use coarse meshes. Thus, the method used to evaluate the pore pressure in the discontinuity may exhibit a strong dependence relative to the mesh refinement. Based on these characteristics, in this study, a formulation of an enriched finite element for application to coupled fluid‐mechanical problems with pre‐existing physical discontinuities saturated by a single fluid is presented. The formulation employs discontinuous interpolation functions and enables the reproduction of jumps of displacement and pore pressure associated with a discontinuity inside the element without the need to discretise it. An approximation to estimate the pore pressure in the discontinuity was developed, one which seeks to minimise the influence of refinement. The element's response is verified by comparison with a one‐dimensional analytical solution and simple examples that are simulated using commercial software. Copyright © 2015 John Wiley & Sons, Ltd.     

Landslide detection in the Himalayas using machine learning algorithms and U-Net

Landslides - Event-based landslide inventories are essential sources to broaden our understanding of the causal relationship between triggering events and the occurring landslides. Moreover,...     

Behaviour of Instrumented Hollow Auger Pile Groups in Sandy Soil

Geotechnical and Geological Engineering - Hollow auger piles are a new solution technique being used more often in recent years as a foundation for buildings of 15 floors or less in the coastal...     

Environmental pollution and natural populations: a biomarkers case study from the Iberian Atlantic coast

The degradation of estuaries is a result of human activities which overloads the environment with substances of both industrial and/or natural origins. Bioindicators have been consistently used to interpret effects of contaminants in the environment. In this study, the use of biomarkers (particular measurable characteristics of a bioindicator organism) was used to evaluate the contamination by xenobiotics of Crangon crangon natural populations. The central aim was to evaluate the capability of a battery of biomarkers to discriminate sites with different types of contamination. The activity of the enzymes cholinesterases (ChE), lactate dehydrogenase (LDH) and glutathione S-transferases (GST) were used as biomarkers. In addition, the ChE form(s) present in the cephalotorax of C. crangon were characterised. Organisms were seasonally sampled from winter 2001/2002 to autumn of 2002, at "reference" sites and at sites that receive agricultural, industrial and/or urban effluents. Results obtained in the characterisation of ChE with different substrates and selective inhibitors demonstrate that the form of ChE present in the cephalotorax of C. crangon shows proprieties of vertebrates' AChE and therefore it may be classified as true AChE-like ChE. The battery of biomarkers exhibited seasonal and local variations, apparently related to agricultural, industrial or urban effluent contamination. The tested biomarkers proved to be able to discriminate sources of environmental contamination, and confirms C. crangon as a sensitive species suitable to be used as a bioindicator.