Comparative Magnetotelluric Modeling of Smooth 2D and 3D Conducting Bodies Using Rayleigh-Fourier Codes

—Recently, a method for 3D magnetotelluric modeling was developed, which is based on the application of the Rayleigh scattering theory. This method, RF-3D, is especially capable of modeling multilayered structures with smooth irregular boundaries. The formulation allows inclusion of layers with vertically anisotropic electrical conductivity.¶Using RF-3D, the response of smooth structures of practical interest is calculated and the importance of 3D effects is evaluated. Two models consisting of a 3D conductive body in the presence of a 2D shallow distortion are analyzed. In the first model, the direction of maximum elongation of the body is perpendicular to the strike direction of the 2D upper structure, and in the second one both directions coincide. In addition, the case of a small 3D shallow conductor over a regional 2D structure is also considered.¶3D effects are compared to those generated by 2D models with identical cross sections. In all the cases, the 3D responses differ from those of the 2D, especially directly over the bodies. A good agreement between the 2D transverse magnetic response and the corresponding components of the 3D response, along centrally located transverse profiles, is expected for elongate, prismatic conductors. Then, the differences obtained for the models considered in this study, particularly for the second and third models, are a consequence of the smooth geometry. They can be explained in terms of galvanic effects produced by boundary charges, which are greater near the vertical sides of a prism than on the sides of a body with smooth contours.¶Equivalent 2D models of the first and second structures are also obtained. In these models, the thickness of the conductor is underestimated, respectively, by about 30% and 24%.¶For the third model, when vertical anisotropy is analyzed, it is found that only the anisotropy of the first layer can be detected. This is because the effect of vertical anisotropy decreases strongly with depth and appears to be important only near the 3D anomaly.     

An Advanced Puff Model Based On A Mixed Eulerian/Lagrangian Approach For Turbulent Dispersion In The Convective Boundary Layer

An advanced model aimed at describing the problem of dispersion in theconvective boundary layer is proposed. The pollutant particles are groupedin clusters and modelled as Gaussian puffs. The expansion of each puff ismodelled according to the concept of relative dispersion and expressed interms of the spectral properties of the energy containing eddies of the turbulent field. The centre of mass of each puff is moved along a stochastic trajectory, obtained using a Lagrangian stochastic model and filtering the velocity with a recursive Kalman filter. At any instant, a filtering procedure, depending both on travel time and on puff size, acts to select spectral components involved in the expansion and in the meandering of the puff. Such an approach requires only a moderate number of puff releases, so that the proposed model is faster to run than a standard Lagrangian model. On the other hand, unlike the traditional puff model, it allows us to simulate both expansion and meandering of the puff. Therefore, it is well suited to simulate dispersion when the turbulent structures are larger thanthe plume dimensions, as for example in convective conditions. Being based onspectral formulations in both Eulerian and Lagrangian parts, the model is consistent in all the turbulent parameterizations utilised. Comparisons with a standard Lagrangian particle model as well as with a classical convective experimental dataset show good performance of the proposed model.     

Waste dump erosional landform stability – a critical issue for mountain mining

Mining is the largest producer of solid wastes which, when released to land or into waterways, can cause harmful environmental impacts. This is mostly due to fluvial erosion, which is highly increased in mountain areas, due to abrupt slopes. We have analysed this situation at a mountain watershed (192 ha), where steep mined sites and their waste dumps are the main source of sediment in a Natural Park. This problem was tackled by building gabion check dams downstream from the mined sites. We used the DEM of Differences (DoD) method to quantify erosion and sediment yield from three waste dumps (5 ha). Their topography and substrate properties were analysed to understand the erosion problem. The sediment trapped by the check dams was quantified by electrical resistivity tomography (ERT). The rainfall characteristics triggering an episode that filled the check dams with sediment in the winter 2009–2010, were studied to confirm whether it was a case of extreme precipitation conditions. The waste dumps sediment yield (353 ± 95 Mg ha^?1 yr^?1) suggests severe landform instability. Analysis of topographic and substrate properties confirmed long, steep slopes combined with highly erodible materials. The check dams proved to be inefficient in controlling sediment loads, as they had only functioned for four years of 31 of existence, having trapped 13 000 ± 660 m³ of sediment, whereas we estimated that the waste dumps have yielded approximately three times more sediment for the same period. Rainfall analyses showed that neither intense nor extreme conditions (return period of 25 to 35 years) triggered the mobilization of 37 ± 2 Mg ha^?1 in a month. This study highlights the fact that mining operations in similar mountainous settings, with equivalent waste dump construction and reclamation practices, are currently unfeasible. We conclude that landform stability cannot be achieved at this site without landform changes. Copyright © 2017 John Wiley & Sons, Ltd.     

On the positional accuracy and maximum allowable scale of UAV-derived photogrammetric products for archaeological site documentation

Blending photogrammetric and Structure from Motion techniques with Unmanned Aerial Vehicles (UAV) is a commonly used approach for the documentation and analysis of archaeological sites. Using the dense 3D point clouds generated from these techniques, two main photogrammetric products are created: orthophotos and Digital Surfaces Models (DSM). Depending on the UAV technology, the flight parameters, the topography and land cover of the flown area, DSMs and orthophotos are delivered with varying positional accuracies and output scales. In this paper, the positional accuracy and maximum allowable scale of these products generated by complete automation of flight mode and processing workflow are assessed. Moreover, three known International Mapping Standards (IMS) are validated using independent checkpoints, obtained by geodetic Global Navigation Satellite Systems receivers, in two Spanish study areas. The results show that accurate photogrammetric products adapted to the IMS can be successfully obtained by the automation of the photogrammetric workflow.     

Hydroelectric Infrastructure and Potential Groundwater Contamination in the Brazilian Amazon: Altamira and the Belo Monte Dam

Heavy investments in hydroelectric development are occurring throughout the Amazon Basin, which holds 42.2 percent of Brazil’s hydroelectric potential. The Belo Monte dam is the most recent and largest project in this region. The prevalence of septic systems in the Amazon, coupled with the widespread use of water wells and rising water table from filling the reservoir, create sanitation and health concerns for upstream communities. Using spatial analytical data and terrain analyses, we identify high-risk locations within the most densely populated neighborhoods in Altamira, Belo Monte’s host city. The purpose of this research is to develop a heuristic for identifying areas susceptible to groundwater and well contamination in relation to existing and proposed hydroelectric projects. Altamira’s city center persists as a high-risk location for contamination of wells because of its population density and relatively low elevation compared to other parts of the city. The methods, tools, and analyses presented in this article provide a framework that can be used to identify vulnerability to groundwater and drinking well contamination. The results presented here can guide implementation of public health and sanitation efforts in areas affected by large hydroelectric projects to avoid future water quality crises. Key Words: Belo Monte, groundwater contamination, hydroelectric infrastructure, risk assessment, spatial and terrain analyses.     

Hydrological heterogeneity, nutrient dynamics and water quality of a non-tidal lentic ecosystem (Lesina Lagoon, Italy)

The dynamics of the Lesina coastal lagoon (Italy) in terms of nutrients, phytoplankton and chemical–physical parameters were evaluated, together with their functional relationships with freshwater inputs, in order to identify ecosystem responses to changes in driving forces in a Mediterranean non-tidal lentic environment. Lesina Lagoon is a shallow coastal environment characterised by limited exchange with coastal waters, which favours enrichment of nutrients and organic matter and benthic fluxes within the system. Lagoon–sea exchanges are influenced by human management. There is a steep salinity gradient from East to West. High nitrogen and silica values were found close to freshwater inputs, indicating wastewater discharges and agricultural runoff, especially in winter. Dissolved oxygen was well below saturation (65%) near sewage and runoff inputs in the western part of the lagoon during summer. Classification in accordance with EEA (2001) guidelines suggests the system is of “poor” or “bad” quality in terms of nitrogen concentrations in the eastern zone during the winter rainy period. In terms of phosphate concentrations, the majority of the stations fall into the “good” category, with only two stations (close to the sewage and runoff inputs) classed as “bad”. In both cases, the raw nitrogen levels make the lagoon a P-limited system, especially in the eastern part. There was wide space–time variability in chlorophyll a concentrations, which ranged from 0.25 to 56 μg l⁻¹. No relationships between chlorophyll a and nutrients were found, suggesting that autotrophic biomass may be controlled by a large number of internal and external forcing factors driving eutrophication processes. Water quality for this type of environment depends heavily on pressure from human activities but also on the management of sewage treatment plants, agricultural practices and the channels connecting the lagoon with the sea.     

Stakeholders’ participation in the fisheries management decision-making process: Fishers’ perceptions of participation

Public participation is a key ingredient of good governance and there are many advantages of involving stakeholders in the decision-making process. The European Commission identified the lack of stakeholder involvement as one of the major weaknesses of the Common Fisheries Policy (CFP). As such, the 2002 Reform of the CFP aimed to improve its system of governance by increasing the involvement of stakeholders in decision-making. Over the last decade, Scottish inshore waters have seen an increase in management measures focused on involving fishers, delegating responsibilities and decentralizing management. The present document investigates commercial inshore fishers’ perceptions of participation in the decision-making process and attitudes towards a new management regime – the Inshore Fisheries Groups (IFGs) – which aims to increase participation in and decentralization of inshore fisheries management. A survey was conducted, through face-to-face interviews, and ordered logistic and multiple regression models created to identify which characteristics influence fishers’ perceptions and attitudes. The present analysis concluded that, 5 years subsequent to the reform of the CFP, the majority of inshore fishers perceive themselves not to be consulted or involved in the decision-making process. However, and despite the fact that fishers are not completely certain of the potential of the IFGs to increase their participation in the management process, they have an overall positive attitude towards their implementation.     

Lateglacial and Holocene palaeoenvironments at Sierra La Madera,northwestern Mexico: Sharp signals of Younger Dryas and North American monsoon

During the last glacial termination, the climate system experienced intense global variations whose causes and impacts are not fully defined, particularly for low latitudes. The northwestern Mexico Sky Islands present a climate-sensitive ideal setting to record palaeoecological and palaeoclimatic changes due to their physiographic complexity and location in the ecotone between temperate and tropical ecosystems. High-resolution pollen analysis and a detailed sedimentological study were conducted at the Ciénega Tonibabi tropical thorn scrub site. The 15 540–0 cal a bp nearly continuous record shows that the North Atlantic Ocean did have a cold and humid climatic influence during the glacial stages of the end of the Pleistocene, including a sharp pulse during the Younger Dryas. However, a shift to the Pacific Ocean influence occurred during the Holocene, which led to the development of the El Niño conditions prevailing today. Colder and warmer phases follow one another with higher or lower winter precipitation, including a sharp Bølling–Allerød and development and intensification of the North American monsoon. They are reflected in hydrological changes as well as in the advances, retreats and intermingling of coniferous forests and tropical thorn scrub.