The role of hydrological processes in ecosystem conservation: Comprehensive water management for a wetland in an arid climate

Water agreements between Mexico and the United States have been crucial to preserving and restoring the Colorado River Delta's wetlands. Nowadays, increased water demand and climate change in the Colorado River Basin could threaten the conservation of the Ciénega de Santa Clara, a 4709 ha coastal wetland at the Sonoran Desert's edge. The international Ramsar convention recognizes the Ciénega de Santa Clara ecosystem for providing vital ecological services, including habitat for endemic, endangered, and migratory species. The hydrology of this wetland has not been completely understood since the 2010–2011 trial run of the Yuma Desalting Plant. Therefore, this study was conducted to identify and quantify the hydrological elements essential for the conservation of this wetland, under three scenarios: (a) normal inflow conditions of the water source – the Wellton-Mohawk canal; (b) inflow reductions, and; (c) an increase of temperature due to global warming. Water and mass balances estimates were conducted every month during 2014–2015; in situ measurements of inflows were carried out on Southern International Boundary in Wellton-Mohawk canal, the Riíto Drain, groundwater, and precipitation: evapotranspiration outputs were estimated using local weather stations and Penman-Monteith formulations. Temperature increases were based on the Intergovernmental Panel on Climate Change projections for the next 100 years. Results showed disconnection in the surface flow of water from the wetland to the adjacent Gulf of California. This behaviour was observed mainly in the summer months in the three scenarios. The disconnections reduced the wetland area and water storage. The hydrological functionality of the Ciénega de Santa Clara wetland depends on the water supply from the Wellton-Mohawk canal, with a minimum continuous discharge of 5.10 m³ s⁻¹ during the summer months.     

Spatial restricted rhomboidal five-body problem and horizontal stability of its periodic solutions

The spatial restricted rhomboidal five-body problem, or shortly, SRRFBP, is a five body problem in which four positive masses, called the primaries, move two by two in coplanar circular motions with the center of mass fixed at the origin such that their configuration is always a rhombus, the fifth mass being negligible and not influencing the motion of the four primaries. The Hamiltonian function that governs the motion of the fifth mass is derived and has three degrees of freedom depending periodically on time. Using a synodical system of coordinates, we fix the primaries in order to eliminate the time dependence. With the help of the Hamiltonian structure, we characterize the regions of possible motion. The vertical $z$ axis is invariant and we study what we call the rhomboidal Sitnikov problem. Unlike the classical Sitnikov problem, no chaos exists and the behavior of the fifth mass is quite predictable, periodic solutions of arbitrary long periods are shown to exist and we study numerically their linear horizontal stability.     

Deep conductivity structure beneath the northern Brasília belt,central Brazil: Evidence for a Neoproterozoic arc-continent collision

The Brasília belt, in central Brazil, experienced a broad range of tectonic events, including several periods of compressional and extensional deformations during the Proterozoic. Magnetotelluric data were collected at 27 sites along a profile crossing the northern part of the belt. Strike analysis and distortion decomposition indicated that most of the data are two-dimensional (2D) and fit a regional geoelectric strike angle of N20E, parallel to the tectonic grain. 2D conductivity model is constrained by available gravity and seismic refraction data and reveals the cumulative effects of the multiple tectonomagmatic episodes that affected the area in the past on current crustal and upper mantle structure. The results show that the resistive lithospheric root of the São Francisco cratonic plate is restricted to the easternmost part of the profile and does not extend westward beneath the Brasília belt. The external zone of the fold belt, composed of slightly metamorphosed rocks at the surface, presents crustal conductors that can be tentatively interpreted as regions with fossil fluid flows at mid-crust depth beneath a gold mineralization zone and as a very shallow mineralized zone within the metamorphic rocks. The external zone is separated to the west from the Goiás massif by a strong conductivity contrast, indicative of a suture zone along the Rio Maranhão fault system. Crustal conductivity structure under the Niquelândia complex is distinct from what is observed in other parts of the Goiás massif, in agreement with the proposal of the complex being an allochthonous block. In spite of the large tectonothermal events that affected the Goiás magmatic arc there are no significant conductive anomalies at crustal depths in its eastern side. The most prominent feature detected in the geoelectric model is a huge high conductivity anomaly below the entire Goiás massif in the central part of the belt, mainly concentrated at the uppermost mantle but also affecting mid to lower crustal depths. It can be interpreted as associated with thermal events either related to Mesoproterozoic and/or Neoproterozoic continental rifting processes or to delamination and detachment processes at the end of the evolution of the belt, in the Neoproterozoic. Effects related to oceanic lithosphere subduction during the collision and accretion of the Goiás massif and Goiás magmatic arc to the western passive margin of the São Francisco cratonic plate in the Neoproterozoic may alternatively explain the anomaly.     

The environmental impact of Aguilar mine on the heavy metal concentrations of the Yacoraite River,Jujuy Province,NW Argentina

The Yacoraite River and its tributaries run down the eastern slope of the Aguilar Range. It is one of the tributaries of the Rio Grande, located in Quebrada de Humahuaca, a UNESCO World Heritage site. The Aguilar underground mine (Pb–Ag–Zn) is located in the upper reaches of the Yacoraite River drainage basin. The aim of this work is to characterize the presence of heavy metals in water and sediments of the Yacoraite River and to identify their sources. The analysis shows the seasonal variation of heavy metals concentration in water and their relation with the World Health Organization (WHO) limits established for human consumption. The Yacoraite basin is naturally anomalous in some metals and some elements, such as As which is controlled by the chemical composition of regional lithology. During the wet season, Al, Co, Mo and Pb concentrations in water samples are higher than during the dry season; in addition, these metals are also higher than WHO limit values. High enrichment factors for Ba, Mo, Pb, Zn and Cd were found in Casa Grande stream, indicating the direct influence of the mining activities. Cd, Pb and Zn are present in the Aguilar ore minerals, such as sphalerite and galena. Sediments collected during the dry season show a drastic increase in the concentration of As, Pb, Ba, Zn, Cd and Mn. The Müller geo-accumulation index in Casa Grande indicates that it is a highly polluted stream. The concentrations of As, Pb, Ba, Zn, Cd are also high in Yacoraite River: Security Quality Guidelines indicates toxicity. A decrease in enrichment factors and geo-accumulation indices observed in sediments indicates the occurrence of precipitation/adsorption processes in the river to restore the equilibrium composition. Strict environmental controls in Aguilar Mine are necessary to avoid the uncontrolled input of toxic metals in Casa Grande stream and Yacoraite River.     

Utilization of ASTER and OLI data for lithological mapping of Nugrus-Hafafit area,South Eastern Desert of Egypt

Lithological discrimination of Neoproterozoic rocks occupying Nugrus-Hafafit area, South Eastern Desert of Egypt, has been carried out using Operational Land Imager (OLI) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensors’ imagery data. The applicable processing enhancement techniques include optimum index factor (OIF), band ratioing, principal component analysis (PCA), and minimum noise fraction (MNF) transform. The area comprises varieties of low-grade metamorphosed ophiolitic mélange and island-arc rocks, thrusting over high-grade metamorphic gneissic core complexes, and intruded by syn-, late-, and post-tectonic granitoids. The OLI band ratio 6/7 discriminates clearly the ophiolitic serpentinites-talc-carbonate rocks, while 4/5 ratio image is able to separate between mafic and felsic rocks. Moreover, the ASTER band ratio 6/8 is used to distinguish the amphibole-bearing rocks, including amphibolite and hornblende gneiss. The OLI and ASTER second principal component (PC2) images reflect the contrast spectral behavior of ophiolitic mélange rocks through visible-near-infrared (VNIR) and shortwave (SWIR) regions. The OLI-PC3 shows the ability to delineate the Fe-rich rocks, including amphibolite and metamafics, while ASTER-PC3 is effective for quartz-feldspathic granites and psammitic gneisses. Visual interpretation and integration of processed data with petrography and field investigation resulted in complete differentiation for the different lithologies and creation of a new detailed geological map of Nugrus-Hafafit area.     

Sequence stratigraphic distribution of diagenetic alterations in coal-bearing, paralic sandstones: evidence from the Rio Bonito Formation (early Permian), southern Brazil

Abstract Linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations, and hence of reservoir quality. A study of the coal-bearing, alluvial, deltaic, estuarine and shallow-marine sandstones of the Rio Bonito Formation, early Permian, Paraná Basin (southern Brazil), reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework. Calcite, dolomite, siderite, kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries, transgressive and maximum flooding surfaces and is systematically distributed within lowstand, transgressive and highstand systems tracts. Diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite (detectable in resistivity wire line logs), concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries, particularly in the transgressive systems tract. Meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones. Carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries, transgressive and maximum flooding surfaces favoured the formation of grain-rimming siderite. The results of this study are relevant to the exploration of coal-bed methane and other coal-bearing reservoirs, where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments.     

THM analysis of a large‐scale heating test incorporating material fabric changes

Engineered barriers are basic elements in the design of repositories for the isolation of high‐level radioactive waste. This paper presents the thermo‐hydro‐mechanical (THM) analysis of a clay barrier subjected to heating and hydration. The study focuses on an ongoing large‐scale heating test, at almost full scale, which is being carried out at the CIEMAT laboratory under well‐controlled boundary conditions. The test is intensely instrumented and it has provided the opportunity to study in detail the evolution of the main THM variables over a long period of time. Comprehensive laboratory tests carried out in the context of the FEBEX and NF‐PRO projects have allowed the identification of the model parameters to describe the THM behaviour of the compacted expansive clay. A conventional THM approach that assumes the swelling clay as a single porosity medium has been initially adopted to analyse the evolution of the test. The model was able to predict correctly the global THM behaviour of the clay barrier in the short term (i.e. for times shorter than three years), but some model limitations were detected concerning the prediction of the long‐term hydration rate. An additional analysis of the test has been carried out using a double structure model to describe the actual behaviour of expansive clays. The double structure model explicitly considers the two dominant pore levels that actually exist in the FEBEX bentonite and it is able to account for the evolution of the material fabric. The simulation of the experiment using this enhanced model provides a more satisfactory reproduction of the long‐term experimental results. It also contributes to a better understanding of the observed test behaviour and it provides a physically based explanation for the very slow hydration of the barrier. Copyright © 2011 John Wiley & Sons, Ltd.     

High-Order Spatial Simulation Using Legendre-Like Orthogonal Splines

High-order sequential simulation techniques for complex non-Gaussian spatially distributed variables have been developed over the last few years. The high-order simulation approach does not require any transformation of initial data and makes no assumptions about any probability distribution function, while it introduces complex spatial relations to the simulated realizations via high-order spatial statistics. This paper presents a new extension where a conditional probability density function (cpdf) is approximated using Legendre-like orthogonal splines. The coefficients of spline approximation are estimated using high-order spatial statistics inferred from the available sample data, additionally complemented by a training image. The advantages of using orthogonal splines with respect to the previously used Legendre polynomials include their ability to better approximate a multidimensional probability density function, reproduce the high-order spatial statistics, and provide a generalization of high-order simulations using Legendre polynomials. The performance of the new method is first tested with a completely known image and compared to both the high-order simulation approach using Legendre polynomials and the conventional sequential Gaussian simulation method. Then, an application in a gold deposit demonstrates the advantages of the proposed method in terms of the reproduction of histograms, variograms, and high-order spatial statistics, including connectivity measures. The C++ course code of the high-order simulation implementation presented herein, along with an example demonstrating its utilization, are provided online as supplementary material.     

An analytical study of the effect of penetration rate on piezocone tests in clay

Finite element cavity expansion analysis investigating the effect of penetration rate on piezocone tests in clay is presented. A coupled analysis was performed, in which the rate of cavity expansion was linked to the penetration rate of the cone and the cone angle, using the assumption that the deformation was wholly radial, and took place only between the cone tip and the cone shoulder. The soil was modelled using modified cam clay with two sets of parameters and varying values of overconsolidation ratio (OCR). The influence of penetration rate on the stress and pore pressure distributions was examined. For slower penetration rates, the excess pore pressure at the cone shoulder is lower since consolidation is permitted coincident with penetration. The radial profiles of post‐penetration voids ratio demonstrate that partially drained penetration is permitted by volume change in the near field, in addition to radial movement in the far field. The radial distribution of excess pore pressure after slow penetration differs from the undrained case, with a relatively low radial gradient existing at the cone face. As a result, the dissipation curves after slow penetration lag behind those following fast penetration. The cone velocity is made dimensionless by normalizing with the coefficient of consolidation and the cone diameter. ‘Backbone’ curves of normalized velocity against normalized tip resistance and excess pore pressure capturing the transition from undrained to drained penetration are derived. The normalized pore pressure backbone curve is unique, whilst the normalized tip resistance shows a small dependency on OCR. These backbone penetration curves are compared with centrifuge model piezocone tests conducted at varying rates, and subsequent dissipation tests. The numerical and experimental results suggest that the value of consolidation coefficient operative during the dissipation phase is 2–4 times higher than the virgin compression value due to changes in the operative soil stiffness, as demonstrated from the stress paths of individual soil elements. The use of multi‐rate penetration tests to deduce values of consolidation coefficient is discussed, in light of these differences. Copyright © 2005 John Wiley & Sons, Ltd.     

Probabilistic modelling of auto-correlation characteristics of heterogeneous slopes

Spatial variability of soil materials has long been recognised as an important factor influencing the reliability of geo-structures. This study stochastically investigates the influence of spatial variability of shear strength on the stability of heterogeneous slopes, focusing on the auto-correlation function, auto-correlation distance and cross-correlation between soil parameters. The finite element method is merged with the random field theory to probabilistically evaluate factor of safety and probability of failure via Monte-Carlo simulations. The simulation procedure is explained in detail with suggestions on improving efficiency of the Monte-Carlo process. A simple procedure to create cross-correlation between random variables, which allows direct comparison of the influence of each strength variable, is discussed. The results show that the auto-correlation distance and cross-correlation can significantly influence slope stability, while the choice of auto-correlation function only has a minor effect. An equation relating the probability of failure with the auto-correlation distance is suggested in light of the analyses performed in this work and other results from the literature.