On constitutive modelling of unsaturated soils

The paper presents a review of constitutive modelling of unsaturated soils. After a brief historical perspective, a number of existing constitutive models are classified and discussed according to the type of stress variables adopted in their formulation. Afterwards, attention is given to recent developments in the proposal of coupled hydraulic-mechanical models and the possibility of casting them in a sound thermodynamical framework. Finally, a double structure model for expansive soils is described. The incorporation of microstructural considerations and its use as a platform for incorporating the influence of new variables are highlighted.     

Late Quaternary paleosols, stratigraphy and landscape evolution in the Northern Pampa, Argentina

The field properties, micromorphology, grain-size, geochemistry, and optically stimulated luminescence (OSL) ages of two late Quaternary sections have been used to reconstruct the sequence of pedosedimentary processes and to provide insights into landscape evolution in part of the Northern Pampa of Argentina. Paleosols developed in paludal sediments adjacent to the Paraná river at Baradero and in loess at Lozada can both be correlated and linked to other sites, thus enabling for the first time the tentative recognition and tracing of a diachronous soil stratigraphic unit that probably spans the equivalent of at least part of marine oxygen isotope stage (OIS) 5. The paleosol at Lozada was truncated and buried beneath fluvial sediments during the time span of OIS 4 and 3. Eolian gradually replaced paludal inputs at Baradero over this period, and there were also two clearly defined breaks in sedimentation and development of paleosols. The period corresponding to OIS 2 was marked by significant loess accumulation at both sites with accretion continuing into the mid-Holocene only at Lozada. The more developed nature of the surface soil at Baradero probably reflects a combination of a moister climate and a longer soil-forming interval.     

Cenozoic tectonic evolution in the Central Andes in northern Chile and west central Bolivia: implications for paleogeographic, magmatic and mountain building evolution

A review of available stratigraphic, structural, and magmatic evolution in northernmost Chile, and adjacent Peru and Bolivia shows that in this region: (1) compression on the Paleogene intra-arc during the middle Eocene Incaic phase formed the NNE-SSW-oriented Incaic range along the present-day Precordillera and Western Cordillera, and (2) post-Incaic tectonic conditions remained compressive until present, contrasting with other regions of the Andes, where extensional episodes occurred during part of this time lapse. A late Oligocene–early Miocene peak of deformation caused further uplift. The Incaic range formed a pop-up structure bounded by two thrusts systems of diverging vergencies; it represented a major paleogeographic feature that separated two domains with different tectonic and paleogeographic evolutions, and probably formed the Andean water divide. This range has been affected by intense erosion and was symmetrically flanked by two major basins, the Pampa del Tamarugal and the Altiplano. Magmatic activity remained located along the previous Late Cretaceous–early Eocene arc with slight eastward shift. Further compression caused westvergent thrusting and uplift along the western Eastern Cordillera bounding the Altiplano basin to the east by another pop-up shaped ridge. Eastward progression of deformation caused eastvergent thrusting of the Eastern Cordillera and Subandean zone.     

Modeling neutral-atmospheric electromagnetic delays in a “big data” world

If left unmodeled, the delay suffered by electromagnetic waves while crossing the neutral atmosphere negatively affects Global Navigation Satellite System positioning. The modeling of the delay has been carried out by means of empirical models formulated based on climatological information or using information extracted from numerical weather prediction (NWP) models. This paper explores the potential use of meteorological information of several types that will become available with the increasing number of sensors (e.g. a cell phone, or the thermometer of a nearby smart home) in cyberspace. How can we make use of these potentially huge data-sets, which may help to provide the best possible representation of the neutral atmosphere at any given time, as readily and as accurately as possible? This situation falls in the realm of Big Data. A few potential scenarios, a sequential improvement of Marini mapping function coefficients, a self-feeding NWP, and near real-time empirical model updates, are discussed in this paper. The pros and cons of each approach are discussed in comparison with what is done today. Experiments indicate that they have potential for a positive contribution.     

Delineating managed land for reporting national greenhouse gas emissions and removals to the United Nations framework convention on climate change

Land use and management activities have a substantial impact on carbon stocks and associated greenhouse gas emissions and removals. However, it is challenging to discriminate between anthropogenic and non-anthropogenic sources and sinks from land. To address this problem, the Intergovernmental Panel on Climate Change developed a managed land proxy to determine which lands are contributing anthropogenic greenhouse gas emissions and removals. Governments report all emissions and removals from managed land to the United Nations Framework Convention on Climate Change based on this proxy, and policy interventions to reduce emissions from land use are expected to focus on managed lands. Our objective was to review the use of the managed land proxy, and summarize the criteria that governments have applied to classify land as managed and unmanaged. We found that the large majority of governments are not reporting on their application of the managed land proxy. Among the governments that do provide information, most have assigned all area in specific land uses as managed, while designating all remaining lands as unmanaged. This designation as managed land is intuitive for croplands and settlements, which would not exist without management interventions, but a portion of forest land, grassland, and wetlands may not be managed in a country. Consequently, Brazil, Canada and the United States have taken the concept further and delineated managed and unmanaged forest land, grassland and wetlands, using additional criteria such as functional use of the land and accessibility of the land to anthropogenic activity. The managed land proxy is imperfect because reported emissions from any area can include non-anthropogenic sources, such as natural disturbances. However, the managed land proxy does make reporting of GHG emissions and removals from land use more tractable and comparable by excluding fluxes from areas that are not directly influenced by anthropogenic activity. Moreover, application of the managed land proxy can be improved by incorporating additional criteria that allow for further discrimination between managed and unmanaged land.     

Characterization of a landslide-triggered debris flow at a rainforest-covered mountain region in Brazil

Natural Hazards - Debris flows represent great hazard to humans due to their high destructive power. Understanding their hydrogeomorphic dynamics is fundamental in hazard assessment studies,...     

The Santa Filomena meteorite shower: Trajectory,classification, and opaque phases as indicators of metamorphic conditions

On August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15^o ± 0.05. The data identified the body as an Apollo object, an Earth-crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5-6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well-defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures <800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr⁻¹.     

Influence of tidal regime,diurnal phase,habitat and season on feeding of an intertidal crab

The relationship between diet and feeding activity of intertidal crabs, and environmental cycles (tidal, daily and seasonal), habitat and level of the intertidal zone (high/low) was studied using Neohelice granulata (Brachyura, Varunidae) as a model. This is a semi‐terrestrial burrowing crab occupying different habitats in the Southwestern Atlantic coasts and estuaries from bare low intertidal mudflats to high intertidal salt marshes, and from fine, organic matter rich sediment to very coarse sediment with low content of organic matter. The study was carried out in two contrasting habitats of three sites with diverse sets of physical and biological conditions. Diet and feeding of adult N. granulata were indirectly studied through the proportion of food items and the presence/absence of food in crab stomachs, respectively. This species has a dual mode of feeding: predominantly herbivorous (live plants or plant litter in salt marshes) or deposit feeder (superficial sediment and detritus in mudflats), but the quantity and quality of ingested food varies among habitats and sites. A trend to omnivory (including algae and conspecifics) was detected in relation to low quality of resources. Feeding activity modulated by a complex interaction of factors varied according to spatial and/or temporal changes in some natural cycles. Males and non‐ovigerous females fed preferably after dark and during submersion periods, but also after emersion periods if mudflat sediment remained wet; salt marsh crab feeding is somewhat independent of light and tidal cycles. Ovigerous females almost never fed. Both diet and feeding activity of this crab seem to be flexible traits adapted to different combinations of physical and biological factors.     

Application of the water table fluctuation method to characterize groundwater recharge in the Pampa plain,Argentina

Abstract

The water table fluctuation (WTF) method is based on accepting that rises of a water table are due to recharge water reaching the groundwater. To apply the method, an estimate of the specific yield of the zone of fluctuation of the groundwater level is required. In this paper, a method for estimation of the specific yield (S_y) is proposed; it consists of a graphical procedure which relates rises in groundwater level to the precipitation from which they originated. The method presents more reliable S_y values as the number of events measured increases. Eighteen years of daily measurements were analysed to obtain a S_y value of 0.09, which was used to apply the WTF method. The obtained recharge values show consistency with values calculated by other authors for the same region.

Editor D. Koutsoyiannis

Citation Varni, M., Comas, R., Weinzettel, P., and Dietrich, S., 2013. Application of water table fluctuation method to characterize the groundwater recharge in the Pampa plain, Argentina. Hydrological Sciences Journal, 58 (7), 1445–1455.     

A multi-media planning model for assessing co-located energy and desalination plants

The co-location of desalination plants with existing or proposed power plants can bring forth economic and ecological advantages in terms of reducing the costs of water intake and reducing fish impingement. However, fossil fuel-based power plants are a source of ozone precursors and the added strain of power needed for the energy intensive desalination process increases these pollutants into the atmosphere. Furthermore, withdrawal from brackish water sources puts a stress on slowly replenishing aquifers. Additionally, the resulting concentrate is highly saline and disposal into ecologically sensitive bays and estuaries may be problematic. Balancing these limitations with the need for freshwater is of great importance for sustainability of water scarce arid and semi-arid regions and also requires a holistic multimedia impact evaluation. Therefore, an integrated system of systems approach is adopted in this study and a decision support system that integrates the flow of water, concentrate and resulting pollutants through two engineered (power plant and desalination plant) as well as three natural systems (coastal bay, aquifer and the atmosphere) is developed to study the co-location of a power plant and a desalination plant near the City of Corpus Christi in South Texas. The objective of the model is to minimize the amount of groundwater extraction and minimize the amount of water extracted from the bay to emphasize water and ecosystem conservation, respectively. These objectives, in turn, are subject to various other constraints including (1) conservation of mass; (2) air quality regulations; (3) salinity regulation policies; (4) groundwater management constraints; (5) water demand requirements; and (6) energy demand constraints. The results indicate that when conservation of the aquifer is weighted more, less water is pulled from the aquifer until later time periods. The salinity of the bay increases and creates a need for a greater amount of power necessary to process the saline water which, in turn, enhances the atmospheric loading of ozone precursors. Therefore, the conservation of groundwater scenario is limited by the air quality standards. Alternatively, when the goal is to conserve the ecological integrity of the bay while meeting freshwater demands, the model is bound by the prescribed drawdown constraint that limits the amount of water that can be extracted from the aquifer. The results from the study indicate that blending saline bay water with brackish groundwater and using cleaner burning fossil fuels that have limited air quality impacts will enhance the performance of the co-located power and desalination operations. The results of the study highlight the need for an integrated multimedia evaluation in assessing the feasibility of desalination in areas with marginal air quality.