Gas-phase molecular structure and energetics of anionic silicates

The gas-phase stabilities of linear, branched and cyclic silicates made of up to five silicon atoms were studied with density functional theory (DFT). The starting geometries for the DFT calculations at the B3LYP/6-311+G(2d,2p) level of theory were obtained from classical molecular dynamics simulations. We have observed that geometric parameters and charges are mainly affected by the degree of deprotonation. Charges on Si atoms are also influenced by their degree of substitution. The enthalpy of deprotonation of the neutral species was found to decrease with the size of the molecule, while the average deprotonation enthalpy of highly charged compounds increased with molecular size. Furthermore, the formation of rings in highly charged silicates is enthalpically preferred to chain growth. These observations result from two competing effects: the easier distribution of negative charge in silicates with low charge density and the strong intramolecular repulsions present in silicates with high charge density. As a consequence, highly charged silicates in the gas phase tend to be as small and as highly condensed as possible, which is in line with experimental observations from solution NMR.     

Identification of the affected areas by mass movement through a physically based model of landslide hazard combined with an empirical model of debris flow

In tropical areas, mass movements are common phenomena, especially during periods of heavy rainfall, which frequently take place in the summer season. These phenomena have caused loss of life and serious damage to infrastructure and properties. The most prominent of these phenomena are landslides that can produce debris flows. Thus, this article aims at determining affected areas using a model to predict landslide prone areas (SHALSTAB) combined with an empirical model designed to define the debris flow travel distance and area of deposition. The methodology of this work consists of the following steps: (a) elaboration of a digital elevation model (DEM), (b) application of the deterministic SHALSTAB model to locate the landslide prone areas, (c) identification of the debris flow travel distance and area of deposition, and (d) mapping of the affected areas (landslides and debris flows). This work was developed in an area in which many mass movements occurred after intense rainfall during the summer season (February 1996) in the state of Rio de Janeiro, southeast Brazil. All of the scars produced by that event were mapped, allowing for validation of the applied models. The model results show that the mapped landslide locations can adequately be simulated by the model.     

Impact of intensive fish farming on methane emission in a tropical hydropower reservoir

Fisheries and aquaculture are important sources of food for hundreds of millions of people around the world. World fish production is projected to increase by 15% in the next 10 years, reaching around 200 million tonnes per year. The main driver of this increase will be based on fish farming management in developing countries. In Brazil, fish farming is increasing due to the climate conditions and large supply of water resources, with the production system based on Nile tilapia (Oreochromis niloticus) farming in reservoirs. Inland waters like reservoirs are a natural source of methane (CH₄) to the atmosphere. However, knowledge of the impact from intensive fish production in net cages on CH₄ fluxes is not well known. This paper presents in situ measurements of CH₄ fluxes and dissolved CH₄ (DM) in the Furnas Hydroelectric Reservoir in order to evaluate the impact of fish farming on methane emissions. Measurements were taken in a control area without fish production and three areas with fish farming. The overall mean of diffusive methane flux (DMF) (5.9?±?4.5 mg CH₄ m^?2 day^?1) was significantly lower when compared to the overall mean of bubble methane flux (BMF) (552.9?±?1003.9 mg CH₄ m^?2 day^?1). The DMF and DM were significantly higher in the two areas with fish farming, whereas the BMF was not significantly different. The DMF and DM were correlated to depth and chlorophyll-a. However, the low production of BMF did not allow the comparison with the limnological parameters measured. This case study shows that CH₄ emissions are influenced more by reservoir characteristics than fish production. Further investigation is necessary to assess the impact of fish farming on the greenhouse gas emissions.     

Yielding of rockfill in relative humidity-controlled triaxial experiments

The paper reports the results of suction-controlled triaxial tests performed on compacted samples of two well-graded granular materials in the range of coarse sand–medium gravel particle sizes: a quartzitic slate and a hard limestone. The evolution of grain size distributions is discussed. Dilatancy rules were investigated. Dilatancy could be described in terms of stress ratio, plastic work input and average confining stress. The shape of the yield locus in a triaxial plane was established by different experimental techniques. Yielding loci in both types of lithology is well represented by approximate elliptic shapes whose major axis follows approximately the K₀ line. Relative humidity was found to affect in a significant way the evolution of grain size distribution, the deviatoric stress–strain response and the dilatancy rules.     

Seasonal variations of water quality in a highly populated drainage basin,SE Brazil: water chemistry assessment and geochemical modeling approaches

The São João Drainage Basin is a very important and strategic waterbody located in the Lagos Region, Rio de Janeiro State, one of the most popular tourist regions of Brazil. However, the fast economic and subsequent population growth in that region has created untreated wastes from several anthropogenic activities, which include the trace metals disposal into the surface waterbody. This study aims to relate the major ions and trace metals behavior during a 1-year sampling campaign and to provide information about the sources of chemical constituents and the factors that control their concentrations in the three main fluvial compartments of the drainage basin, including the Juturnaíba Reservoir which has a crucial role for water supply in the Lagos Region. The chemical data reveal that rainfall is the main factor responsible for the physicochemical parameters and the water dissolved constituent’s variations. The geological and anthropogenic factors which are the main sources of water constituents were assessed by the Inorganic Chemical Index. Those data corroborate the great influence of rainfall and reveal the importance of anthropogenic sources of chemical constituents in some parts of the Juturnaíba Reservoir. The geochemical modeling suggests that hydrolysis reactions are primarily responsible for the trace metals availability in the three fluvial compartments in both dry and wet seasons, followed by carbonate and sulfate complexation.     

Modelling the influence of environmental and weather factors on the density of the invasive polychaete Boccardia proboscidea

The inter‐tidal zone around sewage discharges in a Southwest Atlantic shore (Mar del Plata, Argentina) is currently colonized by extensive inter‐tidal reefs of the invasive spionid Boccardia proboscidea. Understanding the links between both human and natural disturbances and the massive development of non‐indigenous species will help prevent marine bioinvasions, which are already favoured by global oceanic trade. We present herein predictive models for variations in the density of B. proboscidea around sewage discharges of Mar del Plata, using environmental (pH, turbidity, temperature, salinity and total organic matter content), weather (wind direction and storm records), spatial (sites) and temporal (season and year) variables. Density variations were modelled by generalized linear models, and model averaging (multimodel inference) was used to obtain predicted values. The highest predicted values of B. proboscidea density occurred at sites to the south of the sewage effluent in spring. These sites are more affected by urban effluent discharges and they showed increased B. proboscidea density when the north wind was predominant. In addition, B. proboscidea density values were higher in sites with 20–22 °C (seawater temperature), high total organic matter content in sediments and low salinity. The averaged model was only a good ‘predictive model’ for sites to the north of the outfall, but was useful as an ‘explanatory model’ in all sites. Such predictions may help to back up conservation and management policies and decisions.     

SHIA_Landslide: a distributed conceptual and physically based model to forecast the temporal and spatial occurrence of shallow landslides triggered by rainfall in tropical and mountainous basins

Landslides are a main cause of human and economic losses worldwide. For this reason, landslide hazard assessment and the capacity to predict this phenomenon have been topics of great interest within the scientific community for the implementation of early warning systems. Although several models have been proposed to forecast shallow landslides triggered by rainfall, few models have incorporated geotechnical factors into a complete hydrological model of a basin that can simulate the storage and movement of rainwater through the soil profile. These basin and full hydrological models have adopted a physically based approach. This paper develops a conceptual and physically based model called open and distributed hydrological simulation and landslides—SHIA_Landslide (Simulación HIdrológica Abierta, or SHIA, in Spanish)—that is supported by geotechnical and hydrological features occurring on a basin-wide scale in tropical and mountainous terrains. SHIA_Landslide is an original and significant contribution that offers a new perspective with which to analyse shallow landslide processes by incorporating a comprehensive distributed hydrological tank model that includes water storage in the soil coupled with a classical analysis of infinite slope stability under saturated conditions. SHIA_Landslide can be distinguished by the following: (i) its capacity to capture surface topography and effects concerning the subsurface flow; (ii) its use of digital terrain model (DTM) to establish the relationships among cells, geomorphological parameters, slope angle, direction, etc.; (iii) its continuous simulation of rainfall data over long periods and event simulations of specific storms; (iv) its consideration of the effects of horizontal and vertical flow; and (vi) its inclusion of a hydrologically complete water process that allows for hydrological calibration. SHIA_Landslide can be combined with real-time rainfall data and implemented in early warning systems.     

Temporal dynamics of evapotranspiration in semiarid native forests in Brazil and Spain using remote sensing

Evapotranspiration (ET) plays an important role in integrated water resource planning, development and management. This process is particularly relevant in semiarid regions. The aim of this study is, hence, to compare spatial and temporal patterns of actual ET, as well as the temporal trends in two different semiarid forests, Caatinga (Brazil) and Tierra de Pinares (Spain). We used the surface energy balance algorithm for land (SEBAL) to assess actual evapotranspiration (ET_a) in both areas. In the Brazilian semiarid forest, Caatinga is the main vegetation, while it is Pinares in Spain. For this purpose, 69 Landsat-5 and 42 Landsat-8 images (1995–2019) were used. The Mann–Kendall test was applied to assess the occurrence of trends in precipitation, temperature and potential ET data; and the Temporal Stability Index (TSI) to know which areas have greater seasonal ET_a. The annual amplitude of the potential evapotranspiration (ET₀) is the same in both areas, however, the Caatinga values are higher. In the Caatinga forest, when ET₀ presents its highest values throughout the year, ET_a presents the lowest, and vice versa. In the Pinares forest, ET_a follows the ET₀ dynamics during the year, and the difference between ET₀ and ET_a is maximum during the summer. The Caatinga forest showed a greater spatial variation of ET_a than the Pinares forest as well as a greater extension with lower temporal stability of ET_a than the Pinares forest. Both the Caatinga forest and the Pinares forest showed significant positive trends in annual ET₀ and ET_a. We estimate that the value of ET_a increases more rapidly in Pinares than in the Brazilian Caatinga. Taking Caatinga as a hydrological mirror, some consequences are expected to Pinares, such as significant changes in the water balance, increase of biodiversity vulnerability, and reduction of water availability in soil and reservoirs.