Origin and geochemical reaction paths of sabkha brines: Sabkha Jayb Uwayyid, eastern Saudi Arabia

Sabkhas are ubiquitous geomorphic features in eastern Saudi Arabia. Seven brine samples were taken from Sabkha Jayb Uwayyid in eastern Saudi Arabia. Brine chemistry, saturation state with respect to carbonate and evaporate minerals, and evaporation-driven geochemical reaction paths were investigated to delineate the origin of brines and the evolution of both brine chemistry and sabkha mineralogy. The average total dissolved solids in the sabkha brines is 243 g/l. The order of cation dominance is Na⁺   >>  Mg²⁺ >>  Ca²⁺>K⁺, while anion dominance is Cl⁻ >> SO₄ ²⁻ >> HCO₃ ⁻. Based on the chemical divide principle and observed ion ratios, it was concluded that sabkha brines have evolved from deep groundwater rather than from direct rainfall, runoff from the surroundings, or inflow of shallow groundwater. Aqueous speciation simulations show that: (1) all seven brines are supersaturated with respect to calcite, dolomite, and magnesite and undersaturated with respect to halite; (2) three brines are undersaturated with respect to both gypsum and anhydrite, while three brines are supersaturated with respect to both minerals; (3) anhydrite is a more stable solid phase than gypsum in four brines. Evaporation factors required to bring the brines to the halite phase boundary ranged from 1.016 to 4.53. All reaction paths to the halite phase boundary follow the neutral path as CO₂ is degassed and dolomite precipitates from the brines. On average, a sabkha brine containing 1 kg of H₂O precipitates 7.6 g of minerals along the reaction path to the halite phase boundary, of which 52% is anhydrite, 35.3% is gypsum, and 12.7% is dolomite. Bicarbonate is the limiting factor of dolomite precipitation, and sulfate is the limiting factor of gypsum and anhydrite precipitation from sabkha brines.     

A visualization-oriented 3D method for efficient computation of urban solar radiation based on 3D–2D surface mapping

The temporal and spatial distribution of solar energy in urban areas is highly variable because of the complex building structures present. Traditional GIS-based solar radiation models rely on two-dimensional (2D) digital elevation models to calculate insolation, without considering building facades and complicated three-dimensional (3D) shading effects. Inspired by the ‘texture baking’ technique used in computer graphics, we propose a full 3D method for computing and visualizing urban solar radiation based on image-space data representation. First, a surface mapping approach is employed to project each 3D triangular mesh onto a 2D raster surface whose cell size determines the calculation accuracy. Second, the positions and surface normal vectors of each 3D triangular mesh are rasterized onto the associated 2D raster using barycentric interpolation techniques. An efficient compute unified device architecture -accelerated shadow-casting algorithm is presented to accurately capture shading effects for large-scale 3D urban models. Solar radiation is calculated for each raster cell based on the input raster layers containing such information as slope, aspect, and shadow masks. Finally, a resulting insolation raster layer is produced for each triangular mesh and is represented as an RGB texture map using a color ramp. Because a virtual city can be composed of tens of thousands of triangular meshes and texture maps, a texture atlas technique is presented to merge thousands of small images into a single large image to batch draw calls and thereby efficiently render a large number of textured meshes on the graphics processing unit.     

Study of Shoreline Changes Through Digital Shoreline Analysis System and Wave Modeling: Case of the Sandy Coast of Bou-Ismail Bay,Algeria

Ocean Science Journal - This work aims to analyze the evolution of Bou-Ismail coastline in Algeria using aerial photographs and quick-bird satellite image during the elapsed period from 1959 to...     

Assessing the impacts of climate and land use change on streamflow,water quality and suspended sediment in the Kor River Basin,Southwest of Iran

This research addressed the separate and combined impacts of climate and land use change on streamflow, suspended sediment and water quality in the Kor River Basin, Southwest of Iran, using (BASINS–WinHSPF) model. The model was calibrated and validated for hydrology, sediment and water quality for the period 2003–2012. The model was run under two climate changes, two land use changes and four combined change scenarios for near-future period (2020–2049). The results revealed that projected climate change impacts include an increase in streamflow (maximum increases of 52% under RCP 2.6 in December and 170% under RCP 8.5). Projected sediment concentrations under climate change scenarios showed a monthly average decrease of 10%. For land use change scenarios, agricultural development scenario indicated an opposite direction of changes in orthophosphate (increases in all months with an average increase of 6% under agricultural development scenario), leading to the conclusion that land use change is the dominant factor in nutrient concentration changes. Combined impacts results indicated that streamflows in late fall and winter months increased while in summer and early fall decreased. Suspended sediment and orthophosphate concentrations were decreased in all months except for increases in suspended sediment concentrations in September and October and orthophosphate concentrations in late winter and early spring due to the impact of land use change scenarios.     

Impact of tailings dam failure on spatial features of copper contamination (Mazraeh mine area,Iran)

Mining activities pose a potential risk of metal contamination around mining sites. On May 6, 2010, a tailings dam failure of the Mazraeh copper mine near Ahar in East Azerbaijan province, Iran, released vast amounts of mine wastes. To better understand the magnitude of copper contamination in the waste-affected soils, it is important to assess the spatial distribution of soil copper content at unsampled points. A total of 30 soil samples and their surficial sediments together with the 6 uncontaminated control samples (0–10 and 10–30 cm) were collected along the stream flow that joined Ahar-Chai River. Some of soil properties as well as total copper concentration were determined in all samples. The mean value of the latter in the surface contaminated soils was found to be approximately two times more than controls. Furthermore, the mean concentration of copper in the surface loaded material was 10 times more than the soils. High copper concentrations were observed in surficial sediments of the soils near the broken tailings dam. The Inverse Distance Weighting (IDW) method was employed in data analysis. The spherical and Gaussian semivariogram models were properly fitted to the data of copper contents in soils and surficial sediments.     

Use of natural chabazite–phillipsite tuff in wastewater treatment from electroplating factories in Jordan

Chabazite-phillipsite tuff from Tell Rimah volcano was evaluated in industrial wastewater treatment. Samples of two different size fractions have suitable zeolite content and cation exchange capacity, and are characterized by good attrition resistance and high packed bed density. Such properties enable these fractions to be used as ion exchangers under column operation condition. In the presence of high concentration of competing ions, such as Na⁺, Ca⁺² and K⁺, and under conditions of high total ionic concentration of toxic metals, the chabazite-phillipsite tuff exhibits successful performance in removing Cu⁺², Cr⁺³, Ni⁺², Zn⁺² and Fe⁺² from electroplating effluents. The factors that influence selectivity and efficiency of the zeolitic tuff were evaluated. The experimental work indicates that both selectivity and efficiency of the zeolite shows similar trends. The selectivity sequence exhibited by the zeolitic tuff is Ni⁺²>>Zn⁺² and Cr⁺³>Cu⁺²>>Fe⁺².