Applying DC resistivity imaging to investigating the relationship between water quality and transpiration beneath circular islands in the Okavango Delta, Botswana: a case study of Thata Island

An electrical resistivity survey was carried out on Thata Island, one of the numerous circular islands in the Okavango Delta, to investigate the mechanism governing interactions between surface water, vegetation and groundwater. Seven data profiles were collected across the island and modelling results indicated that the centre of the island had low resistivity values (less than 10 ohm-m), while resistivity values increased laterally outside the island. Such lateral resistivity zoning responded to variation in shallow groundwater chemistry below the islands having a high concentration of solutes inside and the presence of fresh water outside the islands. Borehole to surface resistivity imaging results for the island indicated a plume of saline water sinking to depths of 60 m. Groundwater salinity below the island ranged from 11.7 g/l from the margin of the island to 122 g/l at the centre of the island. Beyond the 60m depth, groundwater salinity dropped to about 0.33 g/l at the centre of the island. Lateral and down-hole imaging results, as well as water salinity values, showed a migrating plume of high salinity groundwater from the surface of the island invading a relatively deeper low-density fresh groundwater environment. Combining geochemical, isotopic and electrical resistivity data indicated that capillary evaporation may have been the most important mechanism in creating high saline water under the centre of the island; however, high transpiration rates along the edges of the island may have been important in producing salts which could migrate toward the island\u27s centre. The results of this study showed how high salinity levels may have formed in near surface aquifers in natural inland delta environments in semi-arid areas

Geophysical Investigation of the Old Gaborone Dumpsite, Botswana

A surface geophysical investigation consisting of electromagnetic (EM) and resistivity survey techniques was carried out on the Gaborone old dumpsite that was commissioned in 1982 and decommissioned in 1992. The aim of the study was to map the physical boundaries of the decommissioned dumpsite, map the distribution of waste and identify zones of leachate concentrations within the dumpsite The results of conductivity measurements using the EM technique show a wide distribution of conductive materials, which represents zone of active leaching. This zone is mostly concentrated in the centre of the old dumpsite. Inhase measurements also identified zones occupied by metallic waste that are less distributed over the dumpsite. Results of the resistivity survey indicate a three layer structure in the area. The top layer is a more resistive cover material (68 - 127 \u3a9m.) and varies in thickness from place to place. The second layer is a low resistivity zone (3-40 \u3a9m) and indicates a zone of high leachate activities. At the bottom is a more resistive layer (greater than 500 \u3a9m) which is likely to be basement rocks that underlie the old dumpsite. The resistivity survey results provide better information about the subsurface conditions in the old dumpsite

Chalcopyrite Leaching in Ammonia-Ammonium Chloride Solutions: Insight into the Dissolution Kinetic Studies

The hydrometallurgical method for processing chalcopyrite ore has gained enormous attention due to the environmental problems emanated by the conventional pyrometallurgical route. Here, hydrometallurgy is considered an alternative that may be more of low-cost and environmentally friendly. Thus, alkaline leaching has been considered an effective, efficient, and acceptable leachant for chalcopyrite ore dissolution. The dissolution kinetics of copper from low-grade chalcopyrite ore was examined in an ammonia-ammonium chloride solution. However, the effect of parameters including leachant concentration, reaction temperature, and particle size was considered. . At optimal conditions (o.4 mol/L NH3-NH4Cl; 75 °C; 43 µm), 81.1% dissolution efficiency was achieved within 120 minutes. The leaching kinetics with activation energy (Ea) of 29.95 kJ/mol is by the proposed diffusion control mechanism. Hence, the dissolution rate was confirmed by characterizing the raw ore and un-leached residue using XRD and SEM-EDS analyses for possible industrial utilities

Geophysical investigation of the old Gaborone dumpsite, Botswana

A surface geophysical investigation consisting of electromagnetic (EM) and resistivity survey techniques was carried out on the Gaborone old dumpsite that was commissioned in 1982 and decommissioned in 1992. The aim of the study was to map the physical boundaries of the decommissioned dumpsite, map the distribution of waste and identify zones of leachate concentrations within the dumpsite The results of conductivity measurements using the EM technique show a wide distribution of conductive materials, which represents zone of active leaching. This zone is mostly concentrated in the centre of the old dumpsite. Inhase measurements also identified zones occupied by metallic waste that are less distributed over the dumpsite. Results of the resistivity survey indicate a three layer structure in the area. The top layer is a more resistive cover material (68 - 127 Ωm.) and varies in thickness from place to place. The second layer is a low resistivity zone (3-40 Ωm) and indicates a zone of high leachate activities. At the bottom is a more resistive layer (greater than 500 Ωm) which is likely to be basement rocks that underlie the old dumpsite. The resistivity survey results provide better information about the subsurface conditions in the old dumpsite. Journal of Applied Sciences and Environmental Management Vol. 10 (3) 2006: 87-9

Lichen Species as Bio-accumulator of some Halogens on Mount Cameroon Valcano, West Africa

Lichens diversities are informative indicators for assessing impacts of air pollution climate change environmental health volcanic activities habitat heterogeneity and continuity Lacking roots vascular tissues stomata and waxy cuticle they absorb and accumulate airborne nutrients pollutants from the atmosphere over their entire surface Halogens especially fluorides are released into the atmosphere in large amounts by volcanic eruptions and their pollutants levels in lichens can be determined quantitatively by chemical analysis of specie

Thermal Perturbations beneath the Incipient Okavango Rift Zone, Northwest Botswana

We used aeromagnetic and gravity data to investigate the thermal structure beneath the incipient Okavango Rift Zone (ORZ) in northwestern Botswana in order to understand its role in strain localization during rift initiation. We used three-dimensional (3-D) inversion of aeromagnetic data to estimate the Curie Point Depth (CPD) and heat flow under the rift and surrounding basement. We also used two-dimensional (2-D) power-density spectrum analysis of gravity data to estimate the Moho depth. Our results reveal shallow CPD values (8-15 km) and high heat flow (60-90 mW m-2) beneath a ∼60 km wide NE-trending zone coincident with major rift-related border faults and the boundary between Proterozoic orogenic belts. This is accompanied by thin crust ( \u3c 30 km) in the northeastern and southwestern parts of the ORZ. Within the Precambrian basement areas, the CPD values are deeper (16-30 km) and the heat flow estimates are lower (30-50 mW m-2), corresponding to thicker crust (∼40-50 km). We interpret the thermal structure under the ORZ as due to upward migration of hot mantle fluids through the lithospheric column that utilized the presence of Precambrian lithospheric shear zones as conduits. These fluids weaken the crust, enhancing rift nucleation. Our interpretation is supported by 2-D forward modeling of gravity data suggesting the presence of a wedge of altered lithospheric mantle centered beneath the ORZ. If our interpretation is correct, it may result in a potential paradigm shift in which strain localization at continental rift initiation could be achieved through fluid-assisted lithospheric weakening without asthenospheric involvement

Thermal Perturbations beneath the Incipient Okavango Rift Zone, Northwest Botswana

We used aeromagnetic and gravity data to investigate the thermal structure beneath the incipient Okavango Rift Zone (ORZ) in northwestern Botswana in order to understand its role in strain localization during rift initiation. We used three-dimensional (3-D) inversion of aeromagnetic data to estimate the Curie Point Depth (CPD) and heat flow under the rift and surrounding basement. We also used two-dimensional (2-D) power-density spectrum analysis of gravity data to estimate the Moho depth. Our results reveal shallow CPD values (8-15 km) and high heat flow (60-90 mW m-2) beneath a ∼60 km wide NE-trending zone coincident with major rift-related border faults and the boundary between Proterozoic orogenic belts. This is accompanied by thin crust ( \u3c 30 km) in the northeastern and southwestern parts of the ORZ. Within the Precambrian basement areas, the CPD values are deeper (16-30 km) and the heat flow estimates are lower (30-50 mW m-2), corresponding to thicker crust (∼40-50 km). We interpret the thermal structure under the ORZ as due to upward migration of hot mantle fluids through the lithospheric column that utilized the presence of Precambrian lithospheric shear zones as conduits. These fluids weaken the crust, enhancing rift nucleation. Our interpretation is supported by 2-D forward modeling of gravity data suggesting the presence of a wedge of altered lithospheric mantle centered beneath the ORZ. If our interpretation is correct, it may result in a potential paradigm shift in which strain localization at continental rift initiation could be achieved through fluid-assisted lithospheric weakening without asthenospheric involvement