SummaryThis study was conducted during the rainy season (september) to evaluate the impact of salinity on the soil physical properties. The area of study is composed of agricultural (ZC) and salt production (SA) area, none vegetalized (TV) and little vegetalized (TA) spots.Our methodological approach is based on a sampling of soils in different depth (0-20; 20-40, and 40-60 cm), the measurement of their physical properties (bulk density, infiltration test) and chemical caracteristics (pH, EC, exchangeable bases, etc.).Our results show that the measured values of electric conductivity (14 µS.cm -1 in ZC and 3290 µS.cm -1 in SA) indicate a gradient of salinity from the agricultural activities zone (ZC) towards the salt production zone (SA). The values of bulk density and infiltration, vary according to a gradient of salinity which goes decreasing from the none vegetalized spots (TV, (> 2.40 kg.m -3 ; 0 mm.h -1 ) to the little vegetalized spots (TA, (2.4 kg.m -3 ; 0.2 mm.h -1 ), the salt production area (SA, (2.32 kg.m -3 ; 2.4 mm.h -1 ) and finally to the zone of agricultural activities (ZC, (2.12 kg.m -3 ; 14 mm.h -1 ).This result establishes a relation between the gradient of salinity and the modification of the studied soil physical parameters. The practice of salt production involves an increase in the salinity of the soils.
The analytical results of water samples collected from the Dindefello Plain area revealed the dominant major ions of bicarbonate, silica, calcium, magnesium and sodium, in order of decreasing relative abundance. Spring water exhibited a very low, i.e. similar to rainwater, mineralization status, unlike groundwater. To better understand the origin of mineralization, the data were further analyzed for interrelationships between parameters and for mineral-water relationships using speciation calculations. This provided various tenuous lines of evidence for speculating various modes of groundwater mineralization. Hydrochemical evaluation of major ions suggested an early stage of mineralization which could be attributed to mineral breakdown driven by pH in the vadose zone under the leaching action of H + . Conceivably the soil in recharge areas supplies CO2 to infiltrating rainwater, thus adding to the amount of aqueous CO2 (H2CO3) already entrapped from the atmosphere. Then, H + ions, produced from the dissociation of aqueous CO2 ( 2 3 3 H CO H HCO + − ⇔ + ), reacts along groundwater flow paths with the carbonaceous-sulfated and silicated minerals, resulting in the observed major ion chemistry. The spatial variations in the groundwater chemistry indicated that the type of bedrock aquifer has an effect on the water chemistry.
Samples of laterite soils from the quarries of Lam-Lam and Mont-Rolland (Thiès Department/Western Senegal) were investigated in the laboratory following the standard procedures suggested by the French norms. The main objective was directed at evaluating the geotechnical properties and the suitability for use as aggregates in road construction. The investigation revealed low load-bearing capacity (CBR of 61-65) as the primary technical parameter that constrained their suitability in road structure based on the general technical specifications. The bulk material meets the requirement for use as aggregates in road sub-grades, but does not fulfill the criteria for use as sub-bases in road construction; thus there is the need for necessary pretreatment in order to enhance their mechanical performance. The observed low bearing capacity can be attributed to the relative abundance of fines particles which tends to decrease the mechanical resistance and performance of aggregates, particularly in wet conditions.
The locality of Nioro du Rip is facing intense erosion, loss of agricultural land, soil pollution and soil degradation. Today, there is limited information about the soil physical and chemical properties in the locality. In this work, we describe the main essential factors or mechanism that control the evolution of the soil in the study area. The physical and chemical properties of soils encountered along a NE-SW transect in are analyzed in this paper. The statistical analysis results revealed low structural stability of soils in general, due to their low organic matter content and exchangeable bases and their predominantly silty texture. A net trend towards acidification, which is more pronounced in the lower-bottom and terrace soils, provides information on the conditions that are increasingly unfavorable to agricultural development. The multivariate principal component analysis (PCA) identified the preponderance of two factors among the four primarily involved in soil geochemical composition. These include a mineralization process (expressed through the first principal component (PC1), which causes soils to be rich in elements (Ca2+, K+,C, N, MO) controlling their structure and fertility level; The PC2 axis expresses the spatial differentiation phenomenon of the soil granulometric composition: soils forming cluster poles according to their textural affinity in the projection of the plane formed by these two components , with on one side the sandy-dominated soils of the shallows and terraces and on the other the clay-dominated soils of the plateau and the slope. A clear reversal of textural polarity in the studied topo sequence that must be blamed on the strong water erosion in this area.
In the Senegal River delta, the presence of a shallow salt water table associated with a strong evaporative demand sometimes leads to an upwelling of salts that crystallize on the surface. This phenomenon can be observed in the vicinity of the Diawling Basin, where a powdery structure sensitive to wind deflation and a massive structure with a fractionation into platelets that cannot be transported by the wind are noted. To understand the hydrodynamic characteristics of these soils, we used numerical simulation of water and solute transfers. The hydrodynamic parameters were determined in the laboratory using Wind's method on undisturbed samples. The experimental retention h() and hydraulic conductivity K(h) curves were fitted using the Van Genuchten model. The simulations show that the soil with a powdery structure has hydrodynamic characteristics that favour the ascent of salts from the water table to the surface. For the soil with a massive structure, the hydrodynamic conditions impose a deposition of salts in the subsurface.
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