Evaluation of Groundwater Quality in the Deep Maastrichtian Aquifer of Senegal Using Multivariate Statistics and Water Quality Index-Based GIS
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Abstract:
A regional groundwater quality evaluation was conducted in the deep Maastrichtian aquifer of Senegal through multivariate statistical analysis and a GIS-based water quality index using physicochemical data from 232 boreholes distributed over the whole country. The aim was to 1) identify the water types and likely factors influencing the hydrochemistry, and 2) determine the suitability of groundwater for drinking and irrigation. Results showed that sodium, chloride, and fluoride are highly correlated with electrical conductivity (EC) reflecting the significant contribution of these elements to groundwater mineralization. The principal component analysis evidenced: 1) salinization processes (loaded by Na+, K+, EC, Cl-, F- and HCO3-) controlled by water/rock interaction, seawater intrusion and cation exchange reactions; 2) dolomite dissolution loaded by the couple Ca2+ and Mg2+ and 3) localized mixing with upper aquifers and gypsum dissolution respectively loaded by NO3- and SO42-. The hierarchical clustering analysis distinguished four clusters: 1) freshwater (EC = 594 μs/cm) with mixed-HCO3 water type and ionic contents below WHO standard; 2) brackish (Na-mixed) water type with moderate mineralization content (1310 μs/cm), 3) brackish (Na-Cl) water type depicted by high EC values (3292 μs/cm) and ionic contents above WHO and 4) saline water with Na-Cl water type and very high mineralization contents (5953 μs/cm). The mapping of the groundwater quality index indicated suitable zones for drinking accounting for 54% of the entire area. The occurrence of a central brackish band and its vicinity, which were characterized by high mineralization, yielded unsuitable groundwater for drinking and agricultural uses. The approach used in this study was valuable for assessing groundwater quality for drinking and irrigation, and it can be used for regional studies in other locations, particularly in shallow and vulnerable aquifers.Keywords:
Saline water
Sodium adsorption ratio
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In Tunisia, only 30% of mobilized water resources have salinity less than 2.34 dS/m. The objective of this work was to determine the best irrigation scheduling way when saline and desalinated waters are used. Different irrigation doses of freshwater and saline water are used: T80-20, T50-50 and T1d-1d. 80, 20 and 50 correspond to the percentages of irrigation water supplied in a day. For 1d-1d, this corresponds to irrigation one day with saline water and then the next day with desalinated water. Their effect on crops growth and on soil salinity was measured for three different saline waters (1.56, 4.68 and 7.81 dS/m). For irrigation with water salinity of 1.56 dS/m, the treatments T50-50 gives the better yield. For the 4.68 and 7.81 dS/m, a reduction in height was observed for all treatments. Also, for soil salinity at the end of the lettuce crop cycle, T50-50 is the best treatment that has given the best results at all levels.
Saline water
Irrigation scheduling
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The groundwater geochemistry of Lower Kelantan Basin was evaluated based on major ions characteristic to determine its suitability for drinking, domestic use and irrigation. Groundwater samples from different aquifer layers (shallow, intermediate and deep) were collected and analysed for pH, electrical conductivity (EC), total dissolved solid (TDS), Ca, Mg, Na, K, Cl, SO4, CO3, HCO3, NO3, Fe and Mn. The results show that the shallow groundwater is dominated by Ca-HCO3 and Na-HCO3 while intermediate is dominated by Na-Cl and Na-HCO3, and deep aquifer by Na-HCO3 water facies. The sodium adsorption ratio (SAR) and salinity hazard indicate that the groundwater from shallow and deep aquifer is suitable for irrigation purposes, and part of intermediate aquifer is not suitable for crop irrigation. Groundwater from shallow and deep aquifer is regarded as fresh water and suitable for drinking, domestic and agricultural irrigation use while groundwater from intermediate aquifer is slightly brackish water particularly closed to coastal area.
Sodium adsorption ratio
Total dissolved solids
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Water Salinity Should Be Reduced for Irrigation to Minimize Its Risk of Increased Soil N2O Emissions
To reveal the effect of irrigation salinity on soil nitrous oxide (N2O) emission, pot experiments were designed with three irrigation salinity levels (NaCl and CaCl2 of 1, 2.5 and 4 g/L equivalence, Ec = 3.6, 8.1 and 12.7 ds/m), either for 0 kg N/ha (N0) or 120 kg N/ha (N120) nitrogen inputs. N2O emissions from soils irrigated at different salinity levels varied in a similar pattern which was triggered by soil moisture dynamics. Yet, the magnitudes of pulse N2O fluxes were significantly varied, with the peak flux at 5 g/L irrigation salinity level being much higher than at 2 and 8 g/L. Compared to fresh water irrigated soils, cumulative N2O fluxes were reduced by 22.7% and 39.6% (N0), 29.1% and 39.2% (N120) for soils irrigated with 2 and 8 g/L saline water, while they were increased by 87.7% (N0) and 58.3% (N120) for soils irrigated with 5 g/L saline water. These results suggested that the effect degree of salinity on consumption and production of N2O might vary among irrigation salinity ranges. As such, desalinating brackish water to a low salinity level (such as 2 g/L) before it is used for irrigation might be helpful for solving water resources crises and mitigating soil N2O emissions.
Saline water
Nitrous oxide
Soil salinity control
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