La qualité des eaux de puits à usages domestiques dans les quartiers précaires de quatre communes de la ville d'Abidjan a été étudiée à travers l'analyse des paramètres physico-chimiques et microbiologiques couramment utilisés pour la qualité de l'eau de consommation. Les concentrations en nitrates varient entre 0 et 286 mg/L et celles de l'ammonium entre 3,6 et 39,6 mg/L. Plus de 80% des puits ont des teneurs en nitrates supérieures à la norme de 50 mg/L requise, ce qui traduit que les eaux sont d'une mauvaise qualité pour la boisson, mais subissent l'impact d'une insalubrité urbaine. En plus, la qualité des eaux de puits est variable et dépend d'un certain nombre de facteurs tels que l'emplacement des puits par rapport aux sources de contamination urbaines endogènes. La dégradation de la qualité des eaux est fortement impactée par le défaut d'assainissement des quartiers précaires. L'interprétation des données d'analyse, la corrélation existante entre les eaux de puits et la répartition des eaux de puits en groupes sont réalisées en utilisant l'Analyse en Composante Principale Normée (ACPN). Plusieurs facteurs conditionnent la contamination des eaux de puits par les polluants minéraux tels que NO 3-, NH 4 + , SO 4 2et Cl-. Le défaut d'assainissement dans ces quartiers, la mauvaise gestion des déchets urbains, la faible profondeur de la nappe, la nature des sols et la perméabilité de l'aquifère exploité sont les preuves de la vulnérabilité des eaux des puits. En effet, les résultats acquis font ressortir la forte influence de l'activité urbaine sur la qualité de ces eaux qui sont fortement chargées en ions nitrates et ammonium, signe d'une pollution urbaine.
Objective: Contamination of groundwater by nitrates is a real public health concern that is currently being paid a particular attention worldwide. This study investigates the spatial distribution of nitrates in traditional water supply wells in the Lobo's watershed, in order to derive appropriate measures to protect groundwater resources in this region. Methodology and Results: the origin of nitrate water from traditional wells of Lobo's watershed was determined through the analysis of nitrate concentrations. The samples were collected in March (dry season) and June (wet season) 2007 on the waters of traditional wells in two villages Gbili and Logbozoa and camps on the lobo's watershed. The results show that nitrate concentrations vary on the watershed. In general, concentrations range from 0 mg.L -1 to 71,26 mg L -1 . Wells with a concentration above the guideline value of WHO (50 mg.L -1 ) are found in Buyo and both villages Gbili and Logbozoa. On the other hand, wells of Tchemasso, Buyo Provisoire and camps have nitrate levels complying with the standard. Conclusion and application of results: Well waters of Buyo and two villages Gbili and Logbozoa with higher population densities are richer in nitrate. On the contrary, wells of Tchemasso, Buyo Provisoire and camps, with lower population density and sometimes with wells in plantations have low levels. Thus, the high population density, coupled with the lack of sanitation and incorrectly installed latrines, is the main cause of high nitrate levels in traditional water supply wells in the Lobo's Watershed. Water wells located in plantations with low nitrate levels show that agriculture is not responsible for the contamination of water in this area. In the short term, an appropriately designed awareness campaign on sanitation and public health directed to the populations should be initiated to allow improving and protecting well water quality in the Lobo's watershed.
The invasion of freshwaters and coastal ecosystems by Eichhornia crassipes in tropical and subtropical countries causes serious economic and ecological problems. In the present work, the seasonal distribution of Eichhornia crassipes and abiotic factors that control its distribution in rivers and lagoons from Côte d'Ivoire were reported. Our data show that Eichhornia crassipes proliferation in lagoons was more related to freshwater discharges. By contrast, salinity inhibits its proliferation particularly during dry season when the influence of oceanic waters is significant. In rivers, Echhornia crassipes proliferation in rivers was completely different from one river to another. Higher proliferation of Echhornia crassipes in Comoé and Bia rivers was found during the wet season, while in Tanoé river the maximal proliferation was obtained in the dry season. Nutrient concentrations in rivers and lagoons were generally low due to their uptake by these floating macrophytes. The accumulation of phosphorus in leaves, roots and rhizomes of Echhornia crassipes was different depending on aquatic systems. Higher phosphorus conditions (in rivers), Eichhornia crassipes accumulate more phosphorus in the rhizomes than in the other parts. By contrast, in the lower phosphorus conditions (in lagoons), Eichhornia crassipes accumulates more phosphorus in the leaves than in the other parts.
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