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Les sources de phosphore de la lagune de Porto-Novo (50 km2 de superficie, située au sud-est du Bénin) sont de deux types : les apports diffus (principalement le ruissellement sur les terres cultivées) et les apports ponctuels (rejets industriels ou domestiques). Cette lagune est victime d'une pollution qui se justifie par le développement anarchique de la flore aquatique (eutrophisation).Objectifs: Étudier les différentes fractions biodisponibles du phosphore au niveau des sédiments de la lagune et les conditions de leur relargage dans la colonne d'eau.Méthodologies et résultats: Les eaux et sédiments de la lagune ont été prélevés en cinq (5) points différents et diverses analyses ont été effectuées. Le fractionnement du phosphore a été effectué par la méthode d'extraction séquentielle. Les résultats issus de nos analyses ont été traités avec le logiciel Microsoft Excel et interprétés. Les résultats du fractionnement du phosphore ont permis de constater que la fraction liée à la matière organique est la plus représentative (10612,73 Bg-P/g soit 68,76% de la valeur moyenne du phosphore total), les autres fractions telles que, la fraction particulaire (P-Fe, P-Al, P-Ca) et celle facilement échangeable (P-labile) sont également présentes dans les sédiments prélevés mais à de faibles pourcentage. En moyenne, 58,85Bg-P/g soit 0,38% pour le p-labile ; 20,97Bg-P/g pour P-Fe, 35,42Bg-P/g pour le P-Al et 2,67Bg-P/g pour le P-Ca, soit respectivement 0,13%, 0,22%, 0,017% de la valeur moyenne du phosphore total. Ce pourcentage élevé de P-Org serait dû à l'utilisation des engrais organiques dans l'agriculture sur le bassin versant quicomporte la lagune, et à la présence de matières organiques animales et végétales, vivantes ou en voie de dégradation. En outre, l'effet de la variation du pH sur les échantillons ayant subi le fractionnement après 96 heures de remises en suspension révèle en général une augmentation des différentes fractions du phosphore donc un relargage de ces fractions dans la colonne d'eau (56,84% de P-Al est remobilisable, 96,11% pour le p- Ca, 80,72% pour le p-labile, 33,78% pour le P-Org).Conclusions et applications: Ces résultats pourraient servir de base aux politiques environnementales nationales et autres qui visent à protéger les lagunes côtières et les organismes qui y vivent.Mots clés: Biodisponibilité, mobilité, relargage, fractionnement, extraction séquentielleEnglish Title: Bioavailability and mobility of phosphorus in the sediments of the Porto-Novo LagoonEnglish AbstractPhosphorus sources in the Porto-Novo lagoon (50 km2 of area, located in southeast Benin) are of two types: diffuse inputs (mainly runoff on cultivated land) and point sources (industrial or domestic). This lagoon is therefore the victim of pollution, which is justified by the radical development of the aquatic flora (eutrophication).Objective: To study the different bioavailable fractions of phosphorus in the sediments of the lagoon and the conditions of their release in the water column.Methodology and results: To achieve this, the waters and sediments of the lagoon were collected in five (5) different points and various analyses were carried out. Phosphorus fractionation was performed by the sequential extraction method. The results of phosphorus fractionation revealed that the organic matter fraction is the most representative (10612.73 μg-P/g, either 68.76% of the average value of the total phosphorus), the other fractions (P-Fe, P-Al, P-Ca) and the easily exchangeable (P-labile) are also present in the collected sediments but at a low percentage (On average, 58.85μg-P / g either 0 , 38% for P-labile; 20.97μg-P / g for PFe, 35.42μg-P / g for P-Al and 2.67μg-P / g for P-Ca, respectively 0 , 13%, 0.22%, 0.017% of the mean value of total phosphorus). This high percentage of P-Org could be explained by the use of organic fertilizers in agriculture on the watershed that includes the lagoon, and also the presence of living and degrading organic and animal matter Furthermore, the effect of the pH variation on the samples which have been fractionated after 96 hours of resuspension generally reveals an increase in the various fractions of the phosphorus, thus releasing these fractions into the water column (56, 84% P-Al is remobilizable, 96.11% for p-Ca, 80.72% for plabile, 33.78% for P-Org).Conclusions and applications: These results could serve as a basis for national and other environmental policies aimed at protecting coastal lagoons and the organisms that live there.Keywords: Bioavailability, mobility, release, fractionation, sequential extraction

AbstractThe aim of this study was to assess the risk of drinking water contamination during transportation and storage at the household level of Godomey district in Benin. A survey carried out in 175 households was followed by a microbial analysis of water samples at the point of supply and after transport and storage in households over a period of 4 days. The results of the surveys showed that households obtain their supplies in water mostly from the network of the National Water Company of Benin (SONEB). In addition, they used private boreholes and wells as source of the drinking water. People who did not have direct access to water sources traveled a few meters with different materials (cans, plastics, basins) to obtain water and store it in households for their daily needs. This water was used for several days (1–7) before the renewal of the storage. The microbiological results revealed an increase in microbial contamination, specifically total germs and total coliforms, after transport and storage when compared with the point of supply, and as time passed. The fecal contamination was expressed by the presence of Escherichia coli. According to the study, 17% of well samples are polluted on the first and second days and are classified as dangerous quality. After 4 days, this pollution had spread to 50% of well samples. In addition, 17% of borehole water samples were found to be of poor quality, and none of the SONEB samples were contaminated with E. coli.