Journal of Applied Biosciences (J. Appl. Biosci.) [ISSN 1997 - 5902]
Volume 45: 3032 - 3044. Published September 29, 2011.
Characterization and phosphorus fractionation of the surface sediment of Nokoué Lake (Benin)
Daouda MAMA*1.2, Martin AINA2, Christophe KAKI4, Lyde TOMETIN5, Waris CHOUTI2.5, Odilon CHANGOTADE2, Véronique DELUCHAT1, James BOWEN3 and Michel BAUDU1
1Laboratoire : Groupe de Recherche Eau Sol Environnement- EA 4330. 123. Avenue Albert Thomas. 87060 Limoges Cedex (France) ;
2Laboratoire d’Hydrologie Appliquée (LHA). Faculté des Sciences et Techniques. Université d’Abomey – Calavi 01 BP 526 Cotonou (Bénin);
3Department of Civil Engineering, University of North Carolina at Charlotte. Charlotte NC 28223 (USA);
4Laboratoire de Sédimentologie et d’Hydrologie (LSH). Faculté des Sciences et Techniques. Université d’Abomey – Calavi 01 BP 526 Cotonou (Bénin) ;
5Laboratoire de Chimie Inorganique et de l’Environnement (LACIE) de la Faculté des Sciences et Techniques 01 BP 526 Cotonou (Bénin)
ABSTRACT
Objectives: Lake Nokoué in South of Benin (West Africa) is a eutrophic lake with great area covered by hyacinth during the rainy season (July to October). pH-water and pH-KCl values show short variations and sediment re-suspension. The aim of this study was to estimate the eutrophication status of Nokoué based on nutrients in the sediment and to estimate the amounts and forms of potentially mobile P in surface sediments using sequential P extraction (P-fractionation).
Methodology and results: Different forms of P in sediment samples were determined by extracting P according to the scheme proposed by Rydin and Welch (1998) modified based on Hieltjes and Lijklema (1980) and Psenner (1984) protocol. The application of eutrophication risk framework to sediment nutrient content showed that 75% of the samples were “very bad.” (that indicates a most high eutrophication risk). According to phosphorus fractionation. Fe-bound-P. Al-bound-P and Organic-bound-P comprised the largest phosphorus pool (50% of Total Phosphorus). Phosphorus release was from the Fe-P. Al-P and organic fractions. The organic matter mineralization occurring at the end of summer can also influence P release as illustrated by the difference in total phosphorus content between sediment samples of June (beginning of rainy season) and of September and October. This type of P release was observed in the Lake. High soluble reactive phosphorus content was measured in the water column; however. this part of phosphorus was in particulate form and can release and contribute to macrophyte or algae growth
Conclusion and application: The results showed that it is necessary to reduce P content in the water column in order to decrease primary productivity and subsequent organic matter sedimentation. Sediment is a main internal source of eutrophication in L. Nokoué. The results could serve as a basis for formulating national policies and other environmental policies designed to protect the coastal lagoons and living organisms.
Key words: Eutrophication. surface sediment. phosphorus fractionation.Nokoué lake
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