Qualité bioécologique d’un milieu lacustre hyper-eutrophisé en zone équatoriale (Afrique Centrale) : peuplement de protozoaires ciliés et macro invertébrés bentho-aquatiques

Le lac d’Obili est un écosystème aquatique situé en plein cœur de Yaoundé en Afrique centrale. Les études physique, chimique, et biologique ont été effectuées dans ce milieu aquatique. Des prélèvements ont été effectués durant six mois sur le site en surface et en profondeur, grâce aux méthodes telles que la spectrophotométrie, la respirométrie et la volumétrie. Des échantillons de boues, d’eau et de vase ont été analysés. Les observations à la loupe et l’identification des espèces grâce aux clés d’identifications ont permis d’avoir une idée claire sur l’état trophique du milieu. A partir des résultats découlant de ces analyses, nous avons pu bâtir une matrice de résultat. Sur celle-ci, des analyses statistiques descriptives ont été appliquées avec le logiciel d’analyse SPSS. De ces résultats, nous observons une légère acidité des eaux en profondeur par rapport à celles de la surface qui sont pratiquement neutre. L’oxygène est croissant sur les deux plans d’eaux sur toute la période d’étude. Le Dioxyde de Carbone (CO2) quant à lui présente une courbe en U. La température est globalement élevée en surface par rapport à la profondeur. La concentration en nitrate est plus élevée en profondeur qu’en surface. La DBO5 évolue en dents de scie et présente des courbes qui se croisent pendant le mois de mars. Des bio-indicateurs de polysaprobité telles que Metopus ovatus Caenomorpha medusa, Paramecium africanum révèlent une dystrophie avancée du milieu. Les dysfonctionnement de ce milieu lentique et la surcharge en ortho phosphate et nitrates sont confirmée par l’identification d’une forte peuplent des macrophytes a l’instar de Nymhea lotus, Pistia stratiotes et d’ Eichhornia crassipes. Les fortes corrélations sont observées entre les paramètres physicochimique et biologique et le test de Mann Whitney montre un unique écosystème avec peu de variation spatio-temporelle.Mots-clés : ciliés, macro invertébrés, bio indicateur, hyper eutrophisation.Bio-ecological assessment of a hyper-eutrophic lake in an equatorial region (Central Africa) : population dynamics of ciliated protozoa and bentho-aquatic macro invertebratesThe Obili Lake is an aquatique ecosystem that is positioned in Yaoundé, Cameroon Physico-chemical and biological assessment were carried out in this lake during a six month duration at the surface and the depth level by spectrophotometry, respirometry and volumetry. Analytical statistical studies reveal a slight acidity from surface to base, while Oxygene concentrations were present in the medium. Carbon dioxide showed a U profile, while temperature is higher at the surface due to the direct incidence of solar radiation. BOD values were variable in the medium. Bio-indicators of polysaprobity such as Metopus ovatus Caenomorpha medusa, Paramecium africanum reveal an advance dystrophication of the milieu. The dysfunctioning of this lentic medium and the high load of orthophosphate and nitrates are confirmed by the identification of a high density of macrophytes such as Nymhea lotus, Pistia stratiotes et d’Eichhornia crassipes. The high correlation that is observed between the physico-chimical and biological parameters and the Mann Whitney test proof a unique ecosystem with low spatial dispersionKeywords : ciliated protozoa, benthic macro-invertebrates, bio-indicator, hyper-eutrophication

Morphologie et abondance des stades de développement d’Ilyocoris cimicoïdes Linné 1758 (Heteroptera : Naucoridae) dans un lac anthropisé en zone tropicale (Cameroun)

Objectifs : Une étude conduite au laboratoire de Zoologie et de Biologie Générale de l’Université de Yaoundé I a porté sur l’écologie de la punaise aquatique Ilyocoris cimicoïdes Linné 1758 (Heteroptera : Naucoridae) prélevée dans le lac d’Obili (Yaoundé, Cameroun). Méthodologie et résultats : L’analyse physico-chimique montre que ce lac est dans un état eutrophe à hypereutrophe et ses eaux sont fortement chargées en matière organique. Les observations morphologiques et l’illustration des stades de développement ainsi que l’étude de leurs fluctuations numériques montrent que I. cimicoïdes à six stades post-embryonnaires parmi lesquels cinq sont larvaires. La taille des individus augmente de la larve de 1er stade jusqu’au stade adulte. Les stades larvaires d’I. cimicoïdes se distinguent les uns des autres par la présence ou l’absence du ptérothèque, la forme de la marge postérieure du mésotergum et la taille relative du ptérothèque par rapport à la base du mésotergum. Conclusions : L’abondance des stades de développement d’I.cimicoïdes est influencée par la saisonnalité et l’évolution de certaines variables physico-chimiques. Les larves pullulent pendant la saison sèche et les oeufs et adultes pendant la saison des pluies.Mots clés : Pollution aquatique, morphologie, développement, Ilyocoris cimicoïdes.  Objectives : A study conducted at the Laboratory of Zoology and General Biology, University of Yaoundé I focused on the ecology of aquatic bug Ilyocoris cimicoides Linnaeus 1758 (Heteroptera : Naucoridae) taken from Lake Obili (Yaoundé, Cameroon). Methodology and Results: The physico-chemical analysis showed that this lake is in a eutrophic state and its waters are heavily loaded with organic matter. Morphological observations and illustration stages of development and the study of their digital fluctuations show that I. cimicoides, has six post-embryonic stages of which five are breeding. The sizes of individuals increase the first stage larva to adult. Larval stages of I.cimicoides are distinguished from each other by the presence or absence of pterotheque, the shape of the posterior margin and mesotergum pterotheque relative size with respect to the base of mesotergum. Conclusions : Abundance stages of development I. cimicoides is influenced by seasonality and the evolution of certain physico-chemical variables. Larvae swim in the dry season and eggs and adults during the rainy season.Keywords : Water Pollution, morphology, development, Ilyocoris cimicoides

Biodiversity of Freshwater Shrimp of the Genus Macrobrachium (Decapoda Palaemonidae) in the Nyong Basin of Cameroon

The population of shrimps, especially the macrobrachium genus, has been affected with habitat pollution and overexploitation. Shrimps provide a major protein source to animals higher in the food chain. The importance of studying the ecology of shrimps in their different habitats helps in their preservation and provides possibilities of carcinoculture. This study examines diversity, ecology and reproduction parameters of fresh water shrimps of the genus macrobrachium in the basins of Lepmassoun and Ondoamedza rivers. Lepmassoun and Ondoamedza rivers form part of the larger Nyong river basin in Cameroon. In situ water physicochemical parameters were determined on site, preserved water samples used in mineral analysis and subsequent ecological health assessment. Shrimps were sampled using the scoop method with hand nets and analyzed. Sampling was done in 5 seasons distributed from January 2017 to February 2018. The results of physicochemical parameters indicate that water in the two rivers was slightly mineralized, sufficiently oxygenated and slightly turbid. It was generally a non-polluted ecological zone for shrimps. A total of 113 shrimps distributed among 14 species were collected. The shrimp population included Macrobrachium macrobrachion Macrobrachium idae, Macrobrachium rude, Macrobrachium niloticus , Macrobrachium dux Macrobrachium sp1, Macrobrachium sp2, Macrobrachium sp3,Macrobrachium sp4, Macrobrachium sp4, Macrobrachium sp5, Macrobrachium sp6, Macrobrachium sp7, Macrobrachium sp8 and Macrobrachium sp9.In the river Odoameza 11 species were collected among which Macrobrachium sp8 (26.02%) is abundant, though,in the river Lepmassoun we collected 10 species dominanced by Macrobrachium macrobrachion (22,5%). The species Macrobrachium macrobrachion is most ubiquiste throughout river Lepmassoun (%O = 83.33%) The river basin of Lepmassoun had a higher population of Macrobrachium macrobrachion with a percentage occurrence of 66.67%. then It is concluded that the water in the two river basins is of good ecological quality for shrimp survival with species Macrobrachium macrobrachion dominating in the river lepmassoun. In the river Ondoameza Macrobrachium sp8, Macrobrachium idea, Macrobrachium macrobrachion,Macrobrachium sp4 having all the percentage of occurrence (%O) of 66.67% are relatively represented. Only Macrobrachium dux have Ovigerous females in our study. This Ovigerous females ranged from 50.38 to 64.18 mm and egg size varied from 1.7 to 2 mm. The prawn attained a maximum total length and weight of 64,18 m and 2,96 g respectively. In our basins slope the Macrobrachium dux reproduces twice year during the big dry season and small dry season since production is early and the eggs are rather broad by consequence the larval development is shortened

Determination of the optimum period for ciliated protozoa colonizing of an artificial substrate in a tropical aquatic ecosystem

The optimum period for ciliated protozoa colonizing of an artificial substrate, the polyurethane foams have been assessed in a tropical aquatic ecosystem, the Ekozoa stream of the Mfoundi River Basin in Yaounde (Cameroon). 5 days were calculated as the highest period for the biological indicators of pollution to optimally colonize the artificial substrate. This time interval is the same for all the sampling stations assessed from upstream to downstream and the various microhabitats along the water course. The statistical method applied is that of the completely randomized blocks. The colonization of the substrate increases from the first day to the fifth day, before decreasing to the tenth day. The statistical analysis of variance between the maximum day and the other sampling period was significant at 5 % while the calculation of the value between different points of the same station was not significant. The average number of ciliated protozoan ranges from 20 to 23, from upstream to downstream

Application of biological indices in the assessment of pollution in the Mfoundi River Basin (Cameroon)

No Abstract. JCAS Vol. 6 (2) 2006: pp. 91-9

Zastosowanie symulacyjnego modelu oceny jakości wody w zapobieganiu eutrofizacji tropikalnych systemów wodnych: Przykład jeziora Obili w Yaounde (Kamerun)

Lake Obili is one of the most famous lakes in the city of Yaounde, Cameroon. Studies carried out in this lake showed that it was hyper eutrophic and therefore it represents a great danger because it is used for aquaculture, tourism and a suitable laboratory for hydro-biological engineering. It is thus very vital to restore this lake ecosystem that singles itself in the heart of the city of Yaounde. This can be greatly facilitated through the use of Water Quality Analysis Simulation Program (WASP) of the United State Environmental protection Agency (USEPA). The outcomes of the previous results obtained from EUTRO, a Subroutine of the WASP model specialised in determining eutrophication level have proven that the remediation of this lake can be achievable through the implementation of a wet dredging, the construction and restoration of a wastewater treatment plant, the implementation of environmental incentive policies and the arrangement of the access to the lake. The application of the model is a contribution to the scientific mastery of nutrient flow, lake functioning and possibilities of restauration of highly polluted tropical water bodies subjected to domestic and industrial pollution.Jezioro Obili jest jednym z najbardziej znanych w mieście Yaounde w Kamerunie. Wyniki badań jeziora świadczą o jego skrajnej eutrofizacji, będącej poważnym zagrożeniem, ponieważ jezioro jest wykorzystywane w akwakulturze, do celów turystycznych, stanowi też laboratorium inżynierii hydrobiologicznej. Z tego powodu należałoby przeprowadzić rekultywację tego szczególnego ekosystemu jeziornego. Rekultywację jeziora może znacznie usprawnić zastosowanie programu analizy jakości symulacji wód (WASP) Agencji Ochrony Środowiska Stanów Zjednoczonych (USEPA). Wyniki poprzednich badań uzyskanych z EUTRO (podprogramu modelu WASP) wyspecjalizowanego w ocenie poziomu eutrofizacji dowiodły, że rekultywacja jeziora jest możliwa poprzez usuwanie osadów, budowę i unowocześnienie oczyszczalni ścieków, wdrożenie innowacyjnej polityki wodnej i zorganizowanie dostępu do jeziora. Zastosowanie modelu stanowi wkład w naukowe rozpoznanie przepływu pierwiastków biogennych, funkcjonowania jeziora i możliwości rekultywacji zanieczyszczonych zbiorników wodnych strefy równikowej

Enumeration of Cryptosporidium spp and Giardia spp (oo)cysts in a tropical eutrophic lake: The municipal lake of Yaounde

The biodynamic of Cryptosporidium spp. oocysts and Giadia spp. cysts have been assessed in the municipal lake of Yaounde, which is an artificial eutrophic lake that has been constructed on the Mingoa stream of the Mfoundi River Basin of Cameroon. The oocysts were identified by the Ziehl-Neelsen method while the cysts were identified by the Lugol iodine coloration. The values obtained suggest an increase in (oo)cysts density from the surface to the bottom of the lentic ecosystem. The oocysts varied from 56 oocysts/L in the upper layer to 2640 oocysts/L of water in the lowest layer, while the cysts population dynamics ranged from 24 cysts/L at the surface layer of the lake to 1713 cysts/L at the lowest layers of the lake. There was a considerable reduction in the resistant forms of these emerging pathogenic protozoa between the surface water of the Mingoa stream entering the Lake and that coming out from the Lake. The highest value of Cyptosporidium oocysts determined at the entrance of the lake is 1480 oocysts/L while at the outlet the highest value of oocysts identified is 620 oocysts/L. The highest value of Giardia cysts determined at the entrance of the lake is 352 cysts/L while at the outlet the highest value recorded is 294 cysts/L

Biodiversity and spatial distribution of Rotifera in a shallow hyperuetrophic tropical Lake (Cameroon)

No Abstract.Journal of the Cameroon Academy of Sciences Vol. 6 (3) 2006: pp. 149-16