Evaluation de l’abondance des kystes des protozoaires flagellés dans les eaux usées exploitées en agriculture maraîchère en zone urbaine: Cas de la ville de Yaoundé (Cameroun)

Objectifs: Evaluer l’abondance des formes de dissémination des protozoaires flagellés dans les eaux usées exploitées en agriculture maraîchère dans certains bas fonds de la ville de Yaoundé.Méthodologie et résultats: Une étude a été menée de novembre 2013 à avril 2014 avec une phase d’identification et d’analyse bio-statistique de 2015-2016. Des échantillonnages des eaux ont été effectués. Les kystes des protozoaires flagellés ont été identifiés à l’aide de la coloration au Lugol après concentration des échantillons suivant la méthode par flottaison au sulfate de zinc. Les analyses biologiques des eaux révèlent la présence des kystes des Protozoaires flagellés avec des densités moyennes de 101 ± 70 kystes/L pour Giardia intestinalis, 34 ± 20 kystes/L pour Chilomastix mesnili, 3 ± 6 kystes/L pour Retortamonas intestinalis et 1 ± 3 kystes/L pour Enteromonas hominis. En général, les plus fortes densités de kystes sont enregistrées pendant la petite saison des pluies (172 ± 108 kystes/L). Les analyses statistiques montrent des corrélations significatives (P ≤ 0,05) entre la densité des kystes des protozoaires flagelles identifiées et les paramètres physico-chimiques tels que les MES, l’oxydabilité et la turbidité.Conclusions et application des resultsts: Les plantes doivent être bien lavées, désinfectées et bien cuites avant leurs consommations afin de réduire les risques sanitaires.Mots clés: kystes, protozoaires flagellés, agriculture maraîchère, bas-fonds et zone urbaineEnglish AbstractObjectives: To evaluate the abundance of environmental forms of flagellated protozoa in waste water that is exploited for urban wetland agricultural practices in Yaoundé.Methodology and results: A study was carried out from November 2013 to April 2014, with bioenvironmental and bio-statistical assessment from 2015-2016. Sampling took place on monthly basis. The flagellated protozoan cysts were identified by lugol coloration after concentrating the samples according to the method -of flotation using zinc sulphate. Biological analysis of water showed the presence of flagellated protozoan cysts with average densities of (101 ± 70 cysts/L) for Giardia intestinalis, Chilomastix mesnili (34  ± 20 cysts/L), of Retortamonas intestinalis (3 ± 6 cysts/L) and of Enteromonas hominis (1 ± 3 cysts/L). Generally, the highest cysts densities were registered during the short rainy season (172 ± 108 cysts/L). The Statistical analysis showed positive correlations (P ≤ 0, 05) between the density of these cysts and physic-chemical variables such as suspended solids, oxydability and turbidity. This testifies the importance of colloidal or suspended particles in the transportation of micro-organisms in water.Conclusion and application of results: In view of these results and the importance of urban agricultural practices in Yaoundé, plants must be well washed and properly cooked before consumption in order to avoid a health risk that is limited to the spread of this waterborne pathogen in this metropoly.Keywords: Cyst, flagellated protozoa, wetland agricultural, dregs and urban zon

Spatio-temporal changes in the abundance of the populations of the gastrotrich community in a shallow lake of tropical Africa

AbstractStudies on the biodiversity and population dynamics of freshwater planktonic Gastrotricha have been carried out in conjunction with a physical–chemical analysis of the water in the Yaounde Municipal Lake (Cameroon, Central Africa) over a 14 months period (November 1996–December 1997). The results obtained allow to consider the Yaounde Municipal Lake as an eutrophic lake. It harbours eight species of Gastrotricha belonging to four genera (Chaetonotus, Dasydytes, Neogossea and Polymerurus) of the order Chaetonotida. This community was characterized by high abundances of populations, and was dominated by the genus Neogossea and Chaetonotus reaching up to 2000ind.L−1. Polymerurus was mostly abundant at the almost anoxic bottom layers. The highest abundances were found mostly during the rainy season, when there is an important sedimentation process of organic matter, and were influenced by several different environmental factors such as dissolved oxygen, temperature and pH of the water.Finally this community which may play an important role in the water bodies, is a potential water quality indicator

Peuplement phytoplanctonique et qualité des eaux en milieu lacustre anthropisé: Cas du lac municipal de Yaoundé (Cameroun)

An annual qualitative and quantitative evaluation of phytoplankton and chlorophylla, as well as of some physico-chemical parameters were recorded in the Yaounde Municipal Lake. Physico-chemical measurements were also regularly done in its main tributary (Mingoa stream). The study aimed at demonstrating the cultural eutrophication of this lake. The discharge of untreated urban effluents into the lake seriously threatens his health state. Indeed, the water transparency is globally low and exceptionally exceeds 1m. Water conductivity is higher near the lake bottom, reaching 408 μS cm-1. The strong deficiency in oxygen contents recorded from 2.5m depth leads to the production of high quantities of ammonium nitrogen. The total phosphorus concentrations vary from 80 to 1650 μgP l-1, and the total Kjeldhal nitrogen concentrations fluctuate between 3 and 15 mgNH4 + l-1.  Upstream, the Mingoa exhibits total phosphorus concentrations ranging from 600 to 3800 μgP l-1, and total Kjeldhal nitrogen concentrations ranging from 10 to 22 mgNH4 + l-1. Conditions prevailing in this biotope favour a massive growth of phytoplankton, dominated by Euglenophyta and Chlorophyta. Both spatio-temporal analysis of phosphorus, chlorophyll a, and the composition of the  phytoplanktonic community, stress the anthropogenic impact on the ecosystem. The progression of this hydrosystem towards a dystrophic state is going on, and implies an urgent need for its restoration, followed by a rehabilitation of the “Grand Messa” sewage treatment plant, and the elimination process of solid materials in the tributary, upstream. Key words: sewage, lake, phytoplankton, eutrophication, central Africa

Ecological Influence of Organic Pollution on the Distribution of Benthic Macroinvertebrates in Some Control Forest Watercourses in Cameroon

Monitoring of water quality and distribution of some benthic macroinvertebrates was carried out in a few control watercourses in the Mefou watershed, from August 2022 to June 2023 with the aim of identifying some ecological factors that influence the distribution of benthic organisms in forest areas. The evaluation of granulometric and physicochemical quality was carried out following the appropriate methods and the collection of benthic organisms following the multihabitat approach. The analysis of the particle size parameters shows that the coarse fraction dominates all the points explored, although the beginning of siltation was observed in the middle part of the Abouda and Fam rivers. Physico-chemical analyses revealed a relatively stable environment with well-oxygenated water, low values of organic pollution indicator parameters and low and constant temperatures throughout the watersheds. The analysis of the biological structure shows a total of 8483 individuals collected, all belonging to the arthropod phylum and the insect class. From the orders obtained, Hemiptera dominate the benthic fauna with 6 identified families. The organisational structure of the benthic community was analysed through the calculation of diversity and fairness indices and allows us to affirm that the benthic macroinvertebrate community is diverse and well organised.&nbsp

Isolement et mise en évidence des oocystes de Cyclospora cayetanensis dans un hydrosystème polysaprobe en zone équatoriale, Afrique Centrale

Peu de données sont disponibles sur la distribution des Apicomplexa parasites du tube digestif de l’homme. Ils causent pourtant des maladies diarrhéiques de très grande envergure. Une étude menée de janvier à août 2011, dans le cours d’eau Olézoa à Yaoundé (Cameroun), a visé à rechercher et caractériser les oocystes de Cyclospora cayetanensis. Les échantillonnages ont été effectués en amont et en aval du cours d’eau, sur deux stations localisées en zone fortement anthropisées. L’identification des oocystes de C. cayetanensis isolés à l’aide de l’observation directe après coloration au Lugol et selon la technique de Ziehl-Neelsen, a montré qu’ils sont constitués de deux sporocystes contenant chacun deux sporozoïtes. La dynamique d’abondance de ce microorganisme est significativement corrélée à la turbidité, à la température et au pH de l’eau (p < 0,01). Par ailleurs, les formes non sporulées sont plus abondantes que les formes sporulées dans l’environnement et sont fortement corrélées aux teneurs en oxygène dissous qui est un paramètre très important pour leur sporogénèse. En amont du cours d’eau, l’abondance la plus élevée de C. cayetanensis a été de 407 oocystes•L-1 et la valeur enregistrées en aval été de 250 oocystes•L-1. La population de C. cayetanensis observée a été largement dominée par les formes non sporulées de taille 8 µm. La concentration des oocystes la plus élevée en utilisant la technique directe et celle de Ziehl-Neelsen a été enregistrée respectivement au cours des mois de juin et juillet; ces périodes se situent respectivement à la fin de la petite saison des pluies et au début de la saison sèche.Little information is available on the distribution of enteropathogenic apicomplexa of the human digestive apparatus, these agents being responsible for endemic diarrheic diseases. A study carried out in the Olézoa water course in Yaoundé (Cameroon) revealed that this water contains the oocysts of Cyclospora cayetanensis. Samples for the analysis of biological and physico-chemical characteristics were obtained upstream and downstream with respect to the strongly human polluted zone. The identification of Cyclospora cayetanensis oocysts by direct observation and Ziehl-Neelsen techniques revealed that these oocysts contain two sporocysts, each having two sporozoïtes. Statistically, turbidity, temperature and pH have a significant effect (p<0.01) on the population dynamics of these microorganisms. The highest mean concentration of oocysts identified upstream was 407 oocysts•L-1 in the month of August. The non sporulated forms of oocysts are more abundant than the sporulated forms in the environment and are strongly linked to dissolved oxygen levels, oxygen being a parameter that is very important for the process of sporulation and viability. Non sporulated forms of oocysts, 8 µm in size, are dominant in the ecosystem analyzed in our investigations. These resistant forms of parasites that are present in the surface and wastewater represent a considerable health risk to the inhabitants of the study zone who could easily be exposed to cyclosporiasis.The two methods which have been carried out are complementary in the characterisation of the resistant forms of these enteropathogens

Facteurs environnementaux et répartition spatiale des crustacés dans un cours d'eau peu anthropisé à Makak (Région du Centre Cameroun)

This study examines the influence of environmental factors on the spatial distribution of crustaceans in the Matourou stream, located in a forest area of the District of Makak (Center Region of Cameroon). The physico-chemical analyses reveal good ecological conditions : waters slightly basic (average pH value of 7.28 ± 0.81), well oxygenated (saturation rate = 82.54 ± 8.22 %), slightly mineralized (electrical conductivity = 25.89 ± 6.13 µS/cm) and with low organic matter loads (oxydisability = 1.42 ± 1.70 mg/l). Concerning crustaceans, two freshwater shrimp species known as Caridina sp. (Atyidae) and Macrobrachium sp. (Palaemonidae), and an undetermined species of crab belonging to the genus Soudanonautes (Potamidae), were identified. A total number of 2132 individuals were collected. Caridina sp. is the dominant species with 90.43 % of relative abundance, followed by Soudanonautes spp. (7.83 %) and Macrobrachium sp. (1.74 %). Macrobrachium sp. is absent in the upper stream

Relationships between Physico-Chemical Parameters and Taxonomic Structure of Benthic Macroinvertebrate Assemblages in Streams of West Cameroon

International audienceTropical rivers are strongly influenced by stormwaters, pollutants and agro-pastoral activities. These systems are no longer able to maintain their native biota. Therefore, it seems important to understand how biological assemblages are driven by environmental gradients at different spatial scales. However, information on the relationships between the distribution of aquatic macroinvertebrates and environmental variables remains scarce in Cameroon. To improve our knowledge on the drivers of such distributions, a study was carried out at 11 contrasted sites from three catchments located in West Cameroon. This study aimed at understanding the spatio-temporal variations of 19 taxonomic metrics calculated for the benthic macroinvertebrate assemblages of these sites sampled during 13 months, concurrently with physico-chemical analyses of water quality. Two hundred and twelve taxa were caught. Diptera(rf-S), Shannon-Wiener diversity, 1–GOLD, total richness, Pielou evenness and Heteroptera(rf-S) revealed their high ability to respond to anthropogenic pressures or disturbances. Conductivity, water temperature, dissolved oxygen, nitrates, total hardness and alkalinity were identified as the main physico-chemical drivers of the taxonomic structure of benthic assemblages. These results will allow further exploration of the implementation of a tool for monitoring the ecological quality of West Cameroon rivers

First data on the groundwater quality and aquatic fauna of some wells and springs from Yaounde (Cameroon)

A first approach of the well and spring fauna of Cameroon, based on a study performed in the Yaounde Basin has shown that the organisms collected were mostly exogenous and epigean - probably from surface limnetic origin - but two taxa were strictly stygobiontic species, living only in groundwaters. In the 14 sampled wells, 23 different aquatic taxa were collected and in the 11 springs only 15 species. However the aquatic taxonomic richness, ranging from 1 to 11 in the wells and from 2 to 7 in the springs corresponds to an average number of taxa not very different in the two types of habitat: 4.6 in wells and 4.9 in springs. The main physico-chemical characteristics of the water in the different studied stations were mesured and showed generally a significant level of pollution. The abundance and distribution of animal species were possibly related to some physico-chemical characteristics of the water and moreover to the level of protection of water from external light and disturbances. Multivariate analyses of the station-species matrixes suggested that the first parameters of distribution of these organisms were the physico-chemical characteristics of the water, in wells as well as in springs, and the water quality seemed to be an important ecological characteristic of habitats. Among the 23 taxa collected in wells, the stygobiontic crustaceans (aquatic isopods of the family Stenasellidae) were represented by two different species belonging to the genus Metastenasellus. This genus - and all the family - were reported for the first time from Cameroon. Since the stenasellid crustaceans are considered originated directly from coastal marine ancestors (the whole family is completely absent in the continental worldwide surface waters) the importance and possible geological implications of this occurrence in continental Cameroon groundwaters are briefly discussed

Impact of the anthropogenic activities on the diversity and structure of benthic macroinvertebrates in tropical forest stream

The diversity and structure of benthic macroinvertebrates related to some physico-chemical parameters were studied in the Konglo stream, an affluent of the Nyong river in Cameroon. The benthic macroinvertebrates were collected at three stations according to multihabitat the approach and physic-chemical parameters were sampled and analyzed using classic methods between February 2014 and August 2014. During this study, 1969 individuals belonging to 3 phyla, 7 classes, 16 orders, 63 families and more than 90 genera were sampled. The class of Insects, including 9 orders, 54 families and more than 79 genera, predominates with 74.81 % of the relative abundance, followed by the class of Decapods regrouping 21.94 % of the individuals distributed in 1 order, 2 families and 2 genera, however less varied. The other classes (Achaeta, Oligochaeta, Bivalvia, Gastropoda and Arachnida) represent only 3.25 % of relative abundance. The spatial variation of taxonomical richness shows a decrease of the diversity from upstream to downstream as well as the Ephemeroptera-Plecoptera-Trichoptera (EPT) index. Moreover, the Sörensen similarity index indicates dissimilarity between the station K3 and the two others stations. Otherwise, the rank-frequency diagram of Frontier and the Shannon and Weaver index show that the structure of benthic macroinvertebrates is in ecological starting succession in upstream and middle while it is closed to ageing in downstream

Water Quality And Benthic Macroinvertebrates Of Tropical Forest Stream In South-West Region, Cameroon

A study was carried out in Ndongo stream, located in Buea, from May to October 2017, to assess the water quality and evaluate the structure of benthic macroinvertebrates. Physicochemical analysis showed that water from Ndongo was well oxygenated (82.21 ± 6.59 %), slightly acidic (pH=6.82 ± 0.22 UC) and alkaline with low quantities of nitrogen compound (2.9 ± 3.57 mg/L NO3+; 0.02 ± 0.02 mg/L NO2– and 0.89 ± 1.78 mg/L NH4+). Regarding the biology of macroinvertebrates, a total of 2058 individuals were collected and identified into 4 phyla, 5 classes, 11 orders, 32 families and belonging to 44 genera. The Shannon & Weaver and Pielou evenness reveal that the benthic macroinvertebrates were more diversified in upstream