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

Modifications des propriétés d’abondance bactériennes des eaux souterraines en réponse à une longue durée de stockage dans les récipients à domicile à Yaoundé (Cameroun)

Une étude a été conduite dans le but de déterminer la dynamique d’abondance des bactéries dans les échantillons d’eaux souterraines en condition de stockage. Les échantillons d’eau analysés ont été obtenus des sources et des puits de Yaoundé. La durée de stockage a été de 144 heures et chaque échantillon stocké en duplicat dans deux bidons, l’un ouvert et l’autre fermé a été analysé toutes les 24 heures. Les techniques de dénombrement des germes utilisées ont été celles des membranes filtrantes et d’étalement en surface. Les abondances bactériennes dans les eaux, aux jours de prélèvement, atteignent en moyenne 1470 UFC·mL−1 pour les BHAM, 550 UFC·100 mL−1 pour les staphylocoques et 1365 UFC·100 mL−1 pour les Enterobacteriaceae. Au bout de 144 heures de stockage, on observe une diminution générale de l’abondance des staphylocoques et des entérobactéries aussi bien dans les eaux de source que dans celles de puits. Les taux d’inhibition apparents de croissance des staphylocoques ont atteint −16,4 divisions·jour−1 dans les eaux de source et −68,22 divisions·jour−1 dans les eaux de puits. Ceux des entérobactéries ont atteint −28,78 divisions·jour−1 et −74,69 divisions·jour−1 dans les eaux de source et de puits respectivement. L’abondance des BHAM augmente considérablement au bout de 144 heures de stockage d’eau. Leurs taux de croissance apparents ont été élevés dans les eaux de source comme dans celles de puits et ont atteint 1931,1 divisions·jour−1. Les abondances des staphylocoques et celles des entérobactéries sont positivement corrélées (P 0,05). Les résultats suggèrent que la dynamique d’abondance bactérienne dans l’eau souterraine serait déterminée par les caractéristiques chimiques et biologiques et les activités et interactions des microorganismes des eaux stockées

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

Desarrollo, poscolonialismo y teor\ueda pol\uedtica

The main purpose of this investigation was to rank in the hierarchical order, some factors which may be predominant in the daily changes in the abundance of Enterobacteriaceae in wells, in equatorial area of Cameroon (Central Africa). Those factors included electrical conductivity, color, temperature, total suspended solids (TSS), pH, turbidity, CO2, NH4+ , BOD5, and the cell concentration at the initial moment. The water temperature ranged between 19 and 20 °C. The turbidity in wells varied from 1.2 to 103 FTU. The highest concentrations of TSS varied from 10 to 102 mg.L-1. The values of water color fluctuated between 37 and 494 PtCo. The pH ranged from 4.93 to 8.04. The highest concentrations of dissolved CO2 reached 15.84 mg.L-1 and the lowest value was 8.8 mg.L-1. The values of electrical conductivity fluctuated between 244 and 767 µS.cm-1. The concentrations of NH4+ varied from 2.42 to 10.2 mg.L-1. The BOD5 values ranged from 5 to 125 mg.L-1. The bacteria concentrations at the initial moments for the whole wells points varied from 1.30 to 5 log units.mL-1. After 2 h of incubation, it fluctuated between 1.30 and 5 log units.mL-1. After 4 h incubation, it fluctuated between 1.30 and 4.78 log units.mL-1. It ranged between 1.30 and 4.80 log units.mL-1, 1.30 and 4.78 log units.mL-1, 1.30 and 4.84 log units.mL-1, and 1.30 and 4.90 log units.mL-1 after 6 h, 8 h, 10 h and 12 h of incubation respectively. The cell abundance undergoes fluctuation during incubation in each wells point. The concentration of Enterobacteriaceae decreased during the first hours of incubation in most cases. The decrease was followed after a delay that varied according to the sampling campaign, with an increase of cell abundance. Using the power-law function, it was noted that the dominant factors in the daily changes of instantaneous cell abundances, in decreasing hierarchical order were NH4+ , pH, dissolved CO2, turbidity, color, total suspended solids, and the BOD5. The electrical conductivity and the concentration of cells at the initial moments played a minor role. It also let out that in natural aquatic systems all factors do not impact at the same time