No abstract

The abundance dynamic of some freshwater invertebrates in relation with the abiotic factors of the medium was studied from March 2013 to March 2014 on the main streams of the Wouri and Sanaga basins. Individuals of Copepoda, Atyidae, Chironomidae and Physidae were collected, identified and counted. Samplings were carried out monthly; meanwhile measurements of the environmental variables were taken. Results of the physico-chemical analyses revealed that water of the Sanaga basin is globally well oxygenated (77% -92%) and faintly mineralized (14 -107 µS/cm), excepted in the stations receiving household pollutants. Inversely, in the Wouri basin, waters are hypoxic with high content of organic matters (27.79 ± 9.43 mg/L). During rainy season (June-September), there is a dilution-dispersion of the organic matter due to stormwaters. Concerning biological analyses, the families of Physidae and Chironomidae were more abundant in urban stations than in stations situated in suburban area, especially during low water level period, showing that they are well adapted to anthropogenic and organic pollutions. The hypoxic conditions of urban waterways do not favor the proliferation of sensitive taxa such as Atyidae and Copepoda. These taxa preferred well oxygenated waters with rapid flow, and are more abundant during rainy season in stations located in suburban area or which are less subjected to anthropogenic disturbances.

The present work used multiple linear regression (MLR) models and corrgram to assess the importance of environmental parameters on diversity and abundance dynamics of Vibrio sp. in waters of few landing stages in the city of Douala (Cameroon). It was recorded in all the five selected stations, the presence of four species of Vibrio namely, Vibrio parahaemolyticus, Vibrio cholerae, Vibrio fluvialis and Vibrio alginolyticus whose highest abundance reached 5.65, 6.26, 4.9 and 4.83 log CFU/100 ml respectively. Vibrio cholerae was the most isolated during the study with a frequency of 65%. The abundance dynamics of these germs is strongly influenced by nitrates, salinity, dissolved carbon dioxyde (CO 2 ) and ammonium ions (NH 4 + ). The visualization of corrgram shows high degree of association between studied parameters. We note a coefficient of determination r 2 = 0.50 for the multiple linear regression model for Heterotrophic Aerobic Bacteria (HAB) and a coefficient of determination r 2 = 0.58 for the MLR model for V. cholerae. The physicochemical parameters explain at 43% (r 2 = 0.43) the distribution of the abundances of V. parahaemolyticus, at 45% (r 2 = 0.45) the distribution of abundances of V. alginolyticus and at 26% (r 2 = 0.26) for V. fluvialis.

Microcosm experiments were carried out to investigate the effect of Eucalyptus microcorys aqueous plant extract on pathogenic Escherichia coli survival in water. The results clearly showed that the combined effect of light and extract concentration impacted significantly survival of the bacteria. The dark inhibition coefficient (KD) was 0.102 h-1, 0.116 h-1, 0.111 h-1, 0.123 h-1, 0.136 h-1 and 0.146 h-1 with 0.05%, 0.1%, 0.5%, 1%, 1.5% and 2% of extract concentration respectively. In the light conditions, we noted a relative increase of light inhibition coefficient (KL). The Self-Organizing Map according to incubation duration of cells in the extract solution permitted to group bacterial abundances in three clusters. Cluster I is the abundance of cells registered after 24 hours incubation in the plant extract solution. Cluster II is made up of all cells abundances registered after 9 and 12 hours incubation and Cluster III is constituted by cells abundances obtained after 3 and 6 hours incubation. Globally, for extract concentration 1, 1.5 and 2%, a calculation using Chick-Watson model resulted to a value of log(N/No) = -0.1Ct which is very close to chlorine disinfectant Chick-Watson model log(N/No) = -0.16 Ct. These results can improve in the new alternative method of treatment water by plant extracts.