Microbiological water quality of the Mfoundi River watershed at Yaoundé, Cameroon, as inferred from indicator bacteria of fecal contamination Djuikom, E.; Njine, T.; Nola, M.; Sikati, V.; Jugnia, L.-B. Abstract. Using the membrane filtration technique to count total coliform (TC), fecal coliform (FC) and fecal streptococci (FS), the microbiological water quality of the Mfoundi River and four of its representative tributaries at Yaoundé, Cameroon, was assessed for human use and contact. Sampling was conducted so as to examine the potential origin of fecal contamination and how rainfall affects the measured concentrations of indicators organisms. Our results revealed that waters were not safe for human use or primary contact according to the standards for water quality established by the Word Health Organization (WHO). Indeed, these waters exhibited high concentrations of TC (Mean ± SD = 5.6 × 10 8 ± 2.5 × 10 6 CFU/100 ml), FC (Mean ± SD = 6.8 × 10 5 ± 2.4 × 10 3 CFU/100 ml) and FS (Mean ± SD = 7.3 × 10 5 ± 2.1 × 10 3 CFU/100 ml) that varied with the sampling sites and points. FC/FS ratio suggested that this contamination was more from warm-blooded animals than humans and correlation analysis points to the role of rainfall as a contributing factor, which enhanced the bacterial numbers detected. We conclude that there is a great potential risk of infection for users of waters from the Mfoundi River and its tributaries at Yaoundé.
An experimental passive methane oxidation biocover (PMOB) was constructed within the existing final cover of the St-Nicéphore landfill. Its substrate consisted of a 0.80-m thick mixture of sand and compost. The goal of this experiment was to evaluate the performance of the PMOB in reducing CH 4 emissions when submitted to an increasing methane load. The CH 4 load applied started with 0.3 g CH 4 m −2 h −1 . When the site had to be closed for the winter, the CH 4 input was 27 g CH 4 m −2 h −1 . Throughout the study, practically all the CH 4 input was oxidized, absolute removal rates were linearly correlated to methane loading, and the oxidation zone was established between 0.6-0.8 m. These results seem to indicate that the upper limit potential of this PMOB to oxidize CH 4 was not reached during the study period. Surface CH 4 concentration scans showed no signs of leaks. The substrate offered excellent conditions for the growth of methanotrophs, whose count averaged 3.91 x 10 8 CFU g dw -1 soil.
We examined the impacts of remediation activities aimed at improving the water quality of hypereutrophic Villerest Reservoir, in which Microcystis aeruginosa dominated during the summer. We also compared nutrients and chlorophyll a data from this study with the results of a previous study on the reservoir. Between the two studies, the nitrogen and phosphorus loads into the reservoir from the main tributary decreased by 70% and 80%, respectively. Within the reservoir, the quantities of ammonianitrogen were similar in the two studies, and the total nitrogen was significantly higher in this study compared to the initial study. Both the phosphate-phosphorus and total phosphorus concentrations decreased significantly between the two studies. However, the statistically significant decrease in phosphate-phosphorus and total phosphorus did not always lead to a significant decrease in chlorophyll a concentrations. The nitrogen/phosphorus mass ratio during the present study remained well above five, the critical value below which summer blooms of Microcystis aeruginosa were observed in Villerest Reservoir. These study results indicated that the remediation activities being used to improve the water quality of Villerest Reservoir were off to a good start.
Phytoplankton dynamics, bacterial standing stocks and living microbial biomass (derived from ATP measurements, 0.7-200 mm size class) were examined in 1996 in the newly flooded (1995) Sep Reservoir ('Massif Central,' France), for evidence of the importance of the microbial food web relative to the traditional food chain. Phosphate concentrations were low, N:P ratios were high, and phosphate losses converted into carbon accounted for <50% of phytoplankton biomass and production, indicating that P was limiting phytoplankton development during the study. The observed low availability of P contrasts with the high release of "directly" assimilable P often reported in newly flooded reservoirs, suggesting that factors determining nutrient dynamics in such ecosystems are complex. The phosphate availability, but also the water column stability, seemed to be among the major factors determining phytoplankton dynamics, as (i) large-size phytoplankton species were prominent during the period of increasing water column stability, whereas small-size species dominated phytoplankton assemblages during the period of decreasing stability, and (ii) a Dinobryon divergens bloom occurred during a period when inorganic P was undetectable, coinciding with the lowest values of bacterial standing stocks. Indication of grazing limitation of bacterial populations by the mixotrophic chrysophyte D. divergens (in late spring) and by other potential grazers (mainly rotifers in summer) seemed to be confirmed by the Model II or functional slopes of the bacterial vs phytoplankton regressions, which were always <0.63. Phytoplankton biomass was not correlated with phosphorus sources and its contribution was remarkably low relative to the living microbial biomass which, in contrast, was positively correlated with total phosphorus in summer. We conclude that planktonic microheterotrophs are strongly implicated in the phosphorus dynamics in the Sep Reservoir, and thus support the idea that an important amount of matter and energy flows through the "microbial loop" and food web, shortly after the flooding of a reservoir.
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