Physicochemical water quality of the Mfoundi River watershed at Yaoundé, Cameroon, and its relevance to the distribution of bacterial indicators of faecal contamination.

Water quality of the Mfoundi River and four of its tributaries was studied by assessing some physicochemical variables (temperature, pH, conductivity, chlorides, phosphates and nitrogen ammonia, dissolved oxygen and carbon dioxide, organic matter content and Biological Oxygen Demand) and their influence on the distribution of bacterial indicators of faecal contamination (total coliform, faecal coliform and faecal streptococci). For this, standard methods for the examination of physicochemical parameters in water were followed, and statistical analysis (Pearson correlations) used to establish any relationships between physicochemical and biological variables. Our results revealed that almost all of the examined physicochemical variables exceeded World Health Organization (WHO) guidelines for recreational water. This was in agreement with a previous microbiological study indicating that these waters were not safe for human use or primary contact according to water quality standards established by the WHO. Results of our correlation analysis suggested that physicochemical and biological variables interact in complicated ways reflecting the complex processes occurring in the natural environment. It was also concluded that pollution in the Mfoundi River watershed poses an increased risk of infection for users and there exists an urgent need to control dumping of wastewater into this watershed

An assessment of the impact of Mingoa Stream input to the bacteriological quality of the Municipal Lake of Yaoundé (Cameroon)

International audienceTo investigate the deteriorating bacteriological water quality of Municipal Lake of Yaoundé, the degree of pollution of the Mingoa Stream, the main tributary of the lake, was evaluated for total coliforms, thermotolerant coliforms, and fecal streptococci. Concentrations of these bacterial indicators in Mingoa Stream were higher than those allowed by international norms for the bacteriological quality of recreational water. Thus, this stream contributes to the high levels of bacteria number in the water column of the Municipal Lake

Dynamics and estimates of growth and loss rates of bacterioplankton in a temperate freshwater system

International audienceThe growth rate and losses of bacterioplankton in the epilimnion of an oligo-mesotrophic reservoir were simultaneously estimated using three different methods for each process. Bacterial production was determined by means of the tritiated thymidine incorporation method, the dialysis bag method and the dilution method, while bacterial mortality was assessed with the dilution method, the disappearance of thymidine-labeled natural cells and ingestion of fluorescent bacterial tracers by heterotrophic flagellates. The different methods used to estimate bacterial growth rates yielded similar results. On the other hand, the mortality rates obtained with the dilution method were significantly lower than those obtained with the use of thymidine-labeled natural cells. The bacterial ingestion rate by flagellates accounted on average for 39% of total bacterial mortality estimated by the dilution method, but this value fell to 5% when the total mortality was measured by the thymidine-labeling method. Bacterial abundance and production varied in opposite phase to flagellate abundance and the various bacterial mortality rates. All this points to the critical importance of methodological aspects in the elaboration of quantitative models of matter and energy flows over the time through microbial trophic networks in aquatic systems, and highlights the role of bacterioplankton as a source of carbon for higher trophic levels in the studied system

Dynamics and estimates of growth and loss rates from bacterioplankton in a temperate freshwater system

The growth rate and losses of bacterioplankton in the epilimnion of an oligo-mesotrophic reservoir were simultaneously estimated using three different methods for each process. Bacterial production was determined by means of the tritiated thymidine incorporation method, the dialysis bag method and the dilution method, while bacterial mortality was assessed with the dilution method, the disappearance of thymidine-labeled natural cells and ingestion of fluorescent bacterial tracers by heterotrophic flagellates. The different methods used to estimate bacterial growth rates yielded similar results. On the other hand, the mortality rates obtained with the dilution method were significantly lower than those obtained with the use of thymidine-labeled natural cells. The bacterial ingestion rate by flagellates accounted on average for 39% of total bacterial mortality estimated by the dilution method, but this value fell to 5% when the total mortality was measured by the thymidine-labeling method. Bacterial abundance and production varied in opposite phase to flagellate abundance and the various bacterial mortality rates. All this points to the critical importance of methodological aspects in the elaboration of quantitative models of matter and energy flows over the time through microbial trophic networks in aquatic systems, and highlights the role of bacterioplankton as a source of carbon for higher trophic levels in the studied system.NRC publication: Ye

Methane oxidation within an experimental landfill cover

Abstract: An experimental landfill cover composed of a mixture of sand and compost was installed at the St-Nicéphore landfill in Québec (Canada). The mixture was evaluated as a potential substrate to promote methane (CH4) oxidation by methanotrophic bacteria. One of the objectives of this field project was to assess the efficiency of the cover in reducing CH4 emissions. For this, both CH4 abatement and the extent to which methanotrophic bacteria developed were followed over time and space in relation to environmental and physico-chemical variables. The results obtained during the first 4 months of monitoring indicated that precipitation and air temperature had a great impact on CH4 oxidation. Over the study period, different patterns in CH4 oxidation through the cover soil were observed; in certain cases, oxidation was observed at various depths, although the zone of optimum oxidation occurred mostly near the surface. However, in the second half of the monitoring period, almost no oxidation was observed at depths greater than 10-cm, presumably because of lack of oxygen at deeper zones within the cover. In the 0–10-cm zone, high numbers and large variability of particulate methane monooxygenase gene (pmoA) copy number were also observed. It is concluded that the adopted substrate has proved to be satisfactory in sustaining and promoting growth of methanotrophic bacteria. However, the water content of the soil seems to be a key factor influencing CH4 oxidation, to an extent that requires further investigation. The uppermost 0–10-cm layer seems to play a critical role in CH4 abatement: a closer examination of this role will take place in the near future, in part by conducting more measurements within this zone

Bacterial production in the recently flooded Sep Reservoir : Diel changes in relation to dissolved carbohydrates and combined amino acids

International audienceThe spatial distribution of bacterial abundance and production were measured every 4 h in a recently flooded oligo-mesotrophic reservoir (the Sep Reservoir, Puy-De-Dôme, France), in relation to concentrations of dissolved carbohydrates and combined amino acids. The concentration of dissolved organic matter (DOM) components in the recently flooded Sep Reservoir were higher than those measured in other lakes of similar trophic status. Short-term variations in the bacterial production in this new reservoir appeared cyclical and endogenous to bacterial communities. These results highlight the need for the evaluation of diel changes in bacterial production, if estimation of the daily production rate of bacteria is to be done accurately for a reliable model of carbon flow through bacterioplankton and ultimately through aquatic microbial food webs. Bacterial growth, measured over time and space, did not appear exclusively governed by DOM components from phytoplankton primary production

Variations in the number of active bacteria in the euphotic zone of a recently flooded reservoir

International audienceUsing the CTC (5-cyano-2,3-ditolyl tetrazolium chloride) method, we estimated the active fraction of bacterioplankton in the euphotic zone of the recently flooded Sep Reservoir, France, with the aim of evaluating its importance and dynamics in relation to temperature and some components of dissolved organic matter (DOM) (i.e. dissolved combined amino acids: DCAA; dissolved free monosaccharides: DFCHO; dissolved combined monosaccharides: DCCHO), and its metabolic significance in conjunction with a bacterial growth indicator: 14C-glucose uptake. From our results, it appears that only a small fraction (0.04 to 3.23%) of total bacterial count in this reservoir was metabolically active. Recorded correlations and multivariate regression analysis suggest that temporal variations in the number of active bacteria are mainly (80%) governed by temperature, together with the high concentrations of those components of DOM, which were present in this ecosystem but which apparently were not always available for bacterial metabolism. We also found a positive relation between the number of active bacteria and the potential heterotrophic activity, which suggest that CTC-positive bacteria are responsible for the bulk of bacterial community metabolism in this recently formed reservoir

The microbial food web in the recently flooded Sep reservoir : Diel fluctuations in bacterial biomass and metabolic activity in relation to phytoplankton and flagellate grazers

International audienceThe spatial distribution of the bacterial biomass and production and of potential heterotrophic activity (PHA) were measured every 4 h between 23 July (10:00 h) and 25 July (10:00 h) 1997 in a recently flooded oligo-mesotrophic reservoir (the Sep Reservoir, Puy-de-Dôme, France), in relation to temperature, the phytoplankton biomass and production, and the abundance of heterotrophic flagellates. The temperature varied slightly with time during the study, but the well-established thermal stratification agreed well with vertical distribution of the biological variables that were measured. Only the bacterial production and the PHA showed significant diel changes (t-test, p < 0.05), with maxima at 18:00 h and minima at 02:00 h. A significant positive relation was found between bacterial abundance and that of heterotrophic flagellates, which, rather than being an association related to the thermal stratification of the water column, was considered to reflect a trophic relation between these two communities. A carbon balance analysis suggested that at least 30% of the C from primary production measured during the sampling period was used by bacteria, and that 42% of this secondary production, or 6% of the primary production, would be used for the development of the heterotrophic flagellates present. We conclude that the bacterioplankton forms, at least occasionally, an important source of carbon for higher trophic levels, and reject the hypothesis that bacterial production in the Sep Reservoir depends exclusively on organic matter of allochthonous origin

Effects of compost, nitrogen salts and fertilizers on methanotrophic activity

Abstract: The effects of compost, nitrogen salts, and nitrogen-phosphorous-potassium (NPK) fertilizers on the methane oxidation potential (MOP) of landfill cover soil at various temperatures were assessed. For this, we used batch assays conducted at 5°C, 15°C, and 25°C with microcosms containing landfill cover soil slurries amended with these elements. Results indicated variable impacts dependent on the type of amendment and the incubation temperature. For a given incubation temperature, MOP varied from one compost to another and with the amount of compost added, except for the shrimp/peat compost. With this latter compost, independent of the amount, MOP values remained similar and were significantly higher than those obtained with other composts. Amendment with most of the tested nitrogen salts led to similar improvements in methanotrophic activity, except for urea. MOP with NPK fertilizer addition was amongst the highest in this study; the minimum value obtained with NPK (20-0-20) suggested the importance of P for methanotrophs. MOP generally increased with temperature, and nutrient limitation became less important at higher temperatures. Overall, at each of the three temperatures tested, MOP with NPK fertilizer amendments provided the best results and was comparable to those observed with the addition of the shrimp/peat compost. The results of this study provide the first evidence of the following: (1) compost addition to improve methanotrophic activity in a landfill cover soil should consider the amount and type of compost used and (2) the importance of using NPK fertilizers rather than nitrogen salts, in enhancing this activity, primarily at low temperatures. One can also consider the potential beneficial impact of adding these elements to enhance plant growth, which is an advantage for MOP

Short-term vertical distribution of phytoplankton populations in a shallow tropical lake (Lake Municipal, Yaoundé, Cameroon)

International audienceThe circadian (i.e. 24-hours) vertical distribution of phytoplankton community was examined for the first time in a small, shallow and nutrient-rich tropical lake (Lake Municipal, Yaoundé, Cameroon), in relation to environmental factors. Sampling was done during the late dry season and the water column was very stable. Phytoplankton community was diverse and was dominated by cyanobacterial species which averaged (± SD) 97 ± 1% and 62 ± 14% of total phytoplankton abundance and biovolume, respectively. The abundances of these species consistently peaked in the surface layer. Their dominance was related to their positive buoyancy in stable environments, and the resulting shading of surface waters that possibly outcompeted eukaryotic algae. Although most of the extracted chlorophyll was apparently not from the dominant cyanobacterial species, chlorophyll-a concentrations (25.3 to 234 μg/l), as well as phytoplankton total abundance (1.42 to 11.73 x 108 cells/l) and biovolume (18.24 to 135.78 x 109 μm3/l), were substantial and characteristic of productive waters. The vertical distribution of the dominant phytoplankton species exhibited three different patterns, according to the depths where their maximum abundances were recorded: (1) surface water populations represented by the cyanobacteria Oscillatoria limosa and Synechocystis pevalekii, (2) mid-layer species, the euglenoid flagellate Lepocinclis fusiformis, and (3) populations that actively avoided the surface water during the nighttime, the euglenoid Trachelomonas hispida and the cryptomonad Cryptomonas ovata. We conclude that these patterns were related to several factors, including light conditions, temperature, cell buoyancy, the potential of motile flagellates to avoid adverse conditions such as grazing pressure, and accorded to the autoecologies of algal species involved