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A biostimulation study was conducted on mining waste residue with nutrient (nitrogen and phosphorus) and/or liming agent (ash or CaCO3 ) amendment to assess petroleum hydrocarbon (PHC) biodegradation efficiency by indigenous microorganisms. Compounds accumulated and/or released by treated samples were also monitored to determine the potential for acid mine drainage production during biostimulation. The potential for natural attenuation (i.e., the biodegradation of PHC contamination) was initially low but increased significantly upon nutrient addition. The best results were obtained when nutrient addition was coupled with the addition of a liming agent, notably CaCO3 , which contributed to maintaining near-neutral pH values. In fact, during treatment without a liming agent, pH decreased due to the oxidation of sulfide minerals, resulting in acid mine drainage production with increased metals released into sample leachates. Sulfur- and iron-oxidizing bacteria were detected primarily in samples not amended with liming agents, and the predominant organisms were affiliated with Acidithiobacillus spp. and Acidiphilium spp. Overall, the results of the present study demonstrated that amendment with a liming agent when treating PHC-contaminated mining waste residue contributes to maintaining a pH close to neutrality, mitigates sulfate release, and reduces the release of metals without negatively affecting the activity of PHC degraders.

This study examines the feasibility of oil sands process water (OSPW) treatment in a gravitational flow-through membraneless microbial electrolysis cell (MEC) using crushed metallurgical coke as an electrode material. Synthetic OSPW was composed of the water soluble fraction (WSF) of diesel, naphthenic acids (NAs), and metals with a total chemical oxygen demand (COD) concentration of 200 mg L − 1 and total NA concentration of 9.4 mg L − 1. OSPW treatment under bioelectrochemical conditions (1.4 V applied voltage) was compared with a control system operated at 0 V. Furthermore, in an additional set of experiments, microaerobic conditions were applied to both MEC and control setups to facilitate NA biodegradation. Highest NA and COD removal rates were observed in the MEC with microaeration in electrode compartments, where total NA concentration decreased to 4.2 mg L − 1 at a hydraulic retention time of 4 days. Furthermore, microtox and microalgae toxicological assays showed substantial toxicity decrease in this MEC.

This work describes laboratory experiments aimed at evaluating the feasibility of removing heavy metals from metal‐contaminated water in flow‐through microbial electrolysis cells (MECs) with peat moss as a source of organic carbon. MECs were assembled in upflow glass columns containing granular activated carbon (GAC) bioelectrodes preceded by a layer of peat moss. The MECs were fed with metal‐contaminated surface water collected at a firing range. At hydraulic retention times (HRT) of 4–6 days, up to 99 % removal of Pb, Zn, Cu, and Fe was observed. The removal efficiency of Zn and Cu declined at an HRT of 1.7 days, while effluent Pb concentration remained below the detection limit for all of the HRTs tested. Metal extraction from MEC compartments showed an accumulation of metals in both the peat moss layer and the GAC cathode, i.e., the removal was achieved by a combination of anaerobic and bioelectrochemical pathways of metal reduction. A proliferation of sulphate reducing bacteria in the peat moss layer and electroactive species in GAC electrodes was confirmed by biomolecular analysis. The proposed flow‐through system, which combines sulphate‐reducing and electroactive microbial activities to achieve near‐complete metal removal, can be used for removing a broad range of heavy metals from contaminated water in a low‐cost passive flow treatment system.

Surficial application of waste glycerol (WG) for enhanced bioremediation was tested in situ at an old military range site to address hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) contaminated groundwater. This treatment was effective in inducing strong reducing conditions (range: −4 to −205 mV) and increasing the concentrations of organic carbon (from 10 to 729 mg/L) and fatty acids (from 0 to 940 mg/L) concomitantly with a decrease in RDX concentrations (range: 17 to 143 μg/L) to below detection limits (0.1 μg/L) in 2 of the 3 monitoring wells (MWs) evaluated. None of these changes were observed in the control MW. RDX disappeared without the detection of any common anaerobic nitroso degradation intermediates, with the exception of one MW where the concentration of organics did not significantly increase (range: 10 to 20 mg/L), suggesting the conditions were not favourable for biodegradation. Ecotoxicological analysis suggested that the use of WG may have some dose-related deleterious effects on different soil and aquatic receptors. Analysis of the microbial community composition, using 16S rRNA gene amplicon sequences, which provided insight into whether the process design had selected for and stimulated the optimal microbial populations, indicated co-existence of numerous Operational Taxonomic Units (OTUs) belonging to groups known to be capable of RDX degradation under anaerobic conditions, with a positive link between Geobacter spp. enrichment and the presence of RDX nitroso metabolites. Overall, the results from this field test show that this treatment process can provide an effective long-term, semi-passive remediation option for RDX contaminated groundwater.

This study demonstrated the removal of selenite and selenate in flow-through permeable bioelectrochemical barriers (microbial electrolysis cells, MECs). The bioelectrochemical barriers consisted of cathode and anode electrode compartments filled with granular carbon or metallurgical coke. A voltage of 1.4 V was applied to the electrodes to enable the bioelectrochemical removal of selenium species. For comparison, a similarly designed permeable anaerobic biobarrier filled with granular carbon was operated without voltage. All biobarrier setups were fed with water containing up to 5,000 µg L−1 of either selenite or selenate and 70 mg L−1 of acetate as a source of organic carbon. Significant removal of selenite and selenate was observed in MEC experimental setups, reaching 99.5–99.8% over the course of the experiment, while in the anaerobic biobarrier the removal efficiency did not exceed 88%. By simultaneously operating several setups and changing operating parameters (selenium species, influent Se and acetate concentrations, etc.) we demonstrated enhanced removal of Se species under bioelectrochemical conditions.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a toxic, mobile groundwater contaminant common to military sites. Biodegradation of RDX is an alternative, cost effective and environmentall...

Bioremediation was performed in situ at a former military range site to assess the performance of native bacteria in degrading hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4-dinitrotoluene (2,4-DNT). The fate of these pollutants in soil and soil pore water was investigated as influenced by waste glycerol amendment to the soil. Following waste glycerol application, there was an accumulation of organic carbon that promoted microbial activity, converting organic carbon into acetate and propionate, which are intermediate compounds in anaerobic processes. This augmentation of anaerobic activity strongly correlated to a noticeable reduction in RDX concentrations in the amended soil. Changes in concentrations of RDX in pore water were similar to those observed in the soil suggesting that RDX leaching from the soil matrix, and treatment with waste glycerol, contributed to the enhanced removal of RDX from the water and soil. This was not the case with 2,4-DNT, which was neither found in pore water nor affected by the waste glycerol treatment. Results from saturated conditions and Synthetic Precipitation Leaching Procedure testing, to investigate the environmental fate of 2,4-DNT, indicated that 2,4-DNT found on site was relatively inert and was likely to remain in its current state on the site.

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.

An experimental passive methane oxidation biocover (PMOB) was constructed within the existing final cover of the St-Nicephore 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 CH4 emissions when submitted to an increasing methane load. The CH4 load applied started with 9.3 g CH4 m−2 d−1 . When the site had to be closed for the winter, the CH4 input was 820 g CH4 m−2 d−1 . Throughout the study, practically all the CH4 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 CH4 was not necessarily reached during the study period. Surface CH4 concentration scans showed no signs of leaks. The substrate offered excellent conditions for the growth of methanotrophs, whose count averaged 3.91× 108 CFU g dw−1 soil.

Stable isotope analyses were performed on gas samples collected within two instrumented biocovers, with the goal of evaluating CH4 oxidation efficiencies (f 0). In each of the biocovers, gas probes were installed at four locations and at several depths. One of the biocovers was fed with biogas directly from the waste mass, whereas the other was fed through a gas distribution system that allowed monitoring of biogas fluxes. While the f 0 values obtained at a depth of 0.1 m were low (between 0.0% and 25.2%) for profiles with poor aeration, they were high for profiles with better aeration, reaching 89.7%. Several interrelated factors affecting aeration seem to be influencing f 0, including the degree of water saturation, the magnitude of the biogas flux and the temperature within the substrate. Low f 0 values do not mean necessarily that little CH4 was oxidized. In fact, in certain cases where the CH4 loading was high, the absolute amount of CH4 oxidized was quite high and comparable to the rate of CH4 oxidation for cases with low CH4 loading and high f 0. For the experimental biocover for which the CH4 loading was known, the oxidation efficiency obtained using stable isotopes (f 0 = 55.67% for samples taken inside flux chambers) was compared to the value obtained by mass balance (f 0 = 70.0%). Several factors can explain this discrepancy, including the high sensitivity of f 0 to slight changes in the isotopic fractionation factor for bacterial oxidation, α ox, uncertainties related to mass flow metre readings and to the static chamber method.

An experimental landfill cover composed of a mixture of sand and compost was installed at the St-Nicephore landfill in Quebec (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.

Seasonal and spatial variations in bacterial abundance, biomass and potential heterotrophic activity in a recently flooded reservoir were measured for two consecutive years, in conjunction with phytoplankton biomass (chlorophyll-a concentration) and activity (primary production). The mean value of primary production remained constant between the two study years, while those of the chlorophyll-a concentrations, bacterial abundance, bacterial biomass and bacterial heterotrophic activity decreased. The observed trends in the bacterial variables were linked to changes in the relative importance of allochthonous dissolved organic matter, in addition to selective grazing activity on bacterioplankton. Multivariate regression analyses identified bacterial abundance (29%) and temperature (17%) as dominant correlates of the bacterial potential heterotrophic activity. We concluded that, in a new reservoir, organic matter, other than that from phytoplankton, might be of great importance for bacterioplankton metabolism. Furthermore, grazing activity on bacteria by metazoa in a new reservoir represents, on occasion, an important trophic link between the top consumer and otherwise unavailable dissolved organic carbon sources. Finally, even if little energy is transferred to larger consumers, the microbial route is still important in re-mineralizing organic matter in Sep Reservoir.

International audience; Seasonal and spatial variations in bacterial abundance, biomass and production in a recently flooded reservoir were followed for 2 consecutive years, in conjunction with phytoplankton biomass (chlorophyll a) and activity (primary production). Between the 2 years of the study, the mean value of primary production remained constant, while those of the chlorophyll a concentration, bacterial abundance (BA), bacterial biomass (BB) and bacterial production (BP) decreased. The observed trends of the bacterial variables were linked to changes in the relative importance of allochthonous dissolved organic matter. Moreover, this factor would explain discrepancies observed between the slope of the model II regression equations established from results of the present study and those of the predictive models from the literature, relating to bacterial and phytoplankton variables. An estimate of the carbon budget indicated that 22 and 5% of the ambient primary production in the Sep Reservoir might be channeled through the microbial loop via BP during the 1st and 2nd year of the study, respectively. We conclude that heterotrophic BP in the Sep Reservoir may, on occasion, represent a significant source of carbon for higher order consumers.

The potential activity and diversity of methanotrophic bacteria in samples from forest soil, peat, and sediment from a hydroelectric reservoir (Robert–Bourassa) and lakes located in the sub-arctic taiga were studied. Incubation experiments with soil slurries, methanotrophic bacterial counts, and direct PCR amplification of genes specific to methanotrophic bacteria were carried out on soil and sediment samples from three locations (nonflooded, periodically flooded, and flooded) from the reservoir. Sediments from three lakes located near the reservoir were also sampled to compare with nearby unperturbed aquatic systems. Only the uppermost part (5–10 cm) of soils and sediments was analyzed. Regardless of the incubation temperature, potential methane (CH4) oxidation rates were lower (0.028–0.066 6mol CH4 g j1 soil d j1 )i n nonflooded forest soil compared to lacustrine sediments that exhibited potential oxidation rates generally close to those observed in periodically flooded or flooded forest soil (0.04–0.14 6mol CH4 g j 1 soil d j1 ), but far below the range of values (0.20–0.58 6mol CH4 g j 1 soil d j1 ) recorded in peat systems. Samples from flooded forest soil and peat had higher CH4 uptake activity, but this could not be related to a greater number of methanotrophic bacteria (pmoA probe-positive colonies). Analysis of genes specific to methanotrophic bacteria revealed a low diversity in the methanotrophic community, with the genus Methylocystis being dominant. Overall, samples of flooded soil and peat with higher CH4 production rates also had higher rates of CH4 oxidation by methanotrophic bacteria. Flooding also seems to modify the resilience of the methanotrophic community to temperature fluctuations, an important consideration for future studies. (Soil Science 2006;171:127–137)

L’immersion des sols lors de la création d’un réservoir hydroélectrique pourrait augmenter, au moins à court terme, le flux de méthane vers l’atmosphère. Afin d’évaluer la contribution potentielle de tels aménagements à la production de méthane, nous avons étudié l’activité potentielle des bactéries méthanogènes dans les sols de la forêt boréale non immergés et immergés lors de la mise en eau d’un réservoir, ainsi que des sédiments lacustres. De cette étude comparative, il ressort que les tourbières inondées périodiquement (zone de marnage) ou en permanence, peuvent contribuer d’avantage à la production de méthane que les tourbières non inondées, les sols ou les sédiments de lacs naturels. Toutefois, l’intensité et l’évolution temporelle de l’activité potentielle des bactéries méthanogènes dans les différents milieux pris en compte ont été sous la dépendance d’une combinaison de plusieurs facteurs environnementaux, notamment, la quantité de la matière organique, le niveau d’eau et la présence de certains ions oxydants (SO₄²⁻, Fe³⁺).

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 ammonia-nitrogen 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.

To investigate the deteriorating bacteriological water qualityof Municipal Lake of Yaounde, the degree of pollution of theMingoa Stream, the main tributary of the lake, was evaluated fortotal coliforms, thermotolerant coliforms, and fecal streptococci. Concentrations of these bacterial indicators inMingoa 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.

International audience; The 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.

Circadian and spatial fluctuations in bacterioplankton abundance and cell volume were examined, for the first time, in the Municipal Lake located in the down town area of Yaounde (Capital of Cameroon, Central Africa, ca 3° 52′ N, 11° 31′ E). Bacterial cell volumes (range, 0.05 to 0.2 μm3) were consistent with those reported for other aquatic systems while bacterial densities (0.8 to 2 × 108 cells ml-1) were among the highest values reported in pelagic systems. These variables and chlorophyll a and dissolved oxygen concentrations within a single depth-zone varied from 13 to 61%, while water temperature fluctuated only from 2 to 6%. Spatial fluctuations of physical-chemical and biological variables were generally higher during the day-time than during the night-time. A significant diel variation was provided for bacterial cell volume in the surface waters where synchronized cell division was occurring during the night. The measured bacterial abundances in this study were 4 to 17 fold higher than values known from other lakes of similar trophic status, and both cell abundance and volume were not correlated with chlorophyll. We conclude that this was due to the dependence of bacterial populations to different sources of allochthonous substrates, including untreated sewage from the major influents of the lake, resuspension of benthic material, and substrate releasing from macrophytes which are prevalent in the littoral zone of the lake.

Une etude bacteriologique a ete menee sur 588 echantillons d’eau preleves dans 49 puits de 7 quartiers de la ville de Douala. Les quartiers ont ete choisis suivant la typologie de l’habitat. Les analyses des coliformes ont ete faites suivant la technique par inclusion en une couche, et celle des streptocoques par ensemencement dans les tubes a vis avec bouillon de Rothe. Les resultats montrent que ces eaux abritent de nombreuses bacteries pathogenes, coliformes fecaux et streptocoques fecaux. Leurs densites subissent d’importantes fluctuations spatiales et temporelles, et varient entre 200 et 29*105 UFC/100 ml pour les coliformes totaux et entre 30 et 44*103 UFC/100 ml pour les coliformes fecaux ; les streptocoques fecaux sont le plus souvent presents. Les facteurs de variation sont l’environnement du puits, l’entretien, le niveau de la nappe dans le puits, la situation geographique. Les puits les plus contamines sont ceux qui sont situes a moins de 5 m des sources de pollution telles que les latrines a fond perdu, les depots sauvages des ordures menageres, l’absence ou le traitement regulier de l’eau, le niveau superficiel de l’eau dans le puits. Les puits amenages, c'est-a-dire munis d’un couvercle bien utilise et d’une margelle en beton, avec une profondeur d’au moins 4 m, situes au moins a 15 m en amont d’une quelconque source de pollution et dont le traitement est regulier, presentent tous une eau de qualite beaucoup amelioree ; les contaminations fecales y baissent d’au moins 1000 unites. Les points d’eau non amenages sont tres nombreux et les fortes densites de germes dans ces eaux montrent de grands risques sanitaires a court terme pour les consommateurs. © 2009 International Formulae Group. All rights reserved. Mots cles: Zone urbaine pauvre, coliformes totaux, coliformes fecaux, streptocoques fecaux, eaux de puits.

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.

Three experimental biocovers were installed during the summer of 2006 at the St-Nicephore landfill in Quebec (Canada). The main objectives of the experimental program were to assess the efficiency of these biocovers in reducing CH 4 emissions and to monitor the evolution in space and time of the dynamics and diversity of methanotrophic bacteria that may be responsible for CH 4 abatement. Dynamics of methanotroph populations derived from most probable number (MPN) counts exhibited different steps (lag, growth, and collapse phases), with mean abundances decreasing somewhat with depth. Methanotroph diversity, as assessed by denaturing gradient gel electrophoresis showed changes over time in the community structure. These changes were dependent on the sampling depth and only Type I methanotrophs belonging essentially to the genus Metbylobacter were retrieved from our samples. Given the youthful character of the system under study, together with the reported behavior of this functional group of methanotrophs, it was concluded that Type I methanotrophs forming the community structure might reflect pioneer species with a potentially high growth rate (r-strategists) that become numerically dominant reducing the evenness of species distribution. These results contribute to the generally limited body of knowledge on methanotroph diversity in landfill cover soils.

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We examined the significance and suitability of Aeromonas hydrophila versus fecal coliforms in assessing microbiological water quality. For this, we used the membrane filtration method to simultaneously estimate the abundance level of A. hydrophila and fecal coliforms in waters from the Mfoundi river watershed at Yaounde´, and compared how fluctuations in A. hydrophila abundance matched those observed with fecal coliforms index as an indicator of water quality in the system under study. Our results revealed that waters were not safe according to the standards for water quality established by the Word Health Organization (WHO). They also indicated the prevalence of A. hydrophila as compared to fecal coliforms, and suggested that water from the Mfoundi River and its tributaries could be classified as hypereutrophic based on the density of Aeromonas. Moreover, the spatial distribution of fecal coliforms and A. hydrophila exhibited similar trends within the different water bodies investigated, suggesting that A. hydrophila can be used as indicator of water quality in highly polluted waters. We concluded that waters from the Mfoundi River watershed at Yaounde´ represent a great potential risk of infection for users, and foresee that the next challenge will be to determine, among other factors, the physico-chemical factors influencing the observed spatial distribution.

International audience; The 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.

Functional and structural aspects of the indigenous methanogenic and methanotrophic microbial populations were assessed in soil, peat and sediment from a hydroelectric reservoir (Robert-Bourassa) located in the subarctic Taiga. Three locations (un-flooded, seasonal flooding, and permanent flooding) in the reservoir were selected for sampling of forest soil and peat soil. Lakes located near the reservoir were also sampling for comparison with nearby unperturbed aquatic systems. Using samples incubated in microcosms at 5, 10 and 25°C, methane production and oxidation were quantified by gas chromatography. Structural aspects included bacterial counts of methanotrophic bacteria, and PCR amplification using 16S rDNA universal primers and primers specific for genes involved in methanogenesis or methanotrophy. Methanogenesis in the different systems appeared to depend on a combination of environmental factors, including the amounts and quality of organic carbon, and the abundance of oxidizing ions (Fe3+, SO4 2-). Periodically flooded or flooded peats contributed more to methane production than unflooded peats, soils and natural lake sediments. Similarly, methane oxidation rates were higher in peat soils than in flooded soils or lake sediments. The lowest rate of methane oxidation was observed in the forest soil, which was a typically undisturbed soil where the rate of CH4 production was close to the lower range of values observed in this study. This parallel evolution between the potential rate of methanogenesis and CH4 oxidation suggests an association between CH4 oxidation activity and CH4 supply. Methanogenesis appeared more sensitive to temperature increases than methanotrophy. The nucleotide sequences of PCR amplified and cloned mcrA fragment, a gene specific to methanogenesis revealed that many of the sequences obtained from the soils in this study were closely related to only uncultured clones of methanogens. Methanotrophic bacterial abundance was higher in flooded peat and lake sediment than in flooded soil, but abundance of methanotrophic bacteria in unflooded peat was lower than in unflooded forest soil. PCR amplification of genes specific to methanotrophic bacteria suggested that flooding of soil leads to a shift in populations of methanotrophic bacteria. A comparison of methane production and oxidation values obtained during this study indicated that essentially all of the methane produced in peat, forest soil and sediment could be oxidized within the system with little net atmospheric emission.

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 Yaounde, 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 x 10(8) +/- 2.5 x 10(6) CFU/100 ml), FC (Mean +/- SD = 6.8 x 10(5) +/- 2.4 x 10(3) CFU/100 ml) and FS (Mean +/- SD = 7.3 x 10(5) +/- 2.1 x 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 Yaounde.

Flooding of land associated with the creation of reservoirs may increase, at least in the short term, methane flux to the atmosphere. To evaluate the potential contribution of such land use on methane production, field samples were studied in vitro for the potential activity of methanogenic bacteria in unflooded or flooded boreal forest soils, together with lacustrine sediments. From this comparative study, periodically flooded or flooded peats contribute more to methane production than do unflooded peats, soils, and natural lake sediment. The intensity and temporal changes in the activity of methanogenic archaea in the different systems depended on a combination of environmental factors, such as the amount and quality of organic carbon, the water level, and the concentration of oxidizing ions (SO42-, Fe3+).

International audience; 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

Seasonal and spatial fluctuations in abundance, biomass production, and potential heterotrophic activity (i.e., 14C-glucose uptake) of bacterioplankton assemblages in a 1-year-old reservoir (the Sep Reservoir, Puy-de-Dôme, France) were examined concurrently with water temperature, phytoplankton chlorophyll a concentration, and primary production (PP). Based on the values observed for these biological variables, the Sep Reservoir was considered to have evolved to an oligo-mesotrophic state. Spatiotemporal variations of bacterial variables were a consequence of the seasonal evolution of the reservoir coupled with the resource availability. Multivariate regression analyses suggest that about 14 and 26% of the variance in bacterial standing stock and activity may be explained by the physical environment (i.e., temperature) and a resource availability index (chlorophyll a concentration or primary production), respectively. A carbon budget indicated that 4-126% (mean = 20%) of the ambient PP may be channeled through the microbial loop via bacterial biomass production. Heterotrophic bacterial production in the Sep Reservoir may therefore, on occasion, represent a significant source of carbon for higher order consumers.Key words: reservoirs, plankton, bacteria, heterotrophic uptake, primary and bacterial production.

International audience; The 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.