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AbstractThis article proposes to question the hypothesis presented by Larivée in the Revue des Sciences de l'Education, (vol. VII, no 3, 1981) stating that catechism, as it is taught at the elementary level, is related to dogmatism and tends to interfere with the cognitive development of children. The authors present a discussion of the definition of catechism as a dogmatic pedagogical activity and of the components of cognitive development. The relation between cognitive development and religious development places catechism among the activities which promote human development.

This research reports on the interpretative activity of two schoolteachers during physical education and mathematics sessions. It is part of the research field concerned with the processes of didactic contextualization and the comparatist approach. The processed data was collected by self-confrontation interviews. The results allow to model the interpretative filters mobilized according to three axes (practical epistemology, types of inferences and structuring of the interpretative activity). Our study allows to confront the specificities or genericities, fruits of disciplinary didactics, with the effects of didactic contextualization. The use of contextualization seems to act as a filter thus constituting a professional genre. On the other hand, the contents and the determinants of the interpretation are more specified according to the concerned disciplines.

Keywords: interprétation, contextualisation didactique, approche comparatiste, épistémologique pratique, catégories de Shulman, interpretation, didactic contextualization, comparative approach, practical epistemology, Shulman's categories, interpretación, contextualización didáctica, enfoque comparativo, epistemología práctica, categorías Shulman

AbstractThis survey completes our earlier work on the evolution of the Amazon discharge at Óbidos from 1903 to 1999. In the Amazon basin above Óbidos (4,680·103 km2), 341·103 km2 were deforested between 1976 and 2003. The impact of this deforestation on the mean annual discharge was estimated using a water balance approach from 1940 to 2003. The evolution of the runoff coefficient indicates that there was a 5% increase in the mean annual discharge over the 22 years from 1981 to 2003. The number of strong floods was five time higher during this period than it was before. On the other hand, it seems that there is no influence of the deforestation on the low flows.

Keywords: Amérique du Sud, bassin amazonien, Óbidos, pluviométrie, débit, bilan hydrologique, déboisement, South America, Amazon catchments, Óbidos, rainfall, discharge, water balance, deforestation

AbstractThe objective of this study was to test the general application and the robustness of canonical kriging, a new approach regional hydrological estimation. The evaluation of the robustness was carried out for the estimation of mean annual streamflow over the continental territory of Haiti, under a tropical climate and under non-optimal conditions of data quality and availability. The performances of canonical kriging were studied using cross validation. The results were compared to those of the linear regression between the mean annual streamflow and the watershed area applied for the same conditions. In general, canonical kriging yields slightly higher performances. It produces less biased estimates (mean relative bias of ‑ 13% against ‑ 20% for regression) with slightly less significant relative errors (54.4% against 59.6% for regression). However, the linear regression produced better estimates for the largest basins although the global performances of canonical krigeage remained acceptable. In addition, considering the very unfavourable conditions in which the method was applied, it was not possible to connect the decrease in the performances of canonical krigeage to a lack in the general application of the approach and/or its robustness.

Keywords: hydrologie, estimation régionale, régression linéaire, krigeage canonique, analyse canonique des corrélations, débit moyen, hydrology, regional estimation, linear regression, canonical kriging, mean annual streamflow

A bioevaluation of the state of health of soft bottoms depends on the experimental conditions in which samples of sediment are treated to obtain the water phase to be subjected to chemical and toxicological analyses.In the course of this preliminary study we have considered the action of these principal conditions. We have noted that the inhibiting effect of a sediment on the short-term growth of a microalga Selenastrum capricornutum is not easy to eliminate, whether by a series of washes of the sediment, by a finer filtration of the water extracted from this sediment or by e previous autoclavage of this sediment.This study quickly revealed which sediments in the River Seine (Paris area) inhibited most the test micro-alga Selenastrum capricornutum (Chlorophyceae); the cause of these inhibitions was then sought.There is no correlation between the often high content of heavy metals in the sediment water (Pb 70, Cu 100, Cr 150, Cd 9, Ni 280, Zn 400 µg.L-1) and the development of the algae; the metal pollutants are probably masked by the chelating capacity of these biotopes rich in organic substances. The experimental conditions under which the sediment samples are treated to obtain the water phase used for the chemical and toxicological analyses are also important.One conclusion drawn is that a chemical analysis alone of the sediments is of limited interest. The most reliable data from the ecological point of view are those provided by the bio-assays.

Keywords: Pollution des sédiments, bioessais par l'emploi de microalgues, qualité de l'eau, Sediments pollution, microalgae bioassays, water quality

Coliform occurrences in drinking water in the absence of known breaches of treatment barriers are still a problem inthe drinking water industry. The purpose of this study was to define threshold values for different bacteriological, chemical and physical parameters, beyond which coliforms occurred more frequently along a full scale distribution system in a northern suburb of Paris. A predictive model of coliform occurrence at different sites of a distribution network was produced (AL COL model).This study consisted of two stages. The first one involved following coliform occurrences, epifluorescent counts, temperature, biodegradable dissolved organic carbon (BDOC), and residual chlorine level in the treatment plant effluent and at five distribution sampling sites. Each site was sampled once a week for one year (n=47 ; February 1991 - February 1992). This first stage of study showed that the occurrence of coliforms in the network could be associated with temperatures greater than a threshold value of 15°C, a BDOC consumption greater than 0.15 mg/l, a logarithm of the epifluorescent counts higher than 5.2 and a residual chlorine lower than 0.10 mg/l. Graduation of coliform occurrences was possible by the combination ofoverstepped thresholds for these four parameters. Three levels of risk associated with an increasing frequency of coliform occurrence were defined : site with no risk when no or only one threshold value was exceeded, slightly exposed site when 2 or 3 threshold values were exceeded and exposed site when 4 threshold values were exceeded.The second stage of the study concerned the application of this predictive model. It consisted of following weekly the same parameters as in the first stage at 7 and 10 distribution sites situated on two difrerent distribution systems (Nortlrern and Eastern suburbs of Paris) for 21 weeks (April - September 1992). The threshold values determined were similar for the two distribution systems. They were 15°C for temperature ; 0.10 - 0.15 mg/l for BDOC consumption, 5 - 5.2 for the logarithm of epifluorescent counts and 0.10 mg/l for residual chlorine. The frequency of coliform occurrences was about 60 % at sampling points assessed as exposed sites, 5 % at sampling points assessed as slightly exposed sites and 1 % at sites considered with no risk.Moreover, it was possible to define a model of mean risk of coliform ocurrences over all sites (corresponding to the mean of overstepped thresholds at the different studied sites for a given week). Four levels of mean risk (minimum, non negligible, critical, and maximum) were associatcd with increasing frequencies of coliform observations in the distribution network.The AL COL model could be an efficient and simple tool to control and limit occunences of coliforms in drinking water. When a site is assessed as exposed, disinfection treatments have to be performed in order to reduce this risk and to prevent coliform occurrences during the weeks following this risk. Moreover, it was also possible to define a chlorine level in the water to reduce the bacterial contamination and subsequently decrease the risk of coliform occurrences at the sites of the network.

Keywords: Reviviscence bactérienne, réseau de distribution, coliformes, dénombrements en épifluorescence, carbone organique dissous biodégradable (CODB), chlore résiduel, température, modèle d'alerte, Bacterial regrowth, distribution system, coliform, epifluorescent count, biodegradable dissolved organic carbon (BDOC) consumption, residual chlorine, temperature, predictive model

The extent of the current drought phenomenon in Sudano-Sahelian regions no longer needs to be proven. The study of rainfall deficits in intertropical Africa shows a global climatic degradation which has been going on for about twenty five years. These deficits concern also the humid areas of Western and Central Africa and finally all the african rivers draining the flows to the Atlantic Ocean. Various studies have showed that the current phenomenon greatly differed, in intensity and duration, from other 20th century deficit situations (Sircoulon et Olivry, 1986, Lamb,1985, Nicholson et al, 1988). Despite very great fluctuations which could remind pseudocyclic variations, the current data pointed out a global downward trend since 1860 (Olivry, 1987). Moreover, some authors have seen a statistical break in the rainfall conditions in 1970 (Carbonnel et al, 1985). The necessity to obtain common continual data series led to select the period from 1950 to 1990 with a large number of operational rainfall and jauging stations (Mahe, 1993) (figures 2 et 3).Without expecting a continuation in this trend, or, on the contrary, a return to a humid period, the current drought will obviously have durable consequences on some hydrological parameters. After a relative improvement of rainfall conditions, observed in 1985 and 1986 and even more recently, as shown by the evolution of the Lamb index (1985). African drought and rainfall deficits observed since 25 years have important repercussions on the flow regime of rivers and especially on the annual runoff and the strenght of annual floods. This phenomenon has intensified during the last ten years while, paradoxically, rainfall deficit greatly has diminished. For instance, the upper Niger river ,with the Bani river, (surface basins 250,000 km2) shows an annual runoff deficit of 20% during the 70's and of 46% during the 80's and an annual rainfall deficit respectively of 15 and 20%. In the regional context of Western and Central Africa, the global runoff deficit varies from -7% to -16% for the decades 1970 and 1980 in the humid areas, and from -13% to -27% in the dry areas (deviations calculated in relation to the 1951-1990 mean values) (Olivry,1993 ). The global annual runoff deficit during the 80ís decade reached 430 km3 year-1 for the atlantic african tributaries (figures 4 et 5, table 1).During the two last decades, flood hydrographs of large river basins have been greatly reduced in volume and duration; maximum values are much smaller. the flood hydrographs showed lower annual maximum discharges and shorter high water seasons than during the preceding period. In the equatorial areas, with two flood periods by year, the datas showed that the spring floods were more affected than the autumn floods by the climatic changes. (figure 6). A frequential study of flood maxima shows a clear break in data series, and emphasizes the danger of flooding estimations which are based upon recent years only. The long term effects of rain shortage are more marked still for the low flow regimes and different studies have showed that, in addition to the immediate effects of the drought, a large reduction of the groundwater storage can explain the persistent fall of the hydrological resource. In the case of recession-depletion period and low flows, the memory effect of the current deficit period is particularly clear. An unusual repetition of exceptionally dry low flows can be observed, especially an abrupt change in the depletion regime, unprecedented in hydrological time series. It also may be observed that a return to more favourable climatic conditions does not involve an immediate return to the earlier hydrosystem . The figure 7 shows two representative curves of the variability of the low flows (absolute minimum daily discharge) between 1950 and 1990 for a Sudano-Sahelian basin (the Bani river) and for a tropico-equatorial basin (the Sangha river, tributary of the Congo river). It is clear that the dry Africa is more affected by drought and rainfall deficits than the humid Africa, but during the last decade the low flows of the Sangha river have been divided by 2 in relation to the low waters observed before 1970 (Laraque et al,1996). The large deficit of the low flows was also observed on the flows of the Ubangi, Congo/ZaÔre, Ogowe, Sanaga, Kwilu, Bandama and Konkure rivers in the humid areas during the last decade (Olivry, 1993) .In the dry Africa the deficit of low flows is larger still and it has been observed during the last two decades. After the annual flood and the recession, which occur especially as fast as the rainy season ends, there is a classical pattern of flow drop in the rivers in this region. This corresponds to the basin aquifers draining, also called depletion. This depletion is linked to an exponential law : Qi=Qo e-a(ti-to) with the flow Qo on a to day, the flow Qi on a ti day, and (, a coefficient expressed in days-1, according to the physical and geometrical characteristics of the aquifers. The studies show a significant degradation of the depletion.. This phenomenon, resulting from a deterioration of aquifers, was first noted on the Senegal river in 1983 (Olivry, 1987). Since then, it has been observed again and specified, in relation to all the flows in the Sudano-Sahelian region. On a regional scale, it can be considered as a likely model of the progressive decrease of flows, In the Senegal river (218,000 km_ at Bakel), the depletion coefficient has been relatively stable for over seventy years during humid as well as dry periods. The average is 0.0186 day-1 and the variation coefficient is only 0.075 . With the current drought, the alteration in the pattern only becomes significant after 1975. The depletion coefficient rapidly rises, to reach values such as 0.04 day-1 around 1985. The Niger river (120,000 km_ at Koulikoro and data since 1907) shows before 1975 an average coefficient of 0.023 day-1. The current period shows an average coefficient over the first 8 years as being around 0.028 day-1 and then an abrupt increase to values as high as 0.040 day-1 in the beginning of the 90's.The Bani river(102,000 km_ at Douna), tributary of the Niger river, shows a significant evolution (figures 8 et 9). It is easy to give many examples in the Sudano-Sahelian region and the phenomenon is still likely in humid tropical areas, even it is less marked. Thus in the case of the Ubangui river at Bangui (500,000 km_); the average coefficient from 1935 to 1975 was 0.021 day-1. It has been equal to 0.025 day-1 during the last fifteen years. The increase of the depletion coefficient of the Sangha river is lower, but in the equatorial regions, it is often difficult to observe the depletion periods, the flows being affected by rains during a short dry season ( figure 10) . The depletions similarity in the case of different rivers and even of streams which was observed in the flow time series before the current period must be underlined. The ( values of 0.02 day-1 are characteristic of a low water supply deriving from small hillslope aquifers. These aquifers are typical of the intertropical african geomorphology, where there is no large groundwaters. A good relationship appears between the coefficients variations of recession and of drainage ( Olivry, 1976). According to Darcy's law, the deviations from the norm would therefore mainly correspond to the variations in the aquifers width. The hydrogeological datas showed a drop of 10 m and more of the water table above hillslope aquifers in Senegal, Mali and Burkina Faso during the 80ís. Consequently, there is nothing surprising in the fact that the decrease of these small aquifers results in a comparable ´†hyperdepletion†ª in the basins of various areas affected by the same climatic hazards. A return to better sustained discharges during the dry season first requires the aquifers reconstitution. This cannot happen immediately, as shown by the low effect of the last better rainfall on depletion coefficients. There is no exact convergence between the variations of Lamb's rainfall index and the depletion coefficient ones. Through the aquifers, reactions to the low water restitution are slower ; they require a response time of several years and only become effective with the accumulation of similar climatic variations. The groundwater supply deficit in rivers, considered here, which is noticeable in the dry season, is obviously underlying during the flood period and this also explains the low annual runoff and the poor flood maxima we still observe despite some rainfall recovery. The"memory effect" of the droughtness indicates the important part taken by the base flow in the flood hydrographs of large rivers. A specific stream drought, which could be refered to as a "phreatic drought", is to be added to the climatic drought with a pluriannual gap. The hydrogeological laws are such that, under good rainfall conditions, a restoring of the hydrological regime should last as long as it took to bring it to its current degradation.

Keywords: Afrique tropicale, précipitation, ressources en eau, déficits, Tropical Africa, precipitation, rainfall, water resources, deficits

Potential applications of microalgae and cyanobacteria for treatment of wastewater effluents using membrane-photobioreactors suffer from limited performance due to fouling effects, mainly attributable to exocellular polysaccharides secreted by these micro-organisms. A membrane photobioreactor is defined as a process associating the culture of photosynthetic micro-organisms with a continuous separation by membrane filtration of the biomass and the water treated. The goal of the present laboratory-scale study was to quantify polysaccharide adsorption effects on organic membranes (ultra and microfiltration) characterised by different materials and surface charges. Sodium alginate was used as the "model adsorbate".Seven plane organic membranes were tested. The influence of membrane cut-off (or of pore diameters) as well as that of the material polyethersuphone (PES), polyacrylonitrile (PAN), polyvinilidene fluoride (PVDF) and of its properties (hydrophobicity, surface charges, …) were assessed. The study consisted of two parts :1. the first part was concerned with the kinetics of alginate adsorption and the influence contact time and solute concentrations on the reduction of pore diameter (ZEMAN, 1983) or on the increase of hydraulic resistance (MATTHIASSON, 1983);2. the second part dealt with adsorption equilibrium (formulations of LANGMUIR and FREUNDLICH).The study constituted the first step of a research program aimed at developing membrane photobioreactors for the treatment of specific industrial effluents. The fluid used to test the membranes was quality II pure water (ISO 3696 norm). Tangential velocities were set to 2.5 m.s-1, corresponding to a Reynolds number of 2500. To represent exopolysaccharides, we used alginic acid at concentrations of 1, 10 and 50 g, neutralised with sodium hydroxide at pH 9. New (or clean) membranes were first characterised through pure water flux measurements. J0, the flux of pure water for a new membrane, was obtained (flowrate / unit of surface area), and then the membrane was kept in contact, for a definite duration, with the alginate solution. After adsorption and rinsing, the pure water flux was measured again. Ja, the pure water flux, was measured through the membrane after adsorption.Adsorption model at equilibrium:The effect of adsorption is quantified under the form of the relative pore size reduction as described by ZEMAN (1983) and included in the relation : ∆r / r=1 - (Ja / Jo)1/4. A variation of this quantification is that of the MATTHIASSON model (1983) applied to the pure water flux, based on DARCY's law expressing the relative value of the hydraulic resistance of the adsorbed layer Ra in relation to the intrinsic resistance of the membrane Rm : Ra / Rm=(Jo / Ja) - 1.To express adsorption phenomena at the solid/liquid interface of membranes, we used LANGMUIR's law together with MATTHIASSON's experimental observation (1983): the relative resistance Ra / Rm due to adsorbed compounds is proportional to the mass "x" of solute adsorbed per unit of membrane surface area, x=Kx.Ra. If one assumes that the mass m of a homogeneous plane membrane per unit of membrane surface area is proportional to its adsorbing surface area Ω per unit of membrane surface area (m=Km.Ω), and if one combines the flux equations expressed by DARCY's and POISEUILLE's laws, then the result is m=K'm.Rm in a homogeneous membrane. Substituting x and m in LANGMUIR's law results in the equilibrium model Rae / Rm=(Jo / Ja) - 1=a.c / (1 + bc) in which c=concentration of adsorbing solute; a and b are coefficients; and Rae is the resistance due to compounds adsorbed at equilibrium. Kinetic model: To show the evolution of membrane resistance with time, we suggest the introduction of an empirical exponent j over the time parameter in the AIMAR et al. model (1988).Results: The effect of changing the alginate concentration reveals that the hydraulic resistance of adsorption, at equilibrium, (MATTHIASSON, 1983) evolves according to LANGMUIR's isotherm. The relative decrease of pore radius ∆r / r in the presence of l g.l-1 of sodium alginate shows that a quasi-plateau is obtained after two hours using the most hydrophobic membrane. The curves ∆r / r=f (t) for five membranes made of different materials, monitored during the transition phase before the plateau with common 1 g.l-1 concentrations, reveal similar adsorption behaviour, characterised by the limiting common value ∆r / r=0.06 ± 0.005. However, the uncharged hydrophilic membrane PAN 3038 stands out owing to a much lower ∆r / r value of 0.09. This peculiar behaviour can also be observed in the influence of the alginate concentration: hydrophobic and charged hydrophilic membranes display a saturation effect with ∆r / r little affected by the increase of alginate concentration, whereas the uncharged hydrophilic membrane PAN 3038 displays a ∆r / r value three to six times lower with great sensitivity to concentration effects at concentrations below 10 g.l-1. The model Rae / Rm=(Jo / Ja) - 1=a.c / (1 + bc) is in agreement with the experimental results obtained with hydrophobic and hydrophilic membranes. The proposed kinetic model shows that time dependence of R (t) does not seem to be linked to the nature of membranes. However, compared with concentration, R (c) is very sensitive to the nature of membranes. A comparative study of ultra and microfiltration membranes shows that the reduction in ∆r / r values increases with molecular weight cut-off (or pore diameter).Criteria for the choice of membranes: A comparative study of three polyacrylonitrile membranes reveals that membrane 3038 PAN (neutral) displays a very interesting, peculiar behaviour: its adsorption, expressed by ∆r / r or Rae/(Rae+Rm) is four to six times weaker than that of the other two. The surface charge of membranes seems to influence the intensity of adsorption in a significant way. Wetability also has a strong influence on adsorption. The sum of resistances Rae + Rm of ultrafiltration membrane 3038 PAN is only four times as great as those of hydrophobic microfiltration membranes. Experimentation already showed that, in the presence of microparticles, interactions between the layer of adsorbed alginate and microparticles will increase the likelihood of fouling of microfiltration membranes, decreasing their resistance down to the level of very little adsorbing ultrafiltration membrane IRIS 3038 (ROSSIGNOL et al., 1999).A culture system of marine microalgae in a membrane photobioreactor using ultrafiltration membrane IRIS 3038 PAN displayed a stable permeation flux during 6 weeks and easy regeneration, which meant adsorption was almost nil. The ability of some microalgae to assimilate ammonia nitrogen, nitrates and phosphates contained in waste water with excellent efficiencies (e.g., Phormidium bohneri: SYLVESTRE et al., 1996) allows one to consider using membrane photobioreactors in the treatment of home or industrial effluents. Other microalgae such as Chlorella salina (GARNHAM et al., 1992) are capable of fixing large amounts of heavy metals (Co, Mn, Zn, etc…); grown in membrane photobioreactors, they could depollute industrial effluents.

Keywords: Adsorption, alginate, ultrafiltration, microfiltration, photobioréacteur à membrane, Adsorption, alginate, ultrafiltration, microfiltration, membrane-photobioreactor

Water temperature is a parameter of great importance for water resources. For instance, modifications of the thermal regime of a river can have a significant impact on fish habitat. Therefore, understanding and predicting water temperatures is essential in order to help prevent or forecast high temperature problems. In order to predict water temperatures, data series are necessary. Many data series exist for air temperatures, but water temperature series are relatively scarce and those available are often short or have missing values. This study presents the modelling of water temperature using neural networks and multiple linear regression to relate water temperature to air temperature and discharge in Catamaran Brook, New Brunswick, Canada.Catamaran Brook is a small stream (51 km2) where long-term multidisciplinary habitat research is being carried out. Many variables can impact water temperatures in a river, such as air temperature, solar radiation, wind speed, discharge, groundwater flow, etc. For this study, only air temperature and discharge were used. These were judged to be the most often available parameters for modelling temperatures in rivers, and to have the greatest impact on water temperature. More precisely, input variables included current air temperature (°C), air temperature of the previous day (°C), air temperature two days earlier (°C), discharge (m3 /s) and a trigonometric function of time (days). Data used for the analysis were from 1991 to 2000. Data from 1991 to 1995 were used to calibrate the model while data from 1996 to 2000 were used for validation purposes. Observed and predicted water temperatures for each model were presented for the calibration data and the validation data. The coefficient of determination, R2, was used to compare the efficiency of both models as well as the residual standard deviation and the bias. This is equivalent to basing the comparison on the standard deviation (or variance) of the residuals. Coefficients of determination for calibration were 94.2% for the neural networks and 92.6% for the multiple linear regression, which correspond to a residual standard deviation of 1.01°C for the neural networks and of 1.05°C for the multiple linear regression. For validation, coefficients of determination were 92.2% for the neural networks and 91.6% for the multiple linear regression, which correspond to a residual standard deviation of 1.10°C for the neural networks, and of 1.25°C for the multiple regression. The overall bias during the study period (1991-2000) was calculated at +0.11°C for the neural network model and at -0.26°C for the regression model. Results indicated that it was possible to predict water temperature for a small stream using air temperature, flow and time, as input variables, with neural networks and multiple linear regression. The residual series obtained by both models were very similar. Of the two models, neural networks gave slightly better results in terms of fit, but the small difference in results lets us believe that both approaches are equally good in predicting stream water temperatures.

Keywords: Petit cours d'eau, température de l'eau, modèle, réseaux de neurones, régression linéaire multiple, Small stream, water temperature, model, neural networks, multiple linear regression

The aims of this work were to determine the impacts of releases from two iron and phosphate mines (North West Tunisia) on the physico-chemical water composition of the related alluvial aquifer system. Samples from tailings, soil and water wells were collected and analyzed. The analytical results of tailing samples showed that this matrix contains high concentrations of heavy metals (mainly Cd, Cr, Pb and Zn). These metals were also detected at significant levels in the fine soil fraction downstream from the mine waste discharge due to transport by wind and water. The heavy metal concentrations in groundwater showed that the metal transport from the tailings is completely attenuated by the soil constituents. Overall, the physic-chemical quality of the groundwater is good, except for nitrates, which are present at relatively high concentrations due to intensive agricultural practices and the absence of urban wastewater treatment plants.

Keywords: terrils miniers, métaux lourds, nappe phréatique, pollution, géochimie, mine tailings, heavy metals, groundwater, pollution, geochemistry