Activité de la phosphatase alcaline bactérienne à l'interface eau-sédiment au sein du réservoir Sahela (Maroc)

Les variations temporelles des concentrations en phosphore, celles des abondances bactériennes et de l'activité de la phosphatase alcaline (APA) ont été estimées in situ en chambre benthique placée en deux points du réservoir Sahela (Maroc) durant les mois de septembre et octobre 98. En période de faible oxygénation, nous avons enregistré des élévations relativement faibles des concentrations en orthophosphates (de 0,020 à 0,035 mg. l-1 au point 1 et 0,015 à 0,025 mg. l-1 au point 2) par rapport au phosphore total (0,080 à 0,100 mg. l-1 au point 1 et de 0,035 à 0,040 mg. l-1 au point 2). À cette période, les abondances bactériennes et l'APA montrent des valeurs maximales (8. 106 bact. ml-1 et 0,323 mmol.PNP l-1.h-1 au point 1 et 6.106 bact. ml-1 et 0,438 mmol.PNP l-1.h-1 au point 2 respectivement). L'apparition des conditions anoxiques et la diminution du pH favorisaient la dissolution du phosphore particulaire et la libération du phosphore réactif soluble. Cette libération s'accompagne d'une élévation des abondances de bactéries anaérobies (de 5.106 à 9,2. 106 bact. ml-1 au point 1 et de 3,8.106 à 7,2. 106 bact. ml-1 au point 2) et une diminution progressive d'APA (de 0,200 à 0,025 mmol.PNP l-1.h-1 au point 1 et de 0,125 à 0,077 mmol.PNP l-1.h-1 au point 2). Ce relargage du phosphore à partir du sédiment est accentué par les rejets domestiques et industriels de la ville de Taounate, ce qui accélère le processus d'eutrophisation de ce réservoir.Temporal variations of phosphorus concentrations, bacterial abundance and alkaline phosphatase activity (APA) were estimated in situ in a benthic chamber. The chamber used has a surface of 0.4m2 and a volume of 90 l ; it resembles those used in oceanography, with a tube connecting the interior of the chamber to the lake surface. The water in the chamber was permanently mixed by an electric agitation system. The chamber was placed at two points in the Sahela reservoir (Morocco). Point 1 was located near Guelta El Haila, a site that receives both domestic and industrial effluent, and point 2 was located in the centre of the reservoir. During the two incubations, eight samples were taken over 24 d in September and October 1998 from point 1, and seven samples were taken from point 2 over 29 d in October. After each sampling, an equal volume of water was injected into the chamber to avoid bubble formation.Under low dissolved oxygen concentrations in the benthic chamber, we noticed a relatively small elevation in orthophosphate concentrations (from 0.020 to 0.035 mg×L-1 at point 1 and from 0.015 to 0.025 mg×L-1 at point 2) in relation to total phosphorus (from 0.080 to 0.100 mg×L-1 and from 0.035 to 0.040 mg×L-1 at points 1 and 2 respectively). The low residual oxygenation of hypolimnic layer allowed the oxidation of iron, manganese and led to their binding to phosphorus released from the interstitial water. Dissociation of calcium-phosphorus complexes as a result of a pH decrease may have contributed to phosphorus release. The orthophosphate concentrations were relatively low, a situation that favours the synthesis of alkaline phosphatase by aerobic bacteria and facultative aerobic bacteria. In this period, the bacterial abundance and APA were comparable and showed the maximal values (8. 106 bact. ml-1 and 0.323 mmol. PNP l-1.h-1 (phosphate nitrophenol) in point 1 and 6. 106 bact. ml-1and 0.438 mmol. PNP l-1.h-1 in point 2 respectively). The lack of a significant correlation between total APA and bacterial abundance at the two sampling points is probably due to the decrease of aerobic bacteria followed by a repopulation with anaerobic bacteria. However, the relative contribution of two bacterial populations that have different sizes, as at points 1 and 2, showed that the majority of total APA was produced by bacteria that are attached to organic matter. Therefore we suggest that attached bacteria contribute more than free bacteria to APA production.The beginning of anoxic conditions and the decrease in pH favored the dissolution of particulate phosphorus and the liberation of reactive phosphorus. We noted an elevation in orthophosphate concentrations (from 0.035 to 0.050 mg×L-1 at point 1 and stabilised at 0.025 mg×L-1 at point 2) and total phosphorus (from 0.100 to 0.150 mg×L-1 at point 1 and from 0.040 to 0.050 mg×L-1 at point 2). This liberation followed an increase in anaerobic bacterial abundance (from 5×106 to 9.2×106 bact×mL-1 at point 1 and from 3.8×106 to 7.2×106 bact×mL-1 at point 2) and the progressive decrease in APA (from 0.200 to 0.025 mmol PNP L-1 ×h-1 at point 1 and from 0.125 to 0.077 mmol PNP L-1 ×h-1 at point 2). The anaerobic bacteria did not activate their alkaline phosphatase and the synthesis of their enzyme was progressively inhibited by a de-repression phenomenon caused by high phosphorus concentrations.We conclude that low oxygen and a decrease in pH favoured the release of phosphorus by dissolution of chemical complexes: calcium-phosphorus, iron-phosphorus, manganese-phosphorus and aluminium-phosphorus. This release is also the result of bacterial phosphatase activity to which fixed bacteria contributed the most. The release of phosphorus from water-sediment interface is further amplified by phosphate import from domestic and industrial waste waters originating from Taounate, which accelerates the eutrophication process in this reservoir

Dynamique des populations microphytobenthiques couplée à leur composition biochimique au sein du réservoir Allal El Fassi (Maroc)

L'étude du métabolisme des populations microphytobenthiques par le biais des principaux constituants cellulaires à savoir les glucides, les protéines et les lipides a été réalisée du mois d'août 1996 au mois de juillet 1997 au sein du réservoir Allal El Fassi, situé sous climat semi-aride.Les résultats issus d'un échantillonnage sur substrats artificiels permettent de montrer que :- la température, l'oxygène, l'azote et le phosphore influencent l'orientation métabolique des populations microphytobenthiques ;- les plus fortes concentrations en glucides, en protéines et en lipides correspondent à des populations estivales ;- les lipides sont susceptibles de fournir une estimation satisfaisante de la biomasse microphytobenthiques ;- le métabolisme du microphytobenthos s'oriente vers la synthèse préférentielle des protéines.Most of the works achieved so far in semi-arid lakes have been focused especially on the dynamics, structure and metabolic of phytoplankton. However, this issue has not been addressed in term of metabolic microphytobenthic cells activity. With an aim increasing the relative scientific knowledge relating to the functioning of lacustrian ecosystems in the Maghreb for which the data are still very fragmentary, special attention has been granted to the study of the microphytobenthos metabolism, by means of determining essential cellular constituents (carbohydrates, proteins and lipids) of the reservoir Allal El Fassi.The Allal El Fassi reservoir is about 47 km of Fez. It was built in 1992, and is 7 km long, 0.7 km wide and 34 m maximum depth. The reservoir is classed as mesotrophic and used for irrigation, recreation and to supply drinking water.The study was conducted between August 1996 and July 1997. Samples were taken vertically from the deepest point of the reservoir by means of a Van-Dorn sampler from seven depths: Near the surface, - 2 m, - 5 m, - 10 m, - 15 m, - 20 m and close to the bottom. The samples were analysed for physical, chemical and metabolism of Diatom. Analysis of Nitrogen and phosphate was done following Golterman method and oxygen dissolved by the Winkler method.Given the advantage that presents the artificial substrata (polyethylene leaves) for sample of periphyton, we have opted for the utilization of these substrata similar to these already used by WATANABE et al. (1988). These substrata are submerged during four weeks at different depths.The evaluation of the microphytobenthic biomass has been carried out according to the method of LOHMAN (1908) after enumerations to the microscope Olympus following the technique of LECLERCQ (1984).The dosage of the carbohydrates has been undertaken according to the method of MOAL et al. (1985), while concentrations of proteins have been determined according to the method of LOWRY (1951) and lipids have been extracted according to the method chloroform/methanol.The results show that microphytobenthic biomass presents important fluctuations since extreme values are respectively 0.25·104 µg·cm-2 and 14.95·104 µg·cm-z.Carbohydrates and lipids concentrations (mean=4.52 µg·cm-z and 2.27 µg·cm-z, respectively) are clearly less high than those of proteins (mean=81.84 µg·cm-2). This result indicates that the metabolism of the microphytobenthos of the Allal El Fassi reservoir is oriented towards the preferential protein synthesis. The vertical distribution of proteins, carbohydrates and lipids concentrations shows a well marked stratification, maximal concentrations generally recorded between 0 and 5 m. These high concentrations are attributed to the development of Niztchia, Navicula, Cymbella, Cyclotella, Melosira and Cocconeis.Proteins and carbohydrates concentrations were significantly correlated (r=0.84, p=0.01 at 0m and r=0.52, p=0.10 at 5 m). On the opposite, concentrations of lipids have no correlation neither with those of proteins, nor with those of the carbohydrates.The correlation between the lipids concentrations and the microphytobenthic biomass, is highly significant (r=0.48, p=0.10). This correlation results notably into the fact that lipids visualise well the evolution of the microphytobenthic biomass. However, no significant correlation was found between proteins, carbohydrates concentrations and biomass microphytobenthic.Many works prove the influences of some environmental factors namely light intensity and the temperature on the biochemical composition of the microphytobenthic. In this way, we observe that in period of high temperature, the synthesis of lipids is important. The positive correlation between temperature and lipids (r=0.48, p=0.10) support the observed increase in the concentrations of this variable with increasing temperature. Nevertheless, no significant correlation was found between proteins and carbohydrates concentrations and temperature, which suggests that the synthesis of these components is made independently from this factor. Oxygen dissolved and nitrogen intervene equally in the synthesis of lipids

Étude du régime alimentaire de deux souches de truite arc-en-ciel marocaine et bulgare dans deux plans d'eau du Moyen-Atlas Amghass I et Amghass II

Le présent travail porte sur l'étude du régime alimentaire de deux souches de truites arc-en-ciel : la souche marocaine issue de croisements de truites arc-en-ciel en provenance d'Europe et d'Amérique du nord et la souche bulgare introduite au Maroc en 1987. Les milieux d'étude sont deux plans d'eau du Moyen-Atlas marocain (Amghass I et Amghass II) présentant des eaux de bonne qualité physique et chimique et une diversité biologique (invertébrés) assez importante. Afin de déterminer les préférences alimentaires de ces deux souches nous avons évalué : le spectre alimentaire, déterminé par les abondances relatives, les coefficients d'occurrence des proies ingérées, l'indice alimentaire de Lauzanne pour les différentes catégories de proies et l'intensité de prédation des truites.Les résultats ont montré une similitude au niveau des régimes alimentaires des deux souches caractérisés par une nette préférence pour les larves et nymphes d'Insectes considérées comme proies essentielles.This current work is about the study of the dietary regime of two species of rainbow trout. The Moroccan kind is a cross breed of the European and North American Rainbow trout and the Bulgarian trout introduced into Morocco since 1987.The environments of study are two stretches of water in the "Moyen-Atlas" (Amghass I and Amghass II), which present water of good physical and chemical quality and are of quite important biological diversity.To determine the dietary preferences of the two species, we evaluated several parameters: the dietary spectrum which is determined by the relative abundance and the coefficient of occurence of ingested prey, the index alimentary of Lauzanne for the different categories of prey and how predatory the trout areThe results have shown a similarity in the level of dietary regimes of the two populations outlined by a clear preference for larvae and nymph insects which are considered to be essential prey

Étude préliminaire sur les échanges de phosphore à l'interface eau- sédiment au sein de la retenue d'Al Massira (Maroc)

Les échanges de phosphore à l'interface eau-sédiment ont été étudiés dans la retenue Al Massira. La campagne de prélèvements a été menée pendant la faible oxygénation des eaux profondes au mois d'octobre 1991. Les mesures des échanges de phosphore ont été réalisées in situ en chambre benthique.Les valeurs de pH sont élevées et reflètent clairement l'influence de la nature géologique du bassin versant sur la composition chimique des eaux. Ce bassin versant, formé essentiellement de roches sédimentaires calcaires, est vraisemblablement à l'origine des concentrations élevées en calcium mesurées dans les chambres benthiques.En période de faible oxygénation, on note une augmentation des teneurs en phosphore particulaire dans les eaux surnageantes en raison de la présence de complexes calcium-phosphore, fer-phosphore et manganèse-phosphore. En période d'anoxie, la réduction de ces complexes est accompagnée d'une aug- mentation des teneurs en phosphore.La densité bactérienne et la concentration en phosphore total et notamment en orthophosphates suivent une évolution temporelle comparable. Une fraction non négligeable du phosphore particulaire serait liée aux bactéries.Des mesures drastiques de déphosphatation du tributaire Oum Errbia doivent être prises pour éviter la dissociation des complexes Ca, Fe, Mn-Phosphore et le relargage de phosphore biodisponible.Phosphorus exchange at the sediment-water interface was studied in the Al Massira reservoir. This reservoir, located on the Oum Errbia river, is the most important freshwater resource in Morocco. It provides drinking water to the whole population of Casablanca and contributes to farming and to the functioning of several industrial plants. Our investigations were made in October 1991 and coincided with low oxygen concentrations in the deep layers. The measurements of phosphorus exchange have been made in sitn with a benthic chamber device.The results showed that these exchanges were regulated by a combination ofthe physical chemical variability of the environment and the geological composition of the catchment basin.The pH, which permanently exceeded 7 in Massira, suggests that calcium-bound phosphorus was primarily CaHFO4. Moreover, given the high phosphonrs inputs into the reservoir (570 tonnes. year-1), and despite the fact that, as soon as it reached the reservoir, a large fraction of this element was associated with to calcium, it's likely that the Massira reservoir is subject to eutrophication.In low oxygenated deep layers, we observed an increase in particulate phosphorus concentrations of the overlying water, due to the simultaneous presence of calcium-phosphorus, iron-phosphorus and manganese-phosphorus forms. Under anoxic conditions, the reduction ofthese complexes resulted in an increase of phosphorus concentrations.Bacterial cell numbers and total phosphorus concentratioru showed a comparable temporal behaviour. This would suggest that attached bacteria contributed at least partially to the total particulate phosphoms concentrations.We suggest that a drastic control of phosphorus inputs into the waters must be done through a program of dephosphorylation of tributaries to avoid the dissocation of calcium-, iron-, manganese-bound phosphorus with release upwards of bioavailable phosphorus

Processus d'eutrophisation : activité de la phosphatase alcaline du microplancton d'un réservoir mésotrophe marocain (Allal El Fassi)

L'activité de la phosphatase alcaline (APA) bactérienne et phytoplanctonique a été mesurée bimensuellement du mois de mars au mois de décembre 1998 au sein d'un réservoir mésotrophe situé dans une zone à climat semi-aride (Allal El Fassi, Maroc). Les résultats montrent que l'APA totale est importante (0,107-1,780 mmol PNP·l-1·h-1) et majoritairement d'origine bactérienne (> 60 %) au niveau de l'épilimnion, alors qu'elle est à dominance algale (> 58 %) dans le méta- et l'hypolimnion. L'absence de corrélation entre l'APA totale et les concentrations en orthophosphates suggère que l'hydrolyse par cette enzyme n'est pas significative dans le processus de régénération du phosphore dans ce réservoir. Par conséquent, l'APA ne pourrait pas être un indicateur fiable du déficit en phosphore dans le milieu.Bacterial and phytoplanktonic alkaline phosphatase activity (APA) was measured from march to December 1998 in the mesotrophic Allal El Fassi reservoir located in the semi-arid zone (Morocco). The total APA varied between 0.107-1.780 mmol PNP·L-1·h-1. In epilimnion, the bacterioplankton contributed significantly (> 60%) to total APA. In the meta and hypolimnion, the APA was predominantly algal (> 58%). No correlation between APA and orthophosphates indicate that the hydrolysis by this enzyme was not a significant process in recycling of phosphorus in Allal El Fassi reservoir. Consequently, the APA was not a valid test of phosphorus deficiency

Impact du zooplancton métazoaire sur le phytoplancton et les protozoaires ciliés dans le réservoir Sahela (Maroc)

L'impact du zooplancton métazoaire sur le phytoplancton et les protozoaires ciliés a été mesuré durant la période de juillet à décembre 1999 dans le réservoir Sahela sous climat méditerranéen semi-aride.Les expériences ont été réalisées à l'aide de chambres de diffusion immergées in situ pendant 7 heures en absence (chambres témoins) et en présence (chambres expérimentales) du zooplancton.Les résultats indiquent que la mortalité moyenne à 4 m des algues est de 0,13 + 0,03 h-1, et celle des protozoaires ciliés de 0,07 + 0,03 h-1. Cryptomonas ovata et Halteria grandinella ont subi la plus forte prédation, respectivement, 0,31 + 0,14 h-1 et 0,11 + 0,04 h-1 à 4 m. Toutefois, les algues de grande taille (Pediastrum sp, Ceratium hirundinella et Peridinium cinctum) n'ont été que très peu ou pas consommées.The Sahela reservoir, located in Taounate at 90 km from Fès, lying at an altitude of 325 m, was built to provide drinking water for the population of Taounate and to contribute to irrigate neighbouring farming perimeters.In order to assess the impact of metazoan zooplankton on phytoplankton and protozoan ciliates in the Sahela reservoir under semi-arid climate, we conducted experiments during the period from July to December 1999 at the deepest point in the lake (15 m).Sampling and measurements were carried out in diffusion chambers submerged in situ over a period of 7 h without (control chambers) and with (experimental chambers) zooplankton. During these experiments, counts were conducted on phytoplankton and ciliates to determine the abundance and the mortality of these organisms due to zooplankton in each diffusion chambers at t=0 and t=7 h incubation. The metazooplankton were counted and dry weight of each taxa was calculated.In summer the highest zooplankton biomass (150 µg·L-1) mainly composed of cyclopoid Tropocyclops prasinus, caused mortality of the small-sized ciliates, such as Halteria grandinella (0.10 h-1). In Autumn, the zooplankton biomass (75 µg·l-1), dominated by Daphnia longispina, induced a higher mortality for phytoplankton (0.10 h-1) than for ciliates (0.05 h-1). In Winter, the zooplankton biomass (100 µg·L-1), also represented by Daphnia longispina, had a low impact on ciliate mortality (< 0.02 h-1).The study showed that a heavy predation by the metazoan zooplankton was exerted on small-sized phytoplankton and ciliates and clearly demonstrated the relationships between protozoans and metazoan zooplankton to transfering the matter and energy in aquatic food webs

Dynamics of the relative nitrogen and phosphorus concentrations in a reservoir situated in a semi-arid zone (Sahela, Morocco)

International audienceFluctuations in total nitrogen and phosphorus concentrations and in the N/P ratio (i.e. in terms of mass) were measured at the entry and exit of the Sahela Reservoir (Morocco) throughout an annual cycle. Particulate N and P concentrations in sedimenting particles in the reservoir itself were also measured. The results obtained showed that the spring floods were a major source of N and P inputs, this being especially pronounced for phosphorus that was present mainly in particulate form. In all the compartments of the reservoir analysed, the N/P ratios were high (means between 81 and 314), especially in summer (the only season when the reservoir was emptied) when the supply of P was apparently limited by the drought. However, the values of this ratio in the sedimenting particles remained lower (mean = 21), at levels characteristic of natural communities. This implies that the reservoir's biological communities preferentially store phosphorus, no doubt to maximise their activity in an environment where a large proportion of this element is not bioavailable. Furthermore, it appeared that the quantity of particulate N and P sequestrated by the sediments and the total quantities of N and P leaving the reservoir were greater than the inputs of these nutrients, underlining the importance of lateral and internal nutrient supplies. One spot measurement, made in a single month, showed that nutrient release activity from the sediments was in fact quite considerable

Évolution nycthémérale des composantes biochimiques du phytoplancton de la retenue du barrage Idriss premier (Fès, Maroc)

The diel changes of the biochemical composition of the phytoplankton were studied in the Idriss first reservoir (located on the Inaouen river at thirty Km from the city of Fes, Morrocco) during September 1994. Several biomass and metabolic indicators (proteins, carbohydrates, lipids, chlorophyll a and primary production) were assessed every fourth hour over tow days (7, 8 and 9 September). Since the Protein/Carbohydrates ratio (P/C) is largely recognised as a good integrator of the metabolic functions of the cells, we examined its distribution pattern concomitantly with aforementioned parameters. The results demonstrated enhanced P/C ratios clearly indicating that nutrients were sufficiently available for growth. In addition, this index showed a diel significant variation with levels higher in the night than in the day. Moreover, these results suggest that phytoplankton species during the night used the day-synthesised carbohydrates to insure the cell metabolic functioning. The P/C presents relatively high values in proposition to the ones that have been recorded in temperate regions, and seems to be related to azotic inputs of the Inaouen river

Variations saisonnières de l'activité de la phosphatase alcaline des communautés planctoniques bactériennes et algales dans le lac réservoir Allal El Fassi, Maroc

Les variations verticales et saisonnières de l'activité de la phosphatase alcaline (APA) des communautés microplanctoniques ont été étudiées dans le lac réservoir mésotrophe Allai El Fassi, situé sur l'oued Sebou. Les échantillons ont été collectés à différentes profondeurs au point le plus profond du lac, de mars à décembre 1998. Les résultats montrent que l'APA totale est exclusivement associée à la fraction de taille 0,22-100 μm dont les valeurs moyennes sont comprises entre 0,107 et 1,780 mmol PNP 1-1 h-1 . La fraction dissoute (< 0,22 μm) ne présente aucune activité liée à cette enzyme. Au niveau des couches superficielles, plus de 60 % de l'APA totale sont corrélés à la fraction de taille 0,22-0,65 μm à majorité bactérienne. Cependant, avec la profondeur, l'APA est plutôt associée à la fraction de taille 0,65-100 μm à dominance phytoplanctonique (> 58 % de l'APA totale). Cette activité liée aux algues est significativement corrélée avec la densité phytoplanctonique et avec les concentrations de la chlorophylle a. L'absence de corrélation significative entre l'APA et les teneurs en phosphore total et orthophosphates suggère une indépendance entre l'APA et les orthophosphates