Impact de la sécheresse sur l'évolution de la qualité des eaux du lac Mansour Eddahbi (Ouarzazate, Maroc)

L'objectif de ce travail est d'étudier l'impact d'une année hydrologique très sèche (98/99) sur la qualité physico-chimique et l'évolution de l'état trophique du lac Mansour Eddahbi. Ce lac est situé dans la région de Ouarzazate, au sud du Maroc, caractérisée par un climat aride continental, avec des écarts thermiques hiver-été importants, des précipitations très faibles et une forte évaporation. Ceci induit une réduction considérable du volume total du lac et par suite une baisse de 14 m de son niveau.À la lumière des valeurs de températures enregistrées au niveau de la colonne d'eau, le lac peut être classé dans la catégorie des lacs monomictiques avec une seule période de mélange hivernale. Le pH est légèrement alcalin. La réduction du volume d'eau au niveau du lac a engendré une augmentation de la salinité des eaux. Une corrélation significative est enregistrée entre les deux paramètres (r2 =0,60 pour n=13 et p<0,05).Un déficit marqué en oxygène dissous (7,3 mg d'O2 /l comme moyenne en surface et des valeurs inférieures à 2 mg d'O2 /l voire nulles en profondeur durant la stratification), les teneurs en Chl "a" (24 µg/l) permettent de classer le lac dans la catégorie des lacs eutrophes. Selon les teneurs enregistrées en azote (0,2 mg/l) et en phosphores (0,02 mg/l), le lac est hyper-eutrophe. Deux années auparavant, le lac était considéré comme mésotrophe (ONEP/BRL, 1998). Les conditions climatiques sévères qui ont sévi durant l'année hydrologique 98/99 ont contribué à une évolution accélérée de l'état trophique du lac.Eutrophication is one of the most important water quality problems in lakes. Due to the effects of excessive external inputs of nutrients (phosphorus and nitrogen), compounded with unfavorable climatic and hydrologic conditions, the lake undergoes major changes that involve both the physical-chemical properties of water and the aquatic communities living there. There have been many studies on lake ecosystems and their evolution (HENRY et al., 1984; AFDALI, 1993; HARRAK, 1991; LOUDIKI et al., 1994; SBIYYAA, 1998, MOUHRI et al., 1999). These studies relate especially to the role of nutrients (nitrogen and phosphorus mainly) in the evolution of lakes. The influence of climatic and hydrologic conditions on the structure and dynamics of these ecosystems has been often underestimated. Indeed, there are few studies on the relationship between climatic conditions and the trophic status of aquatic ecosystems.The aim of this paper is to study the behavior of the physical-chemical qualities of water in lake Mansour Eddahbi (Ouarzazate, Morocco) and its trophic status under severe climatic conditions, especially during the very dry hydrological year 1998/99. The Ouarzazate region is characterized by an arid continental climate with very hot summers and cold winters. Due to both great evaporation and increasing demand for water for irrigation, the water levels of the reservoir has been reduced by 14 m and its storage capacity has been considerably reduced. The approach used was to assess water quality in a station at the deepest area of the lake during the hydrological year 1998/99. Sampling was undertaken monthly and different parameters were analyzed including temperature, pH, total suspended solids (TSS), salinity, dissolved oxygen (DO), chlorophyll a, phosphorus (TP and PO43-), and nitrogen (TNK, NO3 - and NH4 +).The results of this study demonstrated important seasonal variations of water temperature in the lake. Temperature varied from 9.5°C in the winter to as high as 28.5°C in the summer. Based on this parameter, the reservoir could be classified as a monomictic hot lake with one mixing period occurring in winter. In the entire water column, the pH values were slightly alkaline and oscillated between 7.8 and 8.5 at the surface and 7.4 to 8.2 at the bottom of the lake. This reflects a well-buffered system with moderate benthic decomposition activity. The decrease in water volume by evaporation and intensive use for irrigation resulted in an increase in water salinity. These two parameters presented a significant correlation (r2 =0.60 for n=13 and p<0.05). A decrease in dissolved oxygen from 7.3 mg O2 /l at the surface to 0 mg O2 /l at the bottom of the lake occurred during summer stratification. However, water of the lake reservoir was well oxygenated during preceding years (concentration of dissolved oxygen oscillated between 2 and 11 mg/l (ONEP/BRL, 1998)). Concentrations of chlorophyll a in the euphotic zone (8 m depth) were very important and varied from 12 µg/L (August 1998) to 49 µg/L (September 1999) with an average of 25 µg/L. Based on the chlorophyll a value, the lake Mansour Eddahbi could be classified as eutrophic.The lake has become shallower and the thermocline, beginning at 12 m below the surface, has moved closer to the deeper layers where exchange between sediments and the water column is important. These exchanges between the two compartments of the lake contributed to enrichment of the water column in summer, creating an internal nutrient load. During the hot period when the lake was stratified, there was a large loss of nitrogen from the system. During the mixing period, nitrates were present at substantial concentrations in the deeper regions, but in summer nitrates were consumed rapidly in the surface layer, leading to a limitation on phytoplankton growth in this period. This same phenomenon was also noticed by HENRY et al. (1984). Furthermore, these losses of nitrogen induce a strong reduction in the N/P ratio during this period.Orthophosphate concentrations decrease from the bottom layers to the surface, with almost total impoverishment in the upper strata. This impoverishment reaches 10 m during the summer period and these values are often limiting for the phytoplankton production. The correlation obtained between orthophosphate concentrations and chlorophyll a was significant, especially in summer (r2 =0.79 for n=13 and p<0.05).Nutrient exchange at the water and sediment interface was favoured by the anoxic conditions at the lake bottom that prevailed during the eight months of stratification. The release of these substances can alone, without external contributions, maintain important primary production. This was confirmed by the importance of phytoplankton development compared to the preceding years. The algae production seemed to be enhanced, even if the reported N/P ratio was not optimal, particularly during the period of stratification and had no significant correlation with chlorophyll a content (r2 =0.19, n=13 and p<0.05). This important production appeared to be the result of an internal enrichment of the lake in nutrients coming from the sediment. According to nitrogen (0.2 mg/L) and phosphorus values (0.02 mg/L), the lake could be classified as hypereutrophic whereas two years earlier it was considered mesotrophic (ONEP/BRL, 1998). This work shows clearly that the severe climate conditions during the hydrological year 1998/99 contributed to a rapid degradation of the trophic status of this lake. It changed from a mesotrophic to a hypereutrophic state, resulting from an important enrichment in nutrients and the consequent algal production

Variations saisonnières des formes de phosphores dans une station de traitement des eaux usées par lagunage, sous climat aride de Marrakech (Maroc)

L'objectif de ce travail est d'étudier dans un premier temps la dynamique du phosphore dans un système de traitement d 'eaux usées par lagunage facultatif, en relation avec les compartiments biologiques: phytoplancton, zooplancton et bactéries, dans un deuxième temps, d'évaluer, sous les conditions du climat aride, les performances épuratoires de ce système en ce qui concerne les formes du phosphore. Un intérêt particulier est porté au phénomène du relargage du phosphore par les sédiments. Les résultats montrent qu'il y a une évolution saisonnière et cyclique du phosphore dans les bassins de lagunage, en étroite corrélation avec le phytoplancton et le zooplancton. Le phytoplancton représente la part importante des formes organiques du phosphore particulaire. Les meilleures performances d'élimination du phosphore sont notées au printemps (77% pour les PO4 et 64 % pour le phosphore total). La période la moins performante est la période automne-hiver où les rendements moyens ne dépassent pas 38%. Le phosphore éliminé est stocké dans les sédiments. En période estivale, des phénomènes de relargage du phosphore à partir des sédiments ont été mis en évidence, favorisés par une zonation verticale des eaux à cette période. Des essais aulaboratoire ont montré la grande aptitude des sédiments de la station de lagunage étudiée à relarguer le phosphore, avec intervention de l'activité biologique du sédiment.Assimilation, sedimentation and release are the principal mechanisms controlling the behavior of phosphorus in aquatic ecosystems. There are numerous investigations of the phosphorus cycle in lakes and rivers in relation to the eutrophication process. There are, however, few studies about phosphorus cycling in waste stabilization ponds and most of these have discussed phosphorus removal. The aims of this paper were: 1) to study phosphorus dynamics in relation to the biomass compartment (zooplancton, phytoplancton and bacteria); and 2) to evaluate the phosphorus removal efficiency of the treatment plant under arid climatic conditions. Of particular interest was the remobilization of phosphorus from the pond sediment, both under laboratory conditions and in the field. The experimental installation consisted of two ponds receiving domestic wastewater (mean flow=120.4+5.8 m3.day-1 and specific organic load=56 kgBOD.ha-1. day-1; pond area=0.5 ha and depth=1.5 m). Samples were taken twice monthly from the surface, B1(S) and B2(S), and from the 1.5 m layers, B1(F) and B2(F). Composite (24 h) samples were taken from the inflow and the outflowof the plant to determine the removal efficiencies. In each sample, soluble reactive phosphorus (PO4), total phosphorus (PT) and total soluble phosphorus (PTD) were determined. Particulate phosphorus (PTP) was calculated as (PT-PTD) and soluble organic phosphorus (POD) as (PTD-PO4). Phosphorus release was measured in a plexiglas flask containing sediment (collected by corer from the pond bottom) overlaid with distilled water. Over 15 days, daily measurements were made of PO4 and total phosphorus. Sediment dry weight (%), volatile matter, organic carbon (%) and total phosphorus were measured before and after each test. Phosphorus contents of the phytoplankton, zooplankton and bacteria were estimated using the methods of BOUGIS (1974).The results show that cyclical and seasonal variations of phosphorus content were closely correlated with variations in the biological components. Significant correlation coefficients were noted between chlorophyll-a and particulate organic phosphorus. Organic phosphorus in algal cells was the more important form of particulate organic phosphorus. Under the arid climate, the waste stabilization ponds were more efficient at phosphate removal during the spring-summer period (77% of PO4 and 64% of total phosphorus in spring). The first pond may play the major role in phosphate removal. Phosphorus is only eliminated from stabilization ponds through accumulation in the sediment. However, part of the phosphorus which accumulates in pond sediments remains potentially mobile. During the summer period, phosphorus release from the sediment, observed in situ, was favored by stratification of the overlying water. The same phenomenon was noted during the autumn, particularly the release of POD. Laboratory studies have shown that phosphorus release may amount to 55 mg P m-2d-1. Biological activity may play a significant role in this mobilization

Effet de certaines espèces fongiques sur le développement de la ternissure des grains de riz (Oryza sativa L.)

Sept (7) espèces fongiques isolées à partir des lésions foliaires et des semences de riz (Helminthosporium oryzae, Helminthosporium sativum, Helminthosporium spiciferum, Helminthosporium australiensis, Curvularia lunata, Fusarium moniliforme et Epicoccum nigrum) ont été utilisées pour inoculer les grains de riz des variétés Arco et Taibonnet dans le but d’observer les symptômes que ces champignons sont capables de provoquer sur ces semences. Trois mois après inoculation des grains par les différentes espèces fongiques et dans les trois mois qui suivent l’expérience, les indices de ternissure et les pourcentages d’altération des grains ont été notés. Les indices de ternissure les plus importants et les pourcentages d’altération des grains les plus élevés sont induits par Fusarium moniliforme, Curvularia lunata et Helminthosporium oryzae

First report on cyanotoxin (Mc-lr) removal from surface water by multi-soil-layering (msl) eco-technology: Preliminary results

Cyanobacteria blooms occur frequently in freshwaters around the world. Some can produce and release toxic compounds called cyanotoxins, which represent a danger to both the environment and human health. Microcystin-LR (MC-LR) is the most toxic variant reported all over the world. Conventional water treatment methods are expensive and require specialized personnel and equipment. Recently, a multi-soil-layering (MSL) system, a natural and low-cost technology, has been introduced as an attractive cost-effective, and environmentally friendly technology that is likely to be an alternative to conventional wastewater treatment methods. This study aims to evaluate, for the first time, the efficiency of MSL eco-technology to remove MC-LR on a laboratory scale using local materials. To this end, an MSL pilot plant was designed to treat distilled water contaminated with MC-LR. The pilot was composed of an alternation of permeable layers (pozzolan) and soil mixture layers (local sandy soil, sawdust, charcoal, and metallic iron on a dry weight ratio of 70, 10, 10, and 10%, respectively) arranged in a brick-layer-like pattern. MSL pilot was continuously fed with synthetic water containing distilled water contaminated with increasing concentrations of MC-LR (0.18–10 µg/L) at a hydraulic loading rate (HLR) of 200 L m−2 day−1. The early results showed MC-LR removal of above 99%. Based on these preliminary results, the multi-soil-layering eco-technology could be considered as a promising solution to treat water contaminated by MC-LR in order to produce quality water for irrigation or recreational activities. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This research has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 823860

Olive phenology as a sensitive indicator of future climatic warming in the Mediterranean

Experimental and modelling work suggests a strong dependence of olive flowering date on spring temperatures. Since airborne pollen concentrations reflect the flowering phenology of olive populations within a radius of 50 km, they may be a sensitive regional indicator of climatic warming. We assessed this potential sensitivity with phenology models fitted to flowering dates inferred from maximum airborne pollen data. Of four models tested, a thermal time model gave the best fit for Montpellier, France, and was the most effective at the regional scale, providing reasonable predictions for 10 sites in the western Mediterranean. This model was forced with replicated future temperature simulations for the western Mediterranean from a coupled ocean-atmosphere general circulation model (GCM). The GCM temperatures rose by 4·5 °C between 1990 and 2099 with a 1% per year increase in greenhouse gases, and modelled flowering date advanced at a rate of 6·2 d per °C. The results indicated that this long-term regional trend in phenology might be statistically significant as early as 2030, but with marked spatial variation in magnitude, with the calculated flowering date between the 1990s and 2030s advancing by 3–23 d. Future monitoring of airborne olive pollen may therefore provide an early biological indicator of climatic warming in the Mediterranean

Spin down of the core rotation in red giants

The space mission Kepler provides us with long and uninterrupted photometric time series of red giants. We are now able to probe the rotational behaviour in their deep interiors using the observations of mixed modes. We aim to measure the rotational splittings in red giants and to derive scaling relations for rotation related to seismic and fundamental stellar parameters. We have developed a dedicated method for automated measurements of the rotational splittings in a large number of red giants. Ensemble asteroseismology, namely the examination of a large number of red giants at different stages of their evolution, allows us to derive global information on stellar evolution. We have measured rotational splittings in a sample of about 300 red giants. We have also shown that these splittings are dominated by the core rotation. Under the assumption that a linear analysis can provide the rotational splitting, we observe a small increase of the core rotation of stars ascending the red giant branch. Alternatively, an important slow down is observed for red-clump stars compared to the red giant branch. We also show that, at fixed stellar radius, the specific angular momentum increases with increasing stellar mass. Ensemble asteroseismology indicates what has been indirectly suspected for a while: our interpretation of the observed rotational splittings leads to the conclusion that the mean core rotation significantly slows down during the red giant phase. The slow-down occurs in the last stages of the red giant branch. This spinning down explains, for instance, the long rotation periods measured in white dwarfsComment: Accepted in A&

Study of KIC 8561221 observed by Kepler: an early red giant showing depressed dipolar modes

The continuous high-precision photometric observations provided by the CoRoT and Kepler space missions have allowed us to better understand the structure and dynamics of red giants using asteroseismic techniques. A small fraction of these stars shows dipole modes with unexpectedly low amplitudes. The reduction in amplitude is more pronounced for stars with higher frequency of maximum power. In this work we want to characterize KIC 8561221 in order to confirm that it is currently the least evolved star among this peculiar subset and to discuss several hypotheses that could help explain the reduction of the dipole mode amplitudes. We used Kepler short- and long-cadence data combined with spectroscopic observations to infer the stellar structure and dynamics of KIC 8561221. We then discussed different scenarios that could contribute to the reduction of the dipole amplitudes such as a fast rotating interior or the effect of a magnetic field on the properties of the modes. We also performed a detailed study of the inertia and damping of the modes. We have been able to characterize 37 oscillations modes, in particular, a few dipole modes above nu_max that exhibit nearly normal amplitudes. We have inferred a surface rotation period of around 91 days and uncovered the existence of a variation in the surface magnetic activity during the last 4 years. As expected, the internal regions of the star probed by the l = 2 and 3 modes spin 4 to 8 times faster than the surface. With our grid of standard models we are able to properly fit the observed frequencies. Our model calculation of mode inertia and damping give no explanation for the depressed dipole modes. A fast rotating core is also ruled out as a possible explanation. Finally, we do not have any observational evidence of the presence of a strong deep magnetic field inside the star.Comment: Accepted in A&A. 17 pages, 16 figure

Haematological evaluation of Wistar rats exposed to chronic doses of cadmium, mercury and combined cadmium and mercury

Cadmium and mercury present in the environment, cause blood disorders. This study was conducted to evaluate the influence of cadmium, mercury and their combination on hematological parameters of Wistar rats. For this purpose, two different doses of each metal and their combination were administered orally for 28 days to six groups of five rats each. Two groups (A and B) were respectively exposed to CdCl2 (0.25 and 2.5 mg/kg), two other groups (C and D) respectively received HgCl2 (0.12 and 1.2 mg/kg) and the last two groups (E and F) were respectively treated with the combination of these two metals: (0.25 mg/kg Cd + 0.12 mg/kg Hg) and (2.5 mg/kg Cd + 1.2 mg/kg Hg). The control group (G) received the same volume of distilled water. At the end of exposure, bodies of rats were weighed and the whole blood was collected by retro-orbital sinus method for analysis of hematological parameters. The results of this study show a significant decrease (p&lt;0.05) in white blood cells (WBC) in the lot treated with the combination (0.25 mg/kg Cd + 012 mg/kg Hg) and also indicate a significant decrease (p&lt;0.05) in WBC, red blood cells (RBC), hemoglobin concentration (HGB) and the mean corpuscular hemoglobin concentration (MCHC) with high levels of mercury (2.5 mg/kg) and the combination (2.5 mg/kg Cd + 1.2 mg/kg Hg). An increase in the number of platelet count (PLT) in all intoxicated lots was observed.Keywords: Cadmium, mercury, hematology, blood parameters, ratsAfrican Journal of BiotechnologyVol. 12(23), pp. 3731-373