L'environnement actuel et le fonctionnement hydroclimatique de quelques systèmes lacustres dans le Moyen Atlas marocain : Cas des lacs Ifrah, Iffer et Afourgagh

This work provides a better understanding of recent Hydroclimatic functioning of lake basins in the Middle Atlas of Morocco. Lakes Ifrah, Iffer and Afourgagh were selected for this research in aim to characterize the climate and anthropogenic impact on their functioning. The methodology undertaken during this research is based on a seasonal physico-chemical analysis of water and sedimentological, geochemical and mineralogical analysis of interface sediment. The rate of sediment accumulation and chronology of events were determined by analysis of radio-isotope 210Pb.The climate and anthropogenic impact on the hydrogeochemical functioning of the three lakes is represented by the significant decrease in lake level and degradation of water quality in the past three decades. This water deficit was manifested primarily by increased salinity of water and supersaturation in alkaline earth responsible for the precipitation of carbonates. The trophic status of lakes is associated with nutrient enrichment, the increase in the particle and the deterioration of the oxygenation of the water. The high evaporation and human consumption of water resulted in a temporary drying up of Ifrah and Afourgagh lakes particularly between 2005 and 2006 and summer 2008.Generally episodic, the mode of the present sedimentation is considerably influenced by climate variability and anthropogenic disturbances. This is mainly represented by the predominance of the organic carbon fraction as a result of the progress of the trophic status of lakes and increased the precipitation of endogenous carbonates. Such a process is linked to the succession of droughts and relative rising of the average temperature during the last century. The periodic increase of the detrital alumino-silicate and ferromagnésiens elements made in cores of the three lakes appear synchronous with the high hydrolysis of soils (already weakened by human activity) during the wet years. The decrease in the rate of accumulation over the past three decades is due to the reduction of surface runoff and to the drying up of some tributaries.The current dysfunction taking experienced by three lakes arouses special attention to minimize the climate and anthropogenic impact on their equilibrium. Involving all sectors concerned, an emergency plan must be implemented for monitoring, management and preservation of this lacustrine environment. Such an arrangement must be accompanied by an improvement to socio-economic conditions of local people who are very attached to their environment.Le présent travail apporte une meilleure compréhension du fonctionnement hydroclimatique récent des bassins lacustres du Moyen Atlas marocain. Les lacs Ifrah, Iffer et Afourgagh ont été retenus pour cette recherche dans le but de caractériser l’impact climatique et anthropique sur leur fonctionnement. La méthodologie entreprise au cours de cette recherche est basée sur l’analyse physico-chimique saisonnière des eaux et de l’analyse sédimentologique, géochimique et minéralogique des sédiments d’interface. Le taux d’accumulation des sédiments et la chronologie des événements ont été déterminés par l’analyse radio-isotopique du 210Pb.L’impact climatique et anthropique sur le fonctionnement hydrogéochimique des trois lacs est représenté par la diminution importante du niveau lacustre et la dégradation de la qualité des eaux au cours des trois dernières décennies. Ce déficit hydrique s’est manifesté essentiellement par l’augmentation de la salinité des eaux et la sursaturation en alcalino-terreux responsables de la précipitation des carbonates. L’état trophique des lacs est en relation avec l’enrichissement en éléments nutritifs, l’augmentation de la charge particulaire et la dégradation de l’oxygénation des eaux. La forte évaporation et la consommation anthropique des eaux ont entraîné un assèchement temporaire des lacs Ifrah et Afourgagh particulièrement entre 2005 et 2006 et en été 2008.Généralement épisodique, le mode de la sédimentation actuelle est considérablement influencé par la variabilité climatique et les perturbations anthropiques. Ceci est représenté principalement par la prédominance de la fraction organo-carbonatée sous l’effet de l’avancement de l’état trophique des lacs et l’augmentation de la précipitation des carbonates endogéniques. Un tel processus est lié à la succession des sécheresses et à l’élévation relative de la température moyenne au cours du dernier siècle. L’augmentation périodique des éléments détritiques alumino-silicatés et ferromagnésiens enregistrés au niveau des carottes des trois lacs paraît synchrone avec la forte hydrolyse des sols (déjà fragilisés par l’activité anthropique) au cours des années pluvieuses. La diminution du taux d’accumulation pendant les trois dernières décennies est due à la réduction de l’écoulement de surface et à l’assèchement de quelques affluents. La sédimentation actuelle dépend essentiellement de l’action éolienne qui redistribue les matériaux au niveau des sols et des terrasses exondées surtout au niveau des bassins versants des lacs Ifrah et Afourgagh.Le dysfonctionnement actuel que connaissent les trois lacs suscite une attention particulière pour atténuer l’impact climatique et anthropique sur leur équilibre. En faisant intervenir tous les secteurs concernés, un plan d’aménagement d’urgence doit être mis en œuvre pour le suivi, la gestion et la préservation de ces milieux lacustres. Un tel aménagement doit être accompagné par une amélioration des conditions socio-économiques de la population locale très attachée à son environnement

Recent environmental changes and human impact since mid 20th century in Mediterranean Lakes : Ifrah, Iffer and Afourgagh, Middle Atlas Morocco.

International audienceThe multidisciplinary study of sediment cores from three middle Atlas lakes (central Morocco) provides a detailed record of environmental, climatic and anthropogenic changes. The paleohydrological reconstructions show fluctuating lake level since the mid-20th century. Human activities have played a significant role in the lakes' hydrological changes. The sedimentology, geochemistry and mineralogy results show three main periods. The first period between 1900 and 1920 is humid with high lake levels, with fine particle size and relatively high contents of organic matter. The second period between 1920 and 1965 is very unstable with varying humidity. The last period between 1965 and 2000 is characterised by increasing human activities (clearing of forest and development of agricultural techniques). This last phase was interrupted by some humid years or sub-periods (between 1976 and 1980, between 1995 and 1996) and dry years (between 1980 and 1990, between 1994 and 1995). This study provides an opportunity to evaluate the relative significance of human and climatic factors in middle Atlas lakes during the 20th century

Sedimentology and geochemistry of lacustrine terraces of three Middle Atlas lakes: Paleohydrological changes for the last 2300 cal BP in Morocco (western Mediterranean region)

International audienceIn the Moroccan Middle Atlas Mountains, three lakes were used to characterize climate variability in the late Holocene. The methodology is based on sedimentological, geochemical, and mineralogical analysis of lacustrine terraces. Lake Ifrah is a natural lake. Waters are calc-magnesian, relatively very alkaline and oxygenated. Lake Afourgagh is of karst origin, with maximum depth 1.5 m. Lake Iffer is a smaller lake, sub-circular and relatively deep. Its area is 3.5 ha. Its maximum depth is 6.5 m at the center of the lake. Seven terraces located in the borders of the lakes were sampled and studied. Seven radiocarbon dates were obtained on organic matter and shells. The time period concerned is between 2300 cal BP and 400 cal BP. The results show high lake levels at about 2300 cal BP related probably to the wetter Iberian - Roman period in northern Mediterranean. Lake Iffer was deeper by about 30 m from its current level. 1000 cal BP probably marks the beginning of the decline with a drop in lake level of 20 m, which is ongoing in connection with drier climate and the beginning of the medieval climate anomaly. (C) 2015 Elsevier Ltd and INQUA. All rights reserved

Impacts climatiques et anthropiques sur le fonctionnement hydrogéochimique du Lac Ifrah (Moyen Atlas marocain)

International audienceMonitoring hydrogeochemical seasonality of Lake Ifrah (Morocco) was carried out between 2003 and 2006 in order to characterize the hydrogeochemical processes in the context of climatic and anthropogenic impacts. Lake Ifrah has declined significantly over the last decade. The waters are fairly alkaline, oxygenated, fairly turbid and oversaturated alkaline. The suspended load is moderately high. The hydrogeochemical facies is typically chloro-sodium bicarbonate magnesium. The lake is experiencing a significant water deficit as a result of recurrent droughts over the last three decades and marked human pressure. This is reflected by the increase in salinity manifested primarily by increased electrical conductivity and alkali contents (Na+ and K+) and chloride. This deficit is also assessed by lower levels of alkaline earth (Ca2+ and Mg2+) as a result of their precipitation as endogenic carbonates. The saturation index of calcite, aragonite and dolomite is always greater than zero. The increase in nutrients (phosphorus and nitrates) and degradation of water oxygenation reflect the acceleration of the eutrophication of the lake which is also evident from the increased particulate load and turbidity of the water