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

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