Human demography changes in Morocco and environmental imprint during the Holocene

The aim of this work is to reconstruct the periods of growth and decline of human populations in Morocco and their potential impacts on the landscape over the past 10,000 years. In order to estimate the trends in the human population size between 10,000 and 3000 years ago, we used a summed probability distribution (SPD) of radiocarbon dates from a wide range of archaeological sites throughout Morocco. Landscape changes were identified and quantified from a dataset of fossil pollen records. Different anthropogenic pollen markers, as well as natural vegetation groups and taxonomic richness were used to analyse the relationship between long-term trends in human population expansion or regression and type of impact on the landscape. The sub-regions of Morocco have different topographies and climates, which have either favoured or prevented the establishment and/or spread of human populations. In order to identify the areas most significantly impacted by humans and the timing of such impacts, we have reconstructed and compared the same past anthropogenic and landscape proxies along with the population trends within the lowlands and mountainous areas. The lowlands were more strongly impacted earlier in the Holocene than the mountainous areas. Anthropogenic markers indicate that farming expanded in the lowlands during the first major expansion of human populations between ca. 7200 and 6700 cal. yr BP at the start of the Neolithic period. In the Atlas and Rif Mountains, anthropogenic impact is not clearly detectable in any of these areas before 4000 cal. BP. </jats:p

Use of bathymetry and clay mineralogy of reservoir sediment to reconstruct the recent changes in sediment yields from a mountain catchment in the Western High Atlas region, Morocco

The dam of Takerkoust, located at the outlet side of N'fis Basin (Western High Atlas of Morocco), is one of the strategic reservoirs in Morocco facing a serious problem of siltation due to soil erosion. A paleo-hydrology approach combining chronological and sedimentological analyses is conducted to understand the evolution of the depositional sediment history of the Takerkoust reservoir between 1988 and 2016. First, a series of 8 bathymetric surveys in the Takerkoust reservoir was used to determine the chronology of flood event deposits. Second, grain size distribution, clay mineralogy (XRD) and organic matter content were analyzed in 2 cores drilled in the Takerkoust reservoir and the newly build Ouirgane reservoir in upstream (from which 46 samples were taken). Third, Soils samples collected from the uppermost soil horizons (First 5 cm) of different localities of the N'fis watershed were also analyzed to identify sediments origins. Eleven couplets with different textures and thickness are identified in the Takerkoust reservoir corresponding to the period 1988–2016. The highest correlation is observed between instantaneous maximum flow and thickness of the sandy component of the couplets. The variation of the siltation rate allows highlighting two distinct periods: the oldest period (1988–1999) characterized by a high sediment yield SY (908.6 t·km−2·yr−1) and a youngest one (1999–2016) characterized by a low SY (203.9 t·km−2·yr−1). The newly built Ouirgane dam, seems to be responsible for the decreasing siltation rate and change of the clay assemblages of the sedimentary series in Takerkoust reservoir

Environnemental changes over the past c. 29,000 years in the Middle Atlas (Morocco) : A record from Lake Ifrah

International audienceA borehole core from Lake Ifrah (Middle Atlas, Morocco) provided a unique, continuous record of environmental change spanning the past c. 29,000 years cal BP (29 ka). A study of its organic matter, carbonates and magnetic susceptibility allowed us to reconstruct past climate changes and their impact on the lake's catchment area. The geochemical and pollen data show that the prevailing climate in the Middle Atlas from c. 29 ka to c. 12 ka was cold with a succession of dry and more humid periods. Prior to 24 ka the area surrounding Lake Ifrah enjoyed a relatively wet climate that allowed the survival of rare tree vegetation despite the overall cold conditions. After 12 ka, an increase in primary productivity and arboreal pollen is documented indicating the development of forest vegetation

Environmental changes over the past c. 29,000 years in the Middle Atlas (Morocco): A record from Lake Ifrah

International audienceA borehole core from Lake Ifrah (Middle Atlas, Morocco) provided a unique, continuous record of environmental change spanning the past c. 29,000 years cal BP (29 ka). A study of its organic matter, carbonates and magnetic susceptibility allowed us to reconstruct past climate changes and their impact on the lake's catchment area. The geochemical and pollen data show that the prevailing climate in the Middle Atlas from c. 29 ka to c. 12 ka was cold with a succession of dry and more humid periods. Prior to 24 ka the area surrounding Lake Ifrah enjoyed a relatively wet climate that allowed the survival of rare tree vegetation despite the overall cold conditions. After 12 ka, an increase in primary productivity and arboreal pollen is documented indicating the development of forest vegetation

Bilans hydrique et hydro-isotopique du lac Aguelmam Azigza (Moyen Atlas, Maroc)

International audienceStable isotopes of water (18O, 2H) and their associated isotope fractionation during water-cycle phase changes produce a natural labelling of the water cycle and can be efficiently use to study hydrological and climatic processes at the local, regional and global scales. Moreover, understanding the seasonal and inter-annualstable isotope behaviour in a lake system is a key for interpretingthe 18O data obtained from inorganic fractions of lake sediments in order to reconstruct past changes in local hydro-climatology. The natural mountain lake system, Aguelmam Azigza (32°58’N, 5°26’W, 1470 m asl), is located in the karstic Tabular Middle Atlas (Morocco), one of the most humid regions of Morocco, which can be seen as the “water tower” of the country. The regional climate receives alternative influences of Mediterranean, Atlantic and Saharan air masses. A lake monitoring has been implemented since October 2012 with a monthly water sampling (precipitation, lake, well and springs) for water isotope measurements,in order to characterize seasonal variations of its water and isotope balance. Precipitation amounts at Azigza lake are very variable and high (1421 mm recorded between Oct. 2012 and Oct. 2013 for ex.). The lake waters isotopic composition plot along an evaporation line, and show a clear seasonality mainly linked to evaporation/rainfall, while groundwaters plot above the GMWL and close to regional rainfall composition suggesting a rapid transfer in the fractured karstic system. A first estimate of the lake water balance using Craig-Gordon equations shows that less than 20% of the water of the lake is lost by evaporation, and that the lake a very sensitiveto climatic parameters

Comportement hydrochimique et sédimentation actuelle des lacs Azigza et Tiguelmamine (Moyen Atlas, Maroc)

International audienceNatural environmental changes may be reconstructed by studying lake sediments that record several climatic, hydrologic and environmental signatures. Such reconstructions must be based on a thorough knowledge of the current lake system conditions. According to this perspective, two karstic lakes in the Moroccan Middle Atlas, Aguelmam Azigza (32°58'N, 5°26'W, 1470 m absl) and Tiguelmamine (32°54'N, 5°21'W, 1650 m absl), have been the subject of hydrochemical and sedimentary investigations. Spatiotemporal monthly monitoring (since October 2012) of the physicochemical characteristics of waters (precipitation, lake, wells, springs and streams) shows that the waters of Azigza lake are alkaline (pH>8) with elevated contents of HCO3-, Ca 2+ and Mg 2+. The Aguelmam Azigza is a monomictic lake (with an overturn water during December to January) and indicates high sensitivity to seasonal climatic changes (temperature and precipitation) that control biogeochemical conditions in the water column. During the wet season, this lake is fed by both meteoric and ground waters. In contrast, during the dry season, the lake supports the water table. Ground waters are highly mineralized and saturated toward carbonates, and lose a large part of their saline load as authigenic, biochemical and biogenic calcite. The waters of Tiguelmamine lake, sampled in July 2012 and April 2013, suggest generally the same physicochemical characteristics such as those of Azigza lake with high contents in Cl-, Na + and SO4 2-due to soil erosion of the lake's watershed. Limnological and sedimentological characterization of subsurface sediments collected across several transects in both lakes, reveal that organic matter contents increase from the edge to the center of the lakes. On the contrary, the carbonate contents of sediments record an opposite distribution

New lacustrine records from the Moroccan Middle Atlas

International audienc