Lake Aguelmame Sidi Ali,Middle Atlas Morocco,Holocene diatom analyses

Lake sidi ali (33° 03'n,5° 00'e) is a natural lake at high altitude (2080 m) in moroccan middle atlas. a long core of 20 m by 38 m deep in the south-western basin was obtained using the coring device uwitec. this core provided a continuous holocene record,and analyzed diatoms contained in the sediments. the sidi ali diatom screening provides valuable information concerning aquatic paleohydrology and corresponding hydroclimatic changes in the middle atlas. the relative amount of shallow-water indicating epiphytic and littoral species is a proxy for former lake levels. in the entire record planktonic cyclotella sp. are dominant indicating relative humid and oligosaline conditions in the closed lake basin. however,cyclotella species change and shallowwater indicating variations in lake-level and salinity. an open taxonomy is adopted for those diatoms which do not fit precisely to any defined taxa. this is the case for cyclotella species,which predominate in the core during the holocene particularly cyclotella sp.3,cycltella sp.1 and also for the specimens cyclotella sp.4. these taxa are separated by their structure and ultra structure and it's a new taxonomic and ecological identity. diatom study shows the species found in the sediments have persisted in the same lake and can provide a direct modern analogue for interpretation. diatom record provided information on the water-level and on changes in water chemistry. our observations allow us to reconstruct the main evaluative phases of aguelmame sidi ali lake: a shallow oligosaline lake occupied the core site during the younger dryas. cyclotella sp. 3 is dominant. during the first half of the early holocene diatom assemblage reflects an important lake level. a small regression of the lake level with shallow water the course of the second half of the early holocene and is characterized by variations in morphologies and sizes and the abundance of diverse species indicate a high variability of the hydroecological setting. fresh water to oligosaline lake occupied the core site during the second half of the mid holocene. this stage reflects a noticeable inflow of dilute waters into the lake basin and a rapidly rising lake level due to the dominance of planktonic littoral cyclotella sp. 4 indicate a change in hydrology and temperature. late holocene: the diatom evidence reflects high lake levels due to the dominance of planktonic cyclotella sp. type 3 which reaches its absolute maximum at the onset. anthropocene is characterized by the high quantities of littoral species and of epiphytic indicate increasing aridity reveal evidences for a low lake level and higher aridity and represent the phases of significant human impact. the diatom study of the sediment sequence aguelmame sidi ali allowed a detailed reconstruction of past hydrology and environments during the holocene. the regional climatic changes have been the major driving factor on ecological and hydro biological changes in middle atlas lakes.