Late Quaternary history of a Mediterranean temporary pool from western Morocco, based on sedimentological and palynological evidence

Using sedimentological and pollen analysis, a reconstruction is presented here for the origin and history of a temporary pool from the quartzitic-sandstone Benslimane Plateau (W. Morocco). The pool is one of many that originated from the dismantling of a past hydrographical network, dated to the end of the Lower Pleistocene. Infilling of the pool began only recently between 5000 and 4000 cal. BP, and probably was in response to Neolithic-induced degradation of the regional vegetation cover. The almost continuous pollen occurrence of Isoetes velata-type, Myriophyllum alterniflorum and Ranunculus-type throughout the palynological sequence indicates that the organisation of local plant communities in concentric belts (a central aquatic community, an intermediate amphibious one, and a peripheral terrestrial one) has remained unchanged since the Mid-Holocene. The stability of the vegetation structure and composition over more than 4000 years confirms the adaptation of the hydrophytic communities to human-induced disturbances (mainly grazing).The long-term pool longevity is attributed to an equilibrium between wind erosion and sedimentation. The sediment accumulation balance that was null or negative during most of the Pleistocene became positive under the influence of Neolithic activities, which may also be linked to unfavourable climatic conditions. These results have important implications for the long-term conservation of biodiversity, as these rare habitats are rapidly declining. Since temporary pools also protect the quartzitic-sandstone plateau from erosion, their disappearance could trigger the reorganisation of the hydrological network and the resumption of soil erosion.