The geological record of environmental changes in southwestern Portuguese coastal lagoons since the Lateglacial

The multidisciplinary study (sedimentology, palaeoecology, geochemistry, isotopic dating) of the sedimentary infill of selected coastal lagoons of the southwestern Portuguese coast suggests that during the Early Holocene, eustasy was the dominating element forcing coastal change and controlled the sedimentation patterns of these areas. The strong decrease of the mean sea-level rise rate observed in the Middle Holocene defined an important threshold of regional significance. The flooded lowlands developed terminal barriers and started to silt up initially driven by natural forcing factors (e.g. climate, sediment supply) of local expression, which were later added or overwhelmed by anthropic influence. The latter relates with deforestation and agriculture, inducing changes of sedimentation rates and sediment delivery to the coast; human interference with the natural rhythms of barrier breaching generated significant change of the whole physico-chemical setting of the lagoonal basins that translated into sediments, water quality and depth and local ecosystem's structure. This paper presents examples of the impacts of global versus local factors and natural versus anthropic influences as driving factors of coastal change since the Lateglacial. The available data suggest that this line of research is crucial to support objective and accurate models of past and future coastal evolution. (C) 2002 Elsevier Science Ltd and INQUA. All rights reserved.