AbstractsEconomics

Tese de doutoramento, Geologia (Geologia Económica e do Ambiente), Universidade de Lisboa, Faculdade de Ciências, 2014 This thesis presents the mesoscale characterization of the evolution of two lagoon systems, Traba (550 years of sedimentary sequence) and Melides (1745 years of sedimentary sequence), using sedimentological, geochemical and biological, particularly diatoms, indicators. Also, a characterization of 18 present-day transitional environments (coastal lakes and ponds, lagoons and estuaries) of the Western Iberian Atlantic Coast (WIAC) was performed, based on the diatom content of 25 samples of surface sediments and water physico-chemical parameters. The study of diatom thanatocoenoses in present-day bottom sediments showed that there are distinct assemblages representative of the major types of environments, and that their distribution is mainly governed by gradients in salinity, PO4 3 -, NO3 - and Dissolved Organic Carbon. From this knowledge, a transfer function for salinity was derived which, plus autoecological data on diatoms, sedimentology, geochemical indicators and geochronology, were used to reconstruct the long-term evolution of two contrasting coastal wetlands in the WIAC. At the considered time scale, the evolution of Traba and Melides was mainly dependent on changes in four natural and anthropogenic factors: sand-barrier breaching (natural and/or human-induced), precipitation, forest cover (natural and/or human-induced), and cultural eutrophication. Sea-level changes played a minor or no role in their recent evolution. The complex interplay among all these factors prompted large ecological regime shifts interpreted in the framework of the Alternative Stable State Hypothesis of Shallow Lakes. Before the systems were impacted by direct human intervention, humid conditions were favourable for the development of turbid phases, generally irrespective of changes in barrier permeability. Whereas this relationship is clear in the Traba record, a higher connection to the ocean in Melides probably gave rise to a much more overlapped signal of the different forcing factors, making more difficult to disentangle the real contribution of climate in its evolution. In recent times cultural eutrophication and artificial barrier breaching accounted for most of the variability in the data, constituting the main drivers of the evolution in the two systems. In spite of concerns on present-day accelerated sea-level rise, palaeoecological research performed in Melides and Traba shows that the difficult task of good management practice in these systems should first focus in reducing nutrient loads to facilitate their natural recovery. Estuários, lagunas e lagos e charcos costeiros são ambientes de transição em constante evolução, por processos naturais ou atividades antrópicas, enfrentando problemas ambientais como a poluição ou assoreamento provocado por sedimentação de materiais de origem marinha ou continental. Este último, tornou-se mais evidente desde há cerca de 5500-7500 anos cal AP (anos calibrados…