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- Towards assessing the resilience of complex coastal systems: examples from Ria Formosa (South Portugal)Publication . Kombiadou, Katerina; Matias, Ana; Carrasco, Rita; Ferreira, Oscar; Costas, S.; Vieira, G.The present paper contributes to assessing the resilience of a complex barrier island environment, namely of the Ria Formosa multi-inlet system in southern Portugal. The long-term morphologic evolution of four study areas during the last 60 years (1947 to 2014) is analysed based on aerial photographs, including the environments of oceanic and backbarrier beaches, dunes and salt marshes. The results show that each study area responded to external drivers (inlet stabilisation works, storms, etc.) differently, evolving in distinct patterns during the study period. All four study areas appear resilient to external pressures and/or forcing conditions, since they are either transforming (Barreta and Culatra islands), or adapting (Cabanas island and Cacela peninsula) or remaining stable at a near-equilibrium state (Tavira island). Based on the analysis of the multi-decadal evolution of the sites, four resilient barrier states are identified, related to the maturity and growth of the barrier. In the next stages, the research will focus on the relation between medium to short-term changes, aiming at understanding the response and feedbacks of the environments to specific drivers of change and relating them to resilience indicators.
- The birth of backbarrier marshes in Culatra Island (Ria Formosa, South Portugal)Publication . Kompiadou, Aikaterini; Carrasco, Rita; Costas, Susana; Ramires, Margarida; Matias, AnaThe rapid elongation of Culatra Island, a sandy barrier in the Ria Formosa chain (S. Portugal), since the mid1940s led to the formation of three new embayments in its backbarrier that were gradually colonised by halophytic vegetation. This provided a rare opportunity to collect information and data on the very early stages of backbarrier marsh plant establishment and evolution. Sediment (surface and subsurface) sampling in two of the recently formed bays, combined with information extracted from vertical aerial photographs, allowed us to assess modern sedimentation characteristics and vertical accretion rates since the shift from a bare sandflat to a vegetated marsh platform. Present-day topography appears largely inherited by overwash or/and inlet-related tidal deposits that provided the necessary sediment pulse for the formation of an intertidal sandy substrate, suitable for colonisation. The variability in accretion rates, noted even within the same embayment, as well as the differences in accretion balance with similarly young backbarrier marshes, highlight the importance of local conditions (sediment import, distance to creeks and marsh edge, storm frequency and intensity) to marsh buildup, even during the very early stages. Variable accretion rates were also identified over intertidal seagrass patches, indicating similar influences. Organic deposition rates were very low in all vegetated intertidal habitats, indicating the dominance of mineral deposition to the vertical growth. A lag, ranging from roughly 10-30 years, was observed between the formation of the intertidal sandy platform and plant establishment in all embayments. The different timescales in the observed lag are likely linked to differences in hydrodynamic conditions, promoted by the embayment morphology (opening width). The lowest lag was observed in protected embayments, which could reflect a 'typical' delay for plant establishment in the system, while the highest lag was associated with higher energy backbarrier environments.