It is rational to assume that salt marshes in regions where sediment loads are high should remain stable or prograde when facing a range of sea-level scenarios, whereas those in sediment-poor systems may erode or drown. Despite extensive theoretical and laboratory studies, additional marsh ‘persistence’ indicators under human pressures and accelerated sea-level rise rates are still needed. This study investigates the recent lateral and volumetric changes occurring in the lagoon marshes of the Ria Formosa lagoon (south Portugal), under human pressures and sea-level rise. Our analysis assesses the past (1947-2014) geomorphological evolution of marshes based on aerial imagery analysis and estimates its potential future adjustment to sea-level rise (~100 years) based on SLAMM (landscape-based model) simulated land cover changes. We highlight the influence of both stressors on marsh ecosystems and examine how their interactions can contribute to understanding sea-level rise impacts and ecological resilience of lagoon marshes. Salt marshes in the Ria Formosa have slowly expanded over the last 70 years (~0.2 mm/yr), with local erosion in front of tidal inlets and along the main navigable channels, associated with inlet migration and dredging activities. Past evolution shows that the ecosystem was able to maintain its functions and cope with sea-level rise. However, future marsh trajectories under a high sea-level rise rate suggest unbalanced vertical marsh accretion and progressive migration of the tidal flat (and water bodies) towards the salt marsh area. The model results show evidence of non-linearity in marsh response to high sea-level rise rates, which could indicate the presence of a system tipping-point and potential positive (disturbance-reinforcing) feedbacks within the system, with significant implications to marsh resilience.
Applying the ecological resilience principles to barrier island geomorphological evolution requires approaches that perceive and interpret resilience far from predefined barrier characteristics and static views. Accepting that barrier islands, like all natural systems, are dynamic and adaptively changing in response to external disturbances is fundamental to the formulated approach. To this aim, geomorphological units and dimensions were used to describe barrier island stability landscape as an actively shifting ‘topography’, reshaping in response to exogenous events and in relation to intrinsic properties. The structure of the subaerial barrier was characterised using the environmental units of Beach, Dune and Marsh (or BDM), where different combinations of BDM structure define distinct barrier stable states, under a simplified framework that is applicable over a wide range of barrier structures. The methodology is based on reconstructing resilience trajectories of barrier islands through identifying the distinct BDM states and related shifts (thresholds crossed) and assessing resilience dimensions (latitude, resistance and precariousness defined as barrier width and height and proximity to mainland, respectively) that, jointly, define the shape of the stability domain. The approach was applied to the Ria Formosa barrier island system (S. Portugal), using multi-decadal geomorphological data and gradually decreasing spatial discretisation, passing from individual barrier transects to sectors and to entire barriers. The joint evolution of two inland-migrating barriers (Cabanas Island and Cacela Peninsula) was used as an exemplar of adaptive capacity in barrier geomorphic change and, therefore, of resilient response to external pressures. Resilience pathways showed that the Ria Formosa barriers have been resilient over the studied timeframe, with a tendency for maintaining or increasing BDM structural complexity. In general, the stability domain tends to shift from low latitude and high resistance forms (narrow-deep basins of attraction) in the west part of the barrier chain, to higher latitudes and lower resistance ones (wide-shallow basins) towards the east. Precariousness peaks near the edges of the system (low lagoon width) and minimises towards the central part (most detached barriers). Scaling issues regarding smoothing of longshore variability and potential consequences on masking thresholds and critical dimensions are highlighted and discussed, along with the key role of the meaning of specified resilience (of what?) in the assessment. The methodology is a novel approach, easily transferable to different systems and spatiotemporal scales of analysis, representing a step forward in interpreting and assessing barrier island resilience.
Multiple ridges across prograding coasts may display variable geometries, commonly expressed through varying elevations. Changes in ridge elevation have been traditionally related to the occurrence of fluctuating progradation rates, which might, in turn, be driven by shifting environmental conditions. Here, we explore the geometry and growth mechanisms of multiple ridges, generated at Barreta Island (Ria Formosa, Southern Portugal), as a consequence of the rapid progradation of the island over the last 70 years, following the artificial fixation of the downdrift Faro‐Olhão inlet with jetties in 1955. The variability in the morphology of these features was analysed in combination with available wind and wave data, in order to better distinguish growth mechanisms and understand the main parameters determining the final geometry of the observed ridges. The results suggest that (1) most of the identified ridges fall in the beach ridge classification, as they have been mostly built by marine processes, and (2) the parameters derived from, or closely related to wave climate variability (e.g. progradation rates, storm occurrence) can jointly explain most of the observed morphological changes, while aeolian processes played a secondary role. Indeed, ridge geometry appears mainly controlled by progradation rates, with higher ridges associated with lower progradation rates. Progradation rate, in turn, is mostly related to longshore wave power, storminess, and the occurrence storm groups. Yet, the final configuration of ridges can also be affected by runup levels and onshore winds. Therefore, establishing the relation between ridge geometry and wave climate is not a straightforward task, because of the complex processes and interactions that control coastal morphodynamics.
A inclusão social em ciência é um tema complexo, todavia têm-se assistido nas últimas décadas a um esforço crescente por parte dos centros de ciência, museus, instituições de investigação científica e outras organizações na promoção de atividades culturais dirigidas a públicos diversificados. Entre fevereiro e dezembro de 2018 foi desenvolvido o projeto “Dar Corpo às Memórias”, que visou a aproximação à ciência de uma comunidade socialmente vulnerável, com recurso à exploração de formas inovadoras de comunicação de ciência através da Ciência & Arte. O público-alvo escolhido foi uma comunidade de emigrantes idosas, na sua maioria iletradas. De cariz colaborativo, o projeto ‘Dar Corpo às Memórias’ envolveu instituições científicas [Instituto Gulbenkian de Ciência (IGC), iNOVA Media Lab, Universidade do Algarve], artísticas (Museu Calouste Gulbenkian) e administrativas (Câmara Municipal de Oeiras), e a comunidade de emigrantes idosas que foi envolvida numa fase muito inicial, durante a conceção deste projeto. O tema do projeto, a Memória, emergiu dos encontros e conversas informais entre os promotores do projeto e os elementos da comunidade, indo ao encontro dos interesses identificados. A fase de implementação do projeto consistiu num conjunto de oito sessões, de 90 a 120 minutos ao longo de mais de dois meses, durante as quais foram abordados vários temas ligados à memória e ao cérebro. As atividades tiveram natureza diversa desde a apresentação de informação científica, narrativa de histórias da neurociência ou casos interessantes, partilha de memórias das participantes até exercícios de movimento livre ou coordenado, de abstração, de desinibição e de estímulo à autoexpressão. Foram também efetuadas uma visita ao Museu Calouste Gulbenkian, uma visita ao IGC e uma apresentação pública do projeto pela comunidade aquando do aniversário do grupo. O projeto foi avaliado com recurso a vários indicadores: 1) pré/pós grupos de foco, 2) avaliação qualitativa feita pela comunidade, 3) registo de assiduidade nas sessões, 4) anotações de elementos informais verbais e não-verbais durante as sessões, 5) narrativa do projeto feita pela comunidade e 6) apresentação pública. Nesta comunicação será apresentado o projeto, desde a sua conceção e implementação à sua avaliação, refletindo sobre os objetivos, impactos, barreiras e metodologia.
Overwash hydrodynamic datasets are mixed in quality and scope, being difficult to obtain due to fieldwork experimental limitations. Nevertheless, these measurements are crucial to develop reliable models to predict overwash. Aiming to overcome such limitations, this work presents accurate fieldwork data on overwash hydrodynamics, further exploring it to model overwash on a low-lying barrier island. Fieldwork was undertaken on Barreta Island (Portugal) in December 2013, during neap tides and under energetic conditions, with significant wave height reaching 2.6 m. During approximately 4 h, more than 120 shallow overwash events were measured with a video-camera, a pressure transducer and a current-meter. This high-frequency fieldwork dataset includes runup, overwash number, depth and velocity. Fieldwork data along with information from literature were used to implement XBeach model in non-hydrostatic mode (wave-resolving). The baseline model was tested for six verification cases; and the model was able to predict overwash in five. Based in performance metrics and the verification cases, it was considered that the Barreta baseline overwash model is a reliable tool for the prediction of overwash hydrodynamics. The baseline model was then forced to simulate overwash under different hydrodynamic conditions (waves and lagoon water level) and morpho-sedimentary settings (nearshore topography and beach grain-size), within the characteristic range of values for the study area. According to the results, the order of importance of factors controlling overwash predictability in the study area are: 1st) wave height (more than wave period) can promote overwash 3–4 times more intense than the one recorded during fieldwork; 2nd) nearshore bathymetry, particularly shallow submerged bars, can promote an average decrease of about 30% in overwash; 3rd) grain-size, finer sediment produced an 11% increase in overwash due to reduced infiltration; and 4th) lagoon water level, only negligible differences were evidenced by changes in the lagoon level. This implies that for model predictions to be reliable, accurate wave forecasts are necessary and topo-bathymetric configuration needs to be monitored frequently.
A number of previous research studies have addressed the enormous role played by biodiversity and ecosystems in human well-being and have placed particular emphasis on the consequences of the reduction or loss of these services. A handful of studies have implemented practical methodologies to quantify the variability of limiting factors leading to reductions in these ecological services. The aim of this article is to document the limited number of studies that have analyzed coastal ecosystem services and acknowledge the impacts of physical changes in habitat provision. In one example, it is clear that the maintenance of salt marshes depends on sedimentary supply and consequent morphological variability in spite of the fact that there is usually no recurrent integration of habitat time-space dynamics (sediment availability) during the quantification and monetization of marsh services (i.e., monetary valuation of salt marsh services). This means that one key challenge facing the analysis of salt marsh (or other ecosystem) services in a global climate context is to predict future value, based on past trends, while at the same time guaranteeing conservation. Research in this field has been very broad and so the use of long-term evolutionary datasets is proposed here to explain future habitat provision. An empirical approximation is also presented here that accounts for service provision and enables time-space analysis. Although improvements will be required, the equation presented here represents a key first step to enable managers to cope with the constraints of resource limitations and is also applicable to other habitats.
Resilience has been used over a wide range of scientific fields and often ambiguously, causing confusion over terminology and concepts and giving rise to distinct interpretations and misconceptions, even within the same scientific discipline. Starting by providing clarifications and definitions of the main terminology and key principles of ecological resilience theory, we pass on to expressing them through geomorphic dimensions of barrier islands. Three distinct environments (beach, dune, marsh) are proposed as the panarchical levels of analysis, along with potential feedbacks between them and geomorphic dimensions that can express the changes of the stability landscape. Morphological changes induced by storms and subsequent recovery are transferred to stability landscapes, over a range of storm impacts and recovery. We postulate that post-perturbation recovery should not be restricted to regaining pre-disturbance barrier dimensions, but should be viewed in terms of reorganisation and adaptation, accounting for maintaining the existence of functions, or the ability of the system to regain them. The proposed scheme and dimensions are tested using geomorphological data from barrier response to distinct disturbances, over different temporal scales that range from event to multi-decadal ones. The case of a barrier island migrating landwards is conceptualised in terms of alternative states and thresholds arising during the process and related phases and changes to the adaptive cycle. The methodology and approach presented is a step towards more holistic views of geomorphic systems' resilience that we hope will contribute to furthering interdisciplinary understanding and cooperation in the area of sustainability and resilience of natural systems.
Human interventions on sandy barriers interfere strongly with natural barrier dynamics, to the extent of having become key moderators of geomorphological evolution. This work identifies and analyses natural and human-induced drivers and their importance to the multi-decadal evolution of a barrier system. The methodology, based on aerial photograph and historical map analysis, is applied to the Ria Formosa barrier island system in South Portugal, where recent human interventions on the barriers and in the surrounding area have interfered with natural processes. The morphologic evolution of the barriers during the last 60 years (1952 to 2014) is investigated, along with storm wave data and information on (hard and soft) coastal works in the area. The analysis focuses on cross-shore changes, morphological characteristics (barrier and dune widths, inlet morphology and migration) and temporal changes in barrier areas. Hard engineering works (marina construction and inlet stabilisations) had strong impacts on barrier tendencies, promoting sediment trapping updrift and causing sediment starvation and barrier narrowing downdrift. The related tidal prism reduction at an interconnected inlet resulted to the attachment of its ebb-shoals to the adjacent barriers. The observed behaviour and response of the barriers to artificial triggers, interacting with natural processes, falls into four evolution regimes: a) artificially enhanced growth; b) stability promoted by natural or natural and artificial factors; c) artificially triggered decay that can lead to inland migration; and d) natural growth. Comparing these responses with other barrier systems facing akin interventions, similarities were identified in barriers regulated mainly by longshore drift and differences were found when related to changes in tidal inlet balance.
Aerial photographic data and historical maps were used to identify trends, growth patterns and responses to anthropogenic disturbances in the barriers of the Ria Formosa system (South Portugal). Hard (inlet stabilizations, jetties) and soft (nourishments, inlet relocations) coastal works have influenced, to different extents, the recent (1952-2014) barrier morphodynamics of the system. Shore-perpendicular works had a profound impact on barrier evolution, with direct (progradation updrift, sediment starvation downdrift) and indirect (shoal attachment due to loss of tidal prism) influences that, in many cases, dominated over natural trends. Overall, barrier area in the system grew by 17% during the study period, mainly due to shoal incorporation and to a much lower extent by sediments transported by longshore drift. Four evolution regimes were identified: a) artificially triggered growth, b) stability, promoted by natural or natural and artificial factors, c) artificially triggered decay that can lead to inland migration and d) natural growth.
https://authors.elsevier.com/a/1YBjuB8ccghei (download for free until 27 January 2019) Storms impact coastal areas often causing damages and losses at occupied areas. On a scenario of increasing human occupation at coastal zones and under climate change conditions (including sea level rise and increasing frequency of extreme sea levels), the consequences of storms are expected to be amplified if no adaptation or further management actions are implemented. The selection of the best possible coastal management measures, considering both costs and effectiveness, will be mandatory in the future, in order to optimise resources. This work analyses the performance of risk reduction measures (beach nourishment and receptors - house and infrastructures - removal), using a decision support system comprised by a morphodynamic numerical model (XBeach) and a Bayesian network based on the source-pathway-receptor concept. The effectiveness of the risk reduction measures is then assessed by a simple index expressing the consequences to the receptors. The approach was tested at Faro Beach by evaluating its performance for a particular storm, Emma (Feb/March 2018), which fiercely impacted the southern coast of Portugal. The output results from the modelling were compared to field observations of the actual damages caused by the storm. The combined use of both measures or the solely use of the nourishment would avoid almost all observed impacts from this storm. The work is pioneer on demonstrating the use of a decision support system for coastal regions validated against observed impacts for a high-energy storm event. The methodology and the proposed index are adaptable to any sandy coastal region and can be used to test (and improve) management options at a broad number of coastal areas worldwide, minimising implementation costs and reducing the risk to the occupation and to the people.
This study evaluates the patterns and effects of relative sea-level rise on the tidal circulation of the basin of the Ria Formosa coastal lagoon using a process-based model that is solved on an unstructured mesh. To predict the changes in the lagoon tidal circulation in the year 2100, the model is forced by tides and a static sea level. The bathymetry and the basin geometry are updated in response to sea-level rise for three morphological response scenarios: no bed updating, barrier island rollover, and basin infilling. Model results indicate that sea-level rise (SLR) will change the baseline current velocity patterns inside the lagoon over the ~100-year study period, due to a strong reduction in the area of the intertidal basin. The basin infilling scenario is associated with the most important adjustments of the tidal circulation (i.e., increases in the flood velocities and delays in the ebb tide), together with an increase in the cumulative discharges of the tidal inlets. Under sea-level rise and in the basin infilling scenario, the salt marshes and tidal flats experience increases in the tidal range and current asymmetry. Basin infilling changes the sediment flushing capacity of the lagoon, leading to the attenuation of the flood dominance in the main inlet and the strengthening of the flood dominance in the two secondary inlets. The predictions resulting from these scenarios provide very useful information on the long-term evolution of similar coastal lagoons that experience varying degrees of SLR. This study highlights the need for research focusing on the quantification of the physical and socio-economic impacts of SLR on lagoon systems, thus enabling the development of effective adaptation strategies.
The services of a coastal ecosystem are critical to the functioning of the Earth’s life-support systems, and they are intimately governed by biotic and geologic couplings. This work assesses the temporal evolution of salt marsh ecosystems in a coastal lagoon, Ria Formosa lagoon, and analysis its triggering processes, both natural processes and human activities. We applied imagery analysis to investigate the capacity of tidal flats and salt marsh to develop and evolve under different hydrodynamics and sediment supply conditions. The studied marsh lays in the backbarrier of Culatra Island. A 60-year time-series of aerial photographs were used to measure states of marsh development and 2D maps were produced based on topography and sediment organic matter distribution. Data analysis showed that the main sediment source for marsh development was driven from the nearby inlet flood delta. The obtained findings help to predict the fate of important ecosystem services facing sea-level rise.
The aim of the present paper is to analyse the recent morphological evolution of the sandy barriers of Ria Formosa, a multi-inlet system located in South Portugal, to assess evolution regimes and related controlling factors and to identify resilience mechanisms in response to natural and artificial drivers of change. The data collected comprise aerial photographs and wave buoy and hindcast time-series, covering the period from the 1950s to 2014. The results show that the barriers have either been growing, or remaining stable. The growth patterns were either promoted by natural mechanisms, or triggered by stabilization works and supported by natural factors (e.g. longshore transport, shoal attachment). The presence of a broad marsh platform in the backbarrier was found to promote barrier stability, while the sustainance of transgressive barriers is advocated by frequent overwash, combined with low depths in the backbarrier lagoon and localised replenishment of sand. These long-term evolution regimes and their relation to artificial and natural factors show that the barriers of Ria Formosa have been resilient during the time-frame of the study, either absorbing disturbances (Armona and Tavira), or adapting to change while maintaining their functions (rest of the barriers).
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.
Overwash hydrodynamics were measured during a storm event. Data from literature and fieldwork were used to setup a numerical model, using XBeach in non-hydrostatic mode. Different simulations were conducted to assess the influence of several factors on overwash statistics. Nearshore morphology was found to greatly influence overwash. Sediment mean grain-size, and less importantly, lagoon water levels also produce measurable effects.
Overwash hydrodynamics datasets are mixed in quality and scope, being hard to obtain due to fieldwork experimental difficulties. Aiming to overcome such limitations, this work presents accurate fieldwork data on overwash hydrodynamics, further exploring it to model overwash on a low-lying barrier island. Fieldwork was performed on Barreta Island (Portugal), in December 2013, during neap to spring-tides, when significant wave height reached 2.64 m. During approximately 4 hours, more than 120 shallow overwash events were measured with a video-camera (at 10 Hz), a pressure transducer (at 4 Hz) and a current-meter (at 4 Hz). This high-frequency fieldwork dataset includes runup, overwash number, depth and velocity. Fieldwork data along with information from literature were used to setup XBeach model in non-hydrostatic mode. The baseline model had variable skills over the duration of the overwash episode, performing better during the rising tide than during the falling tide. Model average number of events RMSE (root-mean-square-error) was 7 events each 30 minutes. The baseline model was forced to simulate overwash with different nearshore morphology, grain-size and lagoon water level. An average decrease of about 30% overwash was obtained due to changes in the nearshore morphology, mostly a small vertical growth of the submerged bar. The coarser and finer grain-sizes tests produced an 11% change in overwash, with less overwash on the coarser barrier. Changing lagoon water levels had a reduced effect on overwash hydraulics.
The present paper focusses on the objectives and methodology of the EVREST project regarding the identification of natural mechanisms that promote resilience in barrier island systems, both in oceanfront and backbarrier environments. The study area of the project is the Ria Formosa barrier island system, located in southern Portugal.