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Research Project
EVREST-Evolution and resilience of barrier island systems
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Authors
Publications
Carbon and nitrogen stocks and burial rates in intertidal vegetated habitats of a Mesotidal coastal lagoon
Publication . Martins, Márcio; de los Santos, Carmen B.; Masqué, Pere; Carrasco, A. Rita; C. Veiga-Pires, C.; Santos, Rui
Coastal vegetated ecosystems such as saltmarshes
and seagrasses are important sinks of organic carbon (OC) and total nitrogen (TN), with large global
and local variability, driven by the confluence of
many physical and ecological factors. Here we
show that sedimentary OC and TN stocks of intertidal saltmarsh (Sporobolus maritimus) and seagrass
(Zostera noltei) habitats increased between two- and
fourfold along a decreasing flow velocity gradient
in Ria Formosa lagoon (south Portugal). A similar
twofold increase was also observed for OC and TN
burial rates of S. maritimus and of almost one order
of magnitude for Z. noltei. Stable isotope mixing models identify allochthonous particulate organic
matter as the main source to the sedimentary pools
in both habitats (39–68%). This is the second estimate of OC stocks and the first of OC burial rates in
Z. noltei, a small, fast-growing species that is widely
distributed in Europe (41,000 ha) and which area is
presently expanding (8600 ha in 2000s). Its wide
range of OC stocks (29–99 Mg ha-1
) and burial
rates (15–122 g m2 y-1
) observed in Ria Formosa
highlight the importance of investigating the drivers of such variability to develop global blue carbon models. The TN stocks (7–11 Mg ha-1
) and
burial rates (2–4 g m-2 y-1
) of Z. noltei were generally higher than seagrasses elsewhere. The OC
and TN stocks (29–101 and 3–11 Mg ha-1
, respectively) and burial rates (19–39 and 3–5 g m-2 y-1
)
in S. maritimus saltmarshes are generally lower than
those located in estuaries subjected to larger accumulation of terrestrial organic matter.
Barrier island resilience assessment: Applying the ecological principles to geomorphological data
Publication . Kombiadou, Katerina; Matias, Ana; Costas, Susana; Carrasco, A. Rita; Plomaritis, Theocharis A.; Ferreira, Óscar
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.
Ecogeomorphic response of a coastal dune in southern Portugal regulated by extrinsic factors
Publication . Costas, Susana; Gallego-Fernández, Juan B.; Bon de Sousa, Luísa; Kombiadou, Katerina
Coastal dunes are complex landforms whose morphology results from various interactions between biotic and abiotic factors. Here, we explore the longshore variability of the morphological features, plant community dis-tribution and accumulation patterns of a dune segment (1.4 km-long) located at the downdrift end of a sandy peninsula in the Ria Formosa, Portugal. To understand the main drivers of the observed variability and the implications for dune morphological response, this information was combined with recent multidecadal shore-line evolution data. The integrated results document significant differences in dune morphology, sedimentation patterns and plant zonation, with two distinct dune configurations or states identified in close proximity. One (western sector) shows a narrower dune system, vegetation cover characterised by pioneer species with low densities, and squeezed plant zonation. Conversely, the other (eastern sector) presents a wider dune system with a new foredune, a more developed plant zonation and relatively high vegetation density. Both states could be partially explained by the recent shoreline trends and inlet shifts, with stable to retreating trends in the western sector and shoreline progradation in the eastern one. Plant zonation and accumulation patterns suggest that the dune along the retreating sector is in a cycle of inland migration, encouraged by the reduced accommodation space and the low retention capacity of the vegetation across the dune stoss. Alternatively, observations along the prograding sector suggest that the greater accommodation space and the stabilising feedback between vegetation and topography promoted the seaward progradation of the system and the development of an incipient foredune. Outcomes support the importance of biogeomorphic feedbacks for the dune configuration, but they also evidence that the role of vegetation within the feedback is primarily regulated by physical factors that ultimately promote or inhibit vegetation effects on dune topograph
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Funders
Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
3599-PPCDT
Funding Award Number
PTDC/MAR-EST/1031/2014