Browsing by Author "Carrasco, Rita"
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- Evaluating the success of vegetation restoration in rewilded salt marshesPublication . Carneiro, Inês; Carrasco, Rita; Didderen, Karin; Sousa, Ana I.Floodbank realignment is a common practice aimed at restoring salt marsh vegetation on previously embanked land. However, experiences indicate that it may take several years before salt marsh vegetation becomes fully established. Various challenges arising from ecogeomorphic feedback mechanisms could pose significant setbacks to vegetation recolonization. The widespread adoption of transplantation techniques for the restoration and rehabilitation of rewilded landscapes has indeed proven to be a valuable tool for accelerating plant development. In the Ria Formosa coastal lagoon (South of Portugal), a pilot plan was implemented, and two salt marsh pioneer species, Spartina maritima (syn. Sporobolus maritimus ) and Sarcocornia perennis (syn. Salicornia perennis ), were transplanted from a natural salt marsh to a rewilded marsh. Biodegradable 3D porous structures were installed to mimic transplant clumping, aid sedimentation, and enhance the plant ' s initial adjustment. Ecological, sediment, and hydrodynamic data were collected during the 12-month pilot restoration plan. The environmental profiles of the donor and restoration sites were compared to substantiate the success of the transplants in the rewilded salt marsh. Results show that although plant shoot density decreased after the transplanting, Spartina maritima acclimated well to the new environmental conditions of the restoration site, showing signs of growth and cover increase, whilst Sarcocornia perennis was not able to acclimatize and survive in the restoration site. The failure behind the Sarcocornia perennis acclimation might be related to the bed properties and topographic properties of the restoration site in the rewilded marsh. Major findings contribute to a more comprehensive understanding of how salt marsh pioneering vegetation successfully colonizes disturbed habitats, facilitated using 3D -biodegradable structures.
- A multi-sensor approach to monitor the ongoing restoration of edaphic conditions for salt marsh species facing sea level rise: An adaptive management case study in Camargue, FrancePublication . Davranche, Aurélie; Arzel, Céline; Pouzet, Pierre; Carrasco, Rita; Lefebvre, Gaëtan; Lague, Dimitri; Thibault, Marc; Newton, Alice; Fleurant, Cyril; Maanan, Mohamed; Poulin, BrigitteThe Camargue or Rhone delta is a coastal wetland in southern France of which parts formerly devoted to salt production are undergoing a renaturation process. This study assessed a multisensor approach to investigate the link between sediment size distribution, habitat development mapped with Worldview 2, flooding durations estimated with time series of SENTINEL 2 images and elevation modelled with a LIDAR point cloud in former saltworks. A Random Forest classification algorithm was used to map the vegetation distributions of Sarcocornia fruticosa and Arthrocnemum macrostachyum, main representatives of the NATURA 2000 "Mediterranean and thermo-Atlantic halophilous scrubs (Sarcocornetea fruticosi)" habitat on the site. The best habitat map was ob-tained when considering the species separately. The random forest Out-of-bag errors were 1.43 % for S. fruticosa and 2.18 % for A. macrostachyum. Both species were generally distributed on different elevation and flooding duration zones considering mean values. Flooding duration was estimated with the Water In Wetland index (WIW) based on 15 Sentinel-2 scenes. Two models related to sediment grain size distribution were developed: one predicting the flooding duration and one predicting the halophilous scrub distribution. Maps of flooding duration, sediment grain size distribution and elevation highlighted two main zones in the study area: a western section with coarser sediments, shorter flooding durations and higher elevations under sea influence; an eastern section with finer sediments, longer hydroperiods and lower elevations under a historic river influence. This multidisciplinary approach offers perspectives for using space-based data over large scales to monitor changes in edaphic conditions of coastal areas facing natural and anthropogenic forcings. The results call for further in-vestigations to predict the dynamic distribution of other coastal habitats following climate change impacts, such as sea level rise.
- Short-term sedimentation dynamics in mesotidal marshesPublication . Carrasco, Rita; Kompiadou, Aikaterini; Matias, AnaOne of the key questions about wetlands resilience to sea-level rise is whether sediment supply will be enough to keep them coping with growing inundation levels. To address this question, researchers have put a lot of effort into field data collection and ecogeomorphic modelling, in an attempt to identify the tipping points of marsh survival. This study uses fieldwork data to characterize the sediment fluxes between the tidal flats and salt marshes, in the Ria Formosa lagoon (Portugal). Sediment fluxes were measured from the tidal channel towards the mid-upper marsh, during neap and spring tide conditions. The flow magnitude was measured, and induced transport was determined based on shear velocities. Deposition rates, instantaneous suspended sediment and near-bed velocities were linked through theoretical formulas and used to characterize time-averaged conditions for sediment delivery and deposition to the site. The results showed that suspended sediment concentrations and sediment deposition varied across the transect with no specific relation to elevation. Maximum water depths were recorded in the vegetated tidal flat, and the maximum currents were flood dominated, in the order of 0.20 m/s, in the low marsh due to flow-plant interactions and an increase of turbulence. Deposition rates ranged between 20 to 45 g/m(2)/hr, after a complete tidal cycle, and were higher in the mid-upper marsh. Hydroperiod was not the main contributor to sediment deposition in the study area. Sediment transport was tidally driven, strongly two-dimension during the cycle, and highly influenced by the vegetation. Measurements of marsh sediment flux obtained in our work are diverse from the ones found in the literature and evidence the importance of considering spatio-temporal variability of vegetated platforms in assessing overall marsh bed level changes.
- 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.
- 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.