Preliminary results of salt marsh transplants in rewilded coastal wetlands
The loss of coastal wetlands in the last decades has been dominated by human-induced pressures an... more The loss of coastal wetlands in the last decades has been dominated by human-induced pressures and sea-level rise. Still, wetlands restoration has gained political momentum (e.g., the UN Decade on Ecosystem Restoration 2021-2030) as means of coastal protection, while supporting nature values and its biodiversity, addressing causes and consequences of climate change and securing ecosystem services for human well-being. Assessing the success of ecological restoration projects is thus critical to support the use of restoration actions as a natural enhancement of ecosystem health and to improve current restoration practices. Though there is plenty of information about seagrass transplant and restoration, less is known about salt marsh restoration.We conducted a salt marsh vegetation transplant experiment in a rewilded wetland in the Ria Formosa coastal lagoon (South Portugal). This study aimed to (1) advance knowledge on the facilitation of pioneer salt marsh species colonization and de...
Vegetation effects and sediment deposition in a mesotidal wetland
<p>Many studies have been carried out in the last decade to assess the rates of sed... more <p>Many studies have been carried out in the last decade to assess the rates of sediment transport and deposition on tidal flats and salt marshes, however, a need to characterize the transport fluxes between the various habitats as a function of tidal range, their position relative to mean sea level, and flow-asymmetries in the vegetation effect remain. This study uses fieldwork data to characterize the sediment fluxes and deposition from the tidal flats towards the marsh platform, in a channel margin of the Ria Formosa coastal lagoon (south Portugal). Sediment fluxes were measured in a cross-shore transect, during neap and spring tide conditions. The dominant intertidal species are <em>Spartina maritima</em> and the seagrass <em>Zostera noltei</em>. Current measurements were used to assess bottom shear stress conditions. 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.</p> <p>The results showed that suspended sediment concentrations and sediment deposition varied across-shore with no specific relation to elevation. Maximum current velocities were recorded in the vegetated tidal flat, in the order of 0.20 m/s, and in the low marsh due to flow-plant interactions and an increase in turbulence. Deposition rates ranged between 20 to 45 g/m<sup>2</sup>/hr, after a complete tidal cycle, and were higher in the mid-upper marsh. The hydroperiod was not the main contributor to sediment deposition in the study area. Measured sediment transport was tidally driven, with shifting current angles during the cycle and major alongshore components during peak flood velocities. Flow-<em>spartina</em> interference in the low marsh significantly affected local sediment resuspension. The obtained results provide insights into the dynamics and variability of flow and mass transfer along a transition from the vegetated tidal flat to the upper marsh and can be used in sediment transport models for mesotidal marsh systems.</p> <p><em>Acknowledgments: A. Rita Carrasco was supported by the contract DL57/2016/CP1361/CT0002, and Katerina Kombiadou was supported by the institutional contract CEECINST/00146/2018, both funded by Fundação para a Ciência e Tecnologia (FCT). This study had also the support of FCT under the project LA/P/0069/2020 granted to the Associate Laboratory ARNET and CIMA BASE UID/00350/2020.</em></p>
Human interventions on sandy barriers disturb natural barrier dynamics, to the extent of having b... more Human interventions on sandy barriers disturb natural barrier dynamics, to the extent of having become key forces in modifying geomorphological evolution. This work identifies natural and human-induced drivers and analyses their importance to the multi-decadal evolution of the Ria Formosa barrier island system, in South Portugal. Aerial photographs from the last six decades and historical maps are used to assess changes in cross-shore rates, morphological characteristics (barrier and dune widths, inlet morphology and migration) and barrier areas, through systematic methods that can be easily transferred to other barrier systems. Interventions, and especially hard engineering ones (jetties, inlet stabilisations), affected barrier evolution trends. Shore-perpendicular works increased shoreline progradation updrift and initiated coastal retreat downdrift, with strongest erosive impacts along the edges of the system. Inlet stabilisations changed tidal inlet hydrodynamics and initiated ebb-shoal attachment to the barriers on either side of a non-migrating inlet that experienced loss of tidal prism. This shoal attachment was the main factor for the increase in total barrier area of Ria Formosa during the 60 years of analysis. Barrier growth after 2005 was slower, which could indicate that the system is reaching morphodynamic stability.
Backbarrier Evolution and Complete Overwash Occurrence
Coastal Sediments '07, 2007
The shoreline changes along the backbarrier of a barrier system are extremely variable and critic... more The shoreline changes along the backbarrier of a barrier system are extremely variable and critically dependent upon geographic location and the inherent interaction with hydrodynamic processes. There are only a few studies describing the backbarrier morphodynamic ...
Flood hazard assessment and management of fetch-limited coastal environments
Ocean & Coastal Management, 2012
ABSTRACT Flooding is a significant environmental threat that can cause loss of human life, damage... more ABSTRACT Flooding is a significant environmental threat that can cause loss of human life, damage to infrastructure, disruption to economic activity, and decline in ecological resources in coastal areas. This paper presents a framework for assessing the potential implications of floods in fetch-limited coastal environments (with no significant wave setup), focused on hazard mapping and risk analysis. Hazard maps are based on defined return periods and risk estimates are determined by computing the extent of affected occupied and ecological areas lying below water levels associated with the return periods. For management purposes, this study chooses the adaptive management approach as the most feasible to improve local economies and mitigate the loss of natural areas, and identifies/recommends specific types of occupation and activity for each flood hazard zone.The proposed framework was applied to a low-energy fetch-limited beach, Ancão Peninsula backbarrier, located in the Ria Formosa barrier system (southern Portugal). Inundation levels predicted for 1-, 10-, and 100-year return periods were 2.02 m, 2.39 m, and 2.84 m above MSL (mean sea level), respectively. On this basis, flood impacts were found to be important in occupied areas, generating physical damage to residences and infrastructure. Ecological impacts of floods affected sub-aerial species inhabiting dunes. Several management options deriving from the framework’s application were recommended for the Ancão Peninsula.
An evolutionary categorisation model for backbarrier environments
Marine Geology, 2008
ABSTRACT Shorelines occurring along restricted fetch environments, such as the backsides of barri... more ABSTRACT Shorelines occurring along restricted fetch environments, such as the backsides of barrier islands, are extremely diverse with respect to their morphologic characteristics and evolution. In order to better understand the morphodynamic evolution of backbarriers and the associated implications for entire barrier systems, this study proposes a backbarrier evolutionary categorisation model based on the development of two types of index: backbarrier evolution tendency and backbarrier maturation condition. The proposed characterisation system is applied to the Ria Formosa backbarrier (located in southern Portugal) for the period 1947 to 2001.Cross-shore and longshore backbarrier trends in Ria Formosa suggest a shrinking of the lagoon system as a consequence of a decrease in the coastal length of the backbarrier coastline and a landward displacement of it. Even though some of the backbarriers examined were found to be in an immature state, the results obtained illustrate a maturing trend for the system overall. Barriers in Ria Formosa fall into two main evolutionary categories: backbarrier reduction and backbarrier growth. This means that neither smoothing nor branching has been significant and therefore that backbarrier recent evolution is closely related to barrier coast length. Application of the proposed characterisation to the Ria Formosa case study has helped reveal backbarrier evolutionary trends and therefore should be of use in the management of backbarrier systems.
Short-Term Sediment Transport at a Backbarrier Beach
Journal of Coastal Research, 2011
ABSTRACT This article defines short-term (tidal cycle) sediment-transport patterns at a backbarri... more ABSTRACT This article defines short-term (tidal cycle) sediment-transport patterns at a backbarrier beach based on detailed field studies. Fieldwork was planned to record nonstorm, spring tide conditions that enable the definition of background sediment dynamics at the study area. The experiment was set at two beach morphologies: beach face and sandbank. Current meters were deployed at both sites. Fluorescent tracer techniques were applied to determine rates and direction of transport. Topographic surveys and sediment sampling were undertaken. During the experiment, limited tracer displacement and small morphological changes occurred. The low magnitude changes are representative of predominant, low-energy hydrodynamic conditions. Sediment transport was primarily longshore orientated and dependent on the velocity of tidal currents. Tidal currents had the potential for sediment transport only during a short period of the tidal cycle and had higher velocities during ebb, which results in a net sediment transport orientated towards the nearby inlet. It is suggested that there is dependence on sediment transport rate at the study site and on the variability of tidal currents, which are greatly influenced by the distance to, and conditions of, the nearby Ancão Inlet. Keywords: Sediment dynamics, fluorescent tracer, hydrodynamic conditions
This study investigates sediment transport at a very low-energy backbarrier beach in southern Por... more This study investigates sediment transport at a very low-energy backbarrier beach in southern Portugal, from a spring-to-neap tide period, during fair-weather conditions. Rates and directions of transport were determined based on the application of fluorescent tracer techniques. Wind and currents were collected locally, whereas the dominant small and short-period wind waves were characterized using a morphodynamic modelling system coupling a circulation model, a spectral wave model, and a bottom evolution model, well validated over the study area. For the recorded conditions sediment transport was small and ebb oriented, with daily transport rates below 0.02 m 3 day-1. Tidal currents (mainly ebb velocities) were found to be the main causative forcing controlling sediment displacements. Transport rates were higher during spring tides, tending towards very small values at neap tides. Results herein reported points towards the distinction between tracer advection and tracer dispersion in this type of environment. Transport by advection was low as a consequence of the prevailing hydrodynamic conditions (H s < 0.1 m, and max. current velocity of 0.5 m s-1) and the tracer adjustment to the transport layer, whereas dispersion was relatively high (few metres per day). Tracer techniques allowed distinguishing the broad picture of transport, but revealed the need for refinement in this type of environments (bi-directional forcing by ebb and flood cycles).
Historic Monuments Threatened by Coastal Hazards at Boca do Rio, Algarve, Portugal
Coastal Management, 2007
The coastal stretch of Boca do Rio, western Algarve, Portugal, is experiencing shoreline retreat.... more The coastal stretch of Boca do Rio, western Algarve, Portugal, is experiencing shoreline retreat. Roman ruins are located along the beach section of the coast, and a 17th-century fort is positioned over the cliff section. Both historic monuments are being destroyed by erosion but need to be protected due to their heritage status. Aerial photograph analysis was used to define the evolution of the coast for the period 1945–2001. Shoreline retreat of 0.3 m/year was measured for the sandy coast and 14 mass movements in the cliff face were identified. Considering the rate and style of shoreline evolution, several types of management scenario were evaluated, with the favored measures being the removal of the Roman ruins to a museum and the relocation of the fort inland.
This study evaluates the patterns and effects of relative sea-level rise on the tidal circulation... more 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 socioeconomic impacts of SLR on lagoon systems, thus enabling the development of effective adaptation strategies.
Past and future marsh adaptation: Lessons learned from the Ria Formosa lagoon
Science of The Total Environment, 2021
Abstract It is rational to assume that salt marshes in regions where sediment loads are high shou... more Abstract 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.
A major concern of coastal engineering is not only to access the damage to coastal structures by ... more A major concern of coastal engineering is not only to access the damage to coastal structures by severe wave overtopping, but also the hazard imposed to users. Local hazard is often associated to the volume of overtopping water per unit of time (called overtopping discharge). Despite two decades of intensive research, it is yet not fully clear to practitioners what is the best method to compute the discharge parameter and its application on the assessment of local hazard. This work provides insight into the overtopping characterization in rubble mound breakwaters, by distinguishing different methods to assess hazardous overtopping. Fieldwork was conducted over a tidal cycle in a breakwater located at Albufeira Harbour (South coast of Portugal) under storm conditions (Hso~ 3 m; Tp ~ 9 s). Mean overtopping discharges were calculated from field measurements of flow depths and velocities at the breakwater slope armour and at the impermeable crest. Two different velocities were calculated: overtopping leading-edge velocity and overtopping peak velocity. The two methods provided similar results, with higher velocities occurring during high-tide (between 2 and 10 m/s). Mean overtopping discharges at the beginning of the impermeable crest ranged between 0.2 and 0.8 l/s/m. Under the measured hydrodynamic conditions, the breakwater offers risk to all types of pedestrians. Additionally it is shown that field measurements compare relatively well with empirical prediction methods (for the overall analysed overtopping events), namely the corrected NN_OVERTOPPING2 neural network tool. Besides contributing to the overall database on wave overtopping in coastal structures, the presented results can also be used for calibration and validation of overtopping evaluation methods (empirical formulae, artificial neural networks and numerical and physical models).
Sediment transport studies are useful tools for the determination of sediment budgets, important ... more Sediment transport studies are useful tools for the determination of sediment budgets, important in the definition of management policies, in particular in environments not fully understood like fetch-limited beaches. Only a few studies have been made with respect to these beaches, ...
Coastal vegetated ecosystems are major organic carbon (OC) and total nitrogen (TN) sinks, but the... more Coastal vegetated ecosystems are major organic carbon (OC) and total nitrogen (TN) sinks, but the mechanisms that regulate their spatial variability need to be better understood. Here we assessed how superficial sedimentary OC and TN within intertidal vegetated assemblages (saltmarsh and seagrass) vary along a flow gradient, which is a major driver of sediment grain size, and thus of organic matter (OM) content. A significant relationship between flow current velocity and OC and TN stocks in the seagrass was found, but not in the saltmarsh. OC and TN stocks of the saltmarsh were larger than the seagrass, even though that habitat experiences shorter hydroperiods. Mixing models revealed that OM sources also varied along the flow gradient within the seagrass, but not in the saltmarsh, showing increasing contributions of microphytobenthos (17-32%) and decreasing contributions of POM (45-35%). As well, OM sources varied vertically as microphytobenthos contribution was highest at the higher intertidal saltmarsh (48%), but not POM (39%). Macroalgae, seagrass and saltmarsh showed low contributions. Local trade-offs between flow current velocities, hydroperiod and structural complexity of vegetation must be considered, at both horizontal and vertical (elevation) spatial dimensions, for better estimates of blue carbon and nitrogen in coastal ecosystems.
Communicating about wetlands to the audiences: what do the experts think?
&amp;lt;p&amp;gt;Understanding and managing wetlands is a matter of great importance, giv... more &amp;lt;p&amp;gt;Understanding and managing wetlands is a matter of great importance, given the fragile nature of its habitats, survival issues under perturbation, and the need for sustainable use of its resources when competing with human print. These are environments particularly sensitive to a number of physical factors and they&amp;amp;#8217;re particularly suited to engage with climate change (e.g. sea-level rise and rising temperature), conservation (e.g., biodiversity, land-use management), and ecosystem services (e.g., carbon storage and water purification). Wetlands deserved raising interest in the last two decades by the scientific community, such as the ecogeomorphologic nature of its dynamics, value and resilience to natural and human drivers, and timescales of change. This interest is reflected in the existence of four EGU Assembly 2022 proposed sessions (BG2.3, GM6.2, GM6.3, GM6.4) particularly devoted to wetlands, where both natural and social perspectives can fit. Given both the scientific and the societal relevance of wetlands, how does communication between both spheres is or should be made? What do the experts think about this? Are they aligned with the deficit model and/or the dialogue model of science communication? This is the underlaying rationale for this study.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We propose to enquire the dozens of coastal experts attending EGU 2022 conference about the science communication of wetlands. Questions about wetland communication include, for example (not comprehensively): 1) What are the key topics to communicate about wetland for audiences; with questions discriminating adult, children (8-12 y) and teenagers (13-17y)? 2) Choose the two most important wetlands threatening factors to communicate; And the two least important factors. 3) Is knowing about coastal evolution more relevant than knowing the names of the most emblematic vegetation species? 4) What is the most usual way that you use to communicate about wetlands to the public?&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We will collect data on wetland communication via an online questionnaire, with mostly closed-ended questions to allow a quicker analysis. We propose that a group of EGU attendees fill in the online questionnaire two days before and the first two days of the conference. The completion of the questionnaire allows anonymity. Fresh results from the survey will be presented and used as a base ground starting point for a discussion with conference participants about their own opinions.&amp;lt;/p&amp;gt;
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