Katerina Kombiadou

This study presents a comprehensive framework for assessing current and future ecosystem services in coastal wetlands, by integrating satellite image classification with simplified predictive modelling. The research was conducted in Ria Formosa, one of Portugal's most important coastal lagoons. Hard classification and soft regression Random Forest algorithms were employed to estimate the fractional coverage of marsh zones in 2025, with the former applied to very high-resolution satellite data (Worldview-3, with metric pixel size) and the latter to high and medium-resolution satellite imagery (PlanetScope and Sentinel-2, with metric to decametric pixel sizes). The results provide valuable insights into the challenges associated with variable satellite sources for automated mapping of ecological succession. Future projections up to 2100, informed by land cover change simulations from the SLAMM model, investigated potential ecological trajectories under sea-level rise (SLR) scenarios. Ecosystem adjustments to SLR were further translated into estimates of future blue ecosystem services (i.e., organic carbon stocks), based on reference values reported in the literature. Under the IPCC SSP5-8.5 pathway, significant transitions were projected, including relevant portions of present-day high marshes converting to low marsh, low marshes transforming into tidal flats, and tidal flats devolving into subtidal bare sediment. The modelling framework suggests that coastal squeeze will lead to a meaningful decline in salt marsh extent. The projected ecogeomorphologic adjustments to SLR allowed for pinpointing vegetated areas of gains and losses in carbon stocks by 2100. Foreseen changes will have key implications for the ecological balance of these wetlands, as the significant loss of high marsh habitat may compromise the ecological succession functioning and potentially lead to a decline in biodiversity within these zones. The integrative approach employed, which combines remote sensing and simplified modelling, offers crucial insights into the dynamics and resilience of wetland ecosystemsunder SLR conditions, supporting informed management and conservation efforts in the face of environmental changes.Acknowledgements: This study contributes to the projects C-Land (CEXC/4647/2024), SYREN (ALGARVE-FEDER-00853600-SYREN-17135), and DEVISE (2022.06615.PTDC), funded by the Fundação para a Ciência e a Tecnologia, as well as to the CLARKS project (CLARKS - 2024-1-ES01-KA220-SCH-000246633) under ERASMUS+ 2024, and to RestLands (ID 705677) funded by Planet Labs.

While improvements in the spectral and spatial resolution of satellite imagery have opened up new prospects for large-scale environmental monitoring, this potential has remained largely unrealised in dune ecogeomorphology. This is especially true for Mediterranean coastal dunes, where the highly mixed and sparse vegetation requires high resolution satellites and spectral unmixing techniques. To achieve this aim, we employed random forest regressors to predict the fractional cover of dune plant species in two of the sandy barriers of Ria Formosa (S. Portugal) from WorldView-2 imagery (June 2024). The algorithm, tested with spatially upscaled multispectral drone data and satellite imagery, detected the fractional cover of major species (most abundant classes and bushy vegetation) with reasonable to very good accuracy (coefficient of determination, CoD: 0.4 to 0.8) for the former and reasonable to good accuracy (CoD: 0.4 to 0.6) for the latter. Additional tests showed that (a) including the distance to the shoreline can increase model accuracy (CoD by ~0.1); (b) the grouping of species resulted in an insignificant increase in model skill; and (c) testing over independent dune plots showed generalisation beyond the training set and low risk of overfitting or noise. Overall, the approach showed promising results for large-scale observations in highly mixed coastal dunes.

Coastal wetland governance involves the institutions, people, policies, laws, and norms that guide decision-making and responsibilities affecting coastal wetlands and their users. The unique wetland ecosystems motivate conservation efforts, while their natural resources can become targets of exploitation, leading to multiple conflicting interests. Co-creation processes between stakeholders, as a practice of collaborative management, can help mitigate conflicts but it requires the willingness to compromise, mutual understanding, and effective dialogue. The current work explores a co-creation process under the scope of an ongoing science-for-policy project, aimed at defining sustainable adaptation pathways for wetlands conservation and carbon sequestration management in the Ria Formosa lagoon. Co-creation methodologies are being employed at various stages, and include the exchange of information (maps, fact sheets, management plans, directives, etc.) and focus groups with involved partners, i.e., researchers, regional decision-makers, and managers. The scientific development of the project, including data collection and modelling scenarios is being guided by the choices made collaboratively between all stakeholders. Three methodologies are being used to evaluate the level of partner engagement and effectiveness of the collaboration: 1) analysis of qualitative information gathered at the beginning and end of the process; 2) monitoring the communication between stakeholders; and 3) analysis of the stakeholder’s perspectives on strategic plans and other documents, shown formally at focus groups meetings or through informal conversations. The results of this co-creation process are relevant to a) the research of methodologies best suited to co-participatory management practices for Natural Parks and b) the establishment of foundations in evidence-based land management foundations.Acknowledgements: This study contributes to the project C-Land (CEXC/4647/2024), funded by the Fundação para a Ciência e a Tecnologia, and RestLands (ID 705677) funded by Planet Labs.

Forecasting the temporal and spatial evolution of coastal wetlands is a complex and challenging endeavour, further complicated by shifting climatic conditions. From a coastal management perspective, however, it remains essential to anticipate local vulnerabilities and the potential compromise of ecological functions. This study aims to assess the skill of subpixel and pixel imagery classification algorithms in sensing the zonation of wetlands through satellite imagery by testing in wetland areas, using high spatial resolution imagery from Unmanned Aerial Vehicles (UAVs) and high and medium spatial resolution satellite imagery and identifying the related challenges. The research was conducted in one of the most important coastal lagoons of Portugal, Ria Formosa Lagoon. Hard and soft Random Forest regression algorithms were employed to estimate the zonation of marsh plants, the former applied to UAV data (centimetric pixel size) and the latter to high and medium resolution satellite imagery (WV-2 & -3 and Sentinel, respectively, metric to decametric pixel size). Employing a gradually increasing pixel size allowed to identify error propagation during the passage from pixel to sub-pixel estimators and lower resolutions. The obtained results provide important insights to the barriers and opportunities related to varying imagery sources, carrying an important message to local managers. When discussed within the context of dominant natural and human drives, the developed maps, along with methodology and monitoring, provide valuable scientific insights into vegetation succession in a mesotidal system. More importantly, they serve as essential tools for local coastal decision-makers in identifying priorities for strategic landscape conservation planning and ensuring the sustainability of ecological function as the carbon sequestration within ecosystems.Acknowledgements: This study contributes to the projects DEVISE (https://doi.org/10.54499/2022.06615.PTDC) and C-Land (CEXC/4647/2024), both funded by the Fundação para a Ciência e a Tecnologia, and to project TraceLands (ID PP0090200), funded by the European Space Agency.

Coastal dunes result from complex interactions between sediment supply, topography and vegetation. However, feedback processes remain uncertain, in part due to the lack of quantitative analyses, integrating plant distribution and morphologic changes. This work seeks to assess how feedback processes are initiated and maintained by analysing the early development stages of a coastal dune, combining data on the evolution of its biotic (plant density and plant communities) and abiotic (morphology) components. For that, we study the establishment and early evolution of a coastal dune (1 ha plot) between 2019 and 2022, using high-resolution images and photogrammetry from Unmanned Aerial Vehicle (UAV) surveys. Results show a gradual plant colonisation with an increasing number of species as the colonised area expanded and plant community composition shifted. Plant distribution appears controlled by environmental conditions (elevation, distance to shoreline and debris presence), explaining three colonisation patterns: 1) over inherited morphological features (ridges) with debris, 2) over nutrient-rich debris lines, and 3) at flat surfaces (platform) with limited sediment supply and debris material. Colonisation initiated along the ridge crests with pioneer and builder species. The ridges also captured and retained most of the aeolian sediment transported under favourable conditions. Plant communities increased their abundance through time and partially shifted to binder plant species. Colonised stranded debris lines displayed greatest plant densities. However, reduced fetch distances inhibited sediment transport and sand accumulation. The platform was the latest area to colonise with pioneer plants shifting to binders and very limited sediment supply. Accumulation of sand was promoted by surface roughness mainly due to changes in slope (3-6°) during the during first months of dune formation, when vegetation was very scarce, and due to the combined influence of slope and plant density at later stages, as plant density increased, gaining relevance. Sand accumulation contributed to reinforce the topography of the inherited morphologies during both phases. Still, low densities (5-20%), more common during early stages, had a higher contribution to the total accumulation of sand in the plot. Builder and perennial pioneer plants were more efficient, while annual pioneer and binders captured less sediment. Interestingly, highly efficient builders colonised areas prone to sand burial, ensuring their success in trapping sand, while binders occupied more protected areas, lacking active sediment supply. Overall, this work elucidates the feedback processes between sediment supply, topography and vegetation during the very early stages of dune formation, with physical feedbacks dominating the onset and biophysical ones dominating a subsequent colonisation stage. The results highlight the relevance of inherited morphologies to the early evolution of a dune and likely to its final configuration, conditioning future responses of the system to disturbances.This work is supported by FCT – Fundação para a Ciência e a Tecnologia, I.P, through the projects 2022.05392.PTDC, 2021.04286.CEECIND/CP1672/CT0001, UIDP/00350/2020, UIDB/00350/2020 and LA/P/0069/2020.

The increase in spectral and spatial resolution offered by satellite imagery opens new opportunities in ecosystem monitoring over broader scales. Combined with advances in machine learning algorithms, like the spectral unmixing methods, it is possible to extract information on features smaller than the pixel size, as previously demonstrated for the case of saltmarsh plants. The present study focuses on transferring subpixel classification algorithms to mid-latitude coastal dunes, a significantly more challenging environment in terms of plant size and density, as well as in terms of complexity and heterogeneity of the existing species. To this aim we obtained WorldView2 imagery over the Ria Formosa barrier islands (South Portugal) during May of 2023 and collected data on dune plant distribution over three barrier islands during the same period. A total of 800 m2 over the foredune (toe to lee) were photographed during fieldwork, identifying a total of 32 plant species. Plant density distribution was assessed at the level of the pansharpened satellite image pixel and the data were introduced to the Random Forest Soft Classification (RFSC) algorithm for training and validation. The sensing ability of the classifier was tested considering different parameters (number of trees, split criteria) and assessing the performance for increasing number of classes, along with the importance of the 8 spectral bands for each class. The results of the analysis provide insights on the strengths and limitations of the RSFC method for the especially challenging environment of mid-latitude coastal dune habitats and provide a step forward in coastal ecosystem remote sensing and monitoring of these environments. Acknowledgements: The work was implemented in the framework of the DEVISE project (2022.06615.PTDC), funded by FCT (Fundação para a Ciência e a Tecnologia), Portugal. K. Kombiadou and S. Costas also recognise the financial support of FCT through contracts CEECINST/00146/2018/CP1493/CT0011 and 2021.04286.CEECIND, respectively, and the support of national funds through FCT by projects LA/P/0069/2020, granted to the Associate Laboratory ARNET, and UID/00350/2020, granted to CIMA.

The Thermaikos Gulf (TG) is a semi-enclosed, river-influenced, marine system situated in the eastern Mediterranean Sea, sustaining both urban coastal regions and ecologically preserved natural areas. Facing a plethora of environmental and anthropogenic pressures, the TG serves as a critical nexus where human activities intersect with marine ecosystems. The quality and health of the TG’s marine environment are tightly linked to the socioeconomic activities of the coastal communities comprising approximately 1.5 million inhabitants. The main features of the TG’s environmental dynamics and ecological status have been scrutinized by dedicated research endeavors during the last 50 years. This review synthesizes the seminal findings of these investigations, offering an evaluation of their contribution to research, their present collective impact, and their trajectory toward the future. A severe deterioration of the TG’s environmental quality was detected in the 1970s and 1980s when the treatment of urban wastewater was completely absent. A steady trend of recovery was observed after the 1990s; however, so far, the goal of a “good environmental state” mandated by national legislation and European directives has not been achieved. A clear reduction in research was detected after 2010, associated with the recession of the Greek economy, following the “golden period” for research in the TG from the mid-1990s until the late 2000s. The most important research gaps and uncertainties are discussed, while specific targeted recommendations for the improvement of monitoring and understanding of the physical, biochemical, and ecological state of the gulf are provided: (i) increase in permanent observational stations (temporally and spatially); (ii) inclusion of all major environmental parameters; (iii) monitoring of the quantity and quality of all land-originated freshwater discharges; (iv) monitoring and management of important aspects of the marine environment that have received minimal attention in the past (e.g., coastal erosion, plastic pollution); (v) development of accurate prediction tools (e.g., numerical techniques) to support first-level responders and efficient management; (vi) establishment of a supervising public entity that would support the holistic overview and management of the entire TG. These suggestions are directed at overcoming the existing uncertainties in the knowledge of the TG, safeguarding its ecological integrity and its role as a crucial link to marine biodiversity and sustainability in the Mediterranean basin.

Thermaikos Gulf (TG) is a semi-enclosed, river-influenced, marine system situated in the eastern Mediterranean Sea, sustaining both urban coastal regions and ecologically preserved natural areas. Facing a plethora of environmental and anthropogenic pressures, the TG serves as a critical nexus where human activities intersect with marine ecosystems. The second largest city of Greece, Thessaloniki, is located in the northern part of the gulf, while a large environmentally protected zone with multiple river deltas is lying along its western coasts. The quality and health of the TG’s marine environment are tightly linked to the socioeconomic activities of the coastal communities comprising approximately 1.5 million inhabitants. The main features of TG’s environmental dynamics and ecological status have been scrutinized by dedicated research endeavours during the last 50 years. This review synthesizes the seminal findings of these investigations, offering an evaluation of their contribution to research, their present collective impact, and their trajectory toward the future. A severe deterioration of the TG’s environmental quality was detected in the 1970s and 1980s when treatment of urban wastewater was completely absent. A steady trend of recovery was observed after the 1990s, however without achieving, so far, the goal of a “good environmental state”, mandated by national legislation and European directives. The most important research gaps and uncertainties are also discussed and specific recommendations for the improvement of monitoring and understanding about the physical, biochemical, and ecological state of the gulf are provided. The most significant discrepancy is related to the fragmentary monitoring of the TG in both space (partial coverage) and time (temporal gaps), which has been intensified after 2010 due to the reduced funding for environmental research and protection under the severe Greek economic recession. This review aspires to highlight the importance of bolstering monitoring initiatives that can provide continuous observations and further understanding on the TG's ecological and physicochemical conditions. Targeted recommendations, aimed at ameliorating the fragmented monitoring processes, are also provided, advocating for a holistic approach that can safeguard the ecological integrity of the Thermaikos Gulf and uphold its role as a crucial link to marine biodiversity and sustainability in the Mediterranean basin.

Process‐based morphodynamic models can be useful in understanding coastal dune responses to disturbances, as well as possible evolutionary patterns. To this aim, we employ Duna, a simplified 1D morphodynamic model, to assess the influence of dune morphology (height and slope) on sand transfer and deposition across the dune profile for different beach widths and wind incidence angles through idealized experiments. Simulations of real conditions show good model performance, both in wind flow reproduction and in topographic change along the dune profiles tested. The idealized experiments show that wind speed increases and sand accumulation decreases logarithmically with dune height and linearly with stoss slope along the dune profile. Fetch and cosine transport limiting parameters are reflected in the sand accumulated windwards from the toe, while sand transfer to the dune appears controlled by multiple factors; the higher the dune and/or the narrower the beach, the likelier that maximum accumulation occurs under oblique winds. Results point to two different types of evolution for high dunes. Either the vegetation is dense enough to maintain the stoss position, in which case vertical growth near‐ceases and seaward progradation is promoted, or the stoss is eroded and landward retreat dominates, in which case sand transfer to the crest and lee continues as a mixture of low input from the beach and recycled sand from the stoss.