Les articles d'Olivier Boutron

Climatic and nutrient drivers affect long-term phytoplankton temporal trends in coastal lagoons

Tue, 3 Feb 2026 11:22:35

de Aurore Moulin, Béatrice Bec, Olivier Boutron, Valerie Derolez, Marie Garrido, Vanina Pasqualini, Nathalie Malet
In Marine pollution bulletin, 224 (March, 2026), 119080
En ligne : www.sciencedirect.com[...]

Understanding how climate influences phytoplankton dynamics is crucial for anticipating temporal trends and cascading consequences on ecosystem functioning under climate change. This study explores long-term dynamics in contrasted Mediterranean lagoons and investigates the effects of climatic (air temperature, rainfall, wind speed) and nutrient (inorganic nutrient concentrations) drivers on phytoplankton chlorophyll a, abundances, and pigment composition. 17 years of summer monitoring were analyzed using univariate trend tests and multivariate approaches to highlight changes and to disentangle the contributions of abiotic factors to phytoplankton variability. Our results revealed contrasts among lagoons in physicochemical conditions and phytoplankton community, which strongly structured their temporal trends. Climatic drivers significantly influenced phytoplankton, but their importance was context-dependent. In nutrient-enriched systems, phytoplankton dynamics were primarily controlled by inorganic nutrient concentrations, while climatic effects were weak by comparison. Conversely, in nutrient-poor systems, climatic signals became more visible and influential: wind events were associated with higher chlorophyll a, warmer conditions with increases in phycoerythrin-rich picocyanobacteria, and rainfall with higher picoeukaryote abundances, potentially through indirect effects on water column stability and nutrient and light availability. However, under nutrient limitation, abundances remained low and dominated by small cells, suggesting that nutrient control exerts the strongest influence on phytoplankton, which may explain why nutrient control tends to mask diffuse climatic signals. Yet, climate change modulates physicochemical patterns and may progressively shape lagoon functioning. This study emphasizes the need to account for lagoon features and vulnerabilities, and supports adaptive and site-specific management strategies to safeguard coastal lagoons under future changes.

Integrated modelling of sediment and organic carbon fluxes in a large catchment: quantifying riverine contributions to the Mediterranean Sea

Tue, 20 Jan 2026 10:48:26

de Clément Fabre, Yoann Copard, Sabine Sauvage, Olivier Radakovitch, Hervé Piégay, Jose Miguel Sanchez-Perez, Mathieu Fressard, Olivier Boutron
In Catena, 264 (March, 2026), 109794
En ligne : www.sciencedirect.com[...]

Within the Land Ocean Aquatic Continuum, the export of dissolved and particulate organic carbon (DOC, POC) is crucial for various processes in aquatic ecosystems and a primary source of greenhouse gas emissions in hydrosystems. Quantifying DOC and POC fluxes at high spatiotemporal resolution is complex because numerous sources and processes influence their dynamics, including climate, geological, and anthropogenic activities. Such quantifications at the catchment scale can be performed using hydrological models that consider OC processes. This study employed the Soil and Water Assessment Tool – Carbon (SWAT-C) to simulate OC dynamics in the large Mediterranean catchment of the Rhône River from 2002 to 2020. We represent hydrological and sediment fluxes at the catchment scale by accounting for sub-catchment diversity and dam operations. The average resulting exports reach 5.52 Mt. y−1, 78.8 kt y−1, and 95.1 kt y−1 with 54.4 %, 71.5 %, and 44.3 % exported during the highest discharges for sediment, POC, and DOC, respectively. The contributions of the southern sub-basins to POC and DOC fluxes are significant, while the northern sub-basins do not show significant patterns. Regarding OC quality, the proportions of labile/refractory OC at the Rhône outlet are 85/15 and 5/95 for POC and DOC, respectively. Global changes could alter flows, such as the labile/refractory OC proportions, which should be quantified using the tool developed in this article to anticipate their impacts on biogeochemical dynamics in the Mediterranean Sea. Finally, our study demonstrates the potential and limitations of SWAT-C for modelling OC dynamics in a large Mediterranean catchment under multiple anthropogenic pressures.

Nature-based adaptation in human dominated coastal ecosystems

Thu, 26 Feb 2026 14:32:57

de Fabienne Horneman, Alice Stocco, Paolo Comandini, Alberto Barausse, Nuno Caiola, Agustin Sanchez-Arcilla, Vicente Gracia, Richard Marijnissen, Sara Pino Cobacho, Luciana Villa Castrillón, et al.
In Ecological Indicators, 183 (February, 2026), 114629
En ligne : www.sciencedirect.com[...]

Ecosystems along river-to-sea continuums face urgent challenges that demand swift restoration interventions, often exceeding the data availability, collection and testing capacity. This makes expert- and consensus-based approaches vital for guiding decisions, particularly in data-scarce coastal regions. With the aim to provide practical guidance for assessing the applicability of different restoration techniques, this study involved a group of 23 experts from various European and Mediterranean regions to evaluate 49 restoration techniques tested recently in nine sites, representing diverse coastal ecosystems. Through a Delphi-based expert elicitation, a series of gray, hybrid, and green restoration techniques was assessed in terms of their structural and functional performance. Additionally, the assessment of the pressures affecting the regions allowed exploring the restoration techniques' resilience to both natural and anthropogenic pressures and impacts. Results from the data collected so far suggest that, while green restoration techniques are environmentally friendly and significantly support natural processes, their limited scale of influence makes them vulnerable when pressures are strong or widespread on the ecosystem. This often leads to opting for hybrid or engineering-based solutions for restoration, as they provide a more robust structure and longevity albeit with reduced capacity to foster natural processes. This result underscores a critical dilemma: while green and/or integrated solutions can help mitigate human-induced impacts and digital tools may support decision-making, restoration efforts alone may sometimes be insufficient if the underlying anthropogenic pressures on human-dominated coastal ecosystems remain unaddressed. Subsequently, the identified techniques and their performance evaluated under current and future conditions have been compiled into an open-source, interactive digital tool, designed to assist decision-makers and practitioners in selecting the most suitable restoration strategies by leveraging the knowledge acquired through ongoing experiences in coastal restoration. This digital platform not only facilitates access to information but also enables the integration of new data on emerging techniques, making it a dynamic and evolving resource for coastal restoration management.

Coastal restoration agreements under climate change: barriers and enablers

Fri, 7 Nov 2025 10:04:49

de Margaret M. Dietrich, Agustin Sanchez-Arcilla, Xavier Sánchez-Artús, Vicente Gracia, Nuno Caiola, Catarina Dabalà, Julien Dalle, Susan Gallon, Rosaria E. Musumeci, Grzegorz Różyński, et al.
In Water, 17(21) (November, 2025), 3154
En ligne : www.mdpi.com[...]

Coastal ecosystems are becoming less resilient under climate (e.g., sea-level rise, warming, acidification) and human (e.g., urbanization, coastal hardening, and river regulation) pressures, forcing local communities to face increasing risk levels. This lack of resilience is linked to an adaptation deficit that can be recovered through restoration. Yet, restoration faces barriers related to governance, funding, technical practice, and social context. To overcome such barriers, the REST-COAST project has developed a framework that reckons with coastal restoration platforms and restoration agreements, supported by “enablers” that support the upscaling and implementation of restoration projects. The proposed agreements and platforms can effectively overcome barriers by embedding governance, technical, financial, and social enablers into the agreements among stakeholders. Tailored, place-based approaches foster collaboration, long-term adaptive management, and the scaling of restoration to address accelerating climate-driven risks. The proposed agreements build on hands-on restoration lessons, offering transferable insights for global coastal resilience.

Interdependencies among hydro-saline dynamics, economic activities, ecological processes, and biodiversity in a deltaic social-ecological system: insights from the Rhône delta (southern France)

Fri, 22 Aug 2025 16:36:54

de Rose Rodier, Olivier Boutron, Arnaud Béchet, Olivier Therond
In Ecology and Society, 30(3) (July, 2025)
En ligne : ecologyandsociety.org[...]

Deltas are complex social-ecological systems (SESs) that involve many economic activities that interconnect closely with ecological processes and biodiversity. Sustainable management of such intricate SESs requires developing an integrated and understandable representation of their main human and ecological entities, processes, and interactions. We developed a formal representation of the Ile de Camargue (center of the Rhône delta), in which hydro-saline dynamics, water management, economic activities (e.g., agriculture, hunting, fishing, tourism), and natural environments (i.e., habitats for biodiversity) interact. The conceptual model was based on four submodels that provided complementary representations of i) water governance, ii) agriculture, and iii) bird and iv) fish communities. The conceptual model highlights the strong relationships (i.e., causal chains, feedback loops, interactions, side effects, and trade-offs) among the multiple entities of this deltaic SES. It provides information about the region and describes deltas as a SES to support decision-making. One major feedback loop in the delta concerned relationships among regulations, rice fields, and use of marshes as a habitat for birds: strengthening pesticide regulations to improve water quality and bird habitats caused the area of rice cultivation to decrease which degraded habitat conditions for birds. Directly related to pesticide use, the most common trade-off is to decide whether water management should prioritize water quality or quantity in the delta’s Vaccarès lagoon, and opinion differs among stakeholders. The conceptual model could be used as a starting point to develop computer-based integrated assessment and modeling to explore dynamics of and resilience to climate change in the Ile de Camargue.

Monitoring coastal dynamics after working with nature practices in the Rhone delta

Wed, 4 Jun 2025 15:53:40

de Morgane Jolivet, Cecile Puigserver, Olivier Boutron, Francois Sabatier, Samuel Meulé, Philippe Larroude, Loic Willm, Emilie Luna-Laurent
In Coastal Engineering Proceedings, 38 (June, 2025), 50
En ligne : icce-ojs-tamu.tdl.org[...]

The site of the “Étangs et Marais des Salins de Camargue” (EMSC) is located southern France in the Rhône Delta, facing Mediterranean sea, at the heart of the Camargue Regional Natural Park. This site, formerly dedicated to salt production, is now owned by the Coastal Conservatory and co-managed by the Camargue Regional Natural Park, Tour du Valat, and the French National Society for the Protection of Nature. A habitat restoration project was initiated in 2011 and continues as part of the development of a 2023-2032 management plan and the site's participation in the European H2020 Rest-Coast project. This restoration aims to facilitate the recolonization of the area by plant (seagrass, salt marsh) and animal species, reestablishing the natural hydrological processes of the site. An adaptive coastal management strategy is also applied on this site, with the decision to no longer maintain the historical dikes of the salt production site facing the sea, leading to their gradual collapsing. Protection against the risk of marine submersion is ensured by an landward seawall, which will be elevated, as part of the coastal strategy defined for the greater Rhône Delta. Natural hydro-morphodynamic processes are reestablishing locally, creating new connections with the sea and the formation of beach and barrier areas through overwash. This results in the emergence of a natural buffer zone that will better address the consequences of climate change or storms, such as marine submersion and salinization.

Large-scale loss of Mediterranean coastal marshes under rising sea levels by 2100

Fri, 28 Feb 2025 10:08:50

de Mark Schuerch, Joshua Kiesel, Olivier Boutron, Anis Guelmami, Claudia Wolff, Wolfgang Cramer, Nuno Caiola, Carles Ibáñez, Athanasios T. Vafeidis
In Communications Earth & Environment, 6(1) (February, 2025), 1-13
En ligne : www.nature.com[...]

Mediterranean coastal wetlands account for important biodiversity and ecosystem services. But climate-change induced sea-level rise poses a critical risk to their survival. Here, we assess these risks for Mediterranean coastal marshes, one key type of Mediterranean coastal wetlands, and identify main drivers for future coastal marsh change for the Mediterranean and comparable coastlines. We apply an integrated modelling approach that accounts for future sea-level rise, sediment accretion, coastal management and marsh inland migration processes. Depending on climate mitigation scenarios, widespread coastal marsh loss is projected, ranging from 8% to 92% of current extents. For Egypt, France, and Algeria, we predict (near) total loss of coastal marshes by 2100 for current coastal management and sediment supply scenarios. Overall, losses could at least be halved if additional inland migration space were created, e.g. through passive or active habitat restoration. Bold climate mitigation and local adaptation are needed to preserve existing coastal marshes.

Exposure of wetlands important for nonbreeding waterbirds to sea-level rise in the Mediterranean

Fri, 17 May 2024 16:11:40

de Fabien Verniest, Thomas Galewski, Olivier Boutron, Laura Dami, Pierre Defos du Rau, Anis Guelmami, Romain Julliard, Nadège Popoff, Marie Suet, Loic Willm, et al.
In Conservation Biology, 2024 (May, 2024), e14288
En ligne : onlinelibrary.wiley.com[...]

Sea-level rise (SLR) is expected to cause major changes to coastal wetlands, which are among the world's most vulnerable ecosystems and are critical for nonbreeding waterbirds. Because strategies for adaptation to SLR, such as nature-based solutions and designation of protected areas, can locally reduce the negative effects of coastal flooding under SLR on coastal wetlands, it is crucial to prioritize adaptation efforts, especially for wetlands of international importance for biodiversity. We assessed the exposure of coastal wetlands important for nonbreeding waterbirds to projected SLR along the Mediterranean coasts of 8 countries by modeling future coastal flooding under 7 scenarios of SLR by 2100 (from 44- to 161-cm rise) with a static inundation approach. Exposure to coastal flooding under future SLR was assessed for 938 Mediterranean coastal sites (≤30 km from the coastline) where 145 species of nonbreeding birds were monitored as part of the International Waterbird Census and for which the monitoring area was delineated by a polygon (64.3% of the coastal sites monitored in the Mediterranean region). Thirty-four percent of sites were threatened by future SLR, even under the most optimistic scenarios. Protected study sites and study sites of international importance for waterbirds were, respectively, 1.5 and 2 times more exposed to SLR than the other sites under the most optimistic scenario. Accordingly, we advocate for the development of a prioritization scheme to be applied to these wetlands for the implementation of strategies for adaptation to SLR to anticipate the effects of coastal flooding. Our study provides major guidance for conservation planning under global change in several countries of the Mediterranean region.

Impacts of environmental conditions and management of sluice gates on glass eel migration

Tue, 15 Nov 2022 17:40:58

de Colin Bouchard, Olivier Boutron, Jordane Labremon, Hilaire Drouineau, Patrick Lambert, Delphine Nicolas
In Estuarine, Coastal and Shelf Science, Online (November, 2022), 108139
En ligne : www.sciencedirect.com[...]

Anthropogenic barriers such as tidal gates impair animal migration and ecological continuity. For migratory fishes, barriers may alter or impeach both upstream and downstream migrations. Juveniles of European eels, namely glass eels, have to pass those barriers when migrating upstream, whereas they have limited swimming capacities and are dependent on several environmental variables. Hydrological conditions, which can be modified by barrier management, are critical for glass eels. Here, we investigated the links between hydrological conditions and barrier management and the recruitment of glass eels at a connection between the Mediterranean Sea and a lagoon. To do that, we modeled the recruitment of glass eels over ten seasons accounting for temporal variations and co-variable effects. We modeled three aspects of recruitment: presence, level, and composition. We found that monthly and inter-annual effects explained the main part of the variations in glass eel recruitment but accounting for environmental effects improved our models, with a positive effect of temperature, for instance. We associated low levels of catches and recruitment of rather old individuals to high water flow rates when water flows out of the lagoon. Those results call for further studies on how sluice gate management may improve glass eel recruitment and seem to indicate that local stakeholders should adjust the number of open gates depending on the water level on both sides of the barrier.

Spatio-temporal variations in glass eel recruitment at the entrance pathways of a Mediterranean delta

Thu, 8 Dec 2022 16:03:27

de Colin Bouchard, Hilaire Drouineau, Patrick Lambert, Olivier Boutron, Delphine Nicolas
In ICES Journal of Marine Science, 79(6) (August, 2022), 1874-1887
En ligne : doi.org[...]

Understanding spatio-temporal dynamics of glass eel recruitment is necessary to characterize eel population status and the stock of future elvers. Despite numerous studies that have characterized recruitment across Europe, multiple systems along the Mediterranean coasts need a deeper look. We built a Bayesian State-Space Model to investigate the temporal variations in glass eel recruitment in the Rhône delta (France). The model was suited to address the spatial heterogeneity due to the complexity of this system constituted by numerous entrance pathways. Over 13 years, we found inter-annual variations without a particular trend. Here, an overall migration peak occurred in February–March for the system, but substantial spatial variations in the resulting recruitment were visible. Spatial variations in the inter-annual dynamics and migration peak pointed out the necessity to account for spatial heterogeneity in the dynamics of glass eel recruitment. The highlighted inter-annual variations are consistent with analysis of coincident time-series in other sites in Europe (e.g. WGEEL), and the migration peak’s timing is similar to peaks observed in other estuaries. Spatial variations in the migration peak suggest a potential effect of local environment conditions on the recruitment. Our model provided a suitable approach to investigate temporal variations while accounting for spatial heterogeneity.

Endorheic Waterbodies Delineation From Remote Sensing as a Tool for Immersed Surface Topography

Wed, 30 Jun 2021 15:30:26

de Carole Delenne, Jean-Stephane Bailly, Antoine Rousseau, Renaud Hostache, Olivier Boutron
In IEEE Geoscience and Remote Sensing Letters, Online (May, 2021), 1-5
En ligne : ieeexplore.ieee.org[...]

For several decades, it becomes possible to delineate waterbodies and their dynamics from optical or radar images, that are now available at high spatial and temporal resolutions. We present here an interpolation approach that takes benefits from this waterbodies delineation in endorheic areas. It consists in computing isovalue contour lines to improve topography estimates classically obtained from measurement points only. The approach, based on a minimization problem, uses thin plate spline (TPS) interpolation functions, the coefficients of which are determined along with the unknown water level of each curve. Results obtained on a generated topography show that this approach, applied with three contour-line curves, yields a lower root mean square error (RMSE) using only one measurement point compared to the one obtained with nine points and the classical approach.

Hydro-Saline Dynamics of a Shallow Mediterranean Coastal Lagoon: Complementary Information from Short and Long Term Monitoring

Wed, 30 Jun 2021 15:30:23

de Olivier Boutron, Caroline Paugam, Emilie Luna-Laurent, Philippe Chauvelon, Damien Sous, Vincent Rey, Samuel Meulé, Yves Chérain, Anais Cheiron, Emmanuelle Migne
In Journal of Marine Science and Engineering, 9(7) (July, 2021), 701
En ligne : www.mdpi.com[...]

The Vaccarès Lagoon System, located in the central part of the Rhône Delta (France), is a complex shallow coastal lagoon, exposed to a typical Mediterranean climate and a specific hydrological regime affected by man-controlled exchanges with the sea and agricultural drainage channels. In this article, we report the results obtained by a series of monitoring programs, with different spatial and temporal resolutions. Long-term datasets from 1999 to 2019 with data collected on a monthly basis and a high spatial resolution highlighted the significant spatial heterogeneity in salinity regimes, and helped to determine the long-term evolution of the total mass of dissolved salt. High-frequency surveys allowed to characterize the water levels and salinity dynamics seasonal response to (i) the exchanges with the Mediterranean Sea, (ii) the exchanges with agricultural drainage channels, and (iii) the rain and evaporation. In addition, wind effects on salinity variations are also explored. This work shows how different spatial and temporal monitoring strategies provide complementary information on the dynamic of such a complex system. Results will be useful and provide insight for the management of similar lagoon systems, accommodating for both human activities and ecological stakes in the context of global change. / Un article sur l'Hydrosystème Vaccarès dans lequel les auteurs ont exploité les différentes mesures existantes sur ce site pour étudier les dynamiques hydro-salines à différentes échelles spatiales et temporelles (quelques heures vs 20 années). les auteurs ont également utilisé toutes ces mesures pour quantifier pour la première fois les contributions respectives à cette dynamique, en termes de volumes, des eaux de drainage agricole, des échanges avec la mer, de la pluie et de l'évaporation.

Context in Landscape Planning: Improving Conservation Outcomes by Identifying Social Values for a Flagship Species

Wed, 30 Jun 2021 15:30:27

de Lisa Ernoul, Angela Wardell-Johnson, Raphael Mathevet, Alain Sandoz, Olivier Boutron, Loic Willm, Stephan Arnassant, Arnaud Béchet
In Sustainability, 13(12) (June 2021), 6827
En ligne : www.mdpi.com[...]

Sustainable conservation planning depends on understanding local context including the way social values impact a landscape. Flamingos are used here as a ﬂagship species to focus the social values of a broad range of people living in and working in the Camargue in France. A survey questionnaire (n = 87) was used to identify the range of ways in which people value the landscape and their perception of effectiveness of ﬂamingo management strategies. Survey analysis was conducted through a multi-method approach, triangulating standard descriptive statistics, qualitative data analysis, and multivariate analysis applying numerical taxonomy. Applying numerical taxonomy allowed us to identify and deﬁne six social assemblages. Each assemblage had geographical characteristics with distinct values and perceptions in relation to management. The primary residence and geographic identity of the participants was deﬁning, showing clear value differences from participants living in different parts of the delta. The participants most frequently agreed that ﬂamingos contributed to the aesthetic, economic, biodiversity, and recreational values of the landscape. We show how identifying points of consensus and points in contest is necessary for navigating differences in values for conservation planning. This research shows the importance of the local social context in sustainably managing landscape change. /La planification d'une conservation durable dépend de la compréhension du contexte local, notamment de l'impact des valeurs sociales sur un paysage. Les flamants roses sont utilisés ici comme une espèce phare pour mettre l'accent sur les valeurs sociales d'un large éventail de personnes vivant et travaillant en Camargue. L'analyse de l'enquête montre que la résidence principale et l'identité géographique des participants ont été déterminantes, montrant des différences de valeurs claires entre les participants vivant dans différentes parties du delta. Les participants ont le plus souvent exprimaient que les flamants roses contribuaient aux valeurs esthétiques, économiques, de biodiversité et récréatives du paysage. Nous montrons comment l'identification des points de consensus et des points de contestation est nécessaire pour naviguer dans les différences de valeurs pour la planification de la conservation. Cette recherche montre l'importance du contexte social local dans la gestion durable du changement de paysage.

Assessing Management Perceptions Linked to a Flagship Species: A New Approach to Increase Landscape Management Legitimacy and Support

Tue, 8 Jun 2021 10:32:39

de Lisa Ernoul, Angela Wardell-Johnson, Raphael Mathevet, Alain Sandoz, Olivier Boutron, Loic Willm, Stephan Arnassant, Arnaud Béchet
In Coastal Management, 49(4) (June, 2021), 1-13
En ligne : www.tandfonline.com[...]

Integrated socio-ecological decision-making is important in improving legitimacy in management decisions through effective solutions that avert conflicts. This research examined social perceptions in landscape planning and management with regard to the Greater flamingo, a flagship species along the southern French Coast. A strategic delivery to a cross-section in a social catchment (n = 87) captured the perception and the recognition of management strategies through a survey questionnaire. Analysis was conducted through a multi-method approach, triangulating qualitative and quantitative results. Results show the importance of the attachment to flamingos in local landscapes. Knowledge on flamingo ecology was relatively high and participants perceived some of the regional management options to be unfavorable for flamingos. Participants identified threats to the species and expressed concern for the future of the flamingos, challenging the legitimacy of some landscape management decisions and planning policies. This research demonstrates the role of flagship species in stimulating reflection on landscape management, addressing both the ecological and human dimensions. Understanding social perceptions of biodiversity management objectives is fundamental for effective coastal conservation.

Estimation of Bathymetry and Benthic Habitat Composition from Hyperspectral Remote Sensing Data (BIODIVERSITY) Using a Semi-Analytical Approach

Fri, 21 May 2021 09:16:30

de Audrey Minghelli, Sayoob Vadakke-Chanat, Malik Chami, Mireille Guillaume, Emmanuelle Migne, Patrick Grillas, Olivier Boutron
In Remote Sensing, 13(10) (May, 2021), 17
En ligne : www.mdpi.com[...]

The relevant beneﬁts of hyperspectral sensors for water column determination and seabed features mapping compared to multispectral data, especially in coastal areas, have been demonstrated in recent studies. In this study, we used hyperspectral satellite data in the accurate mapping of the bathymetry and the composition of water habitats for inland water. Particularly, the identiﬁcation of the bottom diversity for a shallow lagoon (less than 2 m in depth) was examined. Hyperspectral satellite data were simulated based on aerial hyperspectral imagery acquired above a lagoon, namely the Vaccarès lagoon (France), considering the spatial and spectral resolutions, and the signal-to-noise ratio of a satellite sensor, BIODIVERSITY, that is under study by the French space agency (CNES). Various sources of uncertainties such as inter-band calibration errors and atmospheric correction were considered to make the dataset realistic. The results were compared with a recently launched hyperspectral sensor, namely the DESIS sensor (DLR, Germany). The analysis of BIODIVERSITY-like sensor simulated data demonstrated the feasibility to satisfactorily estimate the bathymetry with a root-mean-square error of 0.28 m and a relative error of 14% between 0 and 2 m. In comparison to open coastal waters, the retrieval of bathymetry is a more challenging task for inland waters because the latter usually shows a high abundance of hydrosols (phytoplankton, SPM, and CDOM). The retrieval performance of seabed abundance was estimated through a comparison of the bottom composition with in situ data that were acquired by a recently developed imaging camera (SILIOS Technologies SA., France). Regression coefﬁcients for the retrieval of the fractional species abundances from the theoretical inversion and measurements were obtained to be 0.77 (underwater imaging camera) and 0.80 (in situ macrophytes data), revealing the potential of the sensor characteristics. By contrast, the comparison of the in situ bathymetry and macrophyte data with the DESIS inverted data showed that depth was estimated with an RSME of 0.38 m and a relative error of 17%, and the fractional species abundance was estimated to have a regression coefﬁcient of 0.68.

Wind tides and surface friction coefficient in semi-enclosed shallow lagoons

Tue, 25 May 2021 11:17:05

de Caroline Paugam, Damien Sous, Vincent Rey, Samuel Meulé, Vincent Faure, Olivier Boutron, Emilie Luna-Laurent, Emmanuelle Migne
In Estuarine, Coastal and Shelf Science, 257 (2021)
En ligne : hal.archives-ouvertes.fr[...]

The present paper is specifically focused on enclosed or semi-enclosed basins where the wind is the dominant driver of water surface tilting, leading to the so-called wind tide contributing to water levels rise. Wind-induced free surface tilting is studied using the 1-D steady form of the depth-averaged shallow water (Saint-Venant) momentum equation which reflects the depth-averaged local balance between surface slope and wind stress. Two contrasted field sites, the Berre and Vaccarès lagoons, have been monitored providing water level data along a reference axis. This study highlighted the occurence of wind tides at the two field sites. The bimodal wind exposure ensured the robustness of the observations, with non-linear but symmetric behaviors patterns observed in winds from opposite directions. It is observed that the higher the wind speed, the steeper the slope of the free surface in accordance with the well known basic trend. In addition, a significant effect of depth is observed, with greater surface tilting in the shallower lagoon. The data analysis confirmed the robustness of such a simple approach in the present context. Using the additional assumption of constant, i.e. wind-independent, drag coefficients (C D) allowed a good match with the observations for moderate wind speeds for both sites. However, the depth effect required the C D to be increased in the shallower basin. Classical empirical wind-dependent C D parameterizations provide better wind-tide predictions than the constant-C D approach in very strong wind conditions but totally failed in predicting surface tilting in the shallower site, suggesting that physical parameters other than wind speed should be taken into account for the C D parameterization in very shallow lagoons.

The future for Mediterranean wetlands: 50 key issues and 50 important conservation research questions

Wed, 27 Jan 2021 10:11:49

de Nigel G. Taylor, Patrick Grillas, Hazem Al Hreisha, Özge Balkız, Maud Borie, Olivier Boutron, Ana Catita, Jocelyn Champagnon, Semia Cherif, Kerim Cicek, et al.
In Regional Environmental Change, Online (2021), 25

Wetlands are critically important for biodiversity and human wellbeing, but face a range of challenges. This is especially true in the Mediterranean region, where wetlands support endemic and threatened species and remain integral to human societies, but have been severely degraded in recent decades. Here, in order to raise awareness of future challenges and opportunities for Mediterranean wetlands, and to inform proactive research and management, we identified (a) 50 key issues that might affect Mediterranean wetlands between 2020 and 2050, and (b) 50 important research questions that, if answered, would have the greatest impact on the conservation of Mediterranean wetlands between 2020 and 2050. We gathered ideas through an online survey and review of recent literature. A diverse assessment panel prioritised ideas through an iterative, anonymised, Delphi-like process of scoring, voting and discussion. The prioritised issues included some that are already well known but likely to have a large impact on Mediterranean wetlands in the next 30 years (e.g. the accumulation of dams and reservoirs, plastic pollution and weak governance), and some that are currently overlooked in the context of Mediterranean wetlands (e.g. increasing desalination capacity and development of antimicrobial resistance). Questions largely focused on how best to carry out conservation interventions, or understanding the impacts of threats to inform conservation decision-making. This analysis will support research, policy and practice related to environmental conservation and sustainable development in the Mediterranean, and provides a model for similar analyses elsewhere in the world.

Dynamics of the seagrass Zostera noltei in a shallow Mediterranean lagoon exposed to chemical contamination and other stressors

Tue, 7 May 2019 11:27:11

de Diane Espel, Noël J. Diepens, Olivier Boutron, Evelyne Buffan-Dubau, Yves Chérain, Eric Coulet, Patrick Grillas, Anne Probst, Jérôme Silvestre, Arnaud Elger
In Estuarine, Coastal and Shelf Science, 222 (June, 2019), 1-12
En ligne : linkinghub.elsevier.com[...]

Seagrass decline due to a variety of stressors has been observed worldwide. In the shallow Vaccarès lagoon, Camargue, France, the dominant macrophyte species, Zostera noltei, has suﬀered two major declines since 1996. The ﬁrst decline was well explained by salinity and turbidity variations, while the second one could not be explained by these parameters. Other stressors such as chemical contamination, eutrophication or temperature increase could be explanatory variables for this most recent decline. The aim of our study was to understand, via scientiﬁc monitoring from 2011 to 2015, the inﬂuence of chemical contamination and its possible interactions with other biological and environmental pressures, on seagrass physiology and population dynamics in the Vaccarès lagoon.

Seventy-year chronology of Salinas in southern France

Wed, 17 Apr 2019 10:20:50

de Rutger de Wit, Alice Vincent, Ludovic Foulc, Mario Klesczewski, Olivier Scher, Claudine Loste, Marc Thibault, Brigitte Poulin, Lisa Ernoul, Olivier Boutron
In Journal for Nature Conservation, 49 (June, 2019), 95-107
En ligne : www.sciencedirect.com[...]

After World War II, twenty-nine coastal Salinas (122 km2), located in the vicinity of coastal lagoons and in deltas, were exploited along the Mediterranean coastlines in South France. Today, only five of these are still actively producing salt, currently representing 175 km2. Concomitant with the abandonment of many of the smaller Salinas, the larger Salinas in the Rhône delta (Camargue) strongly increased their surfaces at the expense of natural ecosystems, of which a part has also been abandoned after 2009. This paper documents these changes in landscape use by chronological GIS mapping and describes the fate of the 91 km2 of abandoned Salina surfaces. The majority of this area (88 km2) is included in the Natura 2000 network, among which most (74 km2) has been acquired by the French coastal protection agency (Conservatoire du Littoral) to be designated as Protected Areas. Only a very minor part (<1%) has been lost for industry and harbour development. Managing abandoned Salinas as Protected Areas is a challenge, because of the different landscape, biodiversity conservation, natural and cultural heritages issues at stake. In two cases, abandoned Salinas have been brought back again into exploitation by private initiative thus allowing for the protection of original hypersaline biodiversity. In other cases, the shaping of the landscape by natural processes has been privileged. This has facilitated the spontaneous recreation of temporal Mediterranean wetlands with unique aquatic vegetation, and offered opportunities for managed coastal re-alignment and the restoration of hydrobiological exchanges between land and sea. In other areas, former salt ponds continue to be filled artificially by pumping favouring opportunities for waterfowl. This has often been combined with the creation of artificial islets to provide nesting ground for bird colonies protected from terrestrial predators.

Flux closures and source term models for shallow water models with depth-dependent integral porosity

Thu, 27 Sep 2018 11:06:38

de Guinot, Vincent, Carole Delenne, Antoine Rousseau, Olivier Boutron
In Advances in Water Resources, 122 (December, 2018), 390-400
En ligne : www.sciencedirect.com[...]

A two-dimensional shallow water model with depth-dependent porosity is presented. The purpose is the coarse grid simulation of shallow flows over complex topographies and geometries. Two flux closures are examined: the Integral Porosity (IP) and Dual Integral Porosity (DIP) closures. Energy losses are described using a subgrid scale model that accounts for bottom and wall friction, transient momentum dissipation and energy losses induced by obstacle submersion. A complete wave propagation property analysis is provided for the IP and DIP closures, yielding more accurate numerical stability constraints than published previously. Five computational examples are presented, including transients in compound and meandering channels, urban dambreak problems with building submersion and runoff over variable microtopography. The ability of the model to deal with subgrid-scale features is confirmed. The DIP flux is shown to be superior to the IP closure. The transient dissipation term is essential in reproducing the effect of obstacles and microtopography. Distinguishing between the building wall- and building roof-induced friction is seen to be essential. The model is validated successfully against a scale model experimental dataset for the submersion of a coastal urban area by a tsunami wave.

Integrative science to achieve long-term impact in conservation

Thu, 22 Nov 2018 10:23:32

de Lisa Ernoul, Raphael Mathevet, Angela Wardell-Johnson, Alain Sandoz, Loic Willm, Olivier Boutron
In Frontiers in Ecology and Evolution, 6 (2018)
En ligne : www.frontiersin.org[...]

Participatory mapping: Exploring landscape values associated with an iconic species

Fri, 4 May 2018 11:12:57

de Lisa Ernoul, Angela Wardell-Johnson, Loic Willm, Arnaud Béchet, Olivier Boutron, Raphael Mathevet, Stephan Arnassant, Alain Sandoz
In Applied Geography, 95 (June 2018), 71-78
En ligne : www.sciencedirect.com[...]

Participatory mapping provides a way to collate a wide range of landscape values providing a visual representation to inform conservation planning. We tested the use of an iconic species, the Greater Flamingo, as a lens for participatory mapping to render explicit the socio-cultural values attributed in a landscape. Spatial information on six landscape values in a biodiversity hotspot, the Camargue Biosphere Reserve (southern France) was collected from 113 participants through surveys, interviews and workshops. This data was geo-located through a SoftGIS methodology to map and quantify the overlap of bivariate hotspots identifying value concurrence. The most frequent values recorded through total number of polygons and surface areas were wilderness and recreation. The least frequently mapped values were economic loss and biodiversity. There was frequent concurrence between biodiversity and aesthetic values especially in wetlands (lagoons, salt flats and sea). There was also frequent concurrence between biodiversity and recreational values with more overlap in sites with easy access (along roads and public areas). Our results show that using an iconic species is an effective way to render explicit spatial variations in the values attributed to a landscape and to identify concurrence of values, thus enabling integration of multiple landscape values in conservation planning.

Modeling the spread of avian influenza viruses in aquatic reservoirs: A novel hydrodynamic approach applied to the Rhône delta (southern France)

Fri, 21 Apr 2017 11:54:11

de Marion Vittecoq, Hermann Gauduin, Thibault Oudart, Olivier Bertrand, Benjamin Roche, Matthieu Guillemain, Olivier Boutron
In Science of The Total Environment, 595 (octobre 1, 2017), 787-800
En ligne : www.sciencedirect.com[...]

Wild aquatic birds represent a natural reservoir of avian influenza viruses (AIV) that can be spread to poultry. AIV epizootics were associated with huge economic impacts during the last decades and are still of major concern. Within aquatic bird populations AIV are transmitted either by direct contact or through the ingestion of water that has been contaminated by infected individuals. This second route involving environmental transmission is of utmost importance in AIV dynamics, yet it has received far less attention than direct bird-to-bird contamination. Our objective was to combine a hydrodynamic model with data on mallard abundance and AIV infection rate within the population, so as to characterize virus dissemination within a complex wetland network. We chose the Vaccarès hydrosystem as a wetland model since it represents a large part of the Camargue region, which is a major wintering site for a large diversity of aquatic birds including AIV hosts. We aimed to identify the environmental parameters that drive AIV dynamics within this system and the spatio-temporal pattern of dispersion and persistence of viruses. Our results show that in a complex hydrosystem we can expect a great heterogeneity in AIV risk among wetlands. Our simulations underline how a simple “homogeneous box” approach could in the case of deltaic ecosystems minimize the expected risk by diluting it in the whole system. Moreover, such undermining of the risk perception could affect the predictions relative to risk duration. We present a new approach to identify hotspots of virus concentrations within deltaic areas that could take advantage of the duck count data, AIV surveys and hydrodynamic models that may already be available in several major duck wintering areas comprised of complex hydrosystems, such as the large European deltas. Our method could be of particular interest to optimize surveillance strategies in the current context of highly pathogenic AIV diffusion within wild bird populations. / Les auteurs ont modélisé le devenir des virus des grippes aviaires dans l’hydrosystème Vaccarès selon différents scénarios.Ils ont couplé les données hydrologiques du système avec celles dont nous disposons sur la présence des canards hôtes des virus Influenza A, agents des grippes aviaires, sur leur taux d’infection par ces virus et sur la persistance dans l’eau de ces derniers. Ils ont ensuite étudié comment se répartissaient les virus dans les différentes parties de l’hydrosystème Vaccarès en fonction de leur lieu et de leur date d’arrivée.
Il s’agit d’une première étape dans le développement d’un outil de modélisation des dynamiques des VIA dans l’eau en Camargue qui pourra à terme contribuer à optimiser la surveillance et à guider les prises de décision en cas de crise.

An Unstructured Numerical Model to Study Wind-Driven Circulation Patterns in a Managed Coastal Mediterranean Wetland: The Vaccarès Lagoon System

Tue, 3 May 2016 17:36:51

de Olivier Boutron, Olivier Bertrand, Annie Fiandrino, Patrick Höhener, Alain Sandoz, Yves Chérain, Eric Coulet, Philippe Chauvelon
In Water, 7(11) (October 2016), 5986-6016
En ligne : www.mdpi.com[...]

The spatiotemporal structure of wind-driven circulation patterns and associated water exchanges can drive important bio-hydrodynamic interactions in shallow lagoons. The Vaccarès lagoon system is a complex shallow hydrosystem located in the central part of the Rhône Delta (France). It is internationally recognized as part of a biosphere reserve within the framework of UNESCO’s Man and Biosphere Programme, and as a RAMSAR site. Due to its frequent occurrence in this area, and considering the shallowness of the Vaccarès lagoon system, wind is assumed to play a major role in the hydrodynamic and biological processes. In this study, a hydrodynamic model was developed to investigate the structure of wind-driven circulations in the Vaccarès lagoon system, to provide insights into their role in transport and water exchange processes. The implementation and assessment (calibration and validation) of the model is presented first. Simulations were then performed for two typical steady wind conditions and for one measured unsteady wind event. The results illustrate the influence of the complex geometry of the Vaccarès lagoon system on the wind-driven circulations, and the differences observed between the different sub-lagoons in this system. The differences in wind-induced water exchanges between these sub-lagoons are also discussed.

Etude de l’écologie de Lestes macrostigma et restauration de son habitat

Mon, 29 Aug 2016 15:46:56

de Philippe Lambret, Olivier Boutron, Gregoire Massez
In Courrier de la Nature (Le), 296 (n° spécial), 66-69