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

Rose Rodier, Olivier Boutron, Arnaud Béchet, Olivier Therond

► To cite this version:

Rose Rodier, Olivier Boutron, Arnaud Béchet, Olivier Therond. Interdependencies among hydro-saline dynamics, economic activities, ecological processes, and biodiversity in a deltaic social-ecological system: insights from the Rhône delta (southern France). Ecology and Society, 2025, 30 (3), pp. Article 11. 10.5751/es-16122-300311. hal-05235875

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Research

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

Rose Rodier<fnref n="1" />,², Olivier Boutron<fnref n="1" />, Arnaud Béchet<fnref n="1" /> and Olivier Therond²

**ABSTRACT.** 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.

**Key Words:** biodiversity; deltaic social-ecological system; economic activity; hydro saline dynamic; integrated assessment and modeling

## INTRODUCTION

River deltas are one of the most resource-rich and dynamic ecosystems in the world and thus provide diversified bundles of ecosystem services (ES; Millennium Ecosystem Assessment 2005). These characteristics make deltas attractive to human activities, with nearly 500 million people inhabiting the world's 40 largest deltas (Arto et al. 2019). However, these regions are vulnerable to global changes (e.g., climate change, rising energy prices, agroecological transition), especially due to their low elevation, proximity to the sea, and decreasing sediment loads in rivers; consequently, deltas are sensitive to sea level rise, subsidence, coastal erosion, and river and marine flooding (Milliman et al. 1989, Ericson et al. 2006, De Souza et al. 2015, Dang et al. 2018, Arto et al. 2019, Eslami et al. 2021). Changes in precipitation and temperature influence their hydro-saline dynamics, which can influence ecological dynamics and human activities such as agriculture or fishing (Herbert et al. 2015). In turn, changes in human activities, especially agriculture or water management, can influence the biodiversity and ES of deltas (Syvitski 2008, Syvitski et al. 2009).

Due to the complex relationships between ecological processes and human activities, deltas have been conceptualized and studied as social-ecological systems (SES; McGinnis and Ostrom 2014). For example, studies of deltas have investigated human-environment interactions related to hydraulic engineering (van Staveren and van Tatenhove 2016), the resilience of delta SESs to human activities and the role of science and governance (Norgaard et al. 2009), crisis prevention, and adaptation to climate change (Garschagen 2010), and the influence of urbanization and strategies to address physical processes that

threaten system equilibrium (Redeker and Kantoush 2014). However, these studies focused on specific social-ecological issues without considering interactions, feedback loops, and side effects within and between networks of human activities and biodiversity that influence the current and future sustainability and resilience of deltas. For the environmental dimension, most studies focused on provisioning ES (e.g., shrimp farming, fishing; Hossain et al. 2020), while ignoring regulating or cultural services and the intrinsic and heritage value of biodiversity. In this context, developing integrated models to represent and study these SESs seems appropriate to describe the interactions, feedback loops, and side effects related to human activities, biodiversity, and ES (Fulton et al. 2015, Hamilton et al. 2015, Mijic et al. 2024).

The Rhône River delta (southern France) is a Mediterranean major agricultural area that produces large amounts of cereals. In this area, farming activities and biodiversity are closely connected (Mathevet 2004), with a mosaic of natural habitats (ca. 68% of the area consists of lagoons, marshes, salt steppes, meadows, and woodlands) and agricultural habitats (ca. 25% of the area consists of cereal crops, vineyards, market gardening, and extensive horse and bull farms). The main crop rotations are based on rice (Mouret 1988, Chataigner and Mouret 1997, Mouret and Leclerc 2018), which influences freshwater inflow into the delta through irrigation from the Rhône (20–22,000 m³ per ha of rice; Heurteaux 1996). The diversity of natural and agricultural habitats, spatially arranged along strong hydro-saline gradients, makes the Rhône delta a biodiversity hotspot in France, in both the number of species and their heritage value (Galewski and Devictor 2016).

<footnote n="1">¹Tour du Valat, Research Institute for the Conservation of Mediterranean Wetlands, France, ²LAE, Université de Lorraine, INRAE, France</footnote>
Recently, new external drivers have intensified in the region, especially those related to climate change (PECHAC 2022). In particular, increasing salinization of soils and the central coastal lagoon, in conjunction with larger water deficits, are poised to increase social conflicts related to water management (PECHAC 2022).

For several decades, complex issues related to hydro-saline dynamics have resulted in major conflicts over water management in the delta, which the current system of water governance is unable to resolve (Dervieux 2005, Jalbert 2023). Due to the increase in new and challenging issues related to adaptations to global changes, decision makers have called for more integrated approaches to SES to design sustainable management strategies (Cinotti et al. 2023).

Integrated assessment and modeling (IAM) is one way to integrate and make understandable diverse knowledge, data, methods, and perspectives in a holistic framework to address complex SES (Hamilton et al. 2015). IAM is based on the development of a modeling platform to explore interactions and feedback among social, economic, and ecological entities of a system. IAM has been developed for and applied to several regions and has been used widely at the interface between climate science and policy (van Beek et al. 2020), such as for the Rhine river delta in the Netherlands, for which it enabled a political analysis of water-management issues (Haasnoot et al. 2012). By drawing on transdisciplinary analyses, IAM can overcome the limits of disciplinary fields and focused studies.

Regarding the Rhône delta, a number of modeling tools have been developed in previous studies. For example, hydrodynamic and hydrological models have been used to better understand the management of its lagoons (Boutron et al. 2015, 2011, Loubet 2012), to predict dynamics of its reedbeds and waterbirds in response to water management (Lefebvre et al. 2018), and to predict the risk of coastal flooding (Paris et al. 2017). Agent-based and cognitive representations have focused on different entities of the delta: water management (Espinasse and Franchesquin 2005); agricultural systems (Delmotte et al. 2013); interactions among duck populations, farm decisions, and leasing of hunting rights (Mathevet et al. 2003a); as well as the use of reedbeds (Mathevet et al. 2003b). In addition, Niang et al. (2016) and Mallet et al. (2022a and b) developed models to explore relationships among agroecological infrastructure, farming practices, and farmland biodiversity. These models considered a narrow range of social and ecological entities and processes, and only a few considered the main human activities and biodiversity issues in the Rhône delta (Niang et al. 2016).

Here, we integrated generic and local knowledge into a conceptual integrated model of the SES of the Ile de Camargue, the central part of the Rhône delta. This conceptual representation aimed at overcoming the limits of previous focalized studies by providing an integrated representation of the main human activities in the Ile de Camargue and their relationships with biodiversity and ecological processes. The resulting conceptual representation takes the shape of entity-oriented interaction diagrams corresponding to non-equivalent views about the set of relevant entities and processes to be considered to describe the SES. We used this conceptual modeling approach to identify and highlight the main causal chains, feedback loops, side effects, and trade-offs among social and ecological subsystems that need to be considered for sustainable management

of this SES. This integrated representation was intended to support the development of an IAM platform for local stakeholders to be used to explore the effect of management strategies on sustainability and resilience of the Ile de Camargue SES in the context of climatic and internal and external socioeconomic drivers.

## METHODS

### Study area: the Ile de Camargue

The Ile de Camargue lies in the center of the Rhône delta between the two arms of the Rhône River (i.e., Petit and Grand) and covers nearly 800 km² (Fig. 1). To the north, south-west, and south-east lie the city of Arles (ca. 50,000 inhabitants) and the towns of Saintes-Marie-de-la-Mer (ca. 1900 inhabitants) and Salin-de-Giraud (ca. 1200 inhabitants), respectively. The delta's elevation ranges from 3 m below to 4 m above sea level, and much of the delta lies below mean sea level. The delta has a Mediterranean climate and is home to a wide range of biodiversity and human activities (Appendix 1).

<figure><img src="image_3.png" /><figcaption>Fig. 1. Map of the Ile de Camargue, Rhône delta, France.</figcaption></figure>

### Conceptual modeling approach and model development

We used a stepwise method to integrate scientific and local stakeholder knowledge into the conceptual model. First, we used the ARDI (i.e., Actors, Resources, Dynamics, and Interactions) method (Etienne 2009, Etienne et al. 2011) to identify the main stakeholders, their management entities, the resources used, and the main processes that influence these resources. This step led to the development of a conceptual model of interactions among human activities, resources, and governance systems (Etienne et al. 2011). Even if this initial representation remained coarse and had a relatively high degree of ambiguity (Sibertin-Blanc et al. 2019), we used it for a first identification of the main actors, resources, and processes of the SES and the relationships between actors and resources.

Second, to develop a formal representation with finer detail and less ambiguity, we used the SES modeling method of Sibertin-
Blanc et al. (2019), which provides a formal graphical grammar to develop entity-oriented models that describe the structure (i.e., entities and their relationships) and related social and ecological processes. Actors (i.e., agents with autonomy) and material or cognitive resources (i.e., passive objects) are entities of the system. Processes are events that are likely to happen and change the state of entities or the relationships between them. Processes are classified as human activities, ecological processes, or socioeconomic processes.

To ensure the traceability, ease of development, and reading of the representations, we developed four complementary entity-oriented models, each of which addressed one main issue in the SES: i) governance of water resources, ii) agriculture, iii) bird, and iv) fish communities. We chose these two communities because they comprise the most important taxa in the delta and are considered good ecological and socioeconomic indicators of habitat dynamics in the Camargue (Bouchard et al. 2022b, Galewski and Devictor 2016), with several bird and fish species receiving specific attention due to conservation concerns (e.g., Greater Flamingo, European eel). The Ramsar report and the IUCN Red List identified eight threatened fish species in the Camargue, including the European eel.

These different entity-oriented models provide non-equivalent points of view to be used in parallel in order to grasp an accessible integrated representation of the SES and associated sustainability issues. A final diagram was developed to synthesize and highlight the relationships between the four submodels, using common entities across submodels to connect them. To do so we identified relationships listed in Table 1 which involved entities common to several submodels. We then provide a verbal description of the links between submodels emerging from this assessment.

## Data collection

Developing an integrated conceptual model of an SES requires collecting heterogeneous knowledge (Sibertin-Blanc et al. 2019). We first collected information available in the scientific literature, technical reports, and management plans of environmental organizations. We also attended stakeholder meetings related to water management, creation of an artificial wetland to purify water, and reorganization of hydraulic networks.

In addition, we interviewed stakeholders from i) SMGAS, an organization that brings together the associations in charge of irrigating and draining the Ile de Camargue; ii) Tour du Valat, a research institute for the conservation of Mediterranean wetlands based in the Camargue, with specific expertise in biodiversity conservation, wetland dynamics, and agricultural ecosystems; iii) the French Rice Centre, an organization that brings together individuals (including farmers) and legal entities who help develop, improve, and promote rice in the Ile de Camargue; iv) INRAE for the integrated assessment and modeling expertise. These four organizations represent a wide range of expertise, which provided a good initial representation of the Ile de Camargue. Based on the interviews and information collected, we developed an initial version of the four entity-oriented diagrams from November 2022 to June 2023.

## Validation of the diagrams

A first version of each entity-oriented diagrams was presented for strengthening and validation to local stakeholders and experts with

transversal expertise in the themes covered by the diagrams. We used the snowball sampling method, in which the first stakeholders/ experts connected us to other, which enabled us to improve understanding of the system iteratively. It led us to review the diagrams during five interviews (1-2 hours each) from July-September 2023. The interviews were organized around a set of predetermined open-ended questions to facilitate discussion. During the interview, stakeholders and experts were asked to assess, correct, and improve the initial diagrams by discussing which entities and processes should be modified or added. These interviews enabled to clarify the level of precision and number of entities needed to describe the SES structure and functioning.

In addition, we interviewed researchers from i) Tour du Valat, with specific expertise in biodiversity conservation and on the diagram of bird and fish communities; ii) French Office for Biodiversity (OFB) on bird community; iii) National Centre for Scientific Research (CNRS) on water governance, agriculture, bird, and fish communities.

In January 2023, we also organized a 2-hour workshop with local stakeholders each from SMGAS, Tour du Valat, French Rice Center, Vaccarès resident associations, Camargue National Reserve, Regional Natural Park, Center for International Cooperation in Agricultural Research for Development (CIRAD), Chamber of Agriculture, OFB, and Arvalis (an agricultural technical institute). During the workshop, we presented the objectives and challenges of the modeling approach and the four diagrams. Participants were divided into four groups, and a member of the research team facilitated the workshop. Participants were encouraged to express themselves and write down on sticky notes their thoughts about the main water-management, biodiversity, and agriculture issues in the region. This process identified gaps in the representation of processes and stakeholders in the diagrams. We then reported on the discussions (Appendix 7) and integrated the new issues raised by the workshop participants into the diagrams. This step enabled us to more precisely identify the main processes between the four diagrams and the relationships at the SES level.

## Identification of relationships

Based on interviews and the workshop held with the various experts, researchers and stakeholders (refer to previous section), we identified the key relationships in the conceptual model. For each relationship, tagged with a dedicated ID, we described the nature and number of entities involved in the relationship (n-ary, N being the number of entities in the relationship, rXX, XX being the ID's number). We distinguished 5 types of relationships. As commonly proposed in SES analysis framework (Binder et al. 2013, Kelly et al. 2013, Rodriguez-Gonzalez et al. 2020, Lu et al. 2021, Mijic et al. 2024) we identified:

1. interaction: when two entities influence each other (hereafter coded as ↔, binary)

2. feedback loop: a causal chain in which entity A influences a chain of entities, which then influences A to amplify (positive feedback loop; +→←, n-ary) or dampen (negative feedback loop; →←←, n-ary) the process

3. trade-off: antagonism between two competing processes, i.e., an increase in one decreases the other, which may require a social compromise (↓↑, n-ary).
<table><caption>**Table 1.** ID, type of relationship, number of entities involved, and entities involved that have been identified across the Ile de Camargue conceptual model.</caption><thead><tr><th>ID</th><th>Type</th><th>No</th><th>Entities</th></tr></thead><tbody><tr><td>r1</td><td>↔</td><td>2</td><td>Vaccarès lagoon system / Drainage canal</td></tr><tr><td>r2</td><td>↔</td><td>2</td><td>Vaccarès lagoon system / Former Saltworks</td></tr><tr><td>r3</td><td>→→</td><td>4</td><td>Climate / Sea / Vaccarès / Pertuis de la Comtesse</td></tr><tr><td>r4</td><td>→→</td><td>4</td><td>Farmer / Crop / Irrigable agricultural soil / Surface aquifer</td></tr><tr><td>r5</td><td>→→</td><td>3</td><td>Climate / Irrigation canal / Irrigable agricultural soil</td></tr><tr><td>r6</td><td>→<sup>2</sup></td><td>3</td><td>Surface aquifer / Irrigable agricultural soil / Marsh</td></tr><tr><td>r7</td><td>→→</td><td>4</td><td>Irrigable agricultural soil / Marsh / Surface aquifer / Vaccarès</td></tr><tr><td>r8</td><td>→→</td><td>7</td><td>Farming practice / Farmer / Marsh management strategy / Marsh manager / Irrigation canal / Drainage canal / Marsh</td></tr><tr><td>r9</td><td>→→</td><td>7</td><td>Climate / Rhone / Energy cost / Canal owner / Irrigation pumping station / Pumping station for drainage / Marsh</td></tr><tr><td>r10</td><td>↓↑</td><td>5</td><td>Climate / Vaccarès / Data on salinity, water level and fish / WEC / Valve: Pertuis de la Fourcade</td></tr><tr><td>r11</td><td>↓↑</td><td>3</td><td>Data on salinity, water level and fish / Vaccarès / WEC</td></tr><tr><td>r12</td><td>↓↑</td><td>4</td><td>Climate / Vaccarès / Valve: Pertuis de la Fourcade / Valve: Tampan pond</td></tr><tr><td>r13</td><td>→<sup>2</sup></td><td>4</td><td>Climate / Vaccarès / Valve: Pertuis de la Fourcade / Valve: Tampan pond</td></tr><tr><td>r14</td><td>→→</td><td>4</td><td>Marsh management strategy / Marsh manager / Marsh / Canal owner / Irrigation canal</td></tr><tr><td>r15</td><td>+→←</td><td>6</td><td>Crop management strategy / Farmer / Crop / Irrigation canal / Soil / Water resource</td></tr><tr><td>r16</td><td>→<sup>2</sup></td><td>5</td><td>Crop / Soil / Water resource / Irrigable agricultural field / Irrigation canal</td></tr><tr><td>r17</td><td>→<sup>2</sup></td><td>6</td><td>Pesticide / Irrigable agricultural field / Soil / Crop / Drainage canal / Water resource</td></tr><tr><td>r18</td><td>→<sup>2</sup></td><td>4</td><td>Herd management strategy / Pesticide / Soil / Crop</td></tr><tr><td>r19</td><td>→<sup>2</sup></td><td>5</td><td>Water resource / Pesticide / Cap premium / Crop / Bird</td></tr><tr><td>r20</td><td>→→</td><td>5</td><td>Market for agricultural inputs and products / Farmer / Livestock / Crop management strategy / Crop</td></tr><tr><td>r21</td><td>→→</td><td>21</td><td>Ile de Camargue bird community / Valve opening strategy / Management strategy for hunting / Management strategy for marshes / Crop rotation strategy / Valve, Rousty canal / Valve, Pertuis de la Fourcade / Valve, Tampan pond / Irrigation canal / Structure for impounding water / Farmer / WEC / Camargue National Reserve / Former Saltworks manager / Saltworks manager / Hunting marsh manager / Environmental protection structure / Lagoon / Marsh / Former saltworks / Agricultural plot</td></tr><tr><td>r22</td><td>→→</td><td>9</td><td>Valve opening strategy / Data on salinity, water levels and fish / WEC / Camargue National Reserve / Valve, Rousty canal / Valve, Pertuis de la Fourcade / Valve, Tampan pond / Lagoon / Ile de Camargue Bird community</td></tr><tr><td>r23</td><td>→→</td><td>4</td><td>Management strategy for hunting marshes / Structure for impounding water / Marsh / Ile de Camargue Bird community</td></tr><tr><td>r24</td><td>↔</td><td>2</td><td>Farmer / Hunter</td></tr><tr><td>r25</td><td>→→</td><td>7</td><td>Hedgerow management strategy / Exemption from the ban on disturbing protected species, frightening away / Farmer / Hedgerow / Agricultural plot / Crop / Ile de Camargue bird community</td></tr><tr><td>r26</td><td>→→</td><td>6</td><td>Crop rotation strategy / Farmer / Irrigation canal / Agricultural plot / Crop / Ile de Camargue bird community</td></tr><tr><td>r27</td><td>→→</td><td>4</td><td>Characteristic of other economic activities / Marsh / Agricultural plot / Ile de Camargue bird community</td></tr><tr><td>r28</td><td>→→←</td><td>4</td><td>Farmer / Pesticide / Agricultural plot / Ile de Camargue bird community</td></tr><tr><td>r29</td><td>↓↑</td><td>4</td><td>Farmer / Ile de Camargue bird community / Hunter / Tourist</td></tr><tr><td>r30</td><td>↓↑</td><td>4</td><td>Pesticide / Crop rotation strategy / Lagoon / Marsh</td></tr><tr><td>r31</td><td>→→</td><td>7</td><td>Pesticide / Marsh / Lagoon / Ile de Camargue bird community / Crop rotation strategy / Crop</td></tr><tr><td>r32</td><td>→<sup>2</sup></td><td>4</td><td>Marsh / Lagoon / Agricultural plot / Ile de Camargue bird community</td></tr><tr><td>r33</td><td>→→</td><td>12</td><td>Data on salinity, water level and fish / Valve opening strategy / WEC / Camargue National Reserve / Former saltworks manager / Valve, Pertuis de la Fourcade / Valve Rousty canal / Valve Tampan pond / Vaccarès system fish / Former Saltworks fish / Beaucud pond fish / Sea fish</td></tr><tr><td>r34</td><td>→<sup>2</sup></td><td>5</td><td>Professional fisher / Valve opening strategy / WEC / Data on salinity, water level and fish / Vaccarès</td></tr><tr><td>r35</td><td>→→</td><td>4</td><td>Former Saltworks manager / Former saltwork fish community / Beaucud pond fish / Sea fish</td></tr></tbody></table>

To go further we also decided to highlight (Qiu et al. 2018):

1. causal chain: a succession of impacts between several entities (→→, n-ary)

2. side effect: when implementing actions to meet specific objectives has an unexpected negative or positive impact on other entities (→<sup>2</sup>, n-ary).

## RESULTS

Due to the continuous diking of the Ile de Camargue (sea-dike in the south, and dikes along both arms of the Rhône; Fig. 2a), all surface-water flows between the Rhône, the sea, and the Ile de Camargue are managed, except during rare large floods that breach the dikes (e.g., 1993–1994).

### Water-flow processes

#### Water flows to and from the Rhône River

Except for a few gravity-fed flows (Fig. 2a), most water flows between the Rhône and the Ile de Camargue are pumped (No.1)

and e2 in Fig. 3) to fill irrigation canals (No. e3) and empty drainage canals (No. e4; Appendix 2a). Water drained from agricultural land may contain pesticides and nitrogen leached from crop fields. In 2009, 90% of the pesticide active ingredients found in the Camargue’s lagoon and canal water were due to rice cultivation (Comoretto et al. 2007). Water analyses showed low pesticide contamination in irrigation canals, high contamination in drainage canals, and chronic contamination of marshes and lagoons by drainage water (SNPN 2020). Thus, local agricultural activities strongly influence water, pesticide, nitrogen, and salt flows into the Vaccarès Lagoon System through the drainage canals (No. e10 and e11 in Fig. 3). In addition, management of the Vaccarès hydraulic structures (No. e11, e12 and e13 in Fig. 3) can lead to high water levels which, together with the wind, causes salt water from the Vaccarès to migrate into the drainage canals, impacting their salinity (↔, binary, r1). Some outlets of the drainage (No. e17) and irrigation canals (No. e18) lie at the “former saltworks” (No. e14), another system of lagoons (De Wit et al. 2019). Water inflows depend on the management of each control sluice gate of these outlets.
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Maps of the Ile de Camargue, with a focus on a) infrastructure for water management and b) governance of the catchment and lagoon systems.</figcaption></figure>

### Connections to the sea

As a dike separates the Vaccarès Lagoon System (No. e10) from the Mediterranean Sea (Fig. 2a), the two can exchange water directly only via the Impériaux lagoon (Fig. 2b), through hydraulic structures at La Fourcade (No. e12) and the Pertuis de la Comtesse ("Valve Tampan pond", No. e13). The former saltworks consist of several lagoons, most of which are connected to each other and to the Vaccarès Lagoon System by hydraulic structures (Appendix 2b). As the former saltworks contain several natural connections to the sea (Figs. 2b and 3), under certain opening conditions of the internal sluices gates of the former saltworks and of the Valves of the Tampan pond (No. e13), the Vaccarès Lagoon System can exchange indirectly water with the sea, which involves interactions between them (↔, binary, r2; Boutron et al. 2021).

When the sea level is high, such as during a storm, the Vaccarès Lagoon System can become directly connected to the sea if the Pertuis de la Comtesse (No. e12 Fig. 3) is opened, which influence the total salt mass of the lagoon system (→→, 4-nary, r3), which will drive its salinity.

### Groundwater flows

The hydro-saline dynamics are influenced by whether the fields (No. e5) are flooded to grow rice (No. e6), as flooding a field limits saline upwelling in it by keeping the salt below the rice's root zone (→→, 4-nary, r4; Appendix 2c). This flooding counteracts the Mediterranean precipitation regime (i.e., high in winter and low

in summer), as it provides large volumes of water in summer (→→, ternary, r5; Torres-Rondon 2013). However, flooding can increase the salinity of surrounding non-submerged fields (→², ternary, r6; Fig. 3), as the higher water pressure in the rice fields can redirect the groundwater and its associated salt toward them (Torres-Rondon 2013). The same process occurs when marshes (No. e8) are flooded, but when water level is too low, salinity increases. When a high surface area around the Vaccarès Lagoon System (No. e10) is flooded, high water pressure blocks lateral inflow of groundwater from the Vaccarès lagoon (brackish water) into the surrounding area, and can even reverse it (→→, 4-nary, r7).

### A complex structure and governance of water management

#### Irrigation and drainage

The canals and pumping stations are managed and maintained by private farmers (e.g., landowners near the banks of the Rhône) or farmer associations (e.g., land further inland; No. e24 in Fig. 3., Appendix 3a; Mathevet 2004). The ability to pump water is based on the type of crop, the location of the salt wedge in the Rhône, the price of irrigation water, and the cost of energy required to run the pumps (No. e26).

Management of the hydraulic infrastructures as well as farming practices have a major influence on water quality in natural habitats (→→, 7-nary, r8). Pumping is expensive due to the cost of energy (No. e26, Fig. 3) and pumping costs are higher in winter than in summer due to season-specific electricity prices. Little
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Entity-oriented interaction diagram of water governance, along with water, salt, and pesticide flows. Circled numbers refer to entities in the core text.</figcaption></figure>

water is pumped by canal owners (No. e24; e.g., hydraulic association or farmer) from the Rhône when water levels are high in winter, so that when precipitation is low in winter, water levels in the marshes are also low (→, 7-nary, r9).

### Coastal lagoons

Several environmental protection organizations and institutions are involved in managing the lagoons (Appendix 3b). The Water Executive Commission (WEC, No. e28, Fig. 3.) is an informal association of local stakeholders that coordinates and manages the valves of the Pertuis de la Fourcade (No. e12).

The WEC's management practices aim to keep the total mass of dissolved salt below a certain threshold. Water levels are managed to i) prevent high water levels to avoid flooding of surrounding areas, erosion of lagoon banks, and salinization of surrounding fields, as well as to facilitate agricultural drainage, and ii) prevent low water levels (along with high salinity) to promote fishing in the lagoons. Another objective is to maintain levels of water and salinity typical of Mediterranean wetlands, particularly in response to precipitation and evaporation, as desired by environmental and local authorities. These objectives may not be
met in certain years due to annual variability in precipitation and evaporation, which is common in the Mediterranean climate, as well as the shallow depths of the Vaccarès Lagoon System and the complexity of its hydro-saline functioning. This creates frequent tensions between stakeholders, which requires making compromises in the management of the hydraulic infrastructure (↓↑, 5-nary, r10). Arbitration is needed among the minimum water level that fishermen desire, the variations in water levels and salinity typical of a Mediterranean ecosystem that environmental authorities desire, and the maximum water level that local residents and farmers desire (↓↑, ternary, r11). Another compromise is between long-term and short-term objectives (↓↑, 4-nary, r12): promoting the inflow of seawater into the Vaccarès Lagoon System can decrease its salinity when evaporation is too high (i.e., salinity of the lagoons higher than that of the sea), but doing so over the long-term will increase the salt stock in the system (→², 4-nary, r13). Similar issues exist for the valves at the north of the Tampan pond (Fig. 2a and No. e13 in Fig.3), which are managed by the Camargue National Reserve (Appendix 3b).

### Ponds and marshes in the catchment areas

Marshes in the catchment areas are managed to favor species of interest for hunting or conservation and restauration project and receive water from the canals managed by farmers and farmer associations (→→, 4-nary, r14).

### The importance of agriculture

Rice cultivation is the main reason that large volumes of fresh water are pumped from the Rhône into the Camargue (Mouret 1988, Chataigner and Mouret 1997, Mouret and Leclerc 2018). In most areas, submerging rice fields (No. e6 Fig 3 and 4) decreases salinity enough for them to be cultivated (for other crops), as many fields experience increased salinity and require rice cultivation to maintain agricultural value (Mathevet 2004, Torres-Rondon 2013). Rice yields of conventional farms are influenced by a reduced set of authorized herbicides, which hampers weed management when rice is grown more than one year in a row. In organic farming, long and diversified rotations can mitigate detrimental effect of weed on yield, but the lack of higher-value markets for intermediate crops challenges the economic viability of this approach. Farmers must adapt their practices to the specific characteristics of their land, as some may not have transitioned completely to organic farming due to the salinity of the soil, which prevents long rotations with non-submerged crops. Longer rotations decrease water requirements, including water from irrigation, which in turn salinizes the fields. However, when the soil becomes saline, irrigation is needed to continue cultivating the field (+→←, 6-nary, r15). At lower elevations with highly hydromorphic or salinized soils, rice monoculture is the sole option to keep fields cultivated; consequently, organic rice can be produced only at higher elevations. Market gardening has developed mainly on higher land with lower salinity, which can withstand long periods of non-submerged crops without damage from increasing salinity (Migairou-Leprince 2021). Due to the large decrease in rice area (from 24,000 ha in 1994 to < 12,000 ha in 2021; CFR 2021), the salinity of the aquifer is predicted to increase exponentially if no major irrigation occurs in areas near the Vaccarès Lagoon System. This increase could render much of the land unsuitable for crops (→², 5-nary, r16; Torres-Rondon 2013).

Nitrogen and pesticides (No. e19) applied to rice fields can leach and spread. To limit the spread of pesticides, farmers wait 3–5 days after spraying them before submerging a field. Water drained from the rice fields into canals (No. e4) can transport pesticides into the Rhône or the lagoons. As these natural habitats are biodiversity hotspots, the impact of pesticides on biodiversity conservation can place economic activities related to certain species, such as hunting, fishing, and tourism, at risk. For example, pesticides are suspected to have caused the collapse of the seagrass (Zostera noltei) beds in the Vaccarès lagoon (→², 6-nary, r17; Espel et al. 2019). The current ban on certain herbicides makes it more difficult to grow rice several years in a row. However, non-submerged crops cannot grow on hydromorphic soils due to the salinity, and without technical solutions, fields that are too saline may be abandoned (→², 4-nary, r18).

One side effect comes from the decrease in rice subsidies, with an expectation of an improvement in the ecological state of the Vaccarès Lagoon System (outlet of drainage waters) together with an increased carrying capacity for water birds and fish. Yet, this decision increased open-field market gardening, which as a habitat, supports a lower carrying capacity of waterbirds than rice fields and uses larger amounts of pesticides, which in turn are drained into the Vaccarès Lagoon System (→², 5-nary, r19). Livestock farming (i.e., cattle, sheep, and horses, No. e7 in Fig. 4) are part of Camargue's cultural identity and contribute to its appeal to tourists (Blondel et al. 2013; Appendix 4a). Mixed farmers, livestock farmers, and crop farmers interact frequently, especially regarding fodder crops to feed the herds (Balma 2023). Selling fodder makes it more profitable to diversify rotations and enables farmers to feed their animals locally (→→, 5-nary, r20).

### Interconnected economic activities and impacts on biodiversity

#### Birds

Waterbirds are emblematic species of the Ile de Camargue and are a major cultural and tourist attraction (Appendix 5a, Fig. 5). Waterbirds staging and breeding relies directly on flooded areas, salinity and quality of water. Water management has, therefore, a large influence on the presence and abundance of certain species, depending on the quality and quantity of water, which influences food availability (→→, 21-nary, r21).

Water-management decisions of the WEC (No. e28 in Fig. 5) and the Camargue National Reserve influence water levels and salinity in the Vaccarès Lagoon System due to changes in connections with the drainage channels, the sea, and the former saltworks, via the sluices gates No. e11, e12 and e13. This ultimately influence habitat conditions for waterbirds (No. e22; →→, 9-nary, r22).

Four types of hunting (Appendix 5a; i.e., communal, private, commercial, and business) result in differing hunting density across the region, with the highest density for communal hunting (Mathevet 2004). Managers of the hunting marshes must adapt the periods of flooding of the marshes to favor species of interest during the hunting season (No. e23). Flooding decreases the dryness and salinity of the soil that increased during the summer, which promotes the growth of seagrass beds that ducks use for foraging (→→, 4-nary, r23; Tamisier and Grillas 1994). Managers of hunting estates set up a fee system to authorize hunters to hunt on their property. Most of the marshes are filled via drainage canals, but some are filled via irrigation canals. Fertilizers and
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Entity-oriented interaction diagram of farming systems. Circled numbers refer to entities in the core text.</figcaption></figure>

pesticides in these canals have resulted in eutrophication of the marshes, less diverse seagrass beds, and the proliferation of certain invasive plant species (Vallecillo 2019). Due to the diversity of habitats and managers, marsh management varies across the Ile de Camargue, with certain marshes under strong hunting pressure, while others are managed as a protected area, particularly those belonging to environmental protection organizations. The strategies of local stakeholders depend on their economic activity. Some farmers who manage a marsh may grow more rice nearby to attract waterbirds for hunting or instead alternate fields between a marsh and rice, depending on the potential profit from rice cultivation and hunting. The agricultural activity of a hunting manager can thus influence marsh management choices and, conversely, the hunting activity of a farmer can influence crop rotations in these fields. (↔, binary, r24).

Birds can damage crops greatly. For example, from 2007–2009, Greater Flamingos damaged ca. 2.1% of the area of rice fields (Ernoul et al. 2014). Flamingos enter fields after the rice is sown in early May and remain until rice germinates in June (Mathevet et al. 2002). In winter, common cranes often enter fields of recently sown wheat. Birds can cause high economic losses locally, forcing farmers to resow all or some of the fields (Nilsson et al. 2016). Farmers use several strategies to decrease bird impacts, such as planting hedgerows as a visual barrier for waterbirds and to decrease flamingo incursions in fields (Tourenq et al. 2001; →→, 7-nary, r25). Hedgerows also provide an ecological corridor for species that live in agricultural areas. Bird-scaring practices are

deployed through exemptions to the regulation that prohibits the disturbance of protected species. Crop rotations also influence bird incursions, particularly through alternating the presence of rice fields (→→, 6-nary, r26). For wheat fields, farming practices and the availability of rice stubble provide alternate foraging areas and decrease the risk of crane incursion (Tour du Valat, unpublished data). Conversely, decreasing the number of natural or hunting marshes could encourage more waterfowl to visit agricultural habitats such as rice fields, which could increase yield losses (→→, 4-nary, r27). Extensive livestock farming maintains opens areas such as meadows, which constitute key habitats for some bird species.

Birds may also provide regulating ES to farmers. Flooding harvested fields in winter makes weed seeds available to waterbirds, which can decrease weed abundance (↔, 4-nary, r28). Before recent increases in energy costs, this practice was found to be economically viable, despite the cost of irrigation (Niang et al. 2016).

The presence of waterbirds, such as Greater Flamingos and common crane, influences ecotourism in the Camargue, which is a bird-watching hotspot. For some stakeholders, there is a trade-off between attracting certain bird species for tourism or hunting and the potential impact of these species on crop yields (↓↑, 4-nary, r29). Another major trade-off is the relationship among pesticide regulations, rice area, and natural habitat conditions (↓↑, 4-nary, r30). When the French government strengthened regulations to ban certain herbicides to improve water quality and
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** Entity-oriented diagram of interactions between bird dynamics and economic activities. Circled numbers refer to entities in the core text.</figcaption></figure>

bird habitats, the rice area decreased because without pesticides, rice cannot be grown as a monoculture (→, 7-nary, r31). This decreased the water available for marshes, which degraded habitat conditions by decreasing water levels and water area and, during dry spells, increasing saline upwelling, contrary to the initial objective (→², 4-nary, r32).

## Fish

The quality and quantity of water influence fish communities and seagrass (Zostera noltei) beds (Espel et al. 2019), which in turn influence these communities indirectly (→, 12-nary, r33; Fig. 6). Common lagoon species can tolerate fluctuations in salinity, while freshwater species prefer low salinity (Poizat et al. 2004). Hydraulic infrastructure plays an important role, especially as it connects environments, which may or may not provide ecological continuity. For example, marine species depend on connections to the sea, and opening or closing sluice gates can prevent them from moving and migrating (Poizat et al. 2004). Migratory fish also reproduce and migrate from the lagoons to the sea through these sluice gates (i.e., Pertuis de la Fourcade and Pertuis de la Comtesse). Thus, water management strongly influences the fish community of the Ile de Camargue (Crivelli et al. 2008, Bouchard et al. 2022a, 2022b). The sluice gates are opened according to certain criteria, especially water quality (i.e., salinity and agricultural pollutants), water levels (in the lagoons and the sea so direction and rate of flow), and the presence of fish (at the entrance of the structure). Fishing and the desire to encourage fish migration through improved connectivity can influence water management directly and thus indirectly the transport of salt into the area (→², 5-nary, r34; Appendix 5b).

The Beauduc lagoon, southern part of the former saltworks (Fig. 2b) is frequently connected to the sea, with similar fish communities (Appendix 5b). In the rest of the former saltworks, sluice gates are used to connect lagoons, which makes ecological continuity more complex, and opening or closing the sluice gates influences habitat conditions for fish and their potential movement (→, 4-nary, r35).

## Relationships at the whole SES scale

Beyond the highlighted entities, processes, and relationships for each of the four investigated themes (Figs. 3, 4, 5, and 6), we can highlight links between these themes (Fig. 7). Agriculture determines hydro-saline dynamics on agricultural land, natural habitats in the catchments, and downstream lagoon systems (Fig. 2a). The area of rice and submerged fields influences the salinity in agricultural and natural habitats, and the use of pesticides influences soil fertility, crop area, agricultural profitability, habitat conditions, as well as bird and fish communities (Fig. 7: B, F, and I). Conversely, the submerged fields are a secondary habitat for birds, which forage in the fields, and influences yields (Fig. 7: A). Water governance influences agricultural practices via water and pumping prices, decisions about restrictions, or implementing certain types of management (e.g., increasing/decreasing drainage water discharge into the Vaccarès Lagoon System, not pumping when salinity of the Rhône is high; Fig. 7: E).

Environmental protection organizations aim at promoting natural hydrological cycles and improving water quality to protect fish (Fig. 7: H). In addition, to promote waterbirds protection by improving the quality of their habitat and quantity of food, it is
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Entity-oriented interaction diagram of fish dynamics in interaction with economic activities. Circled numbers refer to entities in the core text.</figcaption></figure>

essential to improve water quality in the lagoons, marshes, and agricultural plots (Fig. 7: C). Water management in the lagoons and marshes directly influences habitat conditions for waterbirds (e.g., food; Fig. 7: D). A decrease in rice area decreases water levels in the lagoons, which generally implies an increase in salinity, which can cause problems for fish and could decrease connectivity between lagoons and thus weaken ecological corridors for fish (Fig. 7: I). Depending on the direction and rate of flow, opening sluice gates may not help fish reproduction and downstream migration (Fig. 7: G). Water level objectives for fishing may conflict with farmers' objectives for agricultural drainage and pesticides (Fig. 7: J).

## Synthesis of entities, processes and relationships

Based on the methodology of Sibertin-Blanc et al. (2019), we identified 101 entities in our SES, including 20 actors, 50 material resources, and 31 cognitive resources. We also identified 165 processes including 62 activities, 103 ecological processes, and 51 connections of actors to cognitive resources they consider. Furthermore, we highlighted 35 key relationships including 17 causal chains, 3 interactions, 2 feedback loops, 5 trade-offs, and 8 side effects (Table 1).

## DISCUSSION

The study integrated a large body of generic (literature) and local knowledge about the Ile de Camargue SES to develop a conceptual model that describes interdependencies among human activities, hydro-saline dynamics, ecological processes,

and biodiversity. Our resulting conceptual model provides a simplified representation of the SES in which selected entities and processes were validated and selected by a range of researchers, experts, and local stakeholders. This approach produced a robust and salient integrated representation of the complexity that stakeholders have to deal with. For example, 29 of the 35 relationships identified involve more than 3 entities, thus highlighting the complexity of this system. To our knowledge, this is the first time diverse disciplines and stakeholder expertise of this region were used to develop a formal conceptual model. This formal representation of the Ile de Camargue can provide stakeholders with an integrated view of the structure and functioning of this complex system, particularly related to social-ecological relationships. It could aid decision-making given the multiple interactions and thus help develop management strategies that increase the sustainability and resilience of the Ile de Camargue.

## Methodological issues

Our process of conceptual model development was based on a stepwise approach, first integrating coarsely a wide amount of heterogenous information (ARDI diagram) and then reducing model ambiguity and improving relevance throughout the process of formal modeling using the Sibertin-Blanc et al. (2019) conceptual approach. Compared to other conceptual modeling approaches, such as qualitative signed digraphs or fuzzy cognitive maps, our methodology describes relationships between entities but places less emphasis on the mathematical formalization of
<figure><img src="image_9.png" /><figcaption>**Fig. 7.** Main relationships between agriculture, water management, birds, fish, and related economic activities in the Ile de Camargue SES. Letters refer to interactions mentioned in the core text.</figcaption></figure>

relationships between variables (e.g., community, adjoint, or adjacency matrices) and the modeling of ecological community dynamics (Dambacher et al. 2003). However, compared to more qualitative cognitive maps, such as ARDI, it requires a much higher degree of formalization. This increased formalization allows it to be directly implemented in numerical models, notably agent-based models (Sibertin et al. 2019). Nevertheless, this objective of formalization can lead to more complex representations, which may be harder for stakeholders to interpret than more qualitative, less computer-oriented approaches.

The hypothesis of working with two taxa to represent biodiversity could be questioned, and other relationships with other taxa might have been highlighted. Yet, we believe that these two taxa are strategic for most stakeholders because of their socioeconomic importance in this biodiversity hotspot.

Finally, our conceptual representation does not hamper further refinement. Political Ecology theories could for instance deepen our approach by enriching the interactions and broadening the scope of our analysis with wider social, historical, and political perspectives. In particular : i) Common Property Theory, would allow to include the potential collective management of the water resource (Kerr 2007), ii) Gender Studies may allow to identify the influence of gender in decision-making in the area, for instance in the WEC as done on other systems with different political and economic contexts (Najjar et al. 2023, Padmaja et al. 2020), while iii) Critical Environmental History would anchor the model in a historical and contextualized

understanding of human-environment relations, taking into account inequalities and socio-ecological transformations (Biggs et al. 2009, Cole 2016). This would be particularly useful to complement the analysis of water, reed, and biodiversity issues with information on economic activities (Mathevet et al. 2015).

## Social-ecological relationships in the Rhône delta

Our study identified the main causal chains, interactions, feedback loops, trade-offs, and side effects of the Ile de Camargue SES thus providing new insights compared to those of existing disciplinary or issue-oriented studies of the Ile de Camargue. The modeling approach highlighted strong interactions between water management by farmers as a function of agricultural system dynamics (e.g., submerged or non-submerged crops, grasslands) and water management in natural habitats (e.g., lagoons, marshes). This is particularly due to the influence of farmers and irrigation/drainage associations on flows of freshwater into the region, which influences, especially through hydro-saline dynamics, the habitat conditions of waterbirds and fish, and thus other economic activities (i.e., hunting, fishing, protecting natural habitats, and tourism).

Our study highlighted several key side effects. Whether they are negative or positive depends on the stakeholder's value and objective through which they are analyzed. For example, the reduction of rice-growing areas leading to saline rises may be considered as negative by farmers or stakeholders associated with agriculture but may be considered as positive by others due to the possible transformation of these plots into more natural habitats (e.g., pastures or salt marshes).
Several of the identified trade-offs are related to water management in the Vaccarès Lagoon System, which results in social compromises between long- and short-term objectives and the quality and quantity of water that enters the system (i.e., water can contain either more pesticides or more salt). The conceptual model indicates that several causal chains are not considered when managing these trade-offs. The WEC focuses on managing the sluice gates of the Pertuis de la Fourcade based on lagoon water level, salinity, and salt mass, as well as sea level. These decisions thus do not consider i) water, pesticide, and salt exchanges among areas of the catchment due to management decisions made by farmers and irrigation/drainage associations or ii) water and salt exchanges with the former saltworks due to management decisions made by former saltwork managers who did not consider the water-management decisions made by the collective drainage association of the Japon (Fig. 2b), which has two canals that transport water and pesticides into the former saltworks. This calls into question the water-management associations that currently exist in the Camargue, especially the WEC, which manages the connection between the Vaccarès Lagoon System and the sea. In fact, the likely weakness of the WEC lies in the fact that it is not a forum for discussing the multiple water issues in the SES, which prevents it from considering at the right scale the multiple relationships among water, pesticide, and salt fluxes highlighted in this study. Such a forum, able to discuss the Integrated Management of the Camargue SES does not exist which appears as a key missing piece regarding governance in our case. Furthermore, there are many barriers to knowledge and data integration, and thus to integrated decision-making, such as commercial interests, privacy concerns, and general lack of trust among stakeholders (Meyer et al. 2020). For instance, fishing in the southern lagoons of the Vaccarès Lagoon System every year is a commercial stake with a significant influence on the decision-making of the WEC. The fishermen, members of the WEC, are calling for the management of the hydraulic structures to ensure fishing activity during the current year, even though this management presents a significant risk of salinization of the system in the medium term (Boutron 2020). Another example is the inadequate administrative and geographical criteria of Agri-environment schemes (AES) supporting the maintenance of hedges to reduce the risk of damage caused by Greater Flamingo incursions into agricultural fields, which leads to the solicitation by farmers of more lucrative AES for less integrated practices (Ernoul et al. 2014). Scepticism due to a lack of understanding is also a significant barrier to integrated decision-making in the Ile de Camargue, and has for instance been identified as hindering the ecological restoration of the former saltworks (Terrisse et al. 2025). Our study highlighted that several relationships related to the future increase of the salt wedge in the Rhône are not usually considered when discussing: i) medium- and long-term agricultural strategies; ii) projects to restore wetlands in the Ile de Camargue catchment, which depend on the quantity and salinity of water in agricultural canals; and iii) projects to develop hydraulic structures to provide more water from the Rhône by gravity to reduce the risks of salinization without the cost of pumping. Not considering these causal chains is a major problem, and could cause many of these projects to fail. In addition, there is currently a lack of trust between agricultural and environmental stakeholders of the Camargue due to historical conflicts and different priorities. Our approach offers a ready to use modeling tool to overcome this issue and develop an ecosystem-based

management strategy that will strike a good balance between socioeconomic development and ecosystem conservation (Frazão Santos et al. 2021).

Such a change will need a greater emphasis on the effectiveness of governance and institutions and their transformative change (Kelly et al. 2019, Stephenson et al. 2019). The assessment of the integrated management of the Gladstone Harbour system in Australia illustrates how a bottom up arrangement involving stakeholders sharing a common vision and consolidated by a memory of understanding provided a successful response to an urgent crise (Stephenson et al. 2023). Such a broad partnership with common vision, and adequate funding in the medium term could allow to overcome the weakness of the limited scope of the WEC in the Camargue SES. This is particularly necessary in views of the tensions surrounding the continuation of several stakeholders activities and the lack of trust between them. Our conceptual model provides stakeholders with an integrated representation of the main relationships and accordingly, offers the opportunity to gain a more comprehensive and shared understanding of sustainability issues in the area. It could enable to rethink their present water discussion tool (WEC) for a more global water forum.

## Towards potential quantitative developments

Our conceptual modeling approach that be used to study other deltas by considering processes, interactions, and feedbacks. Conceptual modeling of a variety of deltas, e.g., of the rivers Ebro (Spain), Danube (Romania and Ukraine), and Po (Italy), could help identify social-ecological characteristics, similarities, effective management strategies, and promote the sustainability and resilience of these complex systems. Exploring the relationships between human and environmental systems could also focus on ES and analyze system functioning. Stakeholders in the Camargue currently do not use the ES framework; thus, doing so could supplement the current analysis to consider ES better. This study's formal representation of the Ile de Camargue is a starting point for developing an IAM platform (Sibertin-Blanc et al. 2019) that could be used to explore quantitatively the positive and negative impacts of management strategies and external changes (e.g., climate change, Hamilton et al. 2015). Simulating the dynamics of this delta could be used to assess the system's resilience to potential climate and socioeconomic hazards, such as changes in farming practices, based on this conceptual model, instead of developing more empirical method. This IAM platform could be adapted from existing models such as platform MAELIA (Modeling of socio-agro-ecological systems for Landscape Integrated Assessment), which is a multi-agent platform for modeling and assessing socio-agro-ecological systems to assess scenarios of agricultural activities, water management, and climate change (Therond et al. 2014, Tribouillois et al. 2022b, 2022a).

## Acknowledgments:

The authors would like to thank INRAE (metaprogram BIOSEFAIR) and the Tour du Valat Foundation for the funding and support. The authors gratefully acknowledge all the experts and stakeholders they interviewed for their time and knowledge, in
particular Raphaël Mathevet, Thomas Galewski, Delphine Nicolas, Matthieu Guillemain, David Vallecillo, Claire Bonnaud, and François Clément. We thank Michelle and Michael Corson, who polished the manuscript via English-language editing.

**Data Availability:**

Data code sharing is not applicable to this article because no data and code were analyzed in this study.

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# Appendix 1: Detailed information on a) geology, b) climate c) ecological context and d) human activities of the Ile de Camargue

## a) Geology

Traditionally, the Ile de Camargue is divided into two morphological units (Bouteyre and Toni 1972): i) fluvio-lagoonal (from Arles to south of the Vaccarès lagoon), composed of a fluvial cover, with riverbanks deposited over lagoonal salt formations (higher elevations), and ii) lagoonal-marine (south of the Vaccarès lagoon to the Mediterranean sea), consisting of marine and lagoonal deposits covered by a shallow fluvial layer (lower elevations) (Fig. 1). The soils are characterized by their marine or fluvial origin, and are classified as "raw mineral soil, slightly developed feeder soils, sodic soils and hydromorphic soils" (Bouteyre and Toni, 1972).

## b) Climate

The Rhône delta has a Mediterranean climate, with large amounts of sunshine (> 2,500 h/yr), summer drought, and abundant autumn precipitation. Summers are hot, and frost is infrequent (Loubet 2012). From 1989 to 2022, precipitation in the Camargue was significantly higher in winter than in summer, with a large mean annual water deficit of 890 mm/year (i.e. 560 mm mean annual precipitation vs. 1450 mm mean annual open-water evaporation).

## c) Ecological context

The Camargue is one of the most biodiverse wetlands in the Mediterranean basin, containing many natural areas (which cover more than 33% of the region) and including a variety of habitat types: ponds, lagoons, marshes, dry grasslands, reedbeds, and salt meadows (with allomorphic vegetation) (Mathevet 2004, Picon 1990). Throughout the year, the Ile de Camargue hosts many waterbird species, which represent the delta's most emblematic taxonomic group, with one of the largest breeding colonies of greater flamingos (*Phoenicopterus roseus*) in the Mediterranean basin (Johnson and Cézilly 2009). In winter, it is a major staging area for common cranes (*Grus grus*), greylag geese (*Anser anser*), ducks (e.g. *Mareca strepera*, *Anas platyrhynchos*, *Anas crecca*), and large amounts of passerines on farmland (Galewski and Devictor 2016).

Due to the abundance and diversity of natural habitats, the region supports many fish species (Crivelli 1981). However, ecological continuity can be complex due to the amount of hydraulic infrastructure in the area (Bouchard et al. 2022, Nicolas et al. 2021). Fish populations include marine and freshwater species, with strong conservation concerns for two heritage species: the European eel (*Anguilla anguilla*) and short-snouted seahorse (*Hippocampus hippocampus*).

The delta was designated a UNESCO Biosphere Reserve in 1977 and a Ramsar site in 1986 due to its international importance for nesting, staging, and wintering waterbirds. France designated the Rhône delta a Regional Natural Park, which is a contract-based park established between national and local governments that must promote conservation of natural and cultural heritage. Strict biodiversity protection is enforced in four nature reserves.

Agricultural land is located in the northern, western, and eastern sections of the region (Fig 1), in three zones (Migairou-Leprince 2021): i) alluvial ridges, near the Rhône, with high agricultural potential and cereal systems, vineyards, some cattle breeding, and market gardening; ii) intermediate elevations, consisting of a mosaic of environments with highly variable agricultural potential; and iii) the lowest hydromorphic and halomorphic elevations, generally in marshes or semi-natural environments, which are sometimes grazed by cattle or
managed for environmental conservation. Flooded rice is cultivated in all of these areas,
especially the lowest.

d) *Human activities*

The main human activities include agriculture, salt production, hunting, fishing, tourism,
(including eco-tourism and birdwatching), and nature conservation. Most of these activities
depend directly on water management, either pumping water from the Rhône (e.g. agriculture,
hunting marshes) or managing the hydraulic structures/pumping stations that connect the region
to the sea (i.e. salt production) (Béchet et al. 2009, Béchet et al. 2012, Béchet and Johnson,
2008, Boutron et al. 2021). Most of the land in the Camargue is privately owned, but ca. 20%
of it is owned by national or regional government conservation organizations, including an
agency for the conservation of coastal wetlands, as nature reserves and publicly managed
marshes.

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Béchet, A., and A. Johnson. 2008. Anthropogenic and environmental determinants of Greater Flamingo Phoenicopterus roseus breeding numbers and productivity in the Camargue (Rhône delta, southern France). Ibis 150, 69–79. https://doi.org/10.1111/j.1474-919X.2007.00740.x

Béchet, A., M. Rendón-Martos, M. Á. Rendón, J. A. Amat, A. R. Johnson, and M. Gauthier-Clerc. 2012. Global economy interacts with climate change to jeopardize species conservation: the case of the greater flamingo in the Mediterranean and West Africa. Environmental Conservation. 39: 1–3. https://doi.org/10.1017/S0376892911000488

Bouchard, C., O. Boutron, J. Lambremon, H. Drouineau, P. Lambert, and D. Nicolas. 2022. Impacts of environmental conditions and management of sluice gates on glass eel migration. Estuarine, Coastal and Shelf Science. 279:108139. https://doi.org/10.1016/j.ecss.2022.108139

Bouteyre, G., and C. Toni. 1972. Géomorphologie et étude des sols sodiques des plaines alluviales: Exemple de la Camargue. Science des Sols 232.

Boutron, O., C. Paugam, E. Luna-Laurent, P. Chauvelon, D. Sous, V. Rey, S. Meulé, Y. Chérain, A. Cheiron, and E. Migne. 2021. Hydro-Saline Dynamics of a Shallow Mediterranean Coastal Lagoon: Complementary Information from Short and Long Term Monitoring. Journal of Marine Science and Engineering 9, 701. https://doi.org/10.3390/jmse9070701

Crivelli, A.J. 1981. Les peuplements de poissons de la Camargue. Revue D'Écologie 35:617-672.

Galewski, T., and V. Devictor. 2016. When Common Birds Became Rare: Historical Records Shed Light on Long-Term Responses of Bird Communities to Global Change in the Largest Wetland of France. PLOS ONE 11, e0165542. https://doi.org/10.1371/journal.pone.0165542

Johnson, A., and F. Cézilly. 2009. The Greater Flamingo, 1st ed. T & AD Poyser.

Loubet, A. 2012. Modélisation de l'hydrosystème Vaccarès : contribution à une gestion adaptive des ressources en eau dans le delta du Rhône, France (These de doctorat). Aix-Marseille.

Mathevet, R. 2004. Camargue incertaine. Sciences, usages et natures, Buchet Chastel. ed, Ecologie. Paris.

Migairou-Leprince, J. 2021. Diversification des exploitations agricoles et conditions d'émergence de l'agroécologie en Camargue. Méthode du diagnostic agraire de la chaire d'agriculture comparée d'AgroParisTech (Mémoire). AgroParisTech, Paris (FRA).

Nicolas, D., P. Contournet, S. Hilaire, T. Crassart, E. Luna-Laurent, D. Milesi, F. Leborne, P. Boulongne, M. Parent, O. Boutron, B. Poulin, and M. Thibault. 2021. Etude de la connectivité
hydrobiologique entre le milieu marin et le complexe lagunaire du Vaccarès via les étangs et marais des salins de Camargue, suivis ichtyologiques 2016-2021. Rapport final, Tour du Valat.
Picon, B. 1990. L'espace et le temps en Camargue. Actes Sud Littérature.
# Appendix 2: Detailed information on water-flow processes

## a) Water flows to and from the Rhône river

When the Rhône's flow is low, seawater can move upstream the river and the pumping stations are stopped to avoid transferring saline water into the irrigation canals (Ibañez et al. 1997, Levasseur and Doutriaux 1992). The canals are used mainly to fill and drain agricultural fields (No. e5) used to grow crops (No. e6), especially rice, or to rear livestock (No. e7), but are also used to flood natural marshes (No. e8), some of which are used for hunting. As livestock can drink from the canals, they have greatly eroded many of the banks (BRL 2004). Along the canals, fields are filled and drained using hydraulic valves, small bags to stop water flow, or short-term mobile pumping stations (photographs S1, S2, and S3 in the Appendix 6).

The canals have low slopes, and even slightly reversed slopes in certain sections, especially after local dredging. Depending on the volume of water pumped and on wind conditions, some canals can flow in either direction. In addition to the ones connected to the Rhône, pumping stations have been installed in several places in the canal network (Nos. e9 and e16) to ensure that upstream canals remain connected to higher-elevation downstream canals.

The aquatic ecosystem in the center of the Ile de Camargue includes three interconnected lagoons that form the Vaccarès lagoon system (No. e10 in Fig. 3): Vaccarès, Impériaux and Lion/Dame (Fig. 2b). The Vaccarès lagoon system receives some of the Ile de Camargue's drainage water that is not pumped back into the Rhône. Water is supplied continuously throughout the year via the Fumemorte drainage canal (Fig. 2a), which outlet has no water-control structure. Four other main drainage canals can supply additional drainage water to the Vaccarès lagoon system: i) Roquemaure (Fig. 2a) (depending on the management of the “Mar” hydraulic structure, 4.5 km from the Vaccarès lagoon system), ii) Rousty (depending on management of the sluice gates at its outlet in the Vaccarès lagoon system; No. e11 in Fig. 3), iii) Sigoulette (depending on management of the sluice gates at its outlet in the Vaccarès lagoon system), and iv) Consécanière (pumping station of the “Three Gorges”). Approximately 10 small drainage canals can supply water to the Vaccarès lagoon system, but their combined volume is much lower (Boutron et al. 2015). As the slopes are shallow, high water levels in the lagoons may cause saline water in them to flow into drainage canals, which prevents pumping water out of fields used for livestock to keep them from being flooded. The wind can also cause or exacerbate this reverse flow.

## b) Connections to the sea

At two locations (Fig. 2a), two pumping stations can be activated to pump additional saline water from the former saltworks into the pre-concentration ponds of the Salins de Giraud saltworks (No. e15), which remains in operation. Exchanges of surface water between the Ile de Camargue and the sea are managed in the coastal lagoons, except for the Station de l'Eolienne pumping station (No.e16), which is used to drain water directly into the sea near the Pertuis de la Fourcade.

## c) Groundwater flows

Groundwater and its associated salt can be exchanged indirectly in the Ile de Camargue due to water management. The Rhône delta contains a deep aquifer and a shallow aquifer composed of fine sediments of fluvio-lagoonal and lagoonal-marine origin. They are separated by a thick layer of clay, silt, and peat, which strongly limits potential exchanges between them (Torres-Rondon 2013). Soil salinity varies greatly within and among the region's agricultural fields due to geomorphology, including the shallowness of groundwater, and the high evapotranspiration, which causes salt to accumulate at lower elevations (Torres-Rondon 2013).
Boutron, O., O. Bertrand, A. Fiandrino, P. Höhener, A. Sandoz, Y. Chérain, E. Coulet, and P. Chauvelon. 2015. An Unstructured Numerical Model to Study Wind-Driven Circulation Patterns in a Managed Coastal Mediterranean Wetland: The Vaccarès Lagoon System. Water 7, 5986–6016. https://doi.org/10.3390/w7115986

BRL, 2004. Etude hydraulique et hydrobiologique des canaux de Camargue. Volume 1 : Etats des lieux - Diagnostique.

Ibañez, C., D. Pont, and N. Prat. 1997. Characterization of the Ebre and Rhone estuaries: A basis for defining and classifying salt-wedge estuaries. Limnology and Oceanography 42:89–101. https://doi.org/10.4319/lo.1997.42.1.0089

Levasseur, L., and E. Doutriaux. 1992. Le coin salé du Grand Rhône et les travaux de creusement du seuil de Terrin. Journée de l'Hydraulique 22:1–9.

Torres-Rondon, L. 2013. Etude et modélisation des transferts d'eau et de sel en milieu deltaïque agricole (Camargue-France). Université d'Avignon.
# Appendix 3: Detailed information on water governance

## a) Irrigation and drainage

The canals and pumping stations are managed and maintained by private farmers or farmer associations (No. e24 in Fig 3. coordinated by SMGAS, except for one that is managed by Saintes-Maries-de-la-Mer. Most private pumping stations are owned by farmers who have land near the banks of the Rhône. Most land further inland depends on collective hydraulic networks (Mathevet 2004). In either case, the price of irrigation water is established by the French Waterways Organization (No. e25). The ability to pump water is based on the type of crop, the location of the salt wedge in the Rhône, the price of irrigation water, and the cost of energy required to run the pumps (No. e26).

Farmer associations are organized into irrigation or drainage associations, which collectively manage 53 pumps at 13 pumping stations:

- 14 irrigation associations: 8 with inlets on the Grand Rhone (151.5-195.8 m³) and 6 with inlets on the Petit Rhone (44.5-63.0 m³). These associations cover 21,300 ha, of which 7850 ha are irrigated.

- 13 drainage associations (Fig. 3b) drain more than 40,000 ha, including 32,240 ha whose water drains into the Rhône via pumping stations, and 7,935 ha whose water drains into the Vaccarès lagoon system, mainly via the Fumemorte, Roquemaure, and Versadou canals (Fig. 3a).

Irrigation and private drainage: 74 farms are irrigated by 100 private pumping stations directly in the Rhone. Approximately 175 million m³ were pumped in 1994. From 1988-1994, 44% of the total volume was pumped by the private sector.

## b) Coastal lagoons

The local stakeholders taking part in the WEC (No. e28, Fig 3.) to managed the valves of the Pertuis de la Fourcade (No. e12) are: French government authorities, farmers, fishermen. SMGAS, representatives of local residents, SNPN, managers of the Impériaux lagoon, city of Saintes-Maries-de-la-Mer, and scientists.

For the 2 following sites, the water management implemented aims to favour hydro-saline conditions beneficial to fish, birds and plant species (e.g. seagrass) of several Mediterranean environments being restored on the site, while seeking to reduce the risks of coastal flooding, erosion and salinization.

i) The Camargue National Reserve, managed by the National Society for the Protection of Nature (SNPN), covers part of the Vaccarès lagoon, where all extractive activities are prohibited. The Impériaux lagoon is designated a sensitive natural space.

ii) The Camargue National Reserve, Tour du Valat, and Regional Natural Park manage the lagoons and marshes of the former saltworks via an ecological restoration programme for abandoned saltworks (No. e27) (Davranche et al. 2023).

Changes in precipitation and evaporation, along with a 3-4 mm increase in sea level per year (PECHAC 2022, Ullmann et al. 2007) in the Ile de Camargue prompted stakeholders to regularly adapt management of these sluices gates.
Davranche, A., C. Arzel, P. Pouzet, A. R. Carrasco, G. Lefebvre, D. Lague, M. Thibault, A. Newton, C. Fleurant, M. Maanan, and B. Poulin. 2024. 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, France. Science of the Total Environment 168289. https://doi.org/10.1016/j.scitotenv.2023.168289

Mathevet, R. 2004. Camargue incertaine. Sciences, usages et natures, Buchet Chastel. ed, Ecologie. Paris.

PECHAC. 2022. Le changement climatique et ses effets dans la Réserve de biosphère de Camargue. Etat des connaissances en 10 questions/réponses.

Ullmann, A., P. A. Pirazzoli, and A. Tomasin. 2007. Sea surges in Camargue: Trends over the 20th century. Continental Shelf Research 27:922–934. https://doi.org/10.1016/j.csr.2006.12.001
# Appendix 4: Detailed information on agriculture

## a) Livestock farming

The Camargue has mixed crop-livestock systems and traditional farms with semi-feral bulls, which allow for crop diversification after a rice monoculture, and livestock farming can replace vineyards on certain fields. Farmers set up grazing areas for livestock on natural meadows, natural marshes, and irrigable fields. Some fields can be managed as marshes to graze bulls or for hunting.

The semi-feral bull farms benefit from a local reputation in bullfighting circles. Some farms are owned, while others rent or have grazing contracts for most of their area. Tourism and leasing marshes for hunting are additional sources of income for the farms. Bull breeding and traditional activities are organized to attract tourists, such as the capturing and branding of bulls, bullfighting, an annual bull race, and horse riding. Many of the farms are organic, as their extensive herds are easier to convert to organic requirements. The ability to produce alfalfa and grassland on the farm also makes it easier to convert the fields to organic farming (Migairou-Leprince 2021).

Migairou-Leprince, J. 2021. Diversification des exploitations agricoles et conditions d'émergence de l'agroécologie en Camargue. Méthode du diagnostic agraire de la chaire d'agriculture comparée d'AgroParisTech (Mémoire). AgroParisTech, Paris (FRA)
# Appendix 5: Detailed information on biodiversity

## a) Bird

Due to the diversity of habitats in the Ile de Camargue, 113 bird species (e.g. flamingos, ducks, herons, cranes) are present for breeding, migration, and wintering periods (Kayser et al. 2008) (Fig. 5).

Waterbirds staging and breeding relies directly on flooded areas, salinity and quality of water. For example, salinity and marshland surface area can decrease the abundance of most duck species (Brochet et al. 2009), these criteria depend to some extent on the irrigation management. Studies have highlighted that annual changes in Eurasian teal (*Anas crecca*) abundance are due to salinity and the open-water area available (Vallecillo et al. 2023). The water level of the Vaccarès lagoon is a good predictor of the abundance of breeding greater flamingos in spring as it correlates with the foraging area available to them (Béchet and Johnson 2008).

The Camargue hosts four types of hunting (Mathevet 2004):

- Communal, with membership of and subscription to the communal association and leased hunting grounds, which are public or private

- Private, in which hunters, who often do not live in the Camargue, lease hunting rights from a landowner or the hunting association. This includes land owned by large landowners, often farmers. The number of ducks taken depends on the price of the hunting right.

- Commercial or day, with the release of farm-raised mallards (*Anas platyrhynchos*)

- Business or social, for a landowner's guests, which may occur along with private hunting, with the guests contributing to the costs of marsh management

## b) Fish

Many fish in the Camargue are of commercial interest, such as the European sea bass (*Dicentrarchus labrax*), sargo (*Diplodus sargus*), gilt-head bream (*Sparus aurata*), sole (*Solea solea*), and turbot (*Scophthalmus maximus*). As the Gulf of Beauduc and the lagoons have high nutrient concentrations and plankton density, they host the most species. Several species of sharks and rays thrive on the sandy seabed of the Camargue. Eels such as the European eel and silver eel are some of Camargue's most emblematic species, which live there before they leave to reproduce in the Sargasso Sea.

The fish community in the irrigation canals comes from the Rhône because its fish pass through pumping stations and then enter the Vaccarès lagoon system (Poizat et al. 1999). The species include the European eel, Rhône shad (*Alosa fallax*), and sea lamprey (*Petromyzon marinus*). Fish require high water quality, which is a concern due to the pesticides used in the Camargue and the increased risk of flows of saline water into the canals. Fish are a strong commercial interest in the Camargue, depending on the type of fishing authorized.

The Ile de Camargue hosts three main types of fishing:

- Professional, mainly in the Vaccarès lagoon system. It requires obtaining authorization to fish. Professional fishing occurs in several types of environments. At sea, nets are used to catch sole, European sea bass, gilt-head bream (*Sparus aurata*), tuna (*Thunnus spp*.), and turbot (*Scophthalmus maximus*). In the ponds, a few dozen fishermen catch mainly eels and silversides (*Atherina spp*). In the Rhône, fishermen catch mainly species with a high commercial value (e.g. sea bass, eels, flounder, mullet (*Mugil spp*.)).

- Licensed recreational, which occurs in the Rhône, the canals, and the former saltworks. It requires obtaining a license from the fishing federation.

Unlicensed recreational, which is allowed only in the sea or the Beauduc lagoon.
Béchet, A., and A. Johnson. 2008. Anthropogenic and environmental determinants of Greater Flamingo Phoenicopterus roseus breeding numbers and productivity in the Camargue (Rhône delta, southern France). Ibis 150, 69–79. https://doi.org/10.1111/j.1474-919X.2007.00740.x

Brochet, A. L., M. Gauthier-Clerc, R. Mathevet, A. Béchet, J. Y. Mondain-Monval, and A. Tamisier. 2009. Marsh management, reserve creation, hunting periods and carrying capacity for wintering ducks and coots. Biodiversity Conservation 18:1879-1894. https://doi.org/10.1007/s10531-008-9562-6

Kayser, Y., M. Gauthier-Clerc, A. Bechet, B. Poulin, G. Massez, Y. Cherain, J. Paoli, N. Sadoul, E. Vialet, G. Paulus, N. Vincent-Martin, P. Pilard, and P. Isenmann. 2008. Compte rendu ornithologique camarguais pour les années 2001-2006. Revue D'Écologie 63:299-349.

Mathevet, R. 2004. Camargue incertaine. Sciences, usages et natures, Buchet Chastel. ed, Ecologie. Paris.

Poizat, G., P. Chauvelon, E. Rosecchi, A. J. Crivelli, P. Contournet. 1999. Passage de poissons du Rhône par les pompes d'irrigation de Camargue : premiers résultats. Bulletin Français de la Pêche et de la Pisciculture. 31-43. https://doi.org/10.1051/kmae:1999019

Vallecillo, D., M. Guillemain, C. Bouchard, S. Roques, and J. Champagnon. 2023. Influence of changes in local environmental variables on the distribution and abundance dynamics of wintering Teal Anas crecca. Biodiversity Conservation. https://doi.org/10.1007/s10531-023-02713-9
<figure><img src="image_10.png" /><figcaption>S1:</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>S2:</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>S3:</figcaption></figure>
# Appendix 7: Report of the meeting with local stakeholders

The main issues to emerge from the meeting could be divided into three groups: the global one, the marginal one and the future one. The global ones are the ones which the majority of the groups spoke about and/or which are an integral part of the questions being asked in the region. The marginal ones are the one cited by only a group or really precise. The future ones are questions that are very likely to arise in the future or prospective scenarios

Global issues:

- Importance of agriculture to the region, and should be adapted to the environment, taking into account natural areas (Vaccarès) and joint management based on multiple objectives (conservation, fishery, hunting). The dynamics of agricultural land must be taken into account. Historically, there have been a number of increases and decreases in agricultural land. At present, the area is shrinking as a result of salinisation and urbanisation.

- Agriculture is particularly affected by changes in subsidies, especially the CAP. Indeed, subsidies have a direct effect on crop rotation, and production systems are highly responsive. Since the reduction in agricultural support and subsidies for industrial tomato growing, rice fields are gradually being replaced by market gardening. The dynamics of organic farming plots show the impact of CAP aid, as there is aid for conversion but not for maintenance, and many plots in the region oscillate between organic and conventional farming.

- There seems to be a need for technical and economic balance in farming systems: solutions that are technically possible and economically viable. In particular, through the possibility of using plant protection products and therefore the acceptance of these products and their correct use. This requires collaboration and negotiation rather than just regulation.

- Farmers finance most of the hydraulic systems in the area (canal network, pumping station). Farmers pay significant costs to maintain the network of canals and pumps. The price of the water and energy needed to bring fresh water to the area is also paid in full by them via the canal network. Energy costs have also undergone very significant inflation, which may raise questions about the future of irrigation based almost entirely on pumping. The seasonal nature of energy costs raises questions, with very high prices in winter preventing pumping even though this is the period when there is the most water in the Rhône. A tax from the French water agency could also be applied in the Camargue. As there is an interconnection between economic activities, farmers pay for water that is used also for other economic activities (hunting, fishing, environmental protection, tourism). Would the system of funding weights need to be reviewed to enable major costs to be shared, so as to avoid the problems of seasonal costs, for example? Another point to emphasise about irrigation funding is that pricing is based on the number of hectares to be irrigated and not on the volume of irrigation used, as this volume is not known.

- The need for lagoon environments such as the Vaccarès (downstream environments) to receive water from agricultural basins.

- Water management around agricultural plots: rice or gravity-fed irrigation solely to manage salt rises: the question of submergence in winter for plots that are irrigated or not, then for the management of hydro saline dynamics, such as alfalfa, which is, now, often irrigated by submergence. With salt rises becoming increasingly common, dry crops will probably require flood irrigation in the future.

- WEC: arena not adapted to water management on the Ile de Camargue, only the Pertuis de la Fourcade is discussed (fish, fishing and seawater inflow), no discussion of freshwater,
created following the floods. Governance does not seem clear to the stakeholders in the area. There seems to be a need to create a new body for freshwater management, such as a local water commission. For some stakeholders in the agricultural sector, there seems to be a problem with managing the balance between salt water and fresh water from the point of view of fish alone, with fishermen deciding on sea entries. A plant purification project that is currently being set up opens up a good prospect.

- Rapid change in the size of farms due to the age pyramid of farmers, leading to rapid changes in practices and crop rotation.

- Diversification constrained by the altitude of the plots

- The balance between salt and fresh water determines the presence and abundance of bird and fish species, and therefore has an impact on other economic activities such as fishing, hunting and tourism.

- Another impact on avifauna is the dynamics of agricultural areas (particularly land use), which can have an impact on their capacity to host birds (particularly with intermediate cover).

## Marginal issues:

- Problem of illegal fishing and poaching in the area (carp, catfish). The main problem is on the Vaccarès. Catfish depend on the connectivity of the canals.

- Commercial exploitation of crayfish limited by regulations (problem of invasive species that cannot be kept alive).

- Need to control water ingress and drainage in the plots to keep the soil alive and introduce conservation agriculture, particularly on plots with hydromorphic conditions.

## Futures issues?

- A change from snow regime to rain regime in the Alps could alter water flows in the Rhône.

- Reconsideration of traditional Camargue activities at regulatory level: Camargue race and bullfighting. This would lead to a reduction in activity, and therefore a reduction in herds and grazing areas, which could have an impact on tourism.

- Developments in crop pests and adapted pesticides

- What is the cost of protecting the coastline and the effect of climate change: a fixed territory or accompanying global change? Taking into account the cost of energy for the volume of water consumed by different activities (agriculture, hunting, fishing, tourism) and therefore sharing the cost of irrigation.

- Water harvesting techniques to access fresh water without the constraints of the Rhône and the sea: dew, humidity, water in the air.