Laurence Amblard
email: laurence.amblard@inrae.fr

The case of diffuse pollution control in European rural areas

Keywords: Diffuse pollution, Agriculture, Collective action, Hybrid policy instruments, Transaction costs, Social-Ecological System (SES) framework

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The European Union (EU) Water Framework Directive, adopted in 2000, set the objective of achieving good water status for all bodies of surface waters and groundwater (EU, 2000). Despite a significant reduction in levels of nutrients in European freshwaters over the past two decades, diffuse pollution from agriculture still poses a major threat to the quality of surface and ground waters in Europe. More particularly, nitrate and phosphorus pollution from agriculture accounts for the largest proportion of diffuse run off (EEA, 2018).

The policy tools available to address diffuse pollution include regulatory instruments, economic instruments (taxes/subsidies) and voluntary compliance approaches (Shortle and Abler, 2001).

Because of the diffuse nature of nitrate pollution, it is not feasible to define policy instruments based on emissions by farmers such as emissions charges or standards [START_REF] Shortle | Reforming Agricultural Nonpoint Pollution Policy in an Increasingly Budget-Constrained Environment[END_REF]. The policies implemented rather aim at modifying the agricultural practices known as influencing the extent of nutrient leaching and runoff [START_REF] Mccann | Transaction Costs of Policies to Reduce Agricultural Phosphorous Pollution in the Minnesota River[END_REF]Shortle and Abler, 2001). Reductions in organic and mineral nitrogen fertilization, the introduction of nitrate catch crops into the cropping plan and the establishment of riparian buffers along watercourses are examples of the different measures that may be implemented.

In the EU context, regulatory instruments (the EU Nitrate Directive) and incentive schemes targeting individual farms (agri-environmental schemes) remain the main policy instruments implemented to control diffuse nitrate pollution from agriculture. Yet, collective approaches to policy implementation have been recently developing [START_REF] Polman | Collective Approaches to Agri-Environmental Management[END_REF]OECD, 2013;[START_REF] Westerink | Collaborative governance arrangements to deliver spatially coordinated agri-environmental management[END_REF]. Since 2014, the EU rural development policy gives an opportunity to groups of farmers to commit jointly to collective agri-environmental schemes (EU, 2013). There also exist some examples of voluntary cooperation among farmers (and other stakeholders) for achieving water quality regulatory objectives, e.g., in drinking water catchments [START_REF] Brouwer | The role of co-operative agreements in agriculture to achieve EU Water Policy targets[END_REF][START_REF] Grolleau | Designing watershed programs to pay farmers for water quality services: case studies of Munich and New York City[END_REF][START_REF] Amblard | Collective action for water quality management in agriculture: The case of drinking water source protection in France[END_REF].

Previous studies have assessed the relevance of cooperation for the provision of ecosystem services by farmers [START_REF] Goldman | Institutional incentives for managing the landscape: Inducing cooperation for the production of ecosystem services[END_REF][START_REF] Stallman | Ecosystem services in agriculture: Determining suitability for provision by collective management[END_REF]Prager, 2015a;[START_REF] Westerink | Collaborative governance arrangements to deliver spatially coordinated agri-environmental management[END_REF], including water quality management [START_REF] Sarker | A common-pool resource approach for water quality management: An Australian case study[END_REF][START_REF] Stallman | Ecosystem services in agriculture: Determining suitability for provision by collective management[END_REF]. The literature also stresses the need to compare individual and collective approaches as well as the range of policy instruments available for environmental public goods provision [START_REF] Polman | Collective Approaches to Agri-Environmental Management[END_REF][START_REF] Stallman | Ecosystem services in agriculture: Determining suitability for provision by collective management[END_REF]OECD, 2013). More particularly, there has been no systematic assessment of the costs and benefits of agri-environmental cooperation as a complement to regulatory or incentive policy tools for the prevention of diffuse pollution.

This article aims at assessing the potential of hybrid policy instruments relying on collective action among farmers for addressing diffuse nitrate pollution from agriculture. Collective action is defined as an "action taken by a group (either directly or on its behalf through an organization) in pursuit of members' perceived shared interests" [START_REF] Marshall | A dictionary of sociology[END_REF]. The hybrid arrangements considered involve public authorities using an external body (cooperative or association) as an intermediary to coordinate the actions of individual actors [START_REF] Van Huylenbroeck | Public good markets: the possible role of hybrid governance structures in institutions for sustainability[END_REF]. In particular, this paper seeks to identify: (i) the benefits and costs of collective policy approaches to diffuse pollution control and (ii) the factors that influence the success of collective action.

A conceptual framework combining the Social-Ecological System (SES) framework with transaction cost economics [START_REF] Amblard | Collective action for water quality management in agriculture: The case of drinking water source protection in France[END_REF] is used to identify the conditions under which hybrid policy instruments are likely to be environmentally effective and cost-efficient tools for diffuse pollution control. Transaction cost economics are used to assess the potential advantages of collective action as a complement to other agri-environmental policy tools. For these advantages to be effective, the gains of collective action have to be superior to the associated costs, including transaction costs, for participating stakeholders. The conditions under which cooperation may be successful are identified using the SES framework [START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF][START_REF] Mcginnis | Social-Ecological system framework: initial changes and continuing challenges[END_REF]. While the SES framework was originally designed for the study of common pool resource problems, its application to diffuse water pollution as an externality problem contributes to recent developments aimed at broadening the scope of application of the framework [START_REF] Villamayor-Tomas | From Sandoz to Salmon: Conceptualizing resource and institutional dynamics in the Rhine watershed through the SES framework[END_REF]Bennet and Gosnell, 2015;[START_REF] Hinkel | A diagnostic procedure for applying the social-ecological systems framework in diverse cases[END_REF][START_REF] Partelow | A review of the social-ecological systems framework: applications, methods, modifications, and challenges[END_REF].

A review of empirical studies focused on cases of collective action for agricultural water pollution prevention in the EU context serves as a basis for a first identification of the factors likely to affect the success/failure of such cooperation. This literature review is structured by the conceptual framework combining transaction cost economics with the SES framework. The analysis relies more particularly on two cases: the Environmental Cooperatives in the Netherlands and the "Ferti-Mieux" operations in France. While the Environmental Cooperatives in the Netherlands constitute an example of collective action initiated by farmers themselves, the "Ferti-Mieux" operations in France were initiated by public agencies. Furthermore, the comparison of two cases in different Member States allows for exploring the role played by factors related to the social, economic and political contexts at the national level.

Previous comparative studies of collaborative arrangements in different Member States have focused on the role of collectives as bridging organizations (Prager, 2015b) or on the diversity of governance approaches to the spatial coordination of agri-environmental management [START_REF] Westerink | Collaborative governance arrangements to deliver spatially coordinated agri-environmental management[END_REF]. To the best of the authors' knowledge, no comparative analysis has been conducted before with the objective of assessing the potential of collective action for water quality management in agriculture.

The paper is organized as follows. The second section of the paper introduces the conceptual framework used for the analysis. Section 3 describes the methodology applied. Potential advantages of collective action as a complementary tool to achieve water quality objectives and factors identified as crucial for the success of cooperation are presented in Section 4. In the final section of the paper, the results are discussed from a conceptual and policy perspective.

Conceptual framework

A comparative perspective in terms of transaction costs is adopted with regard to the alternative policy instruments targeting individual farmers versus collectives (Section 2.1). The factors affecting the benefits and transaction costs of cooperation among farmers are identified on the basis of the SES framework (Section 2.2).

A transaction cost analysis of policy options

Transaction costs are the resources used to define, establish, maintain, and transfer property rights [START_REF] Allen | Transaction costs[END_REF]. Transaction costs arise because information is incomplete and asymmetrically held by parties to exchange [START_REF] North | Institutions, Institutional Change and Economic Performance[END_REF]. Depending on the characteristics of the good or service considered, the level of transaction costs linked to market coordination will be more or less important. Diffuse pollution, as an output of agricultural production affecting the utility of the production activities of other economic agents, is an externality. Externalities are present "whenever some individual A's utility or production relationships, include real (that is nonmonetary) variables, whose values are chosen by others (persons, corporations, governments) without particular attention to the effects on A's welfare" [START_REF] Baumol | The Theory of Environmental Policy[END_REF]. Water pollution, similar to many externalities, presents some characteristics of a public good [START_REF] Holtermann | Externalities and Public Goods[END_REF][START_REF] Baumol | The Theory of Environmental Policy[END_REF]. Pure public goods are goods that are non-exclusive and non-subtractive [START_REF] Samuelson | The Pure Theory of Public Expenditure[END_REF][START_REF] Head | Public goods and public policy[END_REF]. The restoration or maintenance of water quality by farmers constitutes a public good, as (i) everyone can benefit from the resulting improvement in water quality without diminishing others' benefits (non-subtractability) and (ii) it is difficult (impossible) to prevent anyone from enjoying the benefits of water pollution reduction (non-excludability). In this case, the transaction costs associated with decentralized market exchange are so high that the public good will be underprovided. For example, in the case of diffuse water pollution, the costs of identifying the sources of pollution and the other affected individuals will highly constrain market coordination [START_REF] Falconer | Developing Co-operative Approaches to Agri-environmental Policy: a Transaction Cost Perspective on Farmer Participation in Voluntary Schemes[END_REF]. Some form of organization is needed to overcome the suboptimal provision of the public goods [START_REF] Ostrom | Neither Markets nor States: Linking Transformation Processes in Collective Action Arenas[END_REF]. However, the alternative institutional arrangements (including the diverse types of government intervention) also present transaction costs and the question is then which arrangement allows for the provision of the public good at the lowest costs. [START_REF] Coase | The Problem of Social Cost[END_REF] suggested adopting a comparative perspective on the relative benefits and costs (including transaction costs) of the different social arrangements. Such an approach has recently been developed in the field of environmental policy. A growing body of research seeks to include transaction costs in the analysis and evaluation of environmental policies [START_REF] Mccann | Transaction cost measurement for evaluating environmental policies[END_REF][START_REF] Coggan | Influences of transaction costs in environmental policy[END_REF][START_REF] Garrick | Transaction costs and environmental policy: Taking stock[END_REF][START_REF] Mccann | Transaction costs and environmental policy design[END_REF]. In this context, transaction costs correspond to search and information costs, bargaining and decision or contracting costs and monitoring, enforcement and compliance costs [START_REF] Mccann | Transaction cost measurement for evaluating environmental policies[END_REF]. Several studies have empirically measured the extent of transaction costs linked to the implementation of environmental policies, showing their high significance [START_REF] Mccann | Transaction Costs of Policies to Reduce Agricultural Phosphorous Pollution in the Minnesota River[END_REF][START_REF] Falconer | Farm-level constraints on agri-environmental scheme participation: a transactional perspective[END_REF][START_REF] Falconer | An Investigation of Policy Administrative Costs Using Panel Data for the English Environmentally Sensitive Areas[END_REF][START_REF] Mettepenningen | Measuring private transaction costs of European agri-environmental schemes[END_REF].

In the paper, hybrid policy instruments relying on collective action are compared to regulatory and individual incentive instruments in terms of relative benefits and costs, including transaction costs.

The potential of collective action for diffuse pollution control further depends on the potential private benefits and transaction costs borne by participants.

As farmers do not primarily bear the costs of water pollution or do not enjoy the benefits of water quality improvements, they have generally little incentive to engage in collective action to reduce the level of pollution (preventing the public bad) or contribute to the maintenance of water quality (providing the public good). Still, they can draw indirect economic advantages as well as nonmonetary benefits from such cooperation. In some cases, farmers may reap some private economic benefits from changing their agricultural practices towards less polluting practices. A better management of fertilization may lead to some savings in fertilizer expenses without any decrease in yields [START_REF] Brouwer | Occurrence of Co-operative Agreements[END_REF][START_REF] Buckley | The potential to reduce the risk of diffuse pollution from agriculture while improving economic performance at farm level[END_REF]. Another economic motivation for farmers to participate in collective action may include the possibility to maintain or increase their profits through the certification of their products (e.g., ecolabels) or through the development of activities based on the improved quality of the environment (e.g., agritourism) [START_REF] Ribaudo | Ecosystem services from agriculture: Steps for expanding markets[END_REF][START_REF] Grolleau | Designing watershed programs to pay farmers for water quality services: case studies of Munich and New York City[END_REF]OECD, 2013). Finally, besides economic benefits, nonmonetary incentives may play a role in farmers' willingness to participate in collective action. Farmers with preferences for environmental preservation will be more willing to participate in cooperation to reduce water pollution [START_REF] Lubell | Watershed partnerships and the Emergence of Collective Action Institutions[END_REF][START_REF] Dupraz | Threshold effect and co-ordination of agri-environmental efforts[END_REF]. Transaction costs associated with collective action include the costs of defining actions to control diffuse water pollution (information and bargaining costs) and the monitoring and enforcement costs of actions. Collective action for the provision of environmental services with public goods characteristics such as the restoration/maintenance of water quality more particularly entails a potential free-riding problem due to the difficulty in excluding beneficiaries for failing to contribute to the maintenance of the public good [START_REF] Ostrom | How types of goods and property rights jointly affect collective action[END_REF]. The extent of expected benefits and transaction costs and thus the effectiveness of collective action are influenced by a number of factors identified on the basis of the SES framework (Section 2.2).

Identifying the factors affecting collective action: the SES framework

The SES framework was developed as a tool for the analysis of complex Social-Ecological Systems (SESs) [START_REF] Ostrom | A diagnostic approach for going beyond panaceas[END_REF][START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF]Poteete et al., 2010). This ontological framework lists and structures the variables which have been found in previous research to influence the patterns of interactions and outcomes in diverse SES. The SES framework constitutes an extension of the Institutional Analysis and Development approach [START_REF] Ostrom | The Institutional Analysis and Development Approach in[END_REF] with specific attention given to the characteristics of biophysical systems and their impact on natural resource management [START_REF] Ostrom | Background on the Institutional Analysis and Development Framework[END_REF][START_REF] Mcginnis | Social-Ecological system framework: initial changes and continuing challenges[END_REF].

Focal action situations represent the diverse interactions occurring between actors within SESs (e.g., harvesting the resource, information sharing or self-organizing for resource management) leading to social and ecological outcomes (Figure 1). The characteristics of the natural resource considered (resource system and resource unit), the characteristics of actors involved and the characteristics of the governance system are the first-tier variables considered as potentially important to analyze interactions and outcomes achieved in a given SES. The broader social, economic and political contexts and related ecosystems are also included as interacting with the other subsystems. andOstrom, 2014) (Appendix 1). Among the second-tier variables identified as potentially relevant, a subset of ten factors likely to affect the benefits and costs of collective action is seen to be critical for the success of self-organization by users of common-pool resources [START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF] (Table 1).

Table 1: The factors identified as crucial for self-organization by users for CPR management

First-tier variables

Second-tier variables

Resource system (RS) RS3 -Size of resource system RS5 -Productivity of system RS7 -Predictability of system dynamics Resource unit (RU) RU1 -Resource unit mobility Governance system (GS) GS6 -Collective-choice rules Actors (A) A1 -Number of relevant actors A5 -Leadership-entrepreneurship A6 -Norms (trust-reciprocity)/social capital A7 -Knowledge of the SES A8 -Importance of the resource Source: Adapted from [START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF] The characteristics of the resource systems identified as affecting the likelihood of self-organization by users include the size and productivity of the system (RS3, RS5) and the predictability of system dynamics (RS7). A resource system of moderate size is seen as conducive to self-organization, as a larger size means higher management costs while a smaller size may imply a less valuable flow of products from the system [START_REF] Chhatre | Forest commons and local enforcement[END_REF][START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF]. A moderate level of resource scarcity (productivity of the system) is also likely to induce collective action by users, unlike situations in which the resource is either already exhausted or abundant [START_REF] Meinzen-Dick | Beyond panaceas in water institutions[END_REF]. A low predictability of system dynamics will increase the management costs of the resource, thereby reducing the likelihood of self-organization [START_REF] Agrawal | Common Property Institutions and Sustainable Governance of Resources[END_REF]. Management costs also depend on the resource unit mobility (RU1), stationary units (e.g., water in a lake) being less costly to manage than mobile units (e.g., water in a stream) [START_REF] Schlager | Mobile Flows, Storage, and Self-organized Institutions for Governing Common-Pool Resources[END_REF][START_REF] Agrawal | Common Property Institutions and Sustainable Governance of Resources[END_REF]. A larger number of users (A1) means higher transaction costs, however a small group size may constrain the pooling of resources needed to sustain collective action [START_REF] Wade | The management of common property resources: collective action as an alternative to privatisation or state regulation[END_REF][START_REF] Ostrom | Analyzing collective action[END_REF]. The presence of wellrespected local leaders (A5) and the existence of norms of reciprocity and/or social capital within the group (A6) are likely to decrease the transaction costs associated with collective action [START_REF] Pretty | Social Capital and the Environment[END_REF][START_REF] Meinzen-Dick | Beyond panaceas in water institutions[END_REF]Poteete et al., 2010). The sharing of a common knowledge of the SES (A7) is seen as decreasing the perceived costs of organizing by users [START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF]. The importance of the resource to users in terms of economic or noneconomic value (A8) will affect the expected benefits of collective action relative to its costs [START_REF] Acheson | Etude de cas : Les Sources de Gorze, in : Evaluation des politiques d'intervention de l'Agence de l'Eau Rhône Méditerranée et Corse. Actions de lutte contre les pollutions diffuses dans les bassins d'alimentation des captages d'eau potable[END_REF]. Finally, identified as crucial for the success of self-organization is the autonomy users have to define and enforce the rules governing resource management, i.e., their autonomy at the collective-choice level (GS6) [START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF]Poteete et al., 2010).

The SES framework is used to identify the factors influencing collective action for the control of diffuse pollution from agriculture. More particularly, the subset of ten factors highlighted by Ostrom (2009) (Table 1) constitutes an initial set of assumptions with regard to the variables affecting the benefits and costs, including transaction costs, of cooperation.

Methodology

Section 3.1 introduces the case study approach adopted for the analysis. The next subsection briefly describes the cases of Environmental Cooperatives and "Ferti-Mieux" operations. Table 2 presents the main characteristics of the two cases.

A case study approach based on a literature review

The analysis of hybrid policy instruments relying on collective action for nitrate pollution control relies on a review of empirical studies focused on cases of collective action for agricultural water pollution prevention in the EU context. Two cases are more particularly analyzed: the Environmental Cooperatives (ECs) in the Netherlands and the "Ferti-Mieux" operations in France. The two cases were selected because of their historical depth; both initiatives have developed since the beginning of the 1990s. Furthermore, while the ECs in the Netherlands constitute an example of collective action initiated by farmers themselves, the "Ferti-Mieux" operations in France were initiated by public agencies. Finally, the comparison of two cases in different Member States allows for exploring the role played by factors related to the social, economic and political contexts at the national level.

The secondary sources used include scientific and technical journal articles, research and policy reports, PhD and master theses as well as policy briefs. While the case of Environmental Cooperatives has been the subject of multiple analyses published in the academic literature, the Ferti-Mieux operations are mostly documented in technical outlets and policy reports.

The evidence from the diverse secondary sources was reviewed through the lens of the conceptual framework combining transaction cost economics with the SES framework. More particularly, the second-tier variables highlighted by [START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF] (Table 1) served as a frame for identifying the factors affecting the benefits and costs, including transaction costs, borne by the participants to agrienvironmental collective action. Other second-tier variables were selected in the list updated by [START_REF] Mcginnis | Social-Ecological system framework: initial changes and continuing challenges[END_REF] (Appendix 1) when identified as having an impact on cooperation in the documents reviewed. Third-and fourth-tier variables characterizing the second-tier variables [START_REF] Basurto | The social-ecological system framework as a knowledge classificatory system for benthic small-scale fisheries[END_REF][START_REF] Frey | Building a Diagnostic Ontology of Social-Ecological Systems[END_REF][START_REF] Thiel | Evaluating an instrument for institutional crafting: How Ostrom's social-ecological systems framework is applied[END_REF] were also developed if the literature review suggested that they play a role in the success/failure of collective action. The references supporting the influence of each identified factor on cooperation are presented in Appendix 2.

Two cases of collective action in the EU context

The Environmental Cooperatives in the Netherlands

The ECs have developed as a new governance structure since the beginning of the 1990s [START_REF] Glasbergen | The Environmental Cooperative: Self-Governance in Sustainable Rural Development[END_REF][START_REF] Renting | Reconnecting Nature, Farming and Society: Environmental Cooperatives in the Netherlands as Institutional Arrangements for Creating Coherence[END_REF]. They are regional groups of farmers, including in some cases other rural stakeholders (e.g., environmental organizations and local authorities) [START_REF] Wiskerke | Environmental co-operatives as a new mode of rural governance[END_REF]. Most ECs are formal associations, some are foundations, and a few have legal cooperative status [START_REF] Polman | Collective Approaches to Agri-Environmental Management[END_REF].

By 2016, 160 associations involving 10% of the Dutch farming population (65% of which were dairy farmers) managed 25% of the rural area of the Netherlands. Their activities covered land areas ranging from 1,000 up to 130,000 hectares (Ministry of Economic Affairs, 2011; [START_REF] Terwan | The cooperative approach under the new Dutch agri-environment-climate scheme. Background, procedures and legal and institutional implications[END_REF]. The ECs' environmental activities are not restricted to water quality management and one EC can be active in several environmental "domains," including also biodiversity conservation or wildlife management (Franks and Mc Gloin, 2007a). In addition to nature management and the reduction of environmental pollution, some ECs have also developed activities in the fields of rural tourism and regional quality production [START_REF] Renting | Reconnecting Nature, Farming and Society: Environmental Cooperatives in the Netherlands as Institutional Arrangements for Creating Coherence[END_REF]Franks and McGloin, 2007a).

The ECs are generally managed by a board elected annually. Subcommittees are responsible for managing individual projects and developing new activities. Regular meetings take place, as well as an annual general meeting at which changes to the group's plan and constitution can be made (Franks and McGloin, 2007a). Individual members decide for themselves whether to participate in any EC activity.

While they can suggest programs for the ECs to be involved in, only those initiatives supported by a large share of members will be supported by the ECs [START_REF] Franks | Boundary organizations for sustainable land management: The example of Dutch Environmental Co-operatives[END_REF].

The development of ECs led to innovations in the implementation of agri-environmental policy in the Netherlands. In some cases, ECs have been allowed to develop themselves the measures and instruments used to achieve the regulatory objectives defined by state agencies [START_REF] Glasbergen | The Environmental Cooperative: Self-Governance in Sustainable Rural Development[END_REF][START_REF] Renting | Reconnecting Nature, Farming and Society: Environmental Cooperatives in the Netherlands as Institutional Arrangements for Creating Coherence[END_REF][START_REF] Wiskerke | Environmental co-operatives as a new mode of rural governance[END_REF][START_REF] Stobbelaar | Internalization of agrienvironmental policies and the role of institutions[END_REF][START_REF] Termeer | Integrating self-governance in heavily regulated policy fields: insights from a Dutch farmers' cooperative[END_REF].

With regard to the implementation of agri-environmental schemes, priority has been given to collective rather than individual applications since 2000 (Franks and Mc Gloin, 2007a;2007b). While some ECs had received and distributed payments to farmers, contracting with ECs as collectives turned out to be incompatible with the EU regulations at the time. From 2003, ECs were compensated by national funds for their role in coordinating their members' applications to agri-environmental schemes while payments were directed to farmers (Franks and McGloin, 2007b;OECD, 2013).

In anticipation of the recognition of farmer groups as eligible beneficiaries of agri-environmental payments in the 2014-2020 EU rural development program, the Ministry of Agriculture chose four ECs as pilot projects to assess the feasibility and added value of the collective implementation of agrienvironmental measures (Ministry of Economic Affairs, 2011;OECD, 2013;[START_REF] Westerink | Scale and Self-Governance in Agri-Environment Schemes: Experiences with Two Alternative Approaches in the Netherlands[END_REF].

In 2016, the Dutch government chose to implement agri-environmental schemes through collective applications only. New farmer collectives were established as formal contract partners of the regional governments in charge of the implementation of agri-environmental policy. While some of the collectives were initiated by the original ECs, others were created by farmer unions [START_REF] Terwan | The cooperative approach under the new Dutch agri-environment-climate scheme. Background, procedures and legal and institutional implications[END_REF][START_REF] Jongeneel | Farmer groups as a device to ensure the provision of agrienvironmental services in the Netherlands: a procurement perspective[END_REF]. There are currently 40 new collectives, involving more than 6,300 farmers and covering a land area of 68,000 hectares [START_REF] Jongeneel | Farmer groups as a device to ensure the provision of agrienvironmental services in the Netherlands: a procurement perspective[END_REF].

There is no formal appraisal of the environmental impact of ECs, however, they are perceived as being ecologically effective for their positive influence on the participation of farmers in agri-environmental schemes and on the evolution of agricultural practices (Franks and Mc Gloin, 2007a;2007b;[START_REF] Smits | Governing agri-environmental schemes: lessons to be learned from the new institutional economics approach[END_REF][START_REF] Slangen | Economic and ecological effectiveness of collective nature and wildlife conservation contracts[END_REF][START_REF] Van Dijk | Collective agri-environment schemes: How can regional environmental cooperatives enhance farmers' intentions for agrienvironmental schemes?[END_REF]. Data collected between 1995 and 2000 on trends in the nitrogen surpluses of member farms of the two first ECs (VEL and VANLA1 ) and a regional reference group of farms show that member farms realized lower nitrogen surpluses and reduced these losses at a higher rate than the regional average over the five years [START_REF] Renting | Reconnecting Nature, Farming and Society: Environmental Cooperatives in the Netherlands as Institutional Arrangements for Creating Coherence[END_REF].

In 2000, 33% of VEL and VANLA dairy farmers reached nitrogen surpluses below the national policy objectives of 2003 while only 10% of dairy farms at the national level achieved this result [START_REF] Sonneveld | Methodological Considerations for Nitrogen Policies in the Netherlands Including a New Role for Research[END_REF].

The "Ferti-Mieux" operations in France

The "Ferti-Mieux" operations were launched in 1991 by the French Ministry of Agriculture. Managed by the National Association for Agricultural Development (ANDA)2 , the goal was to promote and label local collective actions of farmers for a better management of nitrogen use at a water catchment level [START_REF] Papy | Quelles organisations territoriales pour concilier production agricole et gestion des ressources naturelles? Etudes et Recherches sur les Systèmes agraires et le Développement[END_REF]. Within this frame, farmers voluntary committed to changing their practices to limit water pollution with no financial compensation, along collectively defined prescriptions. Participating farmers benefited from free technical support for modifying their practices, on the basis of a diagnosis of the local context (water resource system, farming systems, sources and risks of nitrate pollution). Participants also benefited from the label "Ferti-Mieux" as official recognition that their farming practices limited the risk of water pollution.

At the national level, a national steering committee gathering representatives from the Ministries of Agriculture and Environment, the Water Agencies and farmers' organizations was in charge of defining the overall orientations of the "Ferti-Mieux" program. A national scientific and technical committee involving researchers and technical representatives of agricultural organizations was responsible for the evaluation of local operations as a basis for the decision to award the "Ferti-Mieux" label. At the local level, a steering committee and a technical committee involving farmers' organizations, local public agencies and in some cases water suppliers and agro-industrial cooperatives were in charge of the management of operations. A coordinator (usually working for a local Agricultural Chamber3 ) was responsible for defining, together with the participating farmers, nitrogen management plans [START_REF] Sebillotte | Ferti-Mieux. Une opération de lutte contre les pollutions par les nitrates[END_REF].

A pre-label was granted to local operations based on two criteria: (i) the area covered by the involvement of farmers in the water catchment and (ii) the adaptation of the nitrogen management plan to the local context. The official "Ferti-Mieux" label was granted and renewed if the agreed changes in farmers' practices were effective [START_REF] Ramonet | Le développement durable, réponse aux enjeux agricoles et environnementaux[END_REF].

Between 1991 and 2001, 65 operations were granted the "Ferti-Mieux" label, involving approximately 35000 farmers and representing 4.6% of the agricultural area. The effects of the "Ferti-Mieux" operations on water pollution were mixed with no evidence of a decrease in nitrate rates in groundwater bodies; however, this could be attributable to the time lags in groundwater quality response to changes in agricultural practices. In areas where surface waters were targeted, more than a half of the operations led to a decrease or stabilization of nitrate rates, demonstrating the environmental relevance of the operations [START_REF] Papy | Quelles organisations territoriales pour concilier production agricole et gestion des ressources naturelles? Etudes et Recherches sur les Systèmes agraires et le Développement[END_REF].

Following the dissolution of ANDA in 2002, the "Ferti-Mieux" operations were officially stopped at the national level. However, Agricultural Chambers and the Water Agency of the Rhin-Meuse water basin decided to undertake similar operations under the name "Agri-Mieux." Indeed, the ongoing "Ferti-Mieux" operations in the area were evaluated as successful in terms of farmers' involvement and water quality improvement. The new "Agri-Mieux" operations have the additional objective of reducing diffuse pesticide pollution [START_REF] Bernard | Gestion concertée de l'eau en Lorraine. Quels enseignements tirer d'une opération locale Ferti-Mieux ?[END_REF]. In Lorraine, eleven "Agri-Mieux" operations gather 22% of farmers, covering 25% of the agricultural area in the region, while in Alsace, 4500 farmers participate in eight operations in the plain area [START_REF] Rettel | Les opérations Agri-Mieux[END_REF][START_REF] Burtin | Rencontre des présidents Agri-Mieux du bassin Rhin-Meuse -12 novembre[END_REF].

Results

The advantages of collective approaches to regulation and incentive schemes for diffuse pollution control are specified in Section 4.1. Factors affecting the potential of cooperation are presented in Section 4.2.

The advantages of hybrid policy instruments relying on collective action for diffuse pollution control

Reaching the objectives of water quality improvement requires action that extends beyond farm boundaries at the scale of the drinking water catchment or watershed. Coordination at the appropriate scale of management can be achieved by regulations through zoning. For example, the EU Nitrate Directive is implemented in areas designated as "vulnerable zones" for nitrate pollution. Agrienvironmental incentive schemes are also frequently offered in specific areas chosen to match the environmentally relevant scales (Prager, 2015a;[START_REF] Westerink | Collaborative governance arrangements to deliver spatially coordinated agri-environmental management[END_REF]. However, the incentives provided, on an individual farm basis, are not linked to the implementation of measures at a larger scale [START_REF] Goldman | Institutional incentives for managing the landscape: Inducing cooperation for the production of ecosystem services[END_REF][START_REF] Mettepenningen | Investigating the influence of the institutional organisation of agri-environmental schemes on scheme adoption[END_REF]. Collective contracts with groups of farmers allow environmental actions to be taken across land management boundaries [START_REF] Falconer | Farm-level constraints on agri-environmental scheme participation: a transactional perspective[END_REF]Franks and McGloin, 2007a;[START_REF] Mettepenningen | Investigating the influence of the institutional organisation of agri-environmental schemes on scheme adoption[END_REF].

The agricultural impact in terms of nitrate diffuse pollution shows high levels of spatial variation depending on hydroclimatic conditions, soil types and agricultural practices. The adaptation of measures to local conditions is thus of importance for an effective reduction of water pollution [START_REF] Lacroix | La territorialisation des politiques environnementales[END_REF]. However, designing precise measures may be very costly for public agencies in terms of information collection and processing. Relying on collective action permits taking advantage of the knowledge held by farmers about their own farming system and local environment (Stuiver et al., 2003;[START_REF] Wiskerke | Environmental co-operatives as a new mode of rural governance[END_REF][START_REF] Franks | Boundary organizations for sustainable land management: The example of Dutch Environmental Co-operatives[END_REF]. In turn, collective action among farmers favors their access to research and extension services [START_REF] Slangen | The Economic Aspects of Environmental Co-operatives for Farmers[END_REF]Franks and McGloin, 2007b).

The level of information asymmetry between public agencies and farms is an important issue in monitoring diffuse nitrate pollution [START_REF] Shortle | The economics of nonpoint pollution control[END_REF]. Relying on a collective for controlling and enforcing farmers' practices will lower public costs [START_REF] Slangen | The Economic Aspects of Environmental Co-operatives for Farmers[END_REF][START_REF] Renting | Reconnecting Nature, Farming and Society: Environmental Cooperatives in the Netherlands as Institutional Arrangements for Creating Coherence[END_REF]. Compared to public agencies, farmers' collectives may be advantaged by easier access to information and the possibility of using enforcement mechanisms such as trust or reputation [START_REF] Falconer | Developing Co-operative Approaches to Agri-environmental Policy: a Transaction Cost Perspective on Farmer Participation in Voluntary Schemes[END_REF][START_REF] Franks | The collective provision of environmental goods: a discussion of contractual issues[END_REF][START_REF] Westerink | Scale and Self-Governance in Agri-Environment Schemes: Experiences with Two Alternative Approaches in the Netherlands[END_REF]. Still, public agencies will remain ultimately accountable for the group's performance and thus will incur some monitoring and enforcement costs (OECD, 1998;[START_REF] Falconer | Developing Co-operative Approaches to Agri-environmental Policy: a Transaction Cost Perspective on Farmer Participation in Voluntary Schemes[END_REF].

Farmers may be more willing to comply with measures they contribute to design than with measures externally imposed to them. There is growing empirical evidence on the effects of external interventions (positive monetary rewards or regulations with sanctions) on the intrinsic motivation of individuals [START_REF] Frey | Motivation crowding theory[END_REF][START_REF] Moller | Self-determination theory and public policy: improving the quality of consumer decisions without using coercion[END_REF][START_REF] Akers | Motivational Crowding in Payments for Ecosystem Service Schemes: a Global Systematic Review[END_REF]. More particularly, external interventions may crowd out motivation if individuals affected perceive them to be controlling. As a result, individuals react by reducing their intrinsic motivation in the activity controlled [START_REF] Frey | Motivation crowding theory[END_REF]. Self-organization for the definition of actions to address diffuse pollution may thus improve the extent to which policy objectives are reached, by enabling farmers to endorse the policy goals [START_REF] Stobbelaar | Internalization of agrienvironmental policies and the role of institutions[END_REF]OECD, 2013).

Several studies have shown that significant transaction costs have been associated with the implementation of agri-environmental schemes in the EU context, both for implementation agencies and for the participating farmers [START_REF] Falconer | Farm-level constraints on agri-environmental scheme participation: a transactional perspective[END_REF][START_REF] Falconer | An Investigation of Policy Administrative Costs Using Panel Data for the English Environmentally Sensitive Areas[END_REF][START_REF] Mettepenningen | Measuring private transaction costs of European agri-environmental schemes[END_REF][START_REF] Mettepenningen | Public transaction costs of agri-environmental schemes and their determinants -Analyzing stakeholders' involvement and perceptions[END_REF]. Transaction costs borne by farmers include the search and information costs involved in their decision to participate in an agri-environmental program as well as the contracting costs linked to the administrative tasks required with participation. Public agencies also incur contracting costs with the management of farmers' applications and monitoring and enforcement costs of farmers' compliance with the prescriptions. The transaction costs borne by farmers have been shown to constrain their participation in the schemes and thus the achievement of environmental objectives. In this regard, smaller farms may be relatively more affected due to the presence of high fixed transaction costs (e.g., required farm audits for participation) [START_REF] Falconer | Farm-level constraints on agri-environmental scheme participation: a transactional perspective[END_REF].

Transactional economies of scale may be achieved by making collective management agreements [START_REF] Falconer | Farm-level constraints on agri-environmental scheme participation: a transactional perspective[END_REF]. Information and knowledge sharing about agri-environmental schemes and implications of participation within a group may reduce the costs of decision-making for individual farmers (OECD, 1998;[START_REF] Franks | Boundary organizations for sustainable land management: The example of Dutch Environmental Co-operatives[END_REF][START_REF] Mettepenningen | Investigating the influence of the institutional organisation of agri-environmental schemes on scheme adoption[END_REF]. Collective applications for participation in agri-environmental schemes may also reduce contracting costs, both for the farmers and for the public agencies in charge [START_REF] Mettepenningen | Public transaction costs of agri-environmental schemes and their determinants -Analyzing stakeholders' involvement and perceptions[END_REF]. Several studies report effective transaction cost savings achieved in the implementation of agri-environmental schemes in the Netherlands with the development of collective contracts between the administration and the Environmental Cooperatives (Franks and McGloin, 2007a;2007b;[START_REF] Smits | Governing agri-environmental schemes: lessons to be learned from the new institutional economics approach[END_REF][START_REF] Slangen | Economic and ecological effectiveness of collective nature and wildlife conservation contracts[END_REF][START_REF] Franks | The collective provision of environmental goods: a discussion of contractual issues[END_REF]Prager, 2015b). [START_REF] Van Dijk | Collective agri-environment schemes: How can regional environmental cooperatives enhance farmers' intentions for agrienvironmental schemes?[END_REF] found, on the basis of a quantitative empirical study, that the facilitating role played by ECs in collective agri-environmental schemes was positively related to farmers' intentions to participate in the schemes.

Collective approaches to regulatory and incentive instruments may thus present some advantages for reaching water quality objectives in a cost-efficient way. The achievement of cooperation among farmers will however depend on a number of conditions identified on the basis of the SES framework.

The factors affecting the potential of collective action

The potential of collective action depends on the expected benefits and transaction costs associated with farmers' participation in cooperation. The first subsection presents the factors likely to affect the extent of benefits that farmers can draw from collective action oriented towards the management of water quality. In the second subsection, the variables that may influence the transaction costs of cooperation are reviewed. The variables identified through the literature review are presented in Table 3. References for each variable are given in Appendix 2.

The factors affecting the private benefits of farmers

As discussed above, farmers have little direct economic incentive to engage in collective action for diffuse pollution control. In some instances, they can benefit from cost savings by changing their farming practices. However, the extent of these cost savings will vary according to the type of farming system (A2.1). In a context of intensive crop farming, reducing mineral fertilization may induce high costs while cattle breeding farms have the potential to substitute organic for mineral fertilization to a certain extent (AE RMC, 2007b;[START_REF] Lacroix | La territorialisation des politiques environnementales[END_REF]. Prevailing inefficiencies in production methods as well as personal characteristics of farmers (attitudes and skills) also affect the potential for increased economic benefits [START_REF] Brouwer | Occurrence of Co-operative Agreements[END_REF][START_REF] Groot | Evolution of farm management, nitrogen efficiency and economic performance on Dutch dairy farms reducing external inputs[END_REF].

The development of ecolabels or ecotourism as additional economic motivations will depend on the existence of a demand for "green" products and activities [START_REF] Ribaudo | Ecosystem services from agriculture: Steps for expanding markets[END_REF][START_REF] Grolleau | Designing watershed programs to pay farmers for water quality services: case studies of Munich and New York City[END_REF]OECD, 2013). Several ECs have pursued initiatives related to regional marketing and agritourism to provide additional benefits to their members [START_REF] Renting | Reconnecting Nature, Farming and Society: Environmental Cooperatives in the Netherlands as Institutional Arrangements for Creating Coherence[END_REF][START_REF] Termeer | Integrating self-governance in heavily regulated policy fields: insights from a Dutch farmers' cooperative[END_REF]. Conversely, if market incentives (S5) are such that participation in collective action leads to drastic income reductions, farmers will be less willing to engage into cooperation. [START_REF] Busca | La mise en oeuvre négociée des dispositifs publics agri-environnementaux : appropriation stratégique, effets d'organisation et enjeux de territoire[END_REF] found farmers' participation in Ferti-Mieux operations to be lower in areas in which the economic weight of supply chains for high quality cereals was high. Restrictions on fertilization have a direct impact on farmers' capacities to access such supply chains in terms of product quality (e.g., the high protein content of the produce) or quantity. Not surprisingly, the "Ferti-Mieux" operations involving agro-industrial cooperatives or other trading partners were identified as attracting stronger support from farmers [START_REF] Busca | La mise en oeuvre négociée des dispositifs agri-environnementaux. Effets d'organisation, enjeux de territoire et dynamique d'appropriation stratégique[END_REF][START_REF] Verron | Synthèse des opérations Ferti-Mieux: opérations de conseils ou protoobservatoires?[END_REF].

Two further motivations can be identified in relation to the expected economic benefits associated with collective action. The threat of regulations or penalties (S4.1.1) may encourage voluntary collective action by reducing expected net farm profits [START_REF] Ayer | Grass Roots Collective Action: Agricultural Opportunities[END_REF]. This can be illustrated by the emergence of the first environmental cooperatives in the Netherlands. The two cooperatives VEL and VANLA were created in the Frisian Woodlands area as a reaction among farmers to a series of national regulations aiming at limiting the environmental impacts of agriculture (including the reduction of nitrogen losses by dairy farms) [START_REF] Glasbergen | The Environmental Cooperative: Self-Governance in Sustainable Rural Development[END_REF][START_REF] Stobbelaar | Internalization of agrienvironmental policies and the role of institutions[END_REF]. Farmers considered these policies to threaten the viability of their local farming systems and to be ineffective with regard to the environmental objectives targeted [START_REF] Renting | Reconnecting Nature, Farming and Society: Environmental Cooperatives in the Netherlands as Institutional Arrangements for Creating Coherence[END_REF][START_REF] Wiskerke | Environmental co-operatives as a new mode of rural governance[END_REF]. The two cooperatives negotiated with the Dutch government for exceptions concerning the application of state regulations and committed in exchange to undertake alternative actions to reduce nitrogen losses [START_REF] Wiskerke | Environmental co-operatives as a new mode of rural governance[END_REF][START_REF] Franks | Boundary organizations for sustainable land management: The example of Dutch Environmental Co-operatives[END_REF]. The threat of regulation by public water utilities was also identified as a factor favoring the participation of farmers in Ferti-Mieux operations in drinking water catchments [START_REF] Bernard | Gestion concertée de l'eau en Lorraine. Quels enseignements tirer d'une opération locale Ferti-Mieux ?[END_REF]AE RMC, 2007b).

Another motivation for cooperation can be to gain political weight. Farmer-led collectives may be seen by farmers as a political tool to influence policy decisions in favor of their economic interests.

The Environmental Cooperatives have become major actors in agri-environmental policy definition in the Netherlands (Franks and McGloin, 2007a). Their emergence and success among farmers may be explained by the initial dominance of ecological expertise in the definition of environmental policies in the Dutch context, which led to a weak representation of farmers' interests [START_REF] Daniel | The multifunctionality of agriculture and contractual policies. A comparative analysis of France and the Netherlands[END_REF]Franks and McGloin, 2007a;2007b;[START_REF] Franks | A blueprint for green co-operatives: organisations for co-ordinating environmental management across farm holdings[END_REF]2010). The role of political representation (S4.1.2) as a strong driver for environmental collective action was less important in France, where an institutionalized co-management of agri-environmental policies between the State and farmers' organizations has for a long time permitted farmers to effectively represent their perspectives [START_REF] Brives | L'environnement, Nouveau Pré Carré Des Chambres D'agriculture ? Ruralia[END_REF][START_REF] Daniel | The multifunctionality of agriculture and contractual policies. A comparative analysis of France and the Netherlands[END_REF]. This may help explain the lack of support provided by agricultural professional organizations to the national Ferti-Mieux program, which was identified as an obstacle to its continuation after the dissolution of ANDA [START_REF] Sebillotte | Ferti-Mieux. Une opération de lutte contre les pollutions par les nitrates[END_REF].

Finally, a stronger sensitivity to water protection (A8.1) was identified as a factor influencing farmers' participation in Ferti-Mieux operations [START_REF] Sebillotte | Ferti-Mieux. Une opération de lutte contre les pollutions par les nitrates[END_REF]. In contrast, [START_REF] Stobbelaar | Internalization of agrienvironmental policies and the role of institutions[END_REF] and [START_REF] Van Dijk | Collective agri-environment schemes: How can regional environmental cooperatives enhance farmers' intentions for agrienvironmental schemes?[END_REF] identified diverse attitudes towards environmental conservation among EC members. This could be explained by the difference in the general objectives of the two cases of collective action. While the Ferti-Mieux program promoted changes in farming practices without any financial compensation, the ECs have aimed at improving both the ecological and economic performance of agriculture.

The factors affecting the transaction costs of collective action

Among the factors affecting the transaction costs of collective action, the characteristics of actors involved were found to play a major role.

In the case of "Ferti-Mieux," the success of operations was clearly related to the number of participants (A1) involved. Operations initially involving a large number of farmers either failed or split up into smaller subgroups [START_REF] Kockmann | La dynamique des opérations Ferti-Mieux : une réponse durable aux questions d'environnement[END_REF][START_REF] Verron | Synthèse des opérations Ferti-Mieux: opérations de conseils ou protoobservatoires?[END_REF]. The environmental cooperatives in the Netherlands show great variation in the number of their members, ranging from 15 to 1700 members (Franks and McGloin, 2007a). [START_REF] Westerink | Collaborative governance arrangements to deliver spatially coordinated agri-environmental management[END_REF] found that the larger size of a cooperative positively influenced its organizational capacity and institutional capital while putting at risk the social links between the association and its members. With regard to group composition, heterogeneity (A2.2) in production systems and individual abatement costs of farmers may increase the bargaining costs of defining the actions to implement for the prevention of water pollution [START_REF] Grolleau | Designing watershed programs to pay farmers for water quality services: case studies of Munich and New York City[END_REF]. Heterogeneity in preferences for environmental preservation of group members is also likely to constrain the agreement process [START_REF] Lubell | Watershed partnerships and the Emergence of Collective Action Institutions[END_REF]. The participation of farmers and non-farmers may also increase decision-making costs. In the case of the ECs, the different goals and perspectives of farmers and other stakeholders (e.g., environmental associations or water suppliers) could lead to conflicts (Franks and McGloin, 2007a). While heterogeneity in preferences and interests among group members appears to be a barrier to collective action, heterogeneity in terms of resources and skills may be a positive factor (OECD, 2013). In some ECs, the participation of nonfarmers was also recognized as bringing complementary resources, knowledge and skills [START_REF] Franks | A blueprint for green co-operatives: organisations for co-ordinating environmental management across farm holdings[END_REF][START_REF] Uetake | Agri-environmental Management Through Collective Action[END_REF].

The presence of a local leader/social entrepreneur (A5) able to stimulate and animate collective action also appears to be an important factor [START_REF] Davies | Challenges in creating local agrienvironmental cooperation action amongst farmers and other stakeholders[END_REF]. The most successful "Ferti-Mieux" operations were characterized by the involvement of a coordinator familiar with the local context and considered to be knowledgeable and trustworthy by farmers [START_REF] Kockmann | La dynamique des opérations Ferti-Mieux : une réponse durable aux questions d'environnement[END_REF]AE RMC, 2007a;2007b;[START_REF] Verron | Synthèse des opérations Ferti-Mieux: opérations de conseils ou protoobservatoires?[END_REF]. The role of respected leaders was identified as crucial in the emergence and success of ECs as well [START_REF] Franks | A blueprint for green co-operatives: organisations for co-ordinating environmental management across farm holdings[END_REF]2011). Political and inter-organizational leadership also proved important for negotiating rules and policies favorable to the development of ECs with public authorities at the local and national levels [START_REF] Franks | Boundary organizations for sustainable land management: The example of Dutch Environmental Co-operatives[END_REF][START_REF] Termeer | Integrating self-governance in heavily regulated policy fields: insights from a Dutch farmers' cooperative[END_REF].

The existence of trust and shared norms of reciprocity (A6) was found to play a crucial role in the success of ECs and Ferti-Mieux operations [START_REF] Polman | Self-organising and self-governing of environmental cooperatives: design principles[END_REF][START_REF] Eshuis | Trust and monitoring in governance processes: lessons from landscape management by farmers in a Dutch municipality[END_REF][START_REF] Kockmann | La dynamique des opérations Ferti-Mieux : une réponse durable aux questions d'environnement[END_REF]. Local networks in small communities favor the development of trust [START_REF] Eshuis | Trust and monitoring in governance processes: lessons from landscape management by farmers in a Dutch municipality[END_REF]. However, [START_REF] Lundqvist | Games Real Farmers Play: knowledge, memory and the fate of collective action to prevent eutrophication of water catchments[END_REF] documents the case of a failed attempt to induce collective action in a water catchment in Sweden where collective memories of trust and reputation within the farming community seemed to rule out any possibility of cooperation. Further, [START_REF] Davies | Challenges in creating local agrienvironmental cooperation action amongst farmers and other stakeholders[END_REF] stress that the match between the optimal management scale and informal social networks is context specific. The authors found in the Scottish context that, most often, strong social relationships do not fall in contiguous spatial patterns, but may be scattered throughout a local area.

Finally, the costs associated with the definition and assessment of actions depend on the knowledge of the hydrogeological system (A7). In both EC and Ferti-Mieux cases, the definition of measures targeting nitrate diffuse pollution benefited from partnerships with research and technical institutes [START_REF] Kockmann | La dynamique des opérations Ferti-Mieux : une réponse durable aux questions d'environnement[END_REF][START_REF] Bernard | Gestion concertée de l'eau en Lorraine. Quels enseignements tirer d'une opération locale Ferti-Mieux ?[END_REF][START_REF] Stuiver | The Vel and Vanla Environmental Co-Operatives as Field Laboratories[END_REF][START_REF] Eshuis | Learning in Context through Conflict and Alignment: Farmers and Scientists in Search of Sustainable Agriculture[END_REF][START_REF] Van Der Ploeg | Dealing with Novelties: A Grassland Experiment Reconsidered[END_REF]AE RMC, 2007a;2007b). The monitoring of water quality may also serve as a tool for enhancing farmers' involvement in collective action to the extent that the response time of the water system allows for short-term and visible results of changes in farming practices [START_REF] Bernard | Gestion concertée de l'eau en Lorraine. Quels enseignements tirer d'une opération locale Ferti-Mieux ?[END_REF]AE RMC, 2007b;[START_REF] Verron | Synthèse des opérations Ferti-Mieux: opérations de conseils ou protoobservatoires?[END_REF].

Further, two variables characterizing the resource system were identified as influencing the level of transaction costs. In relation to the size and heterogeneity of the group of participants, the size of the water catchment or watershed (RS3.1) will affect the likelihood of successful collective action. A larger water basin means a larger number of farmers and potentially more heterogeneity in their farming systems [START_REF] Brouwer | Occurrence of Co-operative Agreements[END_REF]. Ferti-Mieux operations located in large water basins usually split up into groups working at a sub-basin scale [START_REF] Kockmann | La dynamique des opérations Ferti-Mieux : une réponse durable aux questions d'environnement[END_REF]. The predictability of water system dynamics (RS7) is likely to affect the costs of defining the actions to implement and the costs of assessing their impact on water quality [START_REF] Nimmo Smith | Evaluating the Implementation of the Nitrates Directive in Denmark and England using an Actor-Oriented Approach[END_REF][START_REF] Grolleau | Designing watershed programs to pay farmers for water quality services: case studies of Munich and New York City[END_REF].

The short time lag between changes in agricultural practices and the evolution of nitrate concentrations in hydrosystems targeted by Ferti-Mieux operations in the Lorraine region facilitated an evaluation of the effectiveness of actions [START_REF] Bernard | Gestion concertée de l'eau en Lorraine. Quels enseignements tirer d'une opération locale Ferti-Mieux ?[END_REF]AE RMC, 2007b).

Transaction costs of collective action will also strongly depend on the rules defined for the decisionmaking process and the enforcement of decisions within the group.

The two cases of ECs and Ferti-Mieux operations highlight the positive effect of an autonomous design of the rules by participants (GS6.1). In the Netherlands, all Environmental Cooperatives have developed their own rules (Franks and McGloin, 2007a;[START_REF] Franks | A blueprint for green co-operatives: organisations for co-ordinating environmental management across farm holdings[END_REF]2011;[START_REF] Termeer | Integrating self-governance in heavily regulated policy fields: insights from a Dutch farmers' cooperative[END_REF]. In France, farmers created independent structures (e.g., associations), through which they could define and enforce their own rules while remaining within the general "Ferti-Mieux" frame. This greater autonomy among farmers was identified as having a positive effect on the durability of operations [START_REF] Kockmann | La dynamique des opérations Ferti-Mieux : une réponse durable aux questions d'environnement[END_REF]AE RMC 2007b).

Most cooperatives have developed monitoring and sanctioning systems (GS8), involving members or external professionals. Sanctions used by ECs include warnings, exclusion from activities and/or financial penalties [START_REF] Polman | Self-organising and self-governing of environmental cooperatives: design principles[END_REF][START_REF] Eshuis | Trust and monitoring in governance processes: lessons from landscape management by farmers in a Dutch municipality[END_REF]. The board of cooperatives may also exclude individual members who do not respect the agreed rules [START_REF] Wiskerke | Environmental co-operatives as a new mode of rural governance[END_REF]. Evidence suggests that the use of a graduated system of sanctions, observed in some ECs, is effective in preventing free-riding from members [START_REF] Polman | Self-organising and self-governing of environmental cooperatives: design principles[END_REF][START_REF] Eshuis | Trust and monitoring in governance processes: lessons from landscape management by farmers in a Dutch municipality[END_REF][START_REF] Termeer | Integrating self-governance in heavily regulated policy fields: insights from a Dutch farmers' cooperative[END_REF][START_REF] Westerink | Collaborative governance arrangements to deliver spatially coordinated agri-environmental management[END_REF]. In the Ferti-Mieux case, the evaluation of farmers' practices was realized by the local technical committee and then validated at the national level. Evaluation was based on direct visits and checks of a representative sample of individual farms [START_REF] Verron | Synthèse des opérations Ferti-Mieux: opérations de conseils ou protoobservatoires?[END_REF]. The risk of non-renewability of the Ferti-Mieux label was real: 12% of the operations lost their label between 1991 and 2001 [START_REF] Ramonet | Le développement durable, réponse aux enjeux agricoles et environnementaux[END_REF].

Finally, government policies can help lower the transaction costs associated with collective action [START_REF] Lubell | Watershed partnerships and the Emergence of Collective Action Institutions[END_REF]OECD, 2013;[START_REF] Villamayor-Tomas | Diagnosing the role of the state for local collective action: Types of action situations and policy instruments[END_REF]. The Dutch Ministry of Agriculture supported the development of Environmental Cooperatives through grants to cover start-up costs [START_REF] Glasbergen | The Environmental Cooperative: Self-Governance in Sustainable Rural Development[END_REF][START_REF] Franks | A blueprint for green co-operatives: organisations for co-ordinating environmental management across farm holdings[END_REF]2010), by approving exemptions from general regulations and adjusting the national agri-environmental program to include an option of joint applications from EC members [START_REF] Wiskerke | Environmental co-operatives as a new mode of rural governance[END_REF]Franks and Mc Gloin, 2007a;2007b;[START_REF] Franks | Boundary organizations for sustainable land management: The example of Dutch Environmental Co-operatives[END_REF][START_REF] Westerink | Scale and Self-Governance in Agri-Environment Schemes: Experiences with Two Alternative Approaches in the Netherlands[END_REF]. External support from public agencies (S4.1.3) also included the provision of expert knowledge and administrative support as well as research funding [START_REF] Glasbergen | The Environmental Cooperative: Self-Governance in Sustainable Rural Development[END_REF][START_REF] Franks | Boundary organizations for sustainable land management: The example of Dutch Environmental Co-operatives[END_REF][START_REF] Termeer | Integrating self-governance in heavily regulated policy fields: insights from a Dutch farmers' cooperative[END_REF]. [START_REF] Termeer | Integrating self-governance in heavily regulated policy fields: insights from a Dutch farmers' cooperative[END_REF] note that the fragmentation of public organizations in the Netherlands could have acted as a constraint for collectives seeking access to various resources. In the French context, public funding compensated the extra-costs of coordination and follow up of the "Ferti-Mieux" operations [START_REF] Verron | Synthèse des opérations Ferti-Mieux: opérations de conseils ou protoobservatoires?[END_REF]. Public support also took the form of providing rules for framing collective action among farmers and the labeling of operations [START_REF] Kockmann | La dynamique des opérations Ferti-Mieux : une réponse durable aux questions d'environnement[END_REF]. It seems that such support was crucial to the emergence and durability of local collective actions. After the official stop of the policy at the national level, most operations collapsed, except in the Rhin-Meuse water basin area where the Water Agency decided to maintain a similar program at the water basin level [START_REF] Bernard | Gestion concertée de l'eau en Lorraine. Quels enseignements tirer d'une opération locale Ferti-Mieux ?[END_REF].

Discussion and conclusions

The analysis shows that collective action is a relevant tool to consider for improving the effectiveness and cost-effectiveness of regulatory and incentive policies targeting diffuse pollution from agriculture.

Self-organization by farmers for reaching regulatory objectives will be associated with lower design and enforcement costs for public agencies. A greater participation of farmers in the definition of measures that they must implement is also likely to increase their compliance and thus foster the realization of water quality objectives. Collective action for joint applications to agri-environmental schemes allows for transaction cost savings both for farmers and for public agencies compared to individual schemes. Cooperation will also improve environmental outcomes, as water quality improvements require action at a larger scale than at the individual farm level.

However, as stressed by scholars in the field of institutional economics [START_REF] Ostrom | Moving beyond panaceas: a multi-tiered diagnostic approach for socialecological analysis[END_REF][START_REF] Ménard | A new institutional economics perspective on environmental issues[END_REF], no single policy approach or instrument is likely to solve complex environmental problems in all settings. The results suggest that the success of collective action involving farmers depends on a number of conditions related to the characteristics of the resource, the actors involved, the governance of cooperation and the broader economic and political contexts (Table 3).

The size of the water system targeted, in conjunction with the number of potential participants and their degree of heterogeneity, was found to affect the likelihood of successful collective action, with a collective management of larger basins or catchments involving greater transaction costs. The less predictable are the hydrogeological system dynamics, the higher are the management costs.

The level of management costs also depends on the knowledge available to participants regarding the impact of farming practices on water quality. Among the characteristics of actors involved, the type of farming system and the preferences of farmers were found to potentially influence the private benefits drawn from collective action. Farmers incurring fewer costs in changing their practices and/or having strong preferences for environmental preservation will be more likely to participate in collective action. The results suggest that a larger number of farmers together with a greater diversity in preferences and farming systems increase the costs of collective action. However, the participation of non-farmers in collective action was identified as a positive factor for pooling the resources needed for cooperation. The presence of a leader or the existence of trust and social capital within the group of participants were shown to decrease transaction costs.

Characteristics of the governance system are identified as a crucial factor for the success of collective action within the SES framework. Especially, the presence of a control and sanction system was found to be important in limiting free-riding from participants in the two cases (Environmental Cooperatives and "Ferti-Mieux" operations). The analysis also highlights the positive effect of an autonomous design of rules by the participants.

Most factors highlighted by [START_REF] Ostrom | A General Framework for Analyzing Sustainability of Social-Ecological Systems[END_REF] as crucial for self-organization by users of a common-pool resource were also identified in the case of collective action for water pollution control (Table 3). Two variables were not found relevant for the analysis of collective action for diffuse pollution control: the productivity of the resource system and the resource unit mobility, in relation to the non-subtractive character of water quality [START_REF] Hinkel | A diagnostic procedure for applying the social-ecological systems framework in diverse cases[END_REF]. Further, the nature of market incentives, the political context and the existence of government support were identified as strongly determining the emergence and sustainability of agri-environmental cooperation. The importance of these conditions can be related to the public good nature of diffuse pollution control by farmers. In the presence of few direct economic incentives, the success of collective action will substantially depend on external economic and political incentives.

From a policy perspective, the findings of this paper may serve as a basis for assessing whether conditions are gathered for collective action to be an effective and cost-effective tool for diffuse pollution control. When applied to a specific setting, such a diagnostic may inform policy choices regarding the adoption of a collective approach and/or the design of measures addressing the constraints identified as bearing on collective action.

Combining transaction cost economics with the SES framework proved useful to assess the potential of hybrid policy instruments relying on collective action for water quality management in agriculture.

The results presented here were drawn from existing case studies mostly using different conceptual approaches to address this issue. Further investigation is needed, including direct empirical data collection to test the assumptions made on the factors identified as affecting cooperation for water pollution control.

Figure 1 :

 1 Figure 1: The SES framework (Source: McGinnis and Ostrom, 2014) First-tier variables are further characterized by second-tier variables identified in previous studies to influence interactions and outcomes in SESs (McGinnis and Ostrom, 2014) (Appendix 1). Among the

Table 2 :

 2 Two cases of agri-environmental collective action in the EU context: the Environmental Cooperatives in the Netherlands and the "Fertimieux" operations in France.

		Environmental Cooperatives	"Fertimieux" operations
		(The Netherlands)	(France)
	Initiative	Farmers	Public agencies
			(Ministry of Agriculture)
	Composition	Farmers or	Farmers and non-farmers
		Farmers and non-farmers
	Structure	Formal organization	Ad hoc network
	Funding	Member fees	Public agencies (Agricultural
		Public agencies	Chambers, Water Agencies, ANDA,
		(direct support, contracts)	local governments)
	Environmental	Multiple	Water quality
	"domain"	(water quality, biodiversity,
		wildlife)
	Activities	▪ Information sharing and advice	▪ Information sharing and advice
		provision	provision
		▪ Coordination of changes in	▪ Coordination of changes in
		agricultural practices	agricultural practices
		▪ Fundraising
		▪ Interest representation/lobbying
		▪ Research activities
	Sources: Franks and McGloin, 2007a; Verron, 2007.

Table 3 :

 3 The factors identified as affecting the benefits and costs of collective action

	First-tier variables	Second-, third-and fourth-tier variables
	Social, economic and political	S4 -Other governance systems
	settings (S)	S4.1 -Larger scale governance systems
		S4.1.1 -Regulatory threat
		S4.1.2 -Political representation of agricultural interests
		S4.1.3 -Support from public agencies
		S5 -Markets
	Resource system (S)	RS3 -Size of resource system *
		RS3.1 -Size of water catchment
		RS7 -Predictability of system dynamics *
	Governance system (GS)	GS6 -Collective-choice rules *
		GS6.1 -Autonomy at the collective choice level
		GS8 -Monitoring and sanctioning rules
	Actors (A)	A1 -Number of relevant actors *
		A2 -Socioeconomic attributes
		A2.1 -Type of farming system
		A2.2 -Heterogeneity of actors
		A5 -Leadership-entrepreneurship *
		A6 -Norms (trust-reciprocity)/social capital *
		A7 -Knowledge of the SES *
		A8 -Importance of the resource *
		A8.1 -Environmental preferences of farmers
	* Second-tier variables identified by Ostrom (2009) as crucial for self-organization by users for CPR
	management

These respectively are the acronyms for Vereniging Eastermar's Lânsdouwe and Vereniging Agrarish Natuur en Landschapsbeheer Achtkarspelen.

This association, which was disbanded in 2002, had a mixed membership of representatives from agricultural interest groups and the State. Its role was to provide advice to the Ministry of Agriculture and to fund agricultural development programs.

Agricultural Chambers in France are public organizations led by representatives of agricultural and other rural stakeholders. Agricultural Chambers are active at the regional and the department level.

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