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International audience; Local development organisations are now widespread in rural regions of North Africa. In the past, these organisations were usually only involved in a few sector-specific activities. This study investigated the activities of 24 local development organisations in the Saharan regions of Morocco, Algeria and Tunisia. The fields of action of these organisations have expanded in the past decade, thanks to their increased capacity to handle relations with other actors. They have become active in defining what development means at the local level, although public administrations do not yet acknowledge such a role.

International audience

International audience; Groundwater resources are a crucial driver of development. Since the 1970s, the expansion of irrigated land on the margins of the existing 'traditional' oases has been encouraged by the Tunisian authorities to enhance local development. As a result, oases in Southern Tunisia are currently facing sustainability concerns. This situation requires alternative water management approaches, in which local actors collaborate and contribute to the design of new rules. To understand Tunisian oasis farmers' perceptions of water rules and public organisations, in 2021, we conducted an online survey in Jemna, an oasis in the Kebili region in Southern Tunisia. The picture that emerged from the online survey is that farmers in extension areas have distinctive characteristics but also similarities with farmers in the traditional oasis. Both types of farmers mainly cultivate date palm (monoculture), and, like farmers in the extensions, many farmers in the traditional oasis have a private borehole. All farmers in the Jemna oasis clearly perceive the limited availability and poor quality of the groundwater resource. However, they do not believe these problems cause conflict among farmers. They consider that, to solve possible conflicts and to ensure better water management in the oasis, collaboration among farmers is more effective than changes to rules issued by existing organisations. These preliminary results, if confirmed, can have important policy implications, as the farmers' perceptions of water rules and organisations, as well as farmers' willingness to collaborate, are crucial for a possible new approach to water management in the oasis.

The sedimentary contributions of the Medjerda to the coastal zone are poorly measured, and there is no chronicle of observations. In this context, the sediment monitoring appears indispensable for the quantification of sediment transport at the outlet. This study focuses on the largest watershed in Tunisia, the Wadi Medjerda (23 600 km2). The main objective of this work is to assess the reduction of sediment transport following anthropogenic intensification on the basin, especially since the construction of many large dams. In order to collect information on actual deposits over several years, the paleo-hydrological approach was applied through the study of sediment cores sampled in the low valley meanders on alluvial terraces, after the last dam (Sidi Salem, the largest water storage capacity over the basin), but before the estuary to avoid marine influence and near a hydrological station (Jdaida). The sedimentary deposits of the river provide key information on the past sedimentary inputs. A visible succession of sedimentary layers corresponding to the deposits of successive floods on the study site has been determined and the history of the sedimentary contributions of the Medjerda is reconstructed by this approach. The thickest layers of sedimentary deposits are related to exceptional events. They are mainly concentrated on the lower part of the core and are mainly composed of sands. The first 1.2 m of the core from the bottom upward relates to 10 years of river discharges, as can be determined from the 137Cs datation. The next upward 1.05 m of core relates to the following 20 years of discharges, up to 1981, date of the construction of the Sidi Salem dam, and is composed of a mix of sand, silts and clays. The last 75 cm of core near the surface is only composed of clays with thin silt bands, and relates to a period of 32 years. We thus observe that there is no more sand deposits in the river bed since the construction of the Sidi Salem dam. The deficit of sediment supply to the sea is viewed as a major factor to be taken into account for better understanding of the dynamics of coastal areas in the context of global climate change.

Harmful events associated with epibenthic dinoflagellates, have been reported more frequently over the last decades. Occurrence of potentially toxic benthic dinoflagellates, on the leaves of two magnoliophytes (Cymodocea nodosa and Zostera noltei) and thalli of the macroalgae (Ulva rigida), was monitored over one year (From May 2015 to April 2016) in the Bizerte Bay and Lagoon (North of Tunisia, Southern Mediterranean Sea). The investigated lagoon is known to be highly anthropized. This is the first report on the seasonal distribution of epibenthic dinoflagellates hosted by natural substrates, from two contrasted, adjacent coastal Mediterranean ecosystems. The environmental factors promoting the development of the harmful epibenthic dinoflagellates Ostreopsis spp., Prorocentrum lima and Coolia monotis were investigated. The highest cell densities were reached by Ostreopsis spp. (1.9 × 103 cells g−1 FW, in October 2015), P. lima (1.6 × 103 cells g−1 FW, in June 2015) and C. monotis (1.1 × 103 cells g−1 FW, in May 2015). C. nodosa and Z. noltei were the most favorable host macrophytes for C. monotis (in station L2) and Ostreopsis spp. (in station L3), respectively. Positive correlations were recorded between Ostreopsis spp. and temperature. Densities of the epibenthic dinoflagellates varied according to the collection site, and a great disparity was observed between the Bay and the Lagoon. Maximum concentrations were recorded on C. nodosa leaves from the Bizerte Bay, while low epiphytic cell abundances were associated with macrophytes sampled from the Bizerte Lagoon. The observed differences in dinoflagellate abundances between the two ecosystems (Bay-Lagoon) seemed not related to the nutrients, but rather to the poor environmental conditions in the lagoon. This work was supported by the LAGUNOTOX project funded byFondation TOTAL. Thanks to the IRD (Institut de Recherche pour leDéveloppement) and to the LMI COSYS-Med (Laboratoire MixteInternational Contaminants et Ecosystèmes Marins SudMéditerranéens) for funding Hela Ben Gharbia’s Ph.D. We would alsolike to thank the Tunisian National Institute of Agronomy for providingall necessary means forfield trips, and Zeineb Hentati for her help during sampling. Many thanks to Dr. Dorra Ben Gharbia for English improvement and to both anonymous reviewers for their precious help[CG] Appendix A Scopus

Highlights: • Picophytoplankton was able to grow under a wide range of environmental conditions varying seasonally. • Picophytoplankton variability was more marked in the bay than in the lagoon. • Picophytoplankton decreased in the lagoon under enhanced anthropogenic stress. • Synechococcus, the most abundant group of the community, was frequently present in both ecosystems during the monitoring. We investigated at the single cell level during 16months (June 2012 to September 2013) the temporal distribution of picophytoplankton (picoeukaryotes, Synechococcus and Prochlorococcus) communities in two contrasted ecosystems: the Bay of Bizerte characterised by an oligotrophic regime typical of the Mediterranean Sea and the Bizerte Lagoon that exhibits a mesotrophic/eutrophic state. We aimed at depicting seasonal variations and quantifying the relationships between the environmental factors and the structure and abundance of picophytoplankton communities. Results showed that picophytoplankton groups were able to grow under a wide range of environmental conditions varying seasonally, although their abundances and contributions to the total chlorophyll biomass significantly varied and showed importance in the Bay of Bizerte. Synechococcus was the most abundant group reaching 225*103 cells·cm-3 in the Bay and 278*103 cells·cm-3 in the lagoon. This group was present all over the year in both ecosystems. Structural equation model results pointed out a different configuration regarding the picophytoplankton environmental drivers. The complexity of the configuration, i.e. number of significant links within the system, decreased under enhanced eutrophication conditions. The less exposure to anthropogenic stress, i.e. in the Bay of Bizerte, highlight a larger role of nutrient and hydrological conditions on the seasonal variations of picophytoplankton, whereas a negative effect of eutrophication on picophytoplankton communities was unveiled in the Bizerte Lagoon. We stress that such influence may be exacerbated under expected scenarios of Mediterranean warming conditions and nutrient release in coastal ecosystems.

International audience; La cartographie participative est un outil qui peut transformer les représentations des acteurs et utilisateurs du paysage en cartes où cette aménité est classée selon une typologie donnée par les acteurs eux-mêmes. En Tunisie, nous assistons à des transformations et mutations des paysages forestiers et de montagnes dans le territoire Kroumirie – Mogods au Nord-ouest de la Tunisie. Cet ensemble de chaînons montagneux d’orientation NordEst / Sud-Ouest, se caractérise par la diversité des paysages où forêt, mer, lac de barrage, relief, etc. construisent une identité territoriale. Identifier et caractériser les paysages identitaires par le biais d’une approche cartographique et participative s’avère une étape fondamentale pour pouvoir les valoriser.

International audience; Harmful benthic dinoflagellates, usually developing in tropical areas, are expanding to temperate ecosystems facing water warming. Reports on harmful benthic species are particularly scarce in the Southern Mediterranean Sea. For the first time, three thermophilic benthic dinoflagellates (Ostreopsis cf. ovata, Prorocentrum lima and Coolia monotis) were isolated from Bizerte Bay (Tunisia, Mediterranean) and monoclonal cultures established. The ribotyping confirmed the morphological identification of the three species. Maximum growth rates were 0.59 ± 0.08 d−1 for O. cf. ovata, 0.35 ± 0.01 d−1 for C. monotis and 0.33 ± 0.04 d−1 for P. lima. Toxin analyses revealed the presence of ovatoxin-a and ovatoxin-b in O. cf. ovata cells. Okadaic acid and dinophysistoxin-1 were detected in P. lima cultures. For C. monotis, a chromatographic peak at 5.6 min with a mass m/z = 1061.768 was observed, but did not correspond to a mono-sulfated analogue of the yessotoxin. A comparison of the toxicity and growth characteristics of these dinoflagellates, distributed worldwide, is proposed.

In Tunisia the water resource is scarce. The study of the evolution of water management policies shows considerable institutional changes: from a central administration (offices) to associations of water users (GDA).All these institutional changes were not a request of the beneficiaries of irrigated activity. They are caused by a political system subject to the requirements of internal and external environment.Locally these institutional changes have important implications for the governance and performance of irrigation water management in irrigated areas.This thesis aims to understand the relationship between institutional transformation and local governance, on the one hand and to explain the relationship between governance and irrigation water performance, on the other hand,For methodology, it was conducted in three stages. In a first step, we use the model of David Easton to study the interactions between institutional changes and political system. In the second step, we adopt the Strategic Analyses approach of Michel Crozier (1997) to analyze the current governance of irrigation water. In the third step, we employ the game theory, specially prisoner and chicken dilemmas, to assess the effects of local governance on the farms performance. The irrigated areas in the delegation of Nadhour were chosen as investigation area. The results of this study have elucidated the research questions initially formulated. In fact, we confirmed that the difficult situation of the irrigated areas mainly due to problems in the governance of irrigation water. The institutional changes imposed by a political system lead to governance problems. This governance is the cause of the weak performances in the irrigated area.This study has concluded that an institution must be conceived as a social construct, which goes through a process of institutionalization allowing its internalization and acceptance by all local actors.Keywords: Coalition, conflict, cooperation, governance, institutions, games, power, performance, political system, rules, En Tunisie la ressource en eau est en rareté croissante. La concurrence est de plus en plus importante autour de cette ressource notamment en agriculture irriguée. L’étude de l’évolution des politiques de gestion de l’eau montre des transformations institutionnelles considérables allant d’une administration centrale (les offices) à des associations d’usagers de l’eau (les GDA actuels).Toutes ces transformations institutionnelles ne semblent pas être spontanées, ou sous la demande des bénéficiaires de l’activité irriguée, elles sont induites par un système politique soumis à des exigences de l’environnement interne et externe. A l’échelle locale ces changements institutionnels ont des conséquences sur le mode de gouvernance et sur la performance de la gestion d’eau d’irrigation dans les périmètres irrigués (PI). L’objet de cette thèse est double, mieux comprendre l’évolution institutionnelle ayant conduit à la gouvernance actuelle et apprécier les performances de dispositif actuellement opérationnel.Un cadre théorique basé sur la place des ressources naturelles dans les courants de pensées économiques a été adopté. Cette partie de la thèse a montré la limite des instruments fournis par les courants orthodoxes, notamment le marché et l’Etat. Ces limites sont à l’origine de développement des approches hétérodoxes, notamment avec les courants institutionnels qui ont considéré la gestion des ressources naturelles comme un construit social. Avec le développement de ces courants hétérodoxes, on note l’essor d’une nouvelle notion : la gouvernance. Ce terme est aujourd’hui en vogue, avec parfois des acceptions diverses et même divergentes. Raison pour laquelle, nous avons procédé à une conceptualisation puis à une caractérisation de cette notion.Du point de vue méthodologie, elle s’est déroulée en trois temps. Le premier temps, consiste à une étude des interactions entre les transformations des arrangements institutionnels et le système politique à travers le modèle de David Easton. Dans un deuxième temps, l’approche d’analyse stratégique de Crozier (1997) a été mise à profit pour analyser la gouvernance actuelle de l’eau d’irrigation. Dans un troisième temps, nous avons procédé à une appréciation des effets « des variables » de la gouvernance sur les acteurs locaux, notamment les irrigants, et ceci à travers les jeux des dilemmes de prisonnier et de poule mouillée.Dans cette démarche, les périmètres irrigués de la délégation de Nadhour ont été choisis comme terrain d’investigation. Les principaux résultats de ce travail ont permis d’élucider les questions de recherche initialement formulées.Mots clés : Coalition, conflit, coopération, gouvernance, institutions, jeux, pouvoir, performance, système politique, règles

International audience; We present the results of an experimental, theoretical, and also numerical study of free surface buried flows that we have undertaken in the laboratory LSTE of INAT. This work was conducted as part of collaboration with the engineering international office MECATER which included the construction of a new channel with large section in INAT, this channel was designed to study the losses in porous media with high porosity for which Darcy's law is no longer applicable. The experiments consisted in determining the evolution of the free surface for different geometrical characteristics of riprap and different flow rates. These tests were used to verify different laws of head loss proposed in the literature, by performing numerical simulations of the evolution of the water surface for each experiment. The analysis of our results shows that the Stephenson's formula is relevant to calculate the non-linear head loss for flows with high Reynolds number of pore. Furthermore, the simulations have highlighted the important role of porosity. These results should be confirmed by further tests to assess in particular the influence of the slope and to analyze the behavior of the flow at the inlet and outlet of the riprap.

International audience