The GAMELag box-model tool is used in a collaborative approach between scientists and ecosystem managers to determine admissible nutrient load in lagoon environments. This case study of its application in a hypereutrophic French Mediterranean lagoon demonstrated its ability to determine exogenous nutrient flows compatible with good ecological status. A new method, based on the exploratory analysis of simulated scenarios of flow reduction (exogenous and endogenous), revealed the predominant role of sediment stocks and exchanges in the ecological status of this lagoon. Reducing inflows from the catchment area allowed sediment release and initiated the restoration of this compartment. A reduction in exogenous nitrogen inputs by a factor of 0.24 and phosphorus by 0.1 was found to be necessary to achieve EU Water Framework Directive objectives. These results are helping lagoon managers to raise the awareness of local stakeholders and co-construct management measures to encourage a dynamic of restoration.

The sustainable management of water resources, whether surface or underground, requires the identification of the flows involved and the possibility of achieving the water balance of the water resource. These require knowledge of the main flow components with a sufficient level of accuracy. Hydrological simulation models are valuable tools for studying flow at the watershed scale but rely on data that are rarely available; therefore, they require the implementation of field investigations. There is thus a need for simple and practical tools for studying the functioning of a watershed and identifying the different components of the flows. In this paper, a method that uses only weather data, volumes of water abstraction by pumping or diversion, and flows measured at the outlet is proposed. The use of cumulative multi-year curves of measured flows or rainfall provides an assessment of the unknown flows that can take place in the watershed, as well as the order of the respective magnitudes of fast and slow flows. Its application to 20 French Mediterranean watersheds shows that it is possible to properly estimate the order of magnitude of losses or gains linked to karst flows and irrigation input. External inflows or outflows can represent up to 150% of the flow measured at the outlet. The annual volumes estimated by using this method are indeed very close (R-2 = 93%) to those provided by existing knowledge. The proposed method can constitute a first approach for the quantification of flows and help to guide the implementation of field investigations and more sophisticated approaches such as hydrological modelling.

Whatever the causes are water scarcity are likely to hinder the achievement of good status for water as required by the district Master Plans and the European Water Framework Directive In order to conciliate this aim with a sustainable water use satisfaction the water use ways have to evolve to reduce their adverse effects on the aquatic ecosystems Particularly in those areas showing water deficits a good knowledge of the available resource and a quantification of respectively the aquatic communities and the society needs for water is required it is therefore essential (1) to elaborate water protocols in order to share the maximum water volumes which may be abstracted from hydrosystems taking aquatic community needs into account and (2) to set up agreement based management rules where water is lacking The establishment of single structures for irrigation allows to divide fitted water volumes among farmers on relevant areas The Rhone-Mediterranee Water Master Plan aims to make the scarcity appears the later as possible on one hand and in priority the water demand reduction is encouraged through by water saving the optimization of functioning modes for existing equipments aso and when these have been done the building of new equipment for water storage when it has be demonstrated they do not hinder to the water good status achievement On the other hand it promotes restoration measures for the aquatic system morphology the recovering of wetlands aso so as to reduce the sensitivity of the hydrosystems to water scarcity The mid and long term strategies are favoured

La mise en place du programme de surveillance de la Directive-cadre européenne sur l'eau a conduit à une remise à plat des réseaux de collecte de données de la qualité des cours d'eau dans les bassins Rhône-Méditerranée et Corse. Les différents objectifs assignés au travers de ce programme (contrôles de surveillance, opérationnel, additionnel, d'enquête) et des autres besoins pour établir l'état écologique (conditions de référence notamment) ont induit diverses stratégies de collecte des données, tout à la fois spécifiques et complémentaires. La mise en oeuvre concrète de cette collecte de données doit, d'une part, répondre aux exigences des divers rapportages en termes de paramètres, fréquences, protocoles, méthodes, délais et, d'autre part, prendre en compte les contraintes organisationnelles et techniques d'une production, en routine, d'un très grand nombre de prélèvements et d'analyses avec un niveau de qualité compatible avec ces exigences. Cette collecte vise essentiellement à alimenter une base de connaissances à l'échelle nationale, fondée sur l'interopérabilité des bases de données gérées par différentes structures, de manière à mettre à disposition celles-ci via des portails nationaux et à produire des évaluations de l'état des cours d'eau sur des bases communes sur l'ensemble du territoire et cohérentes avec celles de nos voisins européens. Ainsi valorisées, ces données permettront d'affiner les dispositions techniques de la politique de l'eau et d'en évaluer les effets.