The challenge of assessing the proper functioning conditions of coastal lagoons to improve their future management

International audienceThe sustainable management of coastal lagoon hydrosystems is a key issue for the socioeconomic and environmental development of many coastal areas worldwide. Often maintained by direct or indirect groundwater supplies, they provide a large range of ecosystem services, from which human societies take advantage. Twenty years after its implementation, a large majority of the Mediterranean lagoons have still not reached the "good status" required by the WFD. Several questions then arise as to the representativeness of the WFD indicators or the relevance of the restoration objectives considering the complexity, evolutionary and unpredictable nature of lagoon hydrosystems. This study proposes an innovative, multidisciplinary, long-term approach to define the proper functioning conditions of a costal lagoon hydrosystems, i.e. all the factors that contribute to the functioning of coastal lagoon hydrosystems and the connectivity with other biodiversity reservoirs, be they ecological, hydrological, social or political. By considering the lagoons and all its hydrological, ecological and societal proper functioning conditions over almost 200 years, this approach makes it possible to assess the influence of past natural and anthropogenic disturbances and support the implementation of future relevant hydrosystem-based management plans which have to be coordinated and politically driven. Defining proper restoration and management objectives should ensure that ecological functions are maintained based on current and future ecosystem benefits and uses. Considering the highly unpredictable nature of coastal hydrosystems, the state of an ecosystem should not only be evaluated on ecological or chemical criteria but also take into account socioeconomic and politica