Eutrophication of the Mediterranean Sea: a watershed—cascading aquatic filter approach

In this paper, we review causes, effects and trends of coastal eutrophication emphasizing the rivercoastal zone interactions. The Po river-Northern Adriatic Sea system is discussed as a case study, being one of the major eutrophication hot spots in the Mediterranean Sea. First, we review the evolution of eutrophication concepts, and related mitigation and restoration measures, stressing how river and coastal hydro-morphology, soil use, multiple element stoichiometry, biological and biogeochemical interactions, and global changes are becoming major issues. The cascading aquatic filters in the watershed and in the adjacent transitional marine zone are then analyzed for their capacity to retain and transform nutrients, thus controlling the downstream water quality, element stoichiometry and availability. The transitional water system is the end-of-pipe of the watershed, which connects the terrestrial and the coastal domains, acting as either filter or source for nutrients and contaminants. All these issues have to be framed in coherent temporal and spatial scales, adopting long-term ecological studies and integrated river basincoastal zone-adjacent sea management.