Sea, freshwater or saltpans? Foraging ecology of terns to assess mercury inputs in a wetland landscape: The Ebro Delta

► Sediments polluted with mercury at Flix site may affect the whole Ebro catchment. ► SIA and mercury levels of a tern community were studied to monitor pollution impact. ► Terns presented restricted habitat range in the Ebro Delta, except Little Tern. ► Mercury levels are related to foraging habitat and diet. Levels are higher in demersal marine habitats and saltpans than in freshwater ones.