To obtain mechanistic quantitative understanding of aquatic ecosystem functioning and biogeochemical processes, a range of empirical approaches have been used from laboratory to ecosystem scale, such as mesocosms. It is becoming increasingly clear that mesocosm experiments is a powerful approach to obtain such mechanistic quantitative understanding, especially when embedded in long-term observations, theoretical models and experiments conducted at other scales. However, after decades of ecosystem-scale empirical studies, there is still little standardization and collaboration across sites and biomes, especially between freshwater and marine systems. One way to improve this situation is to create interactive fora where such work can be presented and debated. To this session we therefore welcome presenters of ecosystem-scale empirical work where scientific questions about various aspects of aquatic ecosystem functioning has been tested through experimental approaches on more or less complex systems, by e.g. using mesocosms or other large scale empirical approaches. We also welcome contributions such as modeling work on empirical ecosystem scale data. We especially hope to compile an interesting combination of aquatic science from both marine and freshwater environments. The aim is to continue developing the international discussions about: (1) where empirical and model-based aquatic ecosystem science is at today, and (2) what scales and approaches have given and may give the most efficient insight into future development and responses of aquatic ecosystems in a world of changing climate and increased human population.