Das Projekt "Modellierung von Oekosystemen" wird vom Umweltbundesamt gefördert und von Eidgenössische Anstalt für Wasserversorgung, Abwasserreinigung und Gewässerschutz, Abteilung für Umweltphysik durchgeführt. An ecosystem's stability has far too often been associated with the idea of a static equilibrium point generated by a rigid control. However, it is the trade-off between global and local variability arising from the interplay between the levels of the components and the system as a whole that results in functional integrity combined with a high potential for change. In the current project an approach is developed which takes into account different levels of organization. It is based on a general ecosystem framework depicting the structure of ecological networks along the dimensions of time, space and function. Model simulations are used to investigate the importance of spatio-temporal and functional diversity for an ecosystem's dynamics and organization and to seek for regularities in the relationship between ecosystem structure and function. A major result of the research will be descriptors which allow to assess an 'ecosystem's state of health'. A perspective of ecosystems as self-organizing systems operating far from their equilibrium state has major implications for research and management in general and for the role of mathematical models in particular. Models of complex systems may serve as tools to increase and communicate our understanding about the dynamic nature of complex systems and the necessity to admit a pluralism of complementary perspectives. They can highlight a kind of macroscopic uncertainty principle which enables and constrains researchers of complex systems to practice new forms of valuing and disseminating scientific knowledge. Leading Questions: How can we characterize the spatio-temporal organization of the energy and matter network of an ecosystem? What are the characteristics of pelagic systems? How is the organization of a system related to its physical environment - comparison between aquatic and terrestrial systems? What are characteristics of complex ecological (economic) networks? Can we derive quantitative descriptors for ecosystem health?