A multidisciplinary study of processes important for the carbon and nutrient cycling within a tidal flat ecosystem, and between the tidal flat system and the estuary. Investigation of the benthic microbial food web. Tidal flats are important components of macro- and mesotidal estuaries all over the world, yet the mechanistic description of carbon and nutrient cycling within tidal flats and between tidal flats and the water column is far from complete. This description requires the multi-disciplinary study of physical, chemical and biological processes and fluxes at small spatial and temporal scales. In contrast, environmental management of estuarine and coastal areas requires answers and solutions to problems posed at larger scales (estuarine scale, regional scale). The project aims at bridging the gap between the smaller scales at which processes operate and are measured, and the larger scales relevant for management, by explicitly studying the small scale processes and by integrating them in mathematical models. The project's work programme is centered around five joint field campaigns by all participants. The first four of these are executed on a tidal flat in the Westerschelde estuary (S.W. Netherlands). Validation of the models and predictions will be done during a final campaign in a different estuary. The research is subdivided into three work packages. The first package focuses on the quantification and prediction of benthic-pelagic exchange mechanisms involving carbon and nutrients. Physical and biological processes in this exchange are considered; the processes are framed in the context of a detailed hydrodynamical modelling of the flat. The second package considers the processes of production, mineralised and transformation of organic material and nutrients within the sediments. Attention will be paid to primary production and to grazing processes within the benthic small food web. The sensitivity of the overall system to the dynamics of these internal interactions within the benthic system will be investigated. The third package integrates the measurements performed in the first and second packages into detailed mathematical process models for the biogeochemical processes in tidal flats sediments. The process models will be integrated into a general ecosystem model. Upscaling of the results of the process studies to the scale of the estuary will be considered by defining relationships between ecosystem target variables and key forcing factors in the estuary. The former Institute for Nature Conservation was a partner in this project