Input of sediments, organic matter and nutrients in coastal seas by rivers and their impact on the marine ecosystem has been the subject of many research projects. However, the quality and quantity is strongly determined by upstream processes in the river basin. In recent years exercises have been made to describe transport of water, dissolved compounds and suspended or particulate matter at (sub)basin scale. Models are defined at the level of description of ecosystem typology of forests, land use, wetlands etc. along with formulation of the exchange terms between these systems.Where land and water meet we actually find ecotones: transition zones as a result of hydrodynamics with their own flora and fauna, and related intensive transformation and uptake of materials. Therefore, for an accurate description of exchange at (sub)basin scale, a detailed understanding of the functioning of such transition systems is necessary.The main goal of the research project is to investigate how the diverse physical and biological processes and their interactions determines the exchange of water, dissolved compounds and particulate matter in margins and inundation areas of water courses. These two transition systems are characteristic for river basins.To achieve the main aim it is necessary to develop models for margin and inundation area. Multidisciplinary research and integrated modelling of hydrological transport characteristics and biological (transformation) processes is required. The coupling of different models and model descriptions forms a methodological challenge in this proposal. Besides general models on ground water flow, hydraulics and biological features, a few distinctive interaction zones can be recognized, for which exchange processes will be investigated and modelled in detail:1.interaction of shallow ground water with wetland or terrestrial ecosystems 2.interaction of deep ground water with the water course3.interaction of water course with the margin4.interaction of shallow and/or deep ground water with the inundation area5.interaction of water course with inundations areaModel formulations of exchanges and underlying processes is first and foremost determined by the component of study. There are three groups of components with their own characteristic “exchange” descriptions, namely water, dissolved components and particulate or suspended matter. Nitrogen is selected as an “illustrative” element for the models. Its transport is determined by processes in all interaction zones and it may appear in both dissolved and particulate form.