Silica plays a major role in eutrophication of coastal waters around the world. Mechanisms controlling the production and fate of silica in estuarine systems are far from understood. Major indications have been reported that intertidal areas may be an important reservoir of silica in estuarine systems. This project intends to clarify the role of a freshwater marsh in the silica cycle within the Schelde estuary. Different silica pools in the marsh (vegetation, sediment, pore-water, groundwater and surface water) will be quantified. During a whole year, on a two-monthly basis, silica content of these pools will be monitored in different vegetation types. Interactions between the different silica pools will be studied by decomposition and dissolution experiments, both in situ and ex situ. Mass-balances will be performed seasonally to attain insight in exchange of silica between intertidal and subtidal area. In the end, these major goals will allow to construct an integrated view of the role of freshwater tidal marshes in the silica cycle within an estuarine system, by focusing on retention and processing of silica within the marsh.