『Abstract
　Temporal evolution of dissolved and biogenic silica concentrations along the Schledt tidal river and in its tributaries was investigated during 1 year in 2003. In the tributaries, dissolved silica (DSi) concentrations remained high and biogenic silica (BSi) concentrations were low throughout the year. In the tidal river during summer, DSi was completely consumed and BSi concentrations increased. Overall, most of the BSi was associated with living diatoms during the productive period in the tidal river. Nevertheless, the detrital BSi was a significant fraction of the total BSi pool, of which less than 10％ could be attributed to phytoliths. The tidal river was divided into two zones for budgeting purposes. The highest productivity was observed in the zone that received the highest water discharge, as higher riverine DSi input fluxes induced presumably a less restrictive DSi limitation, but the discharge pattern could not explain all by itself the variations in DSi consumption. Silica uptake and retention in the tidal river were important at the seasonal time-scale: from May to September, 48％ of the riverine DSi was consumed and 65％ of the produced BSi was deposited, leading to a silica (DSi + BSi) retention in the tidal river of 30％. However, when annual fluxes were considered, DSi uptake in the tidal river amounted to 14％ of the DSi inputs and only 6％ of the riverine silica (DSi + BSi) was retained in the tidal river.

Keywords: Biogenic silica; Diatoms; Dissolved silica; Scheldt estuary; Silica budget; Tidal freshwater』

Abbreviations
Introduction
Materials and methods
　Description of the study area
　Sampling stations
　Chemical analyses
　　SPM, DSi and BSi
　　Particulate organic carbon and contribution of diatoms to the chlorophyll a concentrations
　Distribution between fractions of BSi associated or not with living diatoms
　Discharge data, silica fluxes and mass-balances calculations
Results
　Distribution of DSi, BSi and DiatChla at the tidal limits of the Scheldt and its tributaries
　Distribution of DSi, BSi and DiatChla along the tidal river
　Fraction of the BSi associated with living diatoms
　Silica budget during the productive period
　Temporal evolution of the DSi uptake
　Annual fluxes discharged to the brackish estuary
Discussion
　Distinction between BSiliv and BSidet
　Phytolith contribution to the BSi pool
　Accuracy and precision of the DSi and BSi fluxes and mass-balance calculation
　Importance of BSi dissolution and DSi recycling
　DSi uptake in Zones 1 and 2 and influence of the freshwater discharge
　Spatial distribution of the BSi deposition: influence of the SPM dynamics
　Silica fluxes at the annual timescale
Acknowledgments
References