Spatial and temporal variability of suspended sediments concentration in Ria de Aveiro lagoon and fluxes between the lagoon and the ocean

摘要

The measurements of suspended sediment concentration in different parts of the Ria de Aveiro coastal lagoon duringfour tidal cycles show a significant spatial and temporal variability. Fluxes of water and suspended sedimentsbetween the lagoon and the coastal ocean were estimated for each tidal cycle applying a hydrodynamic two-dimensional numerical model and using the values measured at the lagoon mouth. The hydrodynamics of the lagoonare essentially dominated by tidal forcing. Tides are predominantly semidiurnal and are present in the entire lagoonThe differences in suspended sediments concentration within the lagoon seem to be largely determined by themagnitude of the currents and by the bottom properties. As in other estuarine systems, the suspended sedimentsconcentration fluctuated with tidal amplitude. In almost all stations, higher mean values occur during spring tidesdue to the strength of the tidal currents. Anomalous higher mean values observed in stations close to the tidal inletduring winter neap tide suggest that wind-induced resuspension and horizontal advection from the adjacent coastalarea is taking place during that period of the year. Semidiurnal variations are explained, especially during thesummer, by tidal-current velocity asymmetry (ebb dominance). Seasonal variability, with winter higher suspendedsediments concentration, is probably related with wind climate, biological activity and coastal wave regime. Ingeneral, the fluxes of water and of suspended sediments between the lagoon and the coastal ocean showed a seawardflux that is consistent with the ebb dominance. Under winter neap tide conditions external factors allowed retentionof suspended sediments in the lagoon.