Suspended Particulate Matter vs. Bottom Sediments in a Mesotidal Lagoon (Ria de Aveiro, Portugal)

Abstract

Within the framework of the Portuguese research project EMERA (Morphodynamic Study of RIA de Aveiro Inlet) bottom sediments and suspended particulate matter (SPM), grain-size and mineralogy were determined for number of sites located near the RIA de Aveiro mouth. Simultaneous measurements of velocity vertical profiles were also acquired. For this purpose four field campaigns were realised in 2007. Our goals were study the influence of the oceanographic regime and the tidal cycles in the sedimentary exchanges between the lagoon and the ocean and to identify places of deposition and resuspension of sediments. In order to achieve these goals three main studies were carried out. Study one consisted of assessing variability in the identified parameters for each site, at a constant distance above the bed (~ 1m) and at a constant phase of the tidal cycle, for winter versus summer, and during neap versus spring tidal conditions. Study two investigated variation in suspended sediments concentration (SSC), grain-size and mineralogy, at a constant distance above the bed and over one tidal cycle during winter under spring tidal conditions. Study three investigated SSC throughout the water column during a given phase of a wintertime spring tide. The SSC, granulometry and mineralogy varied in the studied area with the summer/winter oceanographic regimes (ruled by weather conditions), with the tidal phase and amplitude as well as availability of sediments. This work is a contribution for a better understanding about the sedimentary flux in a lagoonal system considering its interaction with the ocean and the rivers. It allowed evaluating the erosive/depositional character in areas closed to harbouring structues warning for the possible instability of some of them.