Suspended particulate matter sources and residence time in a Mesotidal Lagoon

In the frame of this work the suspended particulate matter (SPM) concentration was measured in February 2002 in seven sites of Ria de Aveiro (located in its four main channels) during one tidal cycle of a neap tide event (at approximately 2-hour intervals, including high tide and low tide measurements) and its mineralogical composition was identified. The purposes of this work are to identify the main sources of sediments for these locations (ocean or rivers), as well as to determine the sediments residence time for this locations and their paths along the channels. The methodology adopted consisted in applying a lagrangian model coupled to a previously calibrated hydrodynamic model of Ria de Aveiro to study the dispersion and mixing processes of passive particles during the sampling period. Considering the sediments represented as passive particles, lagrangian models allow the simulation of sediments transport paths and the computation of residence times. Several simulations were performed in order to simulate the surveys conditions and understand the dynamics and origin of measured SPM. The model results are supported by textural, mineralogical and concentrations field data, revealing that it may constitute an important tool to study the lagoon sediments dynamics and origin