Spatio-temporal variability of suspended sediment concentrations in a shallow and turbid lagoon

Abstract

The Patos Lagoon, located in the southernmost part of Brazil, is a shallow and turbid lagoon of enormous ecological and economical importance. The seasonal, annual, and interannual variability of suspended sediment concentrations (SSC) in the lagoon was investigated in this study based on five years (2002–2006) of hydrodynamics + SSC simulations using the TELEMAC – 3D hydrodynamic model. The model was first calibrated and validated by comparing results with in situ current velocities, salinity, water levels, and SSC measurements, indicating a reasonable/good performance for the majority of the time. Modelling results were then combined with river discharge, wind, precipitation rates, and climate indices (El-Niño Southern Oscillation - ENSO) data to identify their influence on SSC throughout the lagoon. The relation between daily time series of SSC and river discharge was high (r ≈ 0.80), suggesting a strong correlation between these time series in the Patos Lagoon. SSC seasonal variability was also observed, with high SSC from winter to spring, and moderate to low SSC during summer and fall, indicating a relation with the river discharge pattern. On the interannual variability scale, the ENSO influence promoted high SSC values throughout the lagoon, mainly during El Niño years and near the tributaries mouth, while the opposite pattern was observed during La Niña years. Thus, the Patos Lagoon proved to be a dynamic system where SSC are mainly controlled by river discharges at longer timescales and modulated by the wind action at shorter timescales.