Horizontal transport, mixing and retention in a large, shallow estuary: Rio de la Plata

We use field data and a high-resolution three-dimensional (3D) hydrodynamic numerical model to investigate the horizontal transport and dispersion characteristics in the upper reaches of the shallow Rio de la Plata estuary, located between the Argentinean and Uruguayan coasts, with the objective of relating the mixing characteristics to the likelihood of algal bloom formation. The 3D hydrodynamic model was validated with an extensive field experiment including both, synoptic profiling and in situ data, and then used to quantify the geographic variability of the local residence time and rate of dispersion. We show that during a high inflow regime, the aquatic environment near the Uruguayan coast, stretching almost to the middle of the estuary, had short residence time and horizontal dispersion coefficient of around 77 m(2) s(-1), compared to the conditions along the Argentinean coastal regime where the residence time was much longer and the dispersion coefficient (40 m(2) s(-1)) much smaller, making the Argentinian coastal margin more susceptible for algae blooms.