Water exchange between estuarine lagoon and sea through a narrow strait: case study of two Brazilian lagoons

The Patos Lagoon, located in the Southern Brazil, is the largest freshwater lagoon in the World (area is 10 360 km2). It is connected with the Atlantic Ocean by a narrow strait, through which saline sea waters inflows to the lagoon and fresh waters of Patos outflows to the sea. Todos os Santos is the second large bay in the Brazil, which area is 1223 km2. It is located in the Northern Brazil, connected with Atlantic Ocean and remains saline during the whole year. Study of these basins represent difference in water exchange mechanisms between small and large estuarine lagoon.
Based on year-long in situ data from sea mooring and river gauge stations, as well as wind and precipitation reanalysis data, the influence of local meteorological and hydrological conditions on water exchange of these basins was studied.
It was revealed that the distinct seasonal variability of water exchange in Patos is defined mostly by the seasonal river discharge variability, while the variability of local atmospheric circulation does not influence it. Outflows of lagoon waters to the sea are typical during the high river discharge period, while inflows of sea waters to the lagoon are rare and occur under specific wind conditions. During the low river discharge periods, inflows of sea waters to the lagoon are typical, while short-term outflows are induced by increase of river discharge.
Meantime, it was found that synoptical salinity variation in Todos-os-Santos is mostly caused by tides, while seasonal water exchange variability is almost generally wind-driven.