Environmental Responses of a Tropical Coastal Lagoon System to Hydrological Variability: Mundaú-Manguaba, Brazil

The Mundaú-Manguaba complex in north-eastern Brazil is a 79 km2 shallow tropical coastal lagoon system, consisting of two interconnected waterbodies and a channel system linked to the ocean. Mundaú-Manguaba is similar to many tropical lagoon systems in Latin America. The system is characterized by semidiurnal tides, which are reduced in amplitude by more than 88% as compared to the coastal ocean. The lagoons experience a distinct rainy (winter) and dry (summer) season. Anthropogenic inputs from sugar-cane processing and urban growth pose environmental management problems. During the dry season, urban and industrial pollution frequently produce eutrophic conditions in both lagoons. During flood discharge, sudden salinity drops occur in Lagoa Mundaú, causing mass mortality of the abundant estuarine mussel (Mytella falcata) every few years. River discharge controls the oceanward transport of salts and pollutants and produces low salinity in Lagoa Manguaba during the entire year. This is true in Lagoa Mundaú during the rainy season, while currents and salt dispersion in Lagoa Mundaú are tidally driven during the dry season. The tide advects ocean water into the system, mixes the water column, and produces strong currents in the channels. Winds modify the magnitude of currents in Lagoa Manguaba.