What happens on an equatorial beach on the Amazon coast when La Niña occurs during the rainy season?

Abstract

Widespread flooding occurred along the Amazon coast during 2009, starting in the early rainy season, when a La Niña event provoked an abnormal increase in rainfall levels. The present study analyzes hydrological data from ten 25-h campaigns conducted during spring tides between February, 2008, and September, 2009. This allows for the evaluation of the La Niña induced effects on the hydrological and hydrodynamic parameters in this equatorial zone that were caused primarily by this rainfall anomaly. The local climate is characterized by two seasons (rainy and dry). In 2009, the conditions of the coastal waters changed during the La Niña event because of the high rainfall rates (above 3000 mm). Under typical conditions, local coastal waters are well oxygenated, turbid and rich in nutrients, with relatively stable temperatures (27.5 °C–30.8 °C) and chlorophyll a concentrations of up to 30 mg m−3. During the La Niña event, hydrological and hydrodynamic values were exacerbated by increased rainfall levels, which left the water less saline (minimal of 5), but more turbid (maximum values above 100 NTU), and richer in dissolved nutrients and phytoplankton biomass (approximately 40 mg m−3) than normal. These results possible can be extrapolated to other equatorial macrotidal beaches influenced by major estuarine systems.