Seasonal dynamics of nutrients in an Amazon estuary

AbstractThis paper shows the nutrients distribution in the Paracauari estuary over a Amazon hydrological cycle (2008), and at the end of the period of La Niña (April 2008). This estuary is influenced by the humid tropical climate and meso-tidal (3 to 4 m), semi-diurnal. Sampling was conducted at 10 stations in three distinct seasons: rainy (march), intermediate (june) and less rainy season (september). Were measured in situ physical and chemical parameters using a multiparameter probe; analyzed the dissolved nutrients (nitrate, nitrite, ammonia- -N, phosphate and silicate) by spectrophotometry and particulate matter suspension, gravimetrically. We observed large seasonal variations in the concentrations of the studied parameters. The water temperature (average of 28.58 °C) is quite homogeneous, typical of tropical waters. The pH ranged acid (5.80) to alkaline (7.86) and salinity between 0.06 to 7.56, with both maximum values at the mouth because of the greater marine influence. The waters are poorly oxygenated during the rainy season (2.35 mg.L-1) and at the very least rainy (6.55 mg.L-1). The concentrations of the suspended particulate matter and nutrients reached a maximum during the rainy season due to the natural inflow from adjacent areas. In this estuary, the nutrients are mainly controlled by the river discharge, rainfall, wind and tide and exceptionally by la Niña.