Sousa, J.A., Cunha, K.N. and Nunes, Z.M.P., 2013. Influence of seasonal factors on the quality of a tidal creek on the Amazon coast of Brazil.

The nutrients produced by mangrove ecosystems play an important role in the fertility of tropical estuaries. The highly indented Pará-Maranhão littoral is part of the Amazon Coast, and is formed by an extensive array of inlets, bays and estuaries. Tidal creeks connect the local mangroves to the adjacent bays and estuaries. The Emboraí Velho creek is located on a local oyster farm, where the monitoring of the water quality is an essential routine. This study investigated the effects of seasonal variation in conditions on the quality of the water of this tidal creek. The samples were collected each month between April, 2009, and July, 2011, during the spring tide. The temperature, salinity, pH, turbidity, conductivity, and dissolved oxygen concentration of the water were analyzed in situ using a multiparameter probe. Water samples were also collected for nutrients and chlorophyll-a analysis in the laboratory. Salinity and conductivity varied significantly (p < 0.05) among the different periods. Mean salinity ranged from 21±6.90, in the rainy season, to 35±2.66 in the dry, with mean conductivity following the same trend, varying from 33±10.14 mS.cm⁻¹ in the rainy season to 54±3.67 mS.cm⁻¹ in the dry. During the flood tide, the mean chlorophyll-a concentration was higher in the rainy season (12.75±5.13 mg.m⁻³) in comparison with the dry (9.85±1.86mg.m⁻³). None of the other variables varied significantly between the periods analyzed. These results reinforce the need for the regular monitoring of water quality in order to determine the periods when environmental conditions are appropriate for oyster farming.