Relationships between physical, chemical and phytoplankton variables in three estuarine areas of Northern Brazil - São José de Ribamar, Cedral and Cajapió counties, Maranhão State

Abstract

The estuarine areas in São José de Ribamar, Cedral and Cajapió counties, Maranhão State (Brazil), are located between 2° - 3°S and 44° - 45°W. Six superficial samplings at high tide in morning time were carried out during the period from May, 2005 to April, 2006 for each sampling point to determine phytoplankton variables (chlorophyll and cell count) and the hydrological and climatic variables, considering their seasonal variations (the rainy season, from January to June, and the dry season, from July to December). Algal chlorophyll a ranged from 2.4 to 16.56 mg.m-3. Cell counts of phytoplankton varied from 11 to 176 cel.mL-1. Multiple linear regressions revealed that the phosphate were correlated to the chlorophyll, whereas the nitrate and the silicate influenced the cell count. Principal Component Analysis showed a positive correlation between the chlorophyll and the tide height during samplings, such as phytoplankton cell count and water transparency. A diagram with biotic and abiotic variables was constructed in order to better comprehending the interrelations involving the phytoplankton community.