Fitoplâncton do ecossistema estuarino do Rio Ariquindá (Tamandaré, Pernambuco, Brasil): variáveis ambientais, biomassa e produtividade primária.

The Ariquinda River estuary of concerning the hydrology, phytoplankton biomass and productivity, in a monthly sampling programme from August 2005 to July 2006, covering the rainy and dry season, at the surface and at three fixed points, during low and high tides in full moon tide. The water transparency was low in the rainy season and the water salinity varied from oligohaline to euhaline. The dissolved oxygen rates varied from low saturated to supersaturated zone. The silicate values were higher in the rainy season, while the concentrations of the other nutrients (nitrite, nitrate and phosphate) were low and did not show seasonal and spatial patterns, nor even between the different tide stages, the some was observed for phytoplankton biomass and productivity, except in relationship the tides stages. The estuary was classified as mesotrophic and the phytoplankton size fraction < 20μm predominated in the environment, representing more than 69% of the microalgae biomass. The ranges of dissolved oxygen rates, nutrients concentrations, phytoplankton biomass and productivity shows that the estuary is not submitted to strong human impacts, it has a moderate productivity, and the tide pattern was the main controlling physical factor of the system.