Phytoplankton dynamics during sunlight hours in a winter day, Bahía Blanca Estuary, Argentina

GUINDER, V. A; POPOVICH C. A; PERILLO. G. M. E.; HELBLING, W. E.

Pessoa, Brasil

Congreso; Plankton Symposium IV; 2007

Vertical distribution of phytoplankton and physico-chemical variables were studied during sunlight hours of a winter day in Puerto Cuatreros (38°50´ S; 62°20´ O), a harbour at the head of the Bahía Blanca Estuary. This estuary is mesotidal with a semidiurnal cycle and its inner reach is influenced by strong, channel-parallel winds and tidal dynamics. On July 2006, profiles of pH, dissolved oxygen, temperature, turbidity and salinity were measured hourly using a digital multi-sensor. With a radiometer, PAR profiles (photosynthetically active radiation) were obtained, and from them the light extinction coefficient (k), the euphotic zone (Zeu) and the mean light intensity in the mixed layer (Im) were estimated. Water samples were collected from surface and bottom to analyze nutrients (NO3-, NO2=, NH4+, SiO44- and PO43-), chlorophyll a, phaeopigments, particulate suspended matter (PSM), particulate organic matter (POM) and phytoplankton. Besides, 6 samplings were carried out fortnightly in order to describe the phytoplankton dynamics in winter. The results of this research revealed that tide energy increased water turbidity by resuspension of sediments bottom, especially around low tide. It also produced variation on physical and chemical properties of the water column throughout the day. Light intensity greatly fluctuated, and its availability in the vertical profile (Im) specially depended on cloudiness and water turbidity. This study suggested that daily phytoplankton-community abundance (cell density and chl. a concentration) and species composition were affected by tides, and vertical distribution was mainly related to light availability in the water column and with water mixing by turbulent processes. Key words: phytoplankton - light - tides – nutrients – PSM.