Delimitation of domains in the external Río de la Plata estuary, involving phytoplanktonic and hydrographic variables

Abstract

Autumn and spring hydrological (temperature and salinity) and biological (chlorophyll, phaeopigments and phytoplankton species) variables were analysed. Phytoplankton biomass, expressed as chlorophyll a reach a maximum of 6.1 µg L-1in autumn and 22.8 µg L-1 during spring. Maxima were found in the frontal zone and marine adjacent area. Four domains were identified through multivariate analysis: Riverine, Estuarine, Frontal and Oceanic; mainly due to salinity and depth in autumn and due to salinity and chlorophyll in spring. The Riverine and Oceanic domains (West and East boundaries) matched in location in both seasons, while in spring an additional domain was discerned in the Canal Oriental (Channel domain). Salinity and chlorophyll concentration increased from the Riverine to the Frontal domain, being positively correlated for salinities 14, indicating that chlorophyll concentration was modulated mainly by the oceanic influence that improved light availability. While salinity maintains an increasing trend toward the Oceanic domain, phytoplankton biomass decreases. Though in this zone the chlorophyll concentration must be regulated by a combination of light availability and grazing, further investigation is needed.