Phytoplankton photosynthesis-light relationship in the Pas estuary, Cantabria, Spain

Abstract

ABSTRACT. The relationship between the photosynthesis-irradiance (P-I) curves of natural phytoplankton assemblages and environmental conditions was investigated in a partially mixed estuary, the Pas. During an annual cycle, photosynthesis was measured both by in situ and laboratory (light-saturation curve) incubation methods. The initial slope (aB) and the maximum photosynthetic rate (PDrnax) of P-I curves changed significantly over the year. The parameter (a" ranged from 0.001 to 0.04 mgC(mgCh1a) l h-' (FE m-' S l) and PBrnax ranged from 0.6 to 15 mgC(mgCh1a)-' h-'. Maxima for both aB and PBrnax occurred when the community of phytoplankton was dominated by small cell (small diatoms, Cryptornonas sp.) and the minima were obtained when the extinction coefficient was highest. In field (in situ) incubations, the production normalized to chlorophyll a (PDi) correlated positively with salinity and negatively with the nutrient concentration.