PHYTOPLANKTON PRODUCTIVITY IN A HIGHLY COLORED SHALLOW LAKE OF A SOUTH AMERICAN FLOODPLAIN

ABSTRACT We described phytoplankton productivity in a floodplain wetland of the Lower Parana River, Argentina. Four samplings encompassing periods of high and low water levels were conducted in a highly colored shallow lake. Photosynthesis-irradiance (P-E) curves and the areal photosynthetic rate (PA) were estimated following the 14C assimilation technique. Likewise, physical and chemical variables and phytoplankton composition, density, and chlorophyll a concentration were measured. Phytoplankton assemblages shifted from cyanobacteria blooms in summer to cryptophycean dominance in winter, and co-dominance of cryptophytes and chlorophytes in autumn. Assimilation number Pmax ranged from 3–7.8 µg C (µg Chl a h)−1 and peaked in early summer (low water level) when water color was highest, suggesting that phytoplankton productivity was not depressed by the high content of colored humic acids. Photosynthetic efficiency (α) ranged from 0.021–1 µg C (µg Chl a h)−1 µmol photons−1 m2 s and reached its maximum value...