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

RODRÍGUEZ, PATRICIA; PIZARRO, HAYDÉE

WETLANDS

Society of wetlands Scientists

Lugar: Virginia, Estados Unidos; Año: 2007 vol. 27 p. 1152 - 1159

0277-5212

We described phytoplankton productivity in a floodplain wetland of the Lower Paraná 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 between 3 and 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 between 0.021 and 1 µg C (µg Chl a h)-1 µmol photons-1 m2s and reached its maximum value during winter even when the assemblage, dominated by cryptophyceans, did not achieve light saturation. In early and late summer and in autumn, optimal irradiance (Eopt) ranged between 544 and 1397 µmol photons m-2 s-1. The highest PA (207 mg C m-2 h-1) was registered in late summer (high water level) when the lowest mean irradiance (Emean) was observed (341 µmol photons m-2 s-1). The lowest PA (28 mg C m-2 h-1) occurred in winter when Emean was maximum (1432 µmol photons m-2 s-1). Our results indicate that productivity was similar to those recorded for other latitudes and appeared not limited by the humic content of the water because phytoplankton was dominated by algae well-adapted to low light conditions.