Phytoplankton productivity in a highly coloured shallow lake of a South American floodplain wetland.

RODRÍGUEZ, P; H. PIZARRO

WETLANDS

The Journal of the Society of Wetland Scientists

Lugar: Georgia, USA; Año: 2007 vol. 27 p. 1152 - 1159

0277-5212

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 mg C (mg Chl a h)21 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 (a) ranged from 0.021–1 mg C (mg Chl a h)21 mmol photons21 m2 s 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 from 544–1,397 mmol photons m22 s21. The highest PA (207 mg C m22 h21) was registered in late summer (high water level) when the lowest mean irradiance (Emean) was observed (341 mmol photons m22 s21). The lowest PA (28 mg C m22 h21) occurred in winter when Emean was maximum (1,432 mmol photons m22 s21). 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.