Condiciones de luz subacuática como factores determinantes de la eficiencia fotosintética fitoplanctónica. l. Embalse de Rio Tercero (Córdoba, Argentina)

Underwater light conditions as a key factor for phytoplankton photosynthetic efficiency. The Secchi disc depth, the energy of photosynthetic available radiation (PAR) in the water column, the primary production rate and the concentration of photosynthetic pigments were measured in Rio Tercero reservoir (Argentina). The compensation point, the relative intensities of such point and Secchi disc, the photosynthetically stored radiation, and the respective photosynthetic efficiencies were calculated. The percentage of transmitted light fluctuated according to the suspended amount of particulated material (winter) or the presence of high algal concentration (spring-summer). The euphotic stratum in summer (1.1 m to 3 m) reached 5.5 m in winter (August). The mean extinction coefficient up to the euphotic stratum was very highly variable. The photosynthetic efficiency was lower than 1 in surface during spring and summer. The values obtained in the euphotic stratum were intermediate. Other significantly high values were found at deeper levels. The relevant fluctuations of all variables including the extinction coefficient, the relative depth and intensity of Secchi disc, the euphotic stratum depth and the compensation point confirm the eutrophic characteristics of the ecosystem. Eutrophication levels of reservoir are clear from values of other parameters such as the primary production rate, pigment concentration, photosynthetic efficiencies and the seasonal appearance of algal blooms.