Primary production comparison between phytoplankton and periphyton in two shallow lakes from Argentina

RODRÍGUEZ, P; PIZARRO, H

St. John´s, Newfouland Canadá

Congreso; ASLO 2008 Summer Meeting; 2008

American Society of Limnology and Oceanography

Primary production of phytoplankton and periphyton on artificial substrata were studied in two humic shallow lakes from the Lower paraná River Basin from Argentina, from autumn 2006 to summer 2007. Sampligs were carried out monthly in one of them (Grande lake), while in the other (ROL), sampligs were ca. bimonthly. Limnological variables were registered and P-I curves were performed. Grande lake is the largest, less humic and with a fluctuating coverage of floating macrophytes despite at samplings times was completely free. The ROL, a relictual oxbow lake, was completely covered since winter. In Grande lake, maximun photosynthetic rate and assimilation number were higher for phytoplankton than for periphyton (p < 0.05) and the same trend was observed for the light efficiency. Light limitation was not observed after spring neither phytoplankton nor periphyton. In the ROL there were no significant differences between the two communities in terms of photosynthetic parameters. Phytoplankton was light limited since winter to summer, when the coverage was 100 %; and periphyton was light limited only in winter. When comparing the same community at the two lakes, phytoplankton production and light efficiency were highest in the Grande lake (p < 0.05) and no differences were observed when comparing the same parameters normalized to chlorophyll a. Phytoplankton must be well adapted to restricted light conditions. We hipòthezise that plants coverage constrained primary productions at the ROL, since phytoplankton productivity at the ROL was higher than in the Grande lake before winter. Furthermore, motility and buoyancy are strategies that favour phytoplankton over periphyton, that can not positionate in the water column for more light.