Phytoplankton and Primary Production in Clear and Turbid Shallow Lakes from the Pampa Plain (Argentina)

I. IZAGUIRRE; L. ALLENDE; G. PÉREZ; A. TORREMORELL; G. TELL; J. BUSTINGORRY; R. ESCARAY; H. ZAGARESE

João Pessoa, Brazil

Simposio; Plankton Symposium IV & Congreso Brasileiro de Plânkton; 2007

Phytoplankton structure and primary production was studied in ten shallow lakes from the Pampa Plain (Argentina) that are in three different steady states: clear (with submersed macrophytes), turbid (due to high phytoplankton biomass), and turbid (due to inorganic suspended matter). The shallow lakes showed strong differences in their optical properties, resulting in differing light climates conditions for the photosynthetic organisms. Mean attenuation coefficients of PAR varied between 4.5 m-1 (in one vegetated lake) and 64.1 m-1 (in one inorganic turbid lake). The contrasting kd values determined important differences in the euphotic zones of the water bodies. Dissolved organic carbon also differed among the lakes, with highest concentrations in vegetated lakes or in those that showed cyanobacteria blooms. Marked differences in phytoplankton structure, pigments and primary production were also found among lakes. Lowest phytoplankton densities occurred in most vegetated lakes and in inorganic turbid water bodies (870 - 4750 ind.mL- 1), whereas highest figures in lakes with Cyanobacteria blooms (113,250 - 222,880 ind.mL-1). Nanoflagellates dominated in clear water bodies. Autotrophic picoplankton was dominated by ficocianine-rich picocyanobacteria in all cases, varying from 8.61 x 103 cells.mL-1 to 4.17 x 106 cells.mL-1, with the lowest values in the lakes dominated by cyanobacteria > 20 ìm. The most turbid lakes were the more productive in terms of P max and the more efficient, and the clear lakes resulted the less productive and efficient ones.