Phytoplankton responses to the human activities in Pampean shallow lakes (Argentina) and their relation with the alternative stable states

IZAGUIRRE, IRINA; ALLENDE, LUZ; SÁNCHEZ, MARÍA LAURA; TELL, GUILLERMO

S. Michelle all´Adige

Workshop; 16th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP); 2011

International Association of Phytoplankton Taxonomy and Ecology (IAP)

As a consequence of the human activities (agriculture, livestock, fish introduction and urbanization) most of the shallow lakes from the Pampa Plain (Argentina) have experienced an increasing eutrophication, becoming turbid systems. We studied six shallow lakes from this region with contrasting light qualities. Three lakes are turbid, among which, two have high phytoplankton abundances (phytoplankton-turbid), and one shows a high concentration of suspended inorganic matter and would be the consequence of a direct human impact on its drainage basin (inorganic-turbid). Two lakes are clear and profusely colonized by submerged plants (clear-vegetated). Only one lake shows a typical alternative steady states behaviour, alternating turbid periods of high phytoplankton biomass with periods of more transparency and development of submerged macrophytes. The two phytoplankton-turbid lakes showed a more stable phytoplankton composition along the year (with dominance of Cyanobacteria, Bacillariophyceae and Chlorophyceae) and total phytoplankton abundances ranged from 7.56 x 104 to 8.98 x 105 ind. ml-1; in these lakes the main functional phytoplankton groups were SN, D, X1 and J. The inorganic-turbid lake was characterized by low phytoplankton abundances all along the year (1.91 x 103 – 2.52 x 103), was dominated by Bacillariophyceae and Chlorophyceae and the most representative functional groups was P. The two clear lakes presented, most of the time low phytoplankton densities (6.24 x 102 – 5.8 x104) and the community was represented by several mixotrophic species (Cryptophyceae and Chrysophyceae) with accompanying species, mainly belonging to Chlorophyceae (functional groups X1, X2, Y) The pigment composition of the community, achieved by HPLC analyses, showed the adaptations of the algal assemblages to the particular light condition in each type of lake.