PHYTOPLACTON VARIATION AS WATER QUALITY INDICATOR.

GERALDI ALEJANDRA, M. CINTIA PICCOLO, GERARDO PERILLO, CESAR TOMASSI, VALERIA GUINDER

China / Nanjing

Workshop; Meeting GLEON 11; 2010

We evaluated the current trophic state of the shallow lake “Cochicó” by analyzing physicochemical, biological and environmental variables related to water quality. Water samples were collected once a month at two sampling sites, from October 2004 to December 2006. During this study, 36 phytoplankton species were identified. The phytoplankton abundance was maximal in January 2005 (420500 cells ml-1) and minimal in October 2004 (50000 cells ml–1). Within the class of Cianophyceae, two species (Microcystis aeruginosa and Microcystis spurea) were responsible for the high phytoplankton cell density (97%) and for an intense green color of water in summer. The algal bloom was characterized by an average density of 560000 cells ml–1, and chlorophyll concentration increased from 40 mg m-3 (October 2004) to 89 mg m–3 (January 2005). Nutrients showed high concentration values (N: 15 mg l-1), which could be attributed to various non-point sources. Margalef index indicated a decline in diversity and the Shannon & Weaner biotic index indicated strongly eutrophic waters, with the exception of the samples obtained in October, which corresponded to moderately polluted waters. Based on our results, Cochicó shallow lake was classified as hypertrophic. key words: shallow lake, water quality, Cochicó, phytoplankton, trophic state.