Phytoplankton functional groups as environmental indicators at a high neotropical mountain reservoir in Colombia/Grupos funcionales del fitoplancton como indicadores de las condiciones ambientales de un embalse de alta montana neotropical en Colombia

Phytoplankton is a fundamental productive component of lentic ecosystems, which also directly reffects environmental variability. This study evaluated the dynamics of phytoplankton in response to the monthly variability of physicochemical properties of a neotropical high Andes reservoir, El Neusa, from July to October 2004. Samples were collected and analyzed for taxonomic identification to species or the lowest possible level and categorized in functional groups (FGs). A total of 111 species of phytoplankton belonging to nine classes and 20 FGs were recorded. Among these phytoplankton classes, Chlorophyceae (36 species), Euglenophyceae (13 species), Bacillariophyceae, (14 species), and Conjugatophyceae (25 species) were the most species-rich and highest in abundance. The overall phytoplankton abundance was largest in August (8.5*[10.sup.4] [+ or -]2.7 *[10.sup.4] ind.[L.sup.-1]) and September (8.9*[10.sup.4] [+ or -]4.6*[10.sup.4] ind.[L.sup.-1]); however, the distribution of phytoplankton classes was not statistically different among sampling sites (Friedman-ANOVA; p>0.01). Chlorella sp. (2.4*[10.sup.4] [+ or -]2.0*[10.sup.4] ind.[L.sup.-1]), and Chloromonas grovei (2.5*[10.sup.4] [+ or -]4.4*[10.sup.3] ind.[L.sup.-1]), belonging to functional group X1, were dominant, representing together between 54% and 78% of the average monthly abundance. Simple correlations and multivariate analysis between physicochemical variables and phytoplankton revealed that conductivity, pH, and total suspended solids had a key influence on the distribution of both dominant species and FGs. These analyses indicated that hydrological (precipitation and runof) and water stability (stratification and mixing) conditions determined environmental changes and the selection of phytoplankton functional groups. The main features of the dominant FGs and the trophic state of El Neusa were also discussed.