Estructura de la taxocenosis de diatomeas y su relación con variables ambientales en tres cuencas de la provincia de San Luis (Argentina)

Abstract

The composition and distribution of algae associations in lotic ecosystems are the result of conditions in the environment and in particular may reflect their structure and functioning. The objective of this work was to study the relationship of the richness, abundance and diversity of the diatom assemblages with the environmental characteristics in three basins of the province of San Luis. Fourteen sampling sites were selected in three basins: seven sites in the Río de Conlara basin, three sites in the Río Quinto basin and finally four sites in the Bebedero basin. In each sampling site, hydraulic and physicochemical parameters were recorded. Epilithic samples were obtained by scraping small rocks from the bottom of the streams. The structure of the assemblages was characterized by pennate diatoms that prevailed qualitatively and quantitatively. The variations of physicochemical parameters influenced the specific composition of the assemblages and allowed to establish two groups of species: one constituted by Nitzschia palea, Melosira varians, Navicula tripunctata and Halamphora veneta that were associated to streams with highest order number and maximum conductivity values. Geissleria decussis, Epithemia sorex and Cymbella affinis constituted the second group related to highest discharge and pH values. Navicula radiosa and Rhopalodia gibba were related to altitude and dissolved oxygen concentration, respectively. A substantiated floristic reference of diatoms allows to make a trustworthy diagnosis on the ecological state of the analyzed streams, as well as to establish monitoring programs for the province.