Response of Navicula rhynchocephala (Bacillariophyceae) to nutrient enrichment in an andean stream (Colombia)

To evaluate the effect of ammonium (NH 4+) and phosphates (PO432-) addition on the structure of the diatom community in the Tota stream (Boyaca, Colombia), diatom density was quantified on artificial substrates in two reaches (control and impact) with similar environmental conditions, along the Tota stream. Using a nutrient controlled enrichment in the impact reach, concentrations of ammonium and phosphates were increased to twice those in the control reach. Navicula rhynchocephala decreased its densities significantly, suggesting that is species that responds negatively to nutrient enrichment.