Research Article

Drivers of the diversity of diatoms in an oligotrophic Andean stream

¹ Departamento de Biología, Universidad Nacional de Colombia, Bogotá, Colombia
² Universidad Nacional de Colombia, Kilometro 2 vía Tarapacá, Leticia, Amazonas, Colombia
³ Climate Change Institute, School of Biology and Ecology, University of Maine, Orono, Maine 04469, USA
⁴ Instituto Catalán de Investigación del Agua (ICRA), España Universidad de Girona, Girona, Spain

^* Corresponding author: jcdonator@unal.edu.co

Received: 23 June 2021
Accepted: 6 February 2022

Abstract

An in situ experiment determined that the addition of ammonia N-NH₄⁺, nitrate N-NO₃^– and phosphate P-PO₄^3– to an oligotrophic Andean stream significantly affected diatom composition and diversity. Over a nine-month period, fertilized and non-fertilized sections of the stream were studied for their environmental characteristics and diatom composition. Nutrient concentrations were increased three times in a downstream section with respect to those occurring naturally upstream. Alpha diversity (Shannon-Wiener [H”] and Simpson [S] indices) were determined monthly. In the non-fertilized control section, diatom diversity was significantly (p ≤ 0.05) related to water flow and P and N concentrations. In the fertilized section diversity was associated to the enhanced ammonia and phosphorus. A redundancy analysis (RDA) showed that conductivity, water flow and nutrient concentrations contributed to the diatom assemblage composition (83% along the first two axes). Achnanthidium minutissimum, Cocconeis placentula, and Epithemia sorex occurrence was related to low phosphorus concentration. Epithemia adnata var. minor, Nitzschia dissipata, and Reimeria sinuata were associated with high P concentrations, high water flow and low conductivity Navicula rynchocephala, Gomphonema parvulum, Navicula capitatoradiata, and Melosira varians were associated with high P.