CHOICE OF MACROPHYTE SUBSTRATE IN THE USE OF DIATOMS AS INDICATORS OF POND WATER QUALITY ASSESSMENT: PRELIMINARY DATA ON THE CASE OF ALALAY POND (COCHABAMBA, BOLIVIA)

Eduardo A. Morales, Universidad Católica Boliviana, Bolivia / Patrick Center for Environmental Research, The Academy of Natural Sciences of Philadelphia, USA / Centro de Diagnosis de la Calidad Ambiental, Bolivia
Rivera Sinziana F., Universidad Católica Boliviana, Bolivia / Centro de Diagnosis de la Calidad Ambiental, Bolivia

Abstract

Alalay Pond is a 230-hectare, shallow aquatic ecosystem within Cochabamba, the third largest city in Bolivia. With the aim to determine the suitability of epiphytic diatoms for water quality assessment in the pond, the macrophytes Schoenoplectus californicus subsp. tatora, Typha dominguensis, Myriophyllum verticillatum and Azolla filiculoides were selected and differences in community composition and structure were tested. Diatoms were collected during four sampling campaigns in the March-September, 2011 period and from three stations in the pelagic zone. Twenty-cm stem cuttings were extracted from 20 cm below the water surface, stored in plastic bags and transported to the laboratory were epiphytes were removed with a brush and oxidized with hot nitric acid. After repeated rinsing and decantation with distilled water, air-dried aliquots were mounted on permanent glass slides using Naphrax®. At least 600 valves were identified and counted under the light microscope at a magnification of 1000X. In all, 27 samples were collected from which 29 taxa were identified and 10 others could not be assigned names from the literature. Identified taxa are characteristic of eutrophicated environments. Although, principal component and canonical correspondence analyses showed marked differences in all taxa growing on each of the 4 substrata over time, the Shannon-Wiener and Pielou indexes showed no marked differences in dominant taxa within a single campaign. Shifts in rare species, on the contrary, were more notorious since they seem to show preferences for particular substrates. These observations suggest that due to their evergreen character and strong adaptation to eutrophy, Schoenoplectus californicus subsp. tatora and Typha dominguensis are the most suitable substrates for water quality assessments in the pond. As demonstrated by multivariate analyses, differences in community composition and structure were attributable to alkalinity, COD, sulfates, ammonium-nitrogen, conductivity, and dissolved oxygen. More frequent sampling, diversification of substrates and extending the study for a longer period are recommended to establish a monitoring program during any future restoration of the pond.

Keywords: Diatoms, Bacillariophyta, epiphytes, water quality, Alalay Pond, Bolivia