Phytoplankton Community of Alalay Pond, Cochabamba, Bolivia

Algae > Volume 11(2); 1996 > Article

Algae 1996;11(2): 207-215.

Eduardo A. Morales L. and Francis R. Trainor

Department of Ecology and Evolutionary Biology, The University of Connecticut

ABSTRACT

The extensive variety of Bolivian aquatic ecosystems has not yet been studied. The geographic richness of the country makes difficult the compilation of data by a limited number of native limnologists. Most of the isolated studies have been conducted by foreign researchers and do not reflect the variations of aquatic conditions even in the Departments of La Paz and Cochabamba, to which such studies are restricted. In the valley region Alalays Pond is one of the bodies of water that has received attention. This special consideration was driven by the concern for protecting the health of the surrounding population from contaminated and eutrophicated waters. After analysis of the phytoplanktonic community as well as the physico-chemical conditions of the water, we may conclude that the pond was in a eutrophic stage during the period July 1989 June 1990. The concentrations of nitrates, phosphates, and sulfates reveal such a condition. These factors, as well as temperature, alkalinity, and conductivity are inversely correlated to the hydrological fluctuations in the pond. Hydrogen ion concentrations are very high (pH around 10), but remain fairly constant through the year of study, due to a buffer effect provided by the carbonate-bicarbonate system. The phytoplankton assemblage is characteristic of eutrophic waters. Sixty four species belonging to four Divisions were identified: Cyanophyta (22 species), Chlorophyta (25 species), Euglenophyta (5 species), and Bacillariophyta (12 species). There species of blue-green algae (cyanobacteria) were deminant, namely Anabaena spiroides, Spirulina laxa, and Oscillatoric obtusa. The number of individuals was influenced mainly by nitrates; differences in their horizontal distribution may be due the fact that the organism responded differently to varying physico-chemical conditions in each zone. The Shannon species diversity index also confirms the fact that the pond is in a eutrophic stage. Incresases in water level led to high diversity, high diversity, high richness, and high evenness; while lower diversity and low specific richness and evenness were characteristic during the dry season.

Key words: Bolivia, limnology, phytoplankton, South America