Use of epipelic diatoms for evaluation of water quality in the Matanza-Riachuelo (Argentina), a pampean plain river

Epipelic diatom assemblages have been used to evaluate water quality in the Matanza-Riachuelo river basin. Twenty-three sites were sampled in April, May, June and August 1995, before the setup of restoration programs. The Matanza-Riachuelo river basin is located in N.E. Buenos Aires province. It runs across one of the most industrialized and populous zones of Argentina, for which it is subject to strong anthropogenic disturbances. A total number of 97 taxa were identified of which only 37 were abundant. Navicula cryptocephala, Nitzschia palea and N. umbonata occur in the whole basin though more frequent downstream; Stephanodiscus hantzschii and Cyclotella meneghiniana develop where the river becomes wider and deeper. The distribution of the diatomological flora in the Matanza-Riachuelo basin was affected by the increasing concentration of organic matter carried by the river and downstream for the input of chemical compounds, several of which are toxic to aquatic life (i.e. heavy metals, phenols, hydrocarbon, etc.). The assemblage was dominated by pollution-tolerant species, which implies strong to very strong contamination in a great portion of the basin.