El macrobentos y su relación con las fluctuaciones de salinidad en ríos y esteros del Chaco Oriental (Argentina)

Resumen

In the area comprised between the Pilcomayo river (Formosa province) and the Amores river (Santa Fe province) 17 streams and rivers, and 4 swamps ("esteros") were studied in their lower reaches during low and high water periods. The salinity was high in some of them, specially during low water.

Samples were taken with a Dietz-LaFond and modified Drzycimski dredges, according to the substrate characteristics, and filteres through a 500μm mesh size. Relative abundance and density (ind. m^-2) were analized in relation with the main environmental factors, as current speed, conductivity, dissolved oxigen and sediment granulometry.

The benthic macrofauna occurring in the streams and rivers showed important differences in their composition and density, being oligochaetes (Naididae and Tubificidae), chironomids (Chironominae) and molluscs (Hydrobiidae), the main groups.
The swamp bottom fauna was rather poor, with abundance of oligochaetes, which could be due to the scarcity of dissolved oxygen and the high proportion of organic matter.

The well oxigenated lotic environments, with moderate conductivity values, showed the richest and most abundant macrofauna, in contrast with those of high salinity, specially when the water level decreased. Conductivity was negatively correlated with the species number ( P < 0,01) and abundance (P< 0,01).