BENTHONIC FAUNA OF THE ITATA RIVER AND IRRIGATION CANALS (CHILE)

Benthonic fauna and substrate in three areas of the Itata river (rhith ron riffles, rhitron pools, and potamon) and three irrigation canals a t the outtake and about 500 m downstream are analyzed. Benthonic fauna included 56 taxa; of these, 12 were exclusive of the river, 11 were o nly found in irrigation canals, and 33 were in both environments. The widest distributions were found among the Diptera (Heptagyia annulipes and Orthocladiinae), while Trichoptera (Smicridea chilensis) and Ephe meroptera (Baetidae) were more abundant in the river. The highest biom ass contribution corresponded to Gastropoda (Chilina dombeyana) in irr igation canals and in the river, although there was also significant T ipulidae family (Diptera) larval bio mass in the latter. Both specific richness and density were in the latter. Both specific richness and d ensity were higher in the river, while biomass did not show significan t statistical differences. The mineralogical composition of the bottom of the canals and the river was different, the former being soil of g ranitic origin, the latter being sediment of a fluviovolcanic origin. Finally, the canal bottoms showed a higher content of organic matter t han in the river.