Benthonic fauna of the Itata river and irrigation canals (Chile)

Benthonic fauna and substrate in three areas of the Itata river (rhithron riffles, rhitron pools, and potamon) and three irrigation canals at the outtake and about 500 m downstream are analyzed. Benthonic fauna included 56 taxa; of these, 12 were exclusive of the river, 11 were only 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 Ephemeroptera (Baetidae) were more abundant in the river. The highest biomass contribution corresponded to Gastropoda (Chilina dombeyana) in irrigation canals and in the river, although there was also significant Tipulidae family (Diptera) larval biomass in the latter. Both specific richness and density were higher in the river, while biomass did not show significant statistical differences. The mineralogical composition of the bottom of the canals and the river was different, the former being soil of granitic origin, the latter being sediment of a fluviovolcanic origin. Finally, the canal bottoms showed a higher content of organic matter than in the river.