Macrobenthos of lower Zayandehrud River

To study the macrobenthos of the lower reaches of Zayandehrud River, a distance of approximately 160 km, between Birds Garden and Varzaneh Town was investigated. Hence, eight stations, based on substrate structure, were selected using Sorber and Ekman samplers and PVC tube macrobenthos of the river were collected twice each season for a full year (2003-2004). Samples were sorted out and identified based on the available identification keys to genus and, in some, to species level. In the collected samples, 13 orders and 24 families were recognized, among which, 17 taxa were identified to generic and two to specific level. Amongst the identified orders, Ephemeroptera and Trichoptera were the most diverse taxa by the number of families, genera and species and with widest distribution in Esfahan area and west of Esfahan City. The class Oligochaeta with three orders and four families, and the order Diptera, with three families and two genera, were the most abundant groups in east of Esfahan City. The families Lumbriculidae, Lumbricidae and Tubificidae, the genus Chironomus and the species Piscicola geometra were variably present in all stations and seasons. Members of the family Glossiphoniidae and the species of Baetis rhodani, Piscidium amnicum, Hydropsyche instbilis, Agrion virgo and Valvata cristata were present only in certain stations and seasons, probably due to sever changes in the physical and chemical properties of the substrate, their type of life cycle, and or both aforementioned parameters.