Benthic invertebrates' diversity and some physical a:1d
chemical characteristics in Lower Zab tributary and Tigris River were studied. Month l y samples were col l ected from November 2001 to October 2002.
The rt:sLllts of the present study showed the turbidity iu Tigris river
before the confluence to be higher (34.4 NTU) compared to the other stations. Mean salinity was greater in Lower Zab tributary (0.33 %) compared to that in the river. Lower Zab tJibutary and Tigris River were good in Oxygen content, and a high dissolved oxygen value was recorded (7.9 mg/L) in Lower Zab tributary.
31 benthic invertebrate species were identified, 14 of which were
arthropods. 8 species from both of the Ol igochacta and Mollusca .One single species was identi fled from the Nemathelminthes. Species diversity varied from 1.9 in Lower Zab tributary to 2.7 in Tigris River after the conll uence. The h ighest species density was recorded in Tigris River after the confluence was 359.1 indlnl while the lowest species density was 12.74 ind/nl in Lower Zab tributary.