Investigation on drought effects on diversity, frequency and distribution of benthic fauna in Amirkelayeh Wetland

The Possible effects of dry years 1998-2000 on benthic organisms of Amirkalayeh Wetland was studied in the year 2001. Six sampling stations were defined where we seasonally collected benthic organisms using a grab sampler. We identified nine benthic organisms belonging to class Hirudina and orders Odonata and Ephemeroptera and also six families Chironomidae, Chaoborina, Ammaridae, Tubificidae, Xanthidae and Culicedae. Families Xanthidae and Culinidae had not been reported before for the wetland while orders Coleoptera and Trichoptera and families Planorbidae, Lymnaeidae, Coleoptera which were present before the drought, were not detected in the samples. We observed a significant decrease in frequency of benthic organisms changing from 1372 organisms per square meter in 1997 to 165 in 2001. Also, tests showed considerable change in benthic diversity, species richness and distribution in different sampling seasons and stations over the year 2001. These changes may be attributed to the decrease in water depth, dissolved oxygen, available food and increase in water temperature and predation.