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Abstract
Benthic invertebrate species including aquatic insects are differently sensitive to many biotic and abiotic factors in their environment. Therefore, it has commonly been used as an indicator of the conditions and water quality of an aquatic system.
During the period from May 2005 to April 2006, six stations in the River Nile at the Greater Cairo Region were selected to study certain ecological aspects of aquatic insects: 1- Studying some physico-chemical conditions in the River Nile as temperature, electrical conductivity (EC). total dissolved solids (TDS), pH value, dissolved oxygen (DO). biological oxygen demand (BOD), chemical oxygen demand (COD). nitrite, nitrate, ammonia and orthophosphate, 2- Survey and identification of the aquatic insects in the area of study, 3- Studying distribution and monthly variation of the collected insects and its orders and 4- Studying the effect of water quality conditions on the aquatic insects community.
Physico-chemical conditions showed a great variation between the selected stations. The maximum values for temperature were recorded in station (5), DO was found to be completely depleted from station (1) except for a few months, pH values were found in the alkaline side and the minimum values were recorded in station (1), the maximum values of EC, TDS, BOD, COD, ammonia and orthophosphate were recorded in station (1) while the maximum values of nitrite and nitrate were recorded in station (6).Survey of the aquatic insects reveal the existence of 44 genus belonging to 27 families from 7 orders namely Diptera, Ephemeroptera, Odonata, Trichoptera, Hemiptera, Coleoptera and Lepidoptera. order Diptera represents the main component of the total insect fauna in the area of investigation constituting 85.25%, followed by Ephemeroptera 6.19%, Odonata 4.67%, Trichoptera 1.82%, Hemiptera 1.72%, Coleoptera 0.35% and finally Lepidoptera which represents 0.003% of the total insects,
Distribution of the total insects reveals the highest density at station (2), while a remarkable decrease in the other stations was reached to the lowest value at station (5). Monthly Variations of the total insects showed the highest value during December, while the lowest value was recorded during July. Briefly, aquatic insects showed its highest values during winter followed by spring, while the lowest values were recorded during summer and autumn respectively. Also, the distribution and monthly variation of each collected order and its dominant genera were discussed. The aquatic insect fauna appeared closely related to the water quality of the River Nile.
The results of this study indicated that the disturbance in water quality has a major impact on benthic insect communities even in the absence of point source discharges. Also, these results suggest that the diversity, occurrence, dominance and relative abundance of some indicator genera can be used as excellent indicators of water quality. In addition Diptera was found very tolerant to high degrees of pollution which make them a good indicator of water pollution especially organic pollution.