الفهرس 
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Abstract
Lake Manzala is the largest of Egyptian lakes along the Mediterranean coast. Representing a highly dynamic aquatic system, that has been undergoing continuous and pronounced changes, most of the water entering the lakes comes from the canals and drains ditches from the southern, southeastern and northwestern regions. This inflowing water provides the lake with high nutrient loading, causing eutrophic conditions and high productivity. At the beginning of the twentieth century the lake covered some 1,698 km². However, ambitious land reclamation projects had reduced the size of the lake to 905 km² by 1981 and to 770 km² by 1988. It is predicted that existing reclamation plans will reduce its area further to 469 km². Encroachment from adjacent urban centers is threatening to reduce the area of the lake even further. Since the construction of the High Dam and the almost complete cessation of sedimentation, the coasts of the eastern delta have altered from predominantly accretional to erosional. These activities have increased the pollution of the lake. The lake is affected by various external factors, the most important of which are, the progressive increase of industrial and agricultural wastewater discharge. These pollutants are damaging to aquatic organisms specially fishes. It is doubted that the aquatic environment is capable of absorbing the effects of these pollutants without being detrimental to the living resources. The results of the current study indicated a deteriorating water quality of Lake Manzala based on the water quality index categorization.
This study aimed to investigate the link between the contaminated status of Lake Manzala and the response of Chironomus sp., on molecular and morphological levels, in order to enhance the use of these deformities as a bioindicator of environmental health. The sampling stations were chosen to cover the southern sector of Lake Manzala and its inflowing drains. Water of study area is subjected to pollution via several and rather complicated routes; among them domestic, industrial and agricultural discharges are the most significant. Hadous drain has typical agricultural drainage water, which would be of moderate quality for agricultural use. However, water from Bahr El-Baqar, is quite different, Bahr El-Baqar serves as a wastewater stabilizing facility for Cairo sewage, allowing this wastewater to become biologically degraded into nutrient-rich by the time it reaches the lake. El-Matariya is Middle Eastern part of the Lake with extensive fishery activities.
Chironomids, the non-biting midges (Diptera; Chironomidae), are the most abundant macroinvertebrate group encountered in freshwater aquatic habitats. Morphological and molecular techniques were employed to identify the chironomid specimens, the only identified species was Chironomus transvaalensis, an East African species, and is however, considered a first time record in Egypt by this study.
Chironomus transvaalensis was seriously affected throughout the three sampling sites at Lake Manzala, and frequently displayed mentum deformities. Elevated morphological deformity rates in Chironomidae larvae have been attributed to such pollutants as oil tars, pesticides, organochlorines, and heavy metals. In this study, the potential of chironomids as biological indicators of heavy metal contamination and bioavailability in a contaminated ecosystem was assessed, and it can be concluded that the accumulation levels of heavy metals in the larval tissue of Chironomus transvaalensis reflect to high extent the degree of aquatic environmental pollution by such metals. Also, the present study gives a declaration of the elevated levels metal pollution in the different studied areas due to continuously discharging of industrial agricultural and domestic effluents.
Chironomid larvae collected at contaminated sites exhibited mouthpart deformity, where, 92.2% of all examined specimens were observed as deformed. There were even higher frequencies of abnormalities in Chironomus transvaalensis menta at Bahar El-Baqar (93%, n=100) and at Hadous (97%, n=100) in which abnormalities were most prevalent. While at El-Matariya (65%, n=20) in which abnormalities were less frequent. Cd, Fe, Pb, Cu and Cr were determined in both larvae and sediment samples. Significant correlation between metal concentrations and deformity rates were observed for all metals. The principle component analysis suggested the mentum deformities are induced mostly by Fe, Cd and Cu. Results also showed that the effect of the contamination in Lake Manzala was apparent on a molecular level as a degradation and fragmentation in the genomic DNA of the morphologically deformed larvae.
In conclusion, screening of mentum deformities in Chironomidae provides evidence of sub-lethal effect of pollution on the Lake Manzala chironomids and may serve as early indicators of deteriorating water quality. It also provides indication of species health and fitness of chironomids, which could impact on their ability to feed, and perform ecological roles such as serving as a path-way for the transportation and utilization of energy and matter in Lake Manzala. Furthermore, the elevated deformities incidences and the absence of species diversity recorded at the sampling sites are indication of chemical stress in Lake Manzala. Also the deformity types such as missing tooth, splits or multiple deformities which existed at sites Bahar El-Baqar and Hadous drain, which were not found at El-Matariya, suggest that these types of deformities were induced by severe pollution. Overall, the discriminatory capacity of Chironomidae deformities as a biological screening tool could be enhanced if deformity types and severity are linked to different types or concentrations of contaminants.
The incidence of chironomid abnormalities offers a biological contaminant marker applicable to aquatic environments as diverse as drainage canals, small streams, ponds, and lakes. Fortunately, genus Chironomus is among the most abundant. Progress toward a better understanding of specific causes and mechanisms of abnormal larval development, could greatly expand the predictive power of this of this indicator. In this study, although not an indicator of specific contaminants, the occurrence of abnormal chironomid larvae can serve as a biological evaluator and long-term monitor of the benthic environment, and can suggest where more intensive bioassay and chemical testing would be most effectively employed.
Vibrio cholerae, the causative agent of cholera, is a waterborne bacterium inhabiting the aquatic ecosystem. Faecal contamination of water resources, represent modes of dissemination of the bacteria and thus the disease. This study is reporting an association between Vibrio cholerae and chironomids larvae and exuviae, collected from Lake Manzala. Vibrio cholerae was isolated from the larvae and exuviae of Chironomus transvaalensis. The isolation of V. Cholerae was performed according to standard microbiological methods, followed by 16S rRNA sequence analysis. V. cholerae was present in all the examined C. transvaalensis larvae and exuviae. Results showed that the studied areas at Lake Manzala are polluted by sewage, agriculture and industrial wastes. These findings suggest that Chironomids serve as V. cholerae reservoir and play a role in the ecology of the bacterium and possibly take part in the dissemination of the pathogenic serogroups during epidemics; which in turn supports the use of chironomids as a monitoring tool of V. cholerae in endemic areas.