الفهرس 
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Abstract
Abu Qir Bay is a shallow semi-circular basin lies 35 km east of Alexandria City. It is considered a fertile marine habitat, comparing to other Egyptian Mediterranean coastal waters. The bay is suffered from many pollution sources, which discharged through El-Tabia outfall, Maadia outlet and the Rosetta branch of the Nile River. The present study aimed to assess the water quality of Abu Qir Bay by measuring seasonal variation of physical and chemical constituents and nutrient salts in water, in addition to determination of heavy metals in water, sediments and bivalve, Donax venustus, collected from the coastal area of Abu Qir Bay. As well as, study impact the environmental conditions on the distribution, biodiversity and population dynamics of some molluscs in the investigated area. And monitoring of the environmental quality is of great importance to determine the order of effectiveness of all the adopted governmental steps and to determine if further steps are required to improve the quality of the environment.
The results obtained can be summarizes as follows:
Physico-chemical parameters.
- Temperature of surface water in Abu Qir Bay fluctuated between 19.00 oC at stations (II and IV) during winter and 29.20 oC at station I during summer.
- Station IV showed the maximum value of pH (9.07) and reflected the highest mean value through all the study period comparing to the other stations.
- A maximum value of salinity was obtained during winter which reached to 43.90 ‰ at station V. While, a minimum value was given at station II during spring (28.70 ‰).The mean of DO showed its lowest value (7.45 mg O2/l) at station I followed by station II and III (7.85 and 7.93 mg O2/l, respectively). Spring and summer exhibited the lowest values of DO which ranged from 3.99 to 10.44 and 7.65 to 8.98 mg O2/l, respectively.
- BOD recorded high mean value (3.81mg O2/l) at station V.
- Station V showed the highest mean of COD (15.29 mg O2/l) whiles the lowest one was found in station I (9.60 mg O2/l).
Nutrient salts
- The highest values of ammonia were recorded at stations II and III (376.25 and 327.78 μgNH4-N/l).
- According to the seasonal variation, the highest value of nitrite was recorded during winter season. Regionally, station III exhibited the absolute maximum of nitrite with mean value 63.85 μgNO2-N/l.
- The highest mean of nitrate was recorded at station III (45.98 μgNO3-N/l). The minimum value was recorded in summer (9.40 μgNO3-N/l), while the maximum one was in spring (71.80 μgNO3-N/l).
- Phosphate showed the high values during summer and autumn, while the lowest one was recorded during spring. Stations II and III showed the maximum values of phosphate with mean of 96.45 and 87.47 μg PO4-P/l.
- Summer showed the highest value of silicate, while spring recorded the lowest one. Station I exhibited the highest mean of silicate (74.43 μg SiO4-Si/l).
Heavy metals in water
- The highest mean of cadmium was recorded at station III (1.15 g/l).
- Autumn season showed the highest value of Cu which was 18.67 g/l at station I.
- Lead showed its highest value at station V (23.32 g/l).- The absolute maximum concentration of Zn was observed at station IV 92.47, 93.10 g/l during spring and summer seasons.
Heavy metals in sediments
- Station I recorded high values of Cd in sediment during autumn and winter seasons.
- Station V showed the absolute maximum mean of Cu in sediment samples, which was 17.27 g/g.
- Mean of lead showed that the highest value was at station I (42.97 g/g), while the lowest one was at station V (15.74 μg/g).
- Mean of zinc showed its highest value at station III (38.63 g/g).
Heavy metals in Donax venustus
Cadmium showed its highest mean at station III (0.39 g/g wet wt.), Cu and Zn was at station V (18.79 and 33.04 μg/g wet wt.). The mean of Pb showed a range of 10.69 - 15.23 μg/g wet wt. (at stations I and II respectively).
Faunal composition and species distribution
Total of 13 benthic species of Phylum Mollusca were recorded from Abu Qir Bay. They are distributed equally within the classes Bivalves and Gastropoda, with 7 species are belonging to Class Bivalves, and 6 species are gastropods. Species of bivalves were the most frequent and recorded from all studied sites, while members of gastropods were confined to station I and II only. Within bivalves Anadra diluvia, Donax venustus and Mactra glauca were recorded from most sites throughout the year around, particularly during autumn and winter; Modiols barbate was recorded through summer, autumn and winter while Cerastodernama, Lutria and Glycymeris glycymeris were
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confined to certain stations particularly, station I and II, during winter and spring,. Six species of gastropods were recorded from station I during all seasons, but further specimens were detected at station II during winter and spring.
The values of species diversity, density and abundance were seasonally fluctuated. For bivalves, the values of Shannon-Weaver (H), Evenness and Simpsons Indices were high in spring, but declined remarkably in winter, while Margalef’s Index had higher value in winter and lowest one in autumn. In gastropods, the values of Shannon-Weaver, Simpsons and Margalef’s Indices were higher in winter and lower in autumn, while the values of Pielou’s Index (E) were nearly close with the maximum value in autumn and lowest one in summer.
Out of 1483 collected specimens, 1423 specimens representing 95.93% are bivalves and 60 individuals (4.07% belong to gastropods. This ratio was seasonally varied from 95% during spring to 99% during autumn of the total catchment, in comparable to 1% of gastropods during autumn, and 5% during spring. Donax was the over dominated other bivalves. It had 1110 individuals, representing 87.55 % of all bivalves, followed by Mactra in the second order, with 208 specimens (14.72%) and Modiols with 60 specimens (4.24%). For density, Donax venustus was the most frequent species, with an average density of 327.64±274.99 individuals/m², followed by Mactra glauca (104.55±72.67 individuals/ m²), bivalves over dominated gastropods in abundance.