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Abstract §..i.’.·.·.. ,·1 .,& 157 .... _. --- .\- SUMMARY Lake Qarun lies at the lowest part of El-Fayoum depression in the western desert between longitudes 30° 24’ and I 30° 49’ E and latitudes 29° 29’ and 29° 34’ N . The area of Lake Qarun is about 55,000 feddans . It extends for about 40 Km long from east to west and 5.7 Km as a mean breadth . The lake receives drainage water from the neighboring cultivated lands through a system of drains. El-Bats and El-wadi drains are the main channels joining the lake at the east and mid-south sides respectively . The following is a summary of the obtained results . PhysicQ-Chemical features of the lake; 1. Temperature: Water temperature follows that of the air The lowest average of surface water temperature was 12.7 0c during winter while the highest attained 31°C calculated during summer . 2. Transparency : Lake’s water transparency is relatively low (average 35 Cm) . Secchi disc reading varied from 5 to 110 cm. The highest value was recorded in station VI , while the lowest was observed in station I and VIII . --_. --_ .. _~.- ---._---~---------~ 158 3.Depth : Water depth ranged from few centimeters beSide shores to 700 cm at station VI which is the deepest station . 4.Nature of bottom: Bottom sediments of Lake Qarun is nearly homogenous . Most of the studied stations have mUddy bottom except those neighbouring the drains (have sandy mud bottom ). Benthic fauna in Lake Caryn and the feed~ng dkains ; 1. Twenty Species of benthic invertebrates were recorded in Lake Qarun belonging to 18 families and 10 orders. 6 of these species (30 % of the species nUmber) are new to the area. These are one coelenterate (Aiptaslogeton cf comatuS) recorded for the frist time throughoutthe present stUdy,not only from Lake Qarun , but also from the whole Egyptian waters , one polychaete (Polydora ligni), one amphipod (Corophium ascherusicum) , one deacopd (Bracbynotus seXdentatus , one gastropod (Nassarius cuvierl) and one bivalve (Venerupis aurea) . Crustacea are the main zoobenthos component in the lake followed by polychaeta , Mollusca and less so Coelentrata . 2. EI-Bats and El-wadi drains are relatively poor than the lake. In them (8) species belonging to 6 orders of Annelida , Arthropoda and Mollusca were recorded. _..~~-._~-~--_._-- 159 3. The average population density of benthic organisms in the lake attained 1676 organisms/m2/year weighing 81.23 G.F.W./m2/year . The highest denSity was recorded in station VI with an average of 3925 , while the lowest P.o. and biomass (210 individuals/m2/year weighing 18.35 G.F.W./m2/year were recorded in station VII . 4. Winter was the most productive season (produced 2058 organisms/m2/year ) allover the whole area , while spring was the poorest . 5. Concerning biomass, the lowest value was observed during Winter While the highest one (115.39 G.F.W./m2) was observed during autumn . 6. Average P.o. and biomass of benthos in El-Bats Drain (2220 organisms/m2 weighing 6.44 G.F.W./m2 ) was low when compared with the corresponding values in El-Wadi Drain (3690 organisms/m2/year weighing 344.13 G.F.W./m 2 ). The annual standing crop in the drains is higher than that observed in any station in the lake during the whole investigated period . 7. Arthropoda (represented by Crustacea) was the dominant benthic phylum in the lake’s community. They represented about 69.98 % of the P.O. and 35.08 % of the biomass of the total benthos. MaXimum distribution was recorded at station VI during winter. Numerically, Corophi um ascherus.t. cum was the mOist important crustacean species. It constituted 81.23 % of the .~----’_._--_._--~--~--~-----~ 161 glaucumj . The last species represented the main biomass (30.6 %) of the total benthos in the lake. In the feeding drains I Mollusca constituted about 14.36 % and 97.19 % , respectively I of P.O. and biomass of the total benthos in El-Wadi Drain and 1.35 % and 51.39 % respectively of the total P.O. and biomass in El-Bats Drain. They were mainly represented by 3 gastropods (Theodoxus niloticus I Cleopatra bUlimoides and (Physa acuta ) and one bivalve namely Corbicula consbrina. 10. Colentrata was less represented in the lake if compared wi th other benthic organisms. It consti tute about 5.54 % and 1.26 % of the total benthic P.O. and biomass respectively . This group was represented by one odd species of sea anemone namely Aiptasiogaton cf comatus. 11, Lake Qarun is a fertile lake in benthic organisms. Both P.O. and biomass of zoobenthos were higher when compared with other Egyptian lakes . The present stUdy recommends station VI as a sUitable site for a bottom feeders fish farm. As well I the high production of the bivalve Cerastodexma glaucum from the lake and specially station VIII encourages the exploitation and aquaculturaing of this edible species in Lake Qarun . |