الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
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Abstract
Irrigation in Egypt mainly depends on the River Nile water through a system of main canals and Rayahs. These irrigation canals are widespread over the Nile Delta area and it runs towards the Mediterranean coastal plain and discharges their water into the northern lakes or the sea. Rayahs are the main canals of fresh water branched from Damietta and Rosetta branches of the River Nile. These Rayahs are vital for irrigation, navigation, fishing and other domestic uses in many Governorates of Egypt.
Macroinvertebrates can be useful indicators of water quality because these communities respond to integrated stresses over time, which reflect fluctuating environmental conditions. The present study was designed to investigate the distribution and diversity of the most common macroinvertebrates along the three Rayahs and make a taxonomical revision for some of molluscan species by using more advanced technique which depends on Ribosomal RNA gene (18S rRNA gene). During the period from spring 2014 to winter 2015, 25 stations were selected to study the effect of water quality conditions on the macrobenthic invertebrates.
During this work, the physicochemical parameters fluctuated from season to another and through sites. The highest value of water temperature (33 ºC) was recorded at station N5 during summer but the lowest value (14.20 ºC) recorded at station T7 during winter, while electrical conductivity in the investigated area attained its lowest average value during winter in El-Rayah El-Behery (359 µS/cm) and recorded its highest average value during winter in El-Rayah El-Nassery (609.89 µS/cm). The highest value of electrical conductivity was recorded at station B9 (880 µS/cm) during winter but the lowest one (345 µS/cm) occurred B1, N1 during spring and T1 in summer. On the other hand, the highest value of pH at station B9 was (8.73) in summer, while, the lowest one was recorded in station B9 (7.41) during winter .With regard to DO, its highest average value (8.99mg/l) was noticed at station N8 but the lowest one (3.18mg/l) was recorded at station B9. The maximum average value of BOD (7.65 mg/l) was recorded during summer in El-Rayah El-Behery, while minimum average value (3.55mg/l) was recorded during spring in El-Rayah El-Behery and El-Rayah El-Nassery. The highest BOD average value was recorded at station B8 (8.56 mg/l) and the lowest average value was recorded at station N4 (3.96 mg/l).
Forty one macrobenthic invertebrates’ species were identified in the present study in all Rayahs and the River Nile station, belonging to three phyla namely; Mollusca, Annelida and Arthropoda. The highest value of population density (8488 Org.m-2) was estimated at station N2, while the lowest value population density (475 Org.m-2) was estimated at station B2. The macrobenthic population density showed one peak during winter with 6316 Org.m-2 in El-Rayah El-Nassery. On the other hand, autumn showed the lowest population density with 1339 Org.m-2 in El-Rayah El-Tawfiky. The biodiversity of macrobenthic invertebrates revealed that stations T3, N8 and B8 were recorded the highest number of species (18, 19 and 17 respectively) and species richness (2.066, 2.303 and 2.108 respectively). Station B8 had the highest diversity during the study period ( 1.63), while the lowest diversity was recorded at station B5 (0.378), which may be attributed to natural of water pollution at this station which led to the absence of most species and the presence of only high tolerant species as Diptera species.
Annelida (7 species) was the dominant phylum as it attained 78.1%, 55.55%. , 55.14% and 65.24% by number of the total macrobenthic fauna at the River Nile station (RN), El- Rayah El-Tawfiky, El- Nassery and El-Behery, respectively and represented by seven species, namely; Limnodrilus udekemianus, Branchura sowerbyi, Allolopophra caliginosa, Helobdella conifer, Limnatis nilotica, Barbronia assiuti and Batracobdelloides sp..
Limnodrilus udekemianus represented the most dominant species of Annelida. The maximum Annelida population density was recorded at station B5 with an annual average of 4500 Org.m-2, while station T3 was the least with an annual average of 325 Org.m-2. Seasonally, winter was the most populated season with an average of 2750 Org.m-2 in El-Rayah El-Behery, while autumn represented the least populated season with an average of 725 Org.m-2 in El-Rayah El-Tawfiky. Limnodrilus udekemianus contributed about 95.8% of the total Annelida with an overall average of 1652 Org.m-2 in all Rayahs.
Arthropoda (18 species) was the second important group of macrobenthic fauna formed about 15.4% , 37.42%, 40.05% and 21.09% of the total macrobenthic fauna at the River Nile station, El- Rayah El-Tawfiky, El- Nassery and El-Behery, respectively. Insecta constituted the main component of Arthropoda, while Crustacea was sporadically appeared. Fifteen species belong to class Insecta and 3 species belong to class Crustacea. The Chironomidae larvae represented the most dominant component of Arthropoda. The highest average density of Arthropoda was recorded at station N2 with an annual average of 7656 Org.m-2, while station T7 was the least populated station with an annual average of 31 Org.m-2. Seasonally, winter was the most populated season by Arthropoda with an average of 4566 Org.m-2 in El-Rayah El-Nassery, while spring represented the least populated season with an average of 47 Org.m-2 in El-Rayah El-Nassery. Chironomidae larvae formed 12.97% of total benthic invertebrates with an annual average 383Org.m-2 in the three Rayahs.
Mollusca (16 species) formed 7 %, 4.82%, 13.7% and 6.3% in El-Rayah Tawfiky, Nassery, Behery and the River Nile station (RN) respectively. During this investigation, 16 species of Mollusca belonging to two classes, eight orders and eleven families were recorded in all Rayahs and the River Nile station (RN).The distribution of Mollusca showed that station B9 was the most populated station with an annual average of 2500 Org.m-2, while station B1 was the least populated with an annual average density of 19 Org.m-2. Seasonally, summer exhibited the highest molluscan population density with an average of 1189 Org.m-2 in El-Rayah El-Behery, although autumn represented the least density with an average of 28 Org.m-2 in El-Rayah El-Behery. Gabbiella senaariensis is the most populated species and contributed about 39.5 % of the species compositions, with overall average of 97 org.m-2 in the three Rayahs, while it occupied the third position in the River Nile station (RN) with 11.5% of total Mollusca group .
Generally, mud, DO, Temperature, BOD and organic matter were the most influential water variables on macrobenthic communities at all Rayahs.
The study proved that most of stations were polluted, and this is due to presence of Diptera and oligochaete species, which are high tolerant species and show an oxygen consumption that is independent of the dissolved oxygen content of the surrounding medium as a result of morphological or physiological adaptation, These organisms are indicators of the pollution of most studied sites.
Taxonomy of molluscan specimens was studied from the views of morphology and 18S rRNA gene analysis. The Gastropod species -1 and -2 had 5-6 light or dark brown whorls, but the last whorl of Gastropod sp.-2 was larger than that of Gastropod sp.-1. The phylogenetic analyses of 18S rRNA gene showed that both of Gastropod species formed monophyletic cluster, which had paraphyletic lineage with species Viviparus georgianus, implicating two new species under the genus Viviparus. The shell of the Bivalve sp.-1was ovoid with light greenish brownish or yellowish color, while the Bivalve sp.-2 had light brown to grayish elongated shell. Both of Bivalve spp.-1and-2 showed 18S rRNA gene sequence identity; averages of 89% and 92%, respectively, with Lampsilis cardium suggesting new genera within the family Unionidae