DISTRIBUTION OF AQUATIC PLANTS IN RELATION TO ENVIRONMENTAL-FACTORS IN THE NILE DELTA

This paper develops a model of the relationship between aquatic macrop hytes and their environment in the irrigation and drainage canals in t he north-eastern part of the Nile Delta. The study area was sampled fr om 60 sites which were classified by two-way indicator species analysi s into seven vegetation groups (A-G), with the following dominant spec ies: Phragmites australis (Cav.) Trin. ex Steud. and Typha domingensis (Pers.) Poir. ex Steud(A); Eichhornia crassipes (C. Mart.) Solms and Echinochloa stagnina (Retz.) P. Beauv. (B); Azolla filiculoides Lam. ( C); Myriophyllum spicatum L. (D); Potamogeton crispus L. and Potamoget on nodosus Poir. (E); Ceratophyllum demersum L. and Potamogeton pectin atus L. (F); Ceratophyllum demersum L. (G). The first axis of a detren ded correspondence analysis ordination represented a life form gradien t of the aquatic vegetation. It separated vegetation types dominated b y emergent species from free-floating and submerged macrophytes. Group A, consisting mainly of emergent macrophytes, had a higher Shannon di versity index. The highest species richness value was recorded in grou p C, dominated by Azolla filiculoides Lam. Canonical correspondence an alysis was used to study species-environment relationships. The distri bution of emergent and floating species was best correlated with water electrical conductivity, K+ and total phosphorus content. The distrib ution of submerged species showed a high correlation with the increase in canal width and decreased due to shading by marginal trees.