Distribution of aquatic plants in relation to environmental factors in the Nile Delta
This paper develops a model of the relationship between aquatic macrophytes and their environment in the irrigation and drainage canals in the north-eastern part of the Nile Delta. The study area was sampled from 60 sites which were classified by two-way indicator species analysis into seven vegetation groups (A-G), with the following dominant species: 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 Potamogeton nodosus Poir. (E); Ceratophyllum demersum L. and Potamogeton pectinatus L. (F); Ceratophyllum demersum L. (G). The first axis of a detrended correspondence analysis ordination represented a life form gradient of the aquatic vegetation. It separated vegetation types dominated by emergent species from free-floating and submerged macrophytes. Group A, consisting mainly of emergent macrophytes, had a higher Shannon diversity index. The highest species richness value was recorded in group C, dominated by Azolla filiculoides Lam. Canonical correspondence analysis was used to study species-environment relationships. The distribution of emergent and floating species was best correlated with water electrical conductivity, K+ and total phosphorus content. The distribution of submerged species showed a high correlation with the increase in canal width and decreased due to shading by marginal trees.