Environmental relationships of aquatic vegetation in the fresh water ecosystem of the Nile Delta, Egypt

In generalized four sectors, 350 stands (water channels) in 50 selected and geo-referenced sites with eighteen environmental factors were surveyed. The total number of recorded species varied from a sector to another: 21 in the northern, nineteen in the middle, seventeen in the western and sixteen in the eastern. New populations of Cyperus papyrus were explored. Vallisneria spiralis, Elodea canadensis and Najas armata were among seven extinct species that were not recorded few decades ago. The floristic composition alteration may be because of the addition of organic matter of plant and animal origin and the discharge of industrial and sewage effluents. Classification and ordination analyses (DCA) resulted in the segregation of seventeen vegetation groups (communities), three of them were repeatedly recorded; namely Phragmites australis-Eichhornia crassipes, Phragmites australis-Myriophyllum spicatum and Potamogeton pectinatus-Myriophyllum spicatum. Phragmites australis-Cyperus papyrus group was a new community spreading in the eastern sector of the Delta. Electric conductivity, Fe, Hg and chemical oxygen demand (COD) showed high significant variation (P < 0.001) among the vegetation groups. Other significant variables were Cl, Ca, NO3, pH and SO4 (P < 0.047). Redundancy analysis (RDA) was chosen as the appropriate ordination method to perform direct gradient analysis. Trace elements Cu, Fe, Hg and Pb participated in the floristic and chemical composition of each sector. Resume Dans quatre secteurs generalises, 350 emplacements (des canaux) ont ete surveilles dans 50 sites choisis et georeferences, ou eighteen facteurs environnementaux ont ete suivis. Le nombre total d’especes rapportees variait d’un secteur a l’autre, 21 au nord, nineteen au centre, seventeen a l’ouest et sixteen a l’est. De nouvelles populations de Cyperus papyrus ont ete explorees. Vallisneria spiralis, Elodea canadensis et Najas armata faisaient partie de sept especes eteintes qui n’avaient pas ete rapportees il y a quelques decennies. La modification de la composition floristique pourrait etre due a l’addition de matiere organique d’origine vegetale ou animale et au rejet d’effluents industriels ou d’egouts. Des analyses d’ordination et de classification (detrended correspondence analysis – DCA) ont abouti a la segregation de seventeen groupes vegetaux (communautes) dont trois ont ete rapportes de facon repetee, a savoir Phragmites australis-Eichhornia crassipes, Phragmites australis-Myriophyllum spicatum et Potamogeton pectinatus-Myriophyllum spicatum. Le groupe Phragmites australis-Cyperus papyrusetait une nouvelle communaute qui se repand dans le secteur est du delta. La conductiviteelectrique, Fe, Hg et DCO presentaient des variations tres significatives (P < 0,001) selon les groupes vegetaux. Parmi les autres variables significatives, citons Cl, Ca, NO3, le pH et SO4 (P < 0,047). L’analyse de redondance (RDA) fut choisie comme le moyen d’ordination approprie pour realiser une analyse de gradient directe. Des traces des elements Cu, Fe, Hg et Pb se trouvaient dans la composition floristique et chimique de chaque secteur.