On the ecology of Azolla filiculoides Lam. in Damietta district, Egypt

AbstractAzolla filiculoides Lam. is a tiny aquatic fern growing as free floating mats covering the stagnant water of the irrigation and drainage canals of Damietta district, Egypt. Ecological characteristics and distribution of the fern were investigated and results were discussed.Vegetation analysis of Azolla indicate that the most common associated species with Azolla are: Phragmites australis [presence (P) = 93.3%], Echinochloa stagnina (P = 70%), Eichhornia crassipes (P = 57%), Pluchea dioscoridis (P = 56.7%), Persicaria salicifolia (P = 26.7%), Phylla nodiflora (P = 13.3%) and Ludwigia stolonifera (P = 10%). Submerged species, e.g. Ceratophyllum spp. and Potamogeton spp. are completely absent in the stands dominated with solid mats of Azolla. This could be explained by that these mats prevent light penetration and oxygen which are required to submerged plants which in turn are decayed.The pH of the water where Azolla was recorded ranged from 7.1 to 9.0 (mean = 7.8), total dissolved salts ranged from 280 to 2600 mg/l (mean = 880 mg/l). The total phosphorus showed the range from 0.01 to 0.82 mg/l (mean = 0.22 mg/l). The ammonia-N is relatively high, varying from 2 to 18 mg/l (mean = 7.0 mg/l), however, the nitrate-N varied from 2.1 to 54.1 mg/l with a mean value of 20.5 mg/l.The fresh biomass of Azolla ranged from 114 to 4280 g/m2 in irrigation canals and from 506 to 2760 g/m2 in drainage canals. The dry biomass varied from 16 to 23 g/m2 in irrigation canals. The range from 26 to 320 g/m2 was obtained for drainage canals