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– The group (G3) characterized by the absence of hydrophytes phanerogames and made up, beside the filamentous algae, by a mixture of helophytes phanerogames usually described in the rhithral of small eutrophized rivers (Butomus umbellatus, Cyperus eragrostis, Cyperus longus, Lycopus europaeus etc.) associated with some terrestrial species usually described in the temporary rivers (Plantago major, Rumex crispus, Urtica dioica, Xanthium strumarium, etc.) (here in L2 and L3). This mixture of helophytes and terrestrial species describes the various types of disturbances (organic and mineral pollution, low water level) which affect these sectors and which determine the macrophytic composition. Discussion Temperature, depth and current velocity vary according to seasons. This is due to the precipitation, management and the regulation operations especially used for agriculture. Conductivity for all studied stations show that the water is strongly mineralized (Nisbet & Vernaux 1970 – EU requirements). Considering community dynamics, the taxonomic richness and plant cover at the different study sites in Litani River varied both in space and time. Spring and summer 2005 corresponded ecologia mediterranea – Vol. 35 – 2009 Investigation on macrophyte development in Litani River (Lebanon) subjected to human disturbances Figure 5 – Variations in macrophytic cover (average + SD) in the stations according to seasons and groups. 1.0 PO4 V NO2 NO3 - 1.0 - 1.0 MyrS PotC PotP NasO PlaMn PlaM ApiN PolP XanS RumC LemM LycE ButU Vau GycP CypE GalA UrtD VeAa L2 CypL LacS L3 T Clad TDS Cond (G3) RanF PhrA Rum (G1) PhaA Char L1 Figure 6 – CCA applied on the 37 abiotic and biotic variables (average for the quantitative statements) in L1, L2, L3, L4. Projections of the abiotic and biotic variable points and the stations points. Hydophyte: Char, Clad, Vau, LemM, MyrS, PotC, PotP, Ranf. Helophyte: Apin, ButU, CypE, CypL, GycP, LycE, NasO, PhaA, PhrA, PolP, VeAa. Terrestrial: GalA, LacS, PlaM, PlaMn, RumC, Rum, UrtD, XanS. L4 (G2) pH Depth O2 1.0 37
HANADI ISMAÏL, HUSSEIN ABOU-HAMDAN, AHMAD KOUBAYSSI, STÉPHANIE FAYOLLE, GABY KHALAF, ARLETTE CAZAUBON, JACQUES HAURY 38 to the maximum macrophyte cover of hydrophytes in L4, where phanerogams such as Myriophyllum spicatum L., Potamogeton crispus L., Potamogeton pectinatus L. and Ranunculus fluitans Lam. were highly developed as a result of the silty substrate granulometry, the increase in solar radiation and temperature and specially the increase in water flow in this station. Upstream, in station L1, a large cover of macroalgae such as Chara sp., characterizes this station overall in spring and winter. Such variability can be related to the fact that in the Litani River some variables seem to be affected by human activities (conductivity, TDS, mineral nutrient) and disrupted the longitudinal gradient; the abiotic factors mainly contribute to the pattern of macrophyte distribution (Butcher 1933; Abou-Hamdan et al. 2005). The results showed that physical characteristics such as shining, granulometry and rates of flow act directly on plant cover, richness and the composition of the macrophytic communities (Haslam 1978; Thiébaut & Muller 1999; Weigleb 1984). The substrate which is mainly fine in L2, L3 and L4 as well as high light energy (in all stations) are compatible with the development of phanerogams; such conditions disfavour the colonisation and the development of bryophytes. The water quality has influenced the taxonomic composition of the macrophytic stands. As Bernez et al. (2000) have reported in studies on the River Rance and Abou-Hamdan (2004) on Mediterranean rivers in south east of France, the disturbed and eutrophicated stretches of rivers carry a more developed vegetation than the less disturbed parts. This can explain that taxonomic richness is higher in L3 and L4 than L1 (less polluted station) and L2 (more polluted station). Some species such as Chara sp. were well developed only on L1, this taxa disappeared in all other stations (at the more polluted stations) due to strong eutrophication. This xenosaprobic macroalgae, which is thought to be sensitive to pollution, does not grow in polluted sites (Bornette & Arens 2002). Lemna minor L., Vaucheria sp. and Cladophora sp. (favoured by the high nitrate and phosphate concentrations) were well represented at all the stations, with other pollution-resistant species. In contrast to indications in flora literature (Bonnier 1990; Fare et al. 2001) Ranunculus fluitans Lam. was developed not only in rapid water (station L4), but also in still waters (station L1). The disappearance of Ranunculus fluitans Lam. in L2 and L3 and its reappearance in L4 may be related to the variation of water level and pollution degree. Research on its maintenance either with seeds or vegetative fragments should be undertaken. In spite of a strong eutrophication and especially pollution by sewage, Butomus umbellatus L. (rare species in south east of France) seems to profit from the abiotic conditions (physicochemistry, granulometry). This species proliferates in Litani and invades in some sites the totality of the river. It prevents the installation of another species and acts negatively on the biodiversity. It acts like the dense colony of flowering-rush (Butomus umbellatus L.) in Bay St. François, near Lake St. Pierre in Québec. This species introduced about 1905 near Montreal, is today widespread along the St. Lawrence River (Delisle et al. 2003). Conclusion Abiotic and biotic factors revealed strong anthropic disturbances from the source of the Litani River and along the river. All the species and the cover rates of the macrophyte seemed to depend on the following combined two main factors: seasonal and annual climatic variations, which lead to drastic changes in the hydrological conditions (flooding and drought), and anthropogenic disturbances such as organic and domestic pollution, water management and regulation operations. The severe organic pollution combined with low flow rates has favoured the development and the proliferation of filamentous algae in the Litani River. In addition the proliferation of Butomus umbellatus requires further monitoring. This species develops in Litani like an invasive species and it may destroy the ecosystem and reduce the biodiversity of this river already weakened by disturbances of various origins. Further researches are needed in order to obtain more data on Litani River and its effluents during longer periods of time. ecologia mediterranea – Vol. 35 – 2009
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ecologia mediterranea Editeur-in-Ch
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