Vol. 35 – 2009 - Ecologia Mediterranea - Université d'Avignon et des ...

HANADI ISMAÏL, HUSSEIN ABOU-HAMDAN, AHMAD KOUBAYSSI, STÉPHANIE FAYOLLE, GABY KHALAF, ARLETTE CAZAUBON, JACQUES HAURY
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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