EFFETS DES FACTEURS ENVIRONNEMENTAUX SUR LA QUALITE DE L’EAU ET LA PROLIFERATION TOXIQUE DES CYANOBACTERIES DU LAC KARAOUN (LIBAN)
Journal Title: Larhyss Journal - Year 2012, Vol 10, Issue 10
Abstract
The Near East region already suffers from the effects of gradual climate change and will be among the most affected regions to climate change in the future. Consequently, productivity in agriculture is expected to decrease due to high temperatures. In addition, drought, floods and soil degradation will threaten the food security in the Eastern Arabic countries. Water is considered as the critical factor in this region; slight changes in rainfall patterns will have considerable impact. It has been proved that potential climate changes are likely to disrupt most ecosystems through changes in their physicochemical conditions and the population organisms living in these ecosystems. In this context the assessment of impacts on populations and phytoplankton communities has been studied in Lake Karaoun beginning of 1992. The Lake Karaoun was characterized by a diversified algal microflora with the existence of 98 species of phytoplankton and the predominance of about sixty species of diatoms mainly Aulacoseira granulata accompanied by a high concentration of dinoflagellates Ceratium hirundinella. Regional changes in climate and the increasing anthropogenic activities have deeply affected this ecosystem. Excessive external imputs of nutrients (phosphorus and nitrogen) from domestic sewage, the discharge of industrial waste in the Litani river as well as intensive agricultural practices led to eutrophication.The physico-chemical studies showed a deterioration of water quality defined by high levels of eutrophic elements (nitrates and nitrites) and changes in phosphate concentrations (0 to 7.4mg / l) in relation to cyanobacterial bloom populations. In spring 2009 the occurrence of Aphanizomenon ovalisporum Forti for the first time in Karaoun Lake marked the beginning of cyanobacteria blooms formation. During summer and with rising temperatures (between 25 and 32 ˚ C), A. ovalisporum disappears completely and was replaced by Microcystis aeruginosa. The end of 2009 was marked by the reappearance of Ceratium hirundinella and the persistence of M. aeruginosa. In spring 2010, the lake resumed its volume after years of water shortage; biodiversity 30 has emerged with the presence of a dozen species of Chlorophyceae such as: Pediastrum duplex Meyen, P. boryanum, Micrasterias sp., Coelastrum microporum Nag and the dominance of Staurastrum manfeldtü Delponte. In this period cool temperatures did not favor the presence of cyanobacteria species. In summer 2010 increasing water temperatures (between 30 and 35 ˚ C) promoting blooms of unusual M. aeruginosa kütz and leading to cyanotoxin production (16 µg/l of microcystin LR.
Authors and Affiliations
SLIM K. | Université Libanaise, Faculté des sciences, Beyrouth, Liban, Commission Libanaise de l’Energie Atomique (CLEA) CNRSL P.O. Box 11-8281 Beyrouth, Liban, ATOUI A. | Commission Libanaise de l’Energie Atomique (CLEA) CNRSL P.O. Box 11-8281 Beyrouth, Liban, ELZEIN G. | Université Libanaise, Faculté des Sciences Zahlé, Liban, TEMSAH M. | Université Libanaise, Faculté des sciences, Beyrouth, Liban
Keywords
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