Eutrophication of Karaoun reservoir (Lebanon): An overview of water quality and algal succession

Many reservoirs have been constructed throughout the world in the 20th century which often suffers from eutrophication. This worldwide problem increases phytoplankton biomass in reservoirs and impairs their uses. Except for Lake Kinneret, the environmental status of lakes and reservoirs in the Middle East is poorly documented. Karaoun Reservoir, also known as Qaroun, Qaraoun or Qarun, the largest water body in Lebanon, was built for irrigation and hydropower production. In this article, we provide a brief monograph about the reservoir characteristics, uses, water quality and phytoplankton succession, in order to assess the environmental status of the reservoir, based on the few previous publications. Since 2004, 39 years after its construction, the reservoir was found to be hypereutrophic, with low phytoplankton biodiversity and regular blooms of toxic cyanobacteria. The nutrient and trace metals concentrations would not prevent drinking water production for Beirut as is planned, but not all micropollutants are not documented. We compare Karaoun Reservoir to other monitored lakes and reservoirs around the Mediterranean Sea. They share annual toxic cyanobacterial blooms of Aphanizomenon ovalisporum and of Microcystis aeruginosa. The phytoplankton composition and succession of Karaoun Reservoir matches more with El Gergal Reservoir, Spain, than with closer natural lakes like Lake Kinneret, Israel and Lake Trichonis, Greece. Phytoplankton diversity in Karaoun Reservoir was the lowest, due to higher nutrient concentrations and a larger decrease in water level in the dry season. Karaoun Reservoir presents an interesting example of what would be the response of the phytoplankton community in other lakes and reservoirs during the drought periods expected from global climate change.