Water quality and phytoplankton communities in Lake Qarun (Egypt)

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Lake Qarun is a closed saline lake in the northern part of El-Fayoum Depression (Middle Egypt) at the margin of the Great Western Desert. It is almost entirely sustained by inflow from the Nile River and, during the 20th century, lake water salinity has increased strongly. Physico-chemical characteristics and phytoplankton periodicity in the lake were monitored during 2001. All the water quality variables measured showed considerable seasonal variation, and quantitative and qualitative differences in phytoplankton communities were recorded. The maximum crop density was in August, whereas lowest values occurred in December. Highest crop densities coincided with a high abundance of Bacillariophyceae. The Bacillariophyceae were most diverse with 23 species, then Chlorophyceae with 16, Cyanophyceae with 8, and Chrysphyceae and Dinophyceae with one species each. Despite being a saline inland lake, the open-water phytoplankton communities were composed of some marine/brackish forms but mainly of freshwater communities tolerant to high salinity. The identified phytoplankton species indicate a tendency towards eutrophy but total crop densities were relatively low compared with eutrophic lakes elsewhere. Light limitation by suspended solids as well as hydrological related factors are believed responsible for the relatively low phytoplankton abundance. The lake appears to be ecologically unstable and careful limnological monitoring is recommended.