The fluctuations of physicochemical factors and phytoplankton populations of Urmia Lake, Iran

   Urmia Lake is one of the two large hypersaline lakes in the world which have Artemia. It is located in northwest of Iran. Due to a decrease in water inflow and volume, the salinity of Urmia Lake has reached to more than ۳۰۰ g.l-۱ since ۲۰۰۱. The increased salinity has greatly influenced biological aspects of the lake, and caused the lake undergoes at critical conduction. The aim of the present study was to investigate the distribution fluctuations of phytoplanktons and selected physicochemical factors in relation to Artemia distribution in Urmia Lake during ۸ months. Statistical analysis of mean values of ion concentrations and phytoplankton abundance indicated significant differences among sampling months. The minimum and maximum values for the selected factors were, as Cl- ۱۷۶.۲-۲۰۱.۳ g.l-۱ , CO۲ ۹۵-۱۷۵mg.l-۱ , dissolved oxygen (DO) ۰.۱-۲.۸ mg.l-۱ , HCO۳ - ۱۴۴-۴۹۶ mg.l-۱ , PO۴۲+ ۱۰۴-۸۷۵ mg.l-۱, NO۳- ۳۳۰-۴۱۰۴ mg.l-۱, NO۲- ۴-۲۱.۵ mg.l-۱, SO۴۲- ۱۰۴۹۰-۲۹۸۴۰ mg.l-۱, Ca۲+ ۵۶۱-۱۶۰۶ mg.l-۱, Mg۲+ ۳۶۴۹-۱۴۵۸۷ mg.l-۱ while water hardness was ۲۱۰۰۰- ۶۲۰۰۰ mg.l-۱. Fourteen phytoplankton genera included Bacillariophyceae (۱۰ genera),Chlorophyceae (۲ genera) and Cyanophyceae (۲ genera) were identified during sampling period. The smallest average density of phytoplankton ۹۷۲۴۹ L-۱ was observed in December ۲۰۰۵ and the greatest average density ۴۸۱۹۸۳ L-۱ in August ۲۰۰۵. Dunaliella sp. composed ۹۲.۱% of the lake's phytoplankton. Statistical analysis of phytoplanktons fluctuations showed a significant difference among different months (p< ۰.۰۵).