Impact of Climatic Variations and Physical and Chemical Variables of Water on Phytoplankton Communities of Aras Dam Lake

Climate is an important influential element in the field of environment; So that the optimal management of aquatic and terrestrial ecosystems is not possible without serious attention to climatic conditions. In recent decades, water bloom of aquatic ecosystems has grown significantly. This risen growth is due to natural changes in climate patterns and distribution mechanisms of species, affected by environmental factors. The Goals of this study, as a retrospective research, are; a) evaluation of changes in the dominant pattern of phytoplankton communities in Aras Dam Lake in 2008 and 2013, b) investigation of the impact of meteorological, physical and chemical factors on phytoplankton population growth in the study area. Data sampling was carried out seasonally in three positions, namely Dam entrance, middle of lake and Dam output. At each gaging position, data were collected to identify and count phytoplankton and to analyze several water chemical factors. Satellite data were received from the MODIS sensor and chlorophyll a images were obtained. The highest levels of chlorophyll a in summer of 2008 and 2013 were 12.71 and 10 (mg/m3), respectively. Results showed that the abundance of phytoplankton had a high correlation with the concentration of chlorophyll. In summer, the high temperatures and pH affect bloom of Cyanobacterial communities. Usually, Cyanobacterial blooms were related to high values of temperature, pH and high concentration of the dissolved oxygen in summer. The results of principal component analysis and multiple regression showed that the air temperature is the most important factor in chlorophyll changes. The correlation coefficient between chlorophyll and air temperature was calculated to be 0.72. Change in the dominant pattern of phytoplankton communities towards Cyanobacterial pattern was observed in Aras Dam Lake, showing domination of Cyanophyta branch in all seasons of 2008 compared to 2013. This result may be caused by changes in the temperature and precipitation patterns over the study area.