Impact of flood regime on phytoplankton communities in the large African reservoir, Lake Nasser, Egypt

Abstract

Lake Nasser is a reservoir of freshwater for drinking and irrigation in Egypt and it constitutes an important share in  the fisheries sector. This study aims to acquire a better understanding of the status of phytoplankton distribution in  Lake Nasser under the current flood regime and before the construction of the Grand Ethiopian Renaissance Dam  (GERD). Samples were collected from fifteen sites representing different lake sectors along the main channel of the  lake during 2016−2017. Approximately 103 species were recorded, belonging to six different classes, dominated by Cyanobacteria, Bacillariophyceae, Chlorophyceae, whereas Euglenophyceae, Dinophyceae and Chrysophyceae  were rare. Based on the abundance of phytoplankton species, the pre-flood and post-flood seasons were very  well discriminated. A major blooming of Cyanobacteria in the Tushka sector was detected during the pre-flood  season, whereas this phenomenon diminished in the post-flood period when Bacillariophyceae and Chlorophyceae  appeared. The results of this study indicated that the most important factors affecting phytoplankton species  distribution during pre-flood and post-flood seasons are temperature, nutrients and total dissolved solids. The study  confirms that flood regime substantially affects the phytoplankton abundance and distribution in Lake Nasser.