Ecological status of Lake Nasser Khors, Egypt, before operating the Grand Ethiopian Renaissance Dam

Abstract

Lake Nasser is an artificial reservoir that represents the national freshwater reserve of Egypt and has a number of khors (side extensions) along its eastern and western banks. These khors covered approximately 79% of the lake’s total surface area and have an important effect on water quality and fish production in the lake. This study aimed to monitor and assess the water quality, distribution, and structure of the biotic community, including phytoplankton, zooplankton, macrophytes, epiphytes, and macrobenthos in two main khors (Tushka West and Dahmeit) during postflood and preflood periods. There was urgency associated with the study, as it was the last opportunity before the storing of the water behind the Grand Ethiopian Renaissance Dam (GERD), which had begun to fill in July 2020. Although the study confirmed that the water quality of Lake Nasser was good, it is classified as a eutrophic lake (depending on the levels of Chlorophyll-a and nutrients). This study found that pH, NO2, SiO4, NH4, PO4, and temperature were the factors with the greatest effect on the biota community, especially in Dahmeit Khor. In contrast to the phytoplankton and macrobenthos, the highest total density of zooplankton and epiphytic microalgae were detected during the postflood period. This study could be useful in monitoring possible changes in the Lake Nasser environment after the complete filling of the GERD reservoir.