Hydrodynamic and ecological modeling for water quality assessment in Lake Qaroun, Egypt

Lake Qaroun is a closed saline lake located in Fayoum Depression in Egypt. The lake is primarily supplied by an extensive agricultural drainage network, This study presents an integrated hydrodynamic, contaminant transport, and ecological modeling framework to assess the environmental status of Lake Qaroun using the DHI (Danish Hydraulic Institute) modeling systems MIKE_21, MIKE_3, Ecolab, and the Transport module. These models were used to analyze the spatial and temporal variations of key water quality parameters, including salinity, Biochemical Oxygen Demand (BOD), and Dissolved Oxygen (DO), based on hydrological, meteorological, and water quality datasets. The results revealed significantly elevated salinity levels exceeding 40 PSU due to reduced freshwater inflows and the closed hydrological nature of the lake in addition to high BOD concentrations reached approximately 8–10 mg/L reflecting the influence of discharge of agricultural drainage and domestic wastewater, reaching approximately ~ 8–10 mg/L. Moreover, DO levels were declined to 3–5 mg/L in several areas of the lake due to the combined effects of high temperature and elevated salinity, which together reduce oxygen solubility and increase biological stress. Furthermore, the study assessed lake water quality under a maximum contamination scenario, which assumes less freshwater inflow, continuous reuse of drainage water, and elevated temperature conditions. The results highlight the interaction of hydrological, climatic, and pollution pressures and provide a modelling basis for supporting water-quality management of Lake Qaroun.