Hydrodynamic-ecological model analyses of the water quality of Lake Manzala (Nile Delta, Northern Egypt)

Abstract

Lake Manzala remains the largest of the Nile Delta lakes and has undergone substantial recent changes particularly over the last 30 years due to regulation of freshwater inflows, land reclamation and increasing loads of BOD and nutrients. The latter are particularly associated with polluted drains flowing into the lake. An increasing fraction of the N load may also come from the expanding fish farming industry within and around the lake. Over the past 20-25 years, the N load from the drains has increased three times whilst the P load has remained approximately constant. This is despite a 40% reduction in freshwater inflows due to diversion of water towards the Sinai for land development. As a result of these changes, the concentration of total N in the drains has increased 4.5 times while the total P concentration has increased by 50% over the same period. Increases in nutrient concentrations can be attributed to increase in the use of fertilizer combined with an expanding population served by sewers, improved living standards and increased industrial production. Nutrient enrichment has resulted in declining water quality and eutrophication, especially in the southern parts of Lake Manzala. A combined hydrodynamicecological model has been set up for the lake and is used to analyse the development of water quality as a function of the load of organic material and nutrients. Model results show that 86% of the N load and 59% of the P load are retained within the lake. Despite the efficient treatment of wastewater by the lake ecosystem, approximately 6,000 tonnes of N and 1,300 tonnes of P are exported to the Mediterranean through the two main lake-sea connections. This nutrient export has important implications for coastal fisheries production. The present investigation suggests that the current anthropogenic nutrient load to the coastal zone exceeds that of pre-Aswan High Dam conditions despite large reductions in the annual pulse of water and nutrients brought about by the dam. A series of model simulations with reduced nutrient load are investigated in order to identify the conditions required to enable the propagation of vegetation throughout the lake. Submerged rooted vegetation is used as an indicator for water quality as it needs light for growth and in polluted, eutrophicated waters turbidity increases hampering vegetation growth. Simulation results indicate that the nutrient load has to be reduced to approximately 25% of the present loads if submerged rooted vegetation is to become re-established in the more polluted south eastern parts of the lake.

Physicochemical properties of Manzala Lake, Egypt

“…TPAHs were measured by digital spectrofluorometer model 450 from Sequioaturner Corporation. Nutrient salts; NH 3 , NO 2 -, NO 3 -and PO 4 3-were determined by using Beckman Du-6-UV-Visible single beam spectrophotometer.…”

Modeling the Hydrodynamics and Salinity of El-Burullus Lake (Nile Delta, Northern Egypt)

“…However, Amel developed a detailed 2D hydrodynamic model of the shallow lake, and a 2D water quality and eutrophication screening models for the Lake Edku system [9]. Linnersund load may have on Lake El-Manzal water quality through hydrodynamic-ecological modeling [11]. The current study is considered the first study which deals with the water hydrodynamics of El-Burullus Lake.…”

Improving salinity tolerance of Acacia saligna (Labill.) plant by arbuscular mycorrhizal fungi and Rhizobium inoculation

“…Irrigation with low quality water (up to salinity of 4.5 dS/m) is one of many reasons that cause secondary salinization in Egypt (El-Hendawy, 2004). Therefore, planting salttolerant species, particularly N 2 -fixing species, is the most useful approach in rehabilitating salt-affected degraded lands (Rasmussen et al, 2009).…”