Irreversible and Large-Scale Heavy Metal Pollution Arising From Increased Damming and Untreated Water Reuse in the Nile Delta

Abstract

Egypt observes one of the highest water budget deficits in Africa that is mainly compensated by intensive reuse of untreated agricultural drainage water in the Nile Delta. The implications of untreated water reuse on increasing soil pollution levels remain poorly characterized; however, a large-scale pollution can compromise crop production and water quality. To address this deficiency, we evaluate the level of heavy metal pollution in the Nile Delta, identify its sources and explore the implications of damming on heavy metal concentration using integrated pollution indicators and statistical modeling. Pollution indicators show moderate to very high contamination by Pb, Ni, Cr, Cd, Cu, and Zn, with unprecedented Cd levels in the sediments (up to 72.0 ppm) and a northward increase in pollution levels. Statistical modeling and historical datasets reveal the association of Cd and Fe on both Nile branches and the clustering of Pb, Ni, Cu, Zn and Cr, which attribute the heavy metal concentrations to the cumulative addition of untreated agricultural drainage water (9.5 BCM/yr) and wastewater. These processes introduced an accelerated pollution in the Nile Delta system. Though, conservation measures are crucial to reverse this degradation, yet the increasingly engineered Nile flow, the low gradient of the delta and the active silting impede heavy metal flushing causing irreversible pollution. Our findings alarm future increase in heavy metal pollution in response to increased untreated drainage water reuse to mitigate the impacts of ongoing upstream damming and call for implementing international cooperative agreements for integrated water management along the Nile River.