Seasonal fluxes of phosphate across the sediment-water interface in Edku Lagoon, Egypt

Edku Lagoon is a shallow, brackish, coastal wetland located in the north-western part of the Nile Delta. It suffers from a high level of eutrophication, owing to the heavy load of nutrients, especially phosphorus. The purpose of this paper was to study the flux rates of organic and inorganic phosphorus across the sediment water interface in Edku Lagoon. Both the organic and inorganic phosphorus of surface sediments, pore water and their concentrations in the water just above the sediments were used to calculate the flux rates and to derive the geochemical models. These suggest that, at present, the flux of inorganic and organic phosphorus is from water to sediments via the sedimentation of inorganic particles and organic matter. The results show that phosphorus deposition to the sediments exceeds the rate of inorganic phosphorus release from the sediments to the water column. In a steady state, the rates of organic phosphorus release more or less match the rates of deposition. These reflect the imbalance (accumulation) of phosphorus in the geochemical cycle in the lagoon and its highly eutrophic status. Efforts to control the eutrophication of Edku Lagoon have focused on reducing the phosphorus input.