The Danube delta: Filter or bypass for the nutrient input into the Black Sea?
Suciu, Radu; Constantinescu, Adrian; David, Cristina
The role of the Danube delta in the nutrient [total nitrogen (Nt)] and phosphorus from phosphates [P(P04)] inputs of the River Danube into the Black Sea was examined using discharge and water quality data of the general monitoring at the inflow point into the delta and the outflow point into the sea, recorded in the period 1996-1999, and information provided by the Sobek hydraulic model adapted to the particular conditions of the Danube delta. It is shown that the delta as a whole acts like a bypass for the nutrients in the main branches and like a filter in the lakes, swamps and marshes, retaining Nt in any hydrological condition but releasing P(P04) in the period analysed. The quantities of Nt and P(P04) retained or released are strongly correlated with the hydrological regime. The study assisted by the hydraulic model of the delta enables to estimate the volume of nutrients retained or added by its aquatic complexes based on the input discharge data from Ceatal Chilia, at the delta entrance.