Numerical study on pollutant transport in estuary based on age concept

Using a mean age concept defined by Deleersnijder,we apply the three-dimensional hydrodynamic and eutrophication model HEM-3D to investigate the pollutant age distribution under different river discharge conditions in the Pamlico river estuary (PRE),North Carolina.The model results reveal that it takes about 65 days for pollutant to be transported out of PRE during normal season,while,it takes 230 days and 20 days for pollutant substances to be transported out of PRE during dry and flood seasons,respectively.The time differences indicate that the transport process is a function of river discharge.The spatial variation of the pollutant transport age is significantly affected by the salinity intrusion in the PRE; the later forms a salinity front at its most upstream location.The front inhibits the outward transport of pollutant.The salinity stratification plays an important role in the vertical distribution of the pollutant transport age.The vertical difference in age is enhanced as the salinity stratification increases.