A study of dissolved and particulate material exchanges among different waterbodies and between shallow water and deep channel

Understanding physical processes controlling material transport pathway and the time associated with transport processes are of importance for studying pollutant retention and fate in estuaries and coastal seas. In this study, the concept of the water age has been applied to investigate the spatial and temporal patterns of material transport processes and timescales among multiple waterbodies and between shallow water and deep channel of the Chesapeake Bay. For a complex estuary, the material retention time in deep channels and shallow water regions can vary substantially, and the lateral transport timescale is a useful indicator for material exchanges (both dissolved and particulate) between shoal regions and deep waters. The influences of freshwater, density-driven circulation, wind-induced transport, and lateral bathymetry variations on material exchanges and age distribution have been investigated using a three-dimensional hydrodynamic model. Results show that river inflows, wind stress, and density-driven circulation play important roles in controlling the cross-section structure of transport time and the lateral material exchange. An increase of river discharge results in increased gravitational circulation and downstream residual transport, and thus reduces material retention time in shoal regions. Lateral induced water motion can have a large influence on horizontal material transport. The upstream (southeasterly and southwesterly) wind causes strong lateral and vertical mixing, which further reduces gravitational circulation resulting in a decrease of material transport out of the Bay.