Modeling water exchange between Baltimore Harbor and Chesapeake Bay using artificial tracers: seasonal variations

Understanding the dynamics of water exchange between Baltimore Harbor and the Chesapeake Bay is essential when evaluating transport and fate of dissolved substances in both of these systems. Conservative artificial tracers are used in this study to investigate transport processes through a three-dimensional hydrodynamic model (CH3D). The model well reproduced the three-layered circulation pattern in Baltimore Harbor. Several numerical experiments are performed to trace the water mass coming from different sources. The results indicate that both the upper and lower layers of the Harbor are the dominant pathways of transporting dissolved substances from Susquehanna River to the Harbor. Such inward transport is intensified (suppressed) during the high-discharge (low-discharge) period. The upper layer inflow transports water mass with high concentrations of dissolved substances while the inflow from the lower layer transports water mass with low concentrations of dissolved substances. The bottom layer is the dominant pathway for transporting dissolved substances from the lower Bay to the Harbor. Lower river discharge and stronger along-Bay pressure gradient (resulting in stronger landward residual flow in the bottom layer of the Bay) facilitate the bottom intrusion of dissolved substances from lower Bay to the Harbor. Once contaminants are transported into the Harbor, they usually stay for a longer time in the mid-depth of the Harbor than those in other layers due to the three-layer circulation in the Harbor. The time needed for the contaminants being transported out of the Harbor during a typical low-discharge period is about 1 month longer than that needed during a typical high-discharge period. The results, from the environmental perspective, provide new insights for quantitative evaluation on the transport processes of the dissolved biogeochemical substances between Baltimore Harbor and Chesapeake Bay.