River suspended sediment plays an important role in the health of aquatic and coastal ecosystems. Although it is well known that river engineering (e.g., dam construction), land use and land cover change (LULCC), and climate change are the major drivers of river suspended sediment in the Anthropocene, the quantification of their relative importance to river sediment in large spatial domains is still rare. Here, we use the new model capabilities of coupled land/river sediment dynamics in the Energy Exascale Earth System Model (E3SM) to investigate the historic and future change of river sediment in four coastal watersheds, including Susquehanna River, Potomac River, James River, and Delaware River, which are the major rivers draining to Chesapeake Bay and Delaware Bay. We find that in the 20^th century LULCC and dam construction jointly drove the change of river suspended sediment in the heavily regulated Susquehanna River, whereas LULCC is the dominant driver in the other rivers. We also show that suspended sediment concentrations vary substantially along the channels of these rivers and were in decline in the 20^th century due to reservoir trapping and reforestation. As a result, the river reaches of high turbidity, once concerning the residents in the watersheds, have almost disappeared. We predict that climate change and dam decommissioning will not imperil the improvement of water clarity in the mid-Atlantic rivers in the 21^st century.