Upland and Coastal Sediment Sources in a Chesapeake Bay Estuary

Rapid sedimentation in the upper and central portions of tributary estuaries of the Chesapeake Bay typically has been attributed to clearing of land and subsequent upland erosion since European settlement. New data from the South River, Maryland and re-examination of existing literature suggest that coastal erosion may be the dominant process driving sediment inputs along the entire length of many tributary estuaries of the Chesapeake over the past several centuries. Shoreline erosion rates derived from historical shoreline maps and aerial photographs, coupled with information on fluvial inputs obtained from sediment rating curves, indicate that coastal contributions to the estuarine sediment budget of the South River are 4 to 12 times higher than fluvial inputs. Rates of subtidal accumulation estimated from pollen and 210Pb dating of cores and changes in estuarine bathymetry suggest that most sediment from streams is trapped in river mouth marshes and subtidal storage within 1 km of river mouths. Sediment inputs from streams therefore have little direct effect on sediment accumulation in the majority of the South River estuary. These findings imply that existing runoff-based efforts to control estuarine sedimentation also need to include nonstructural measures to reduce shoreline erosion in order to alleviate sediment-related problems in tributary estuaries of the western Chesapeake.