Upland and Coasta in a Chesapea Sediment Sources ce Bay Estuary

Rapid sedimentation in the upper and central portions of tributary estuaries of the Chesapeake Bay typically has been attrib- uted to clearing of land and subsequent up- land 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 ero- sion 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 bud- get of the South River are 4 to 12 times higher than fluvial inputs. Rates of subtidal accu- mulation estimated from pollen and 21aPb dat- ing of cores and changes in estuarine bathym- etry 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 di- rect effect on sediment accumulation in the majority of the South River estuary. These findings imply that existing runoff-based ef- forts to control estuarine sedimentation also need to include nonstructural measures to re- duce shoreline erosion in order to alleviate sediment-related problems in tributary estu- aries of the western Chesapeake.