Historic and Future Land Loss for Upland and Marsh Islands in the Chesapeake Bay, Maryland, U.S.A.

Abstract

This is the first study where historic perimeter land loss was quantified for both upland and marsh islands in the Chesapeake Bay. Rates and patterns of land loss were quantified for the years 1848 to1987 using digitized data from historical maps and vertical aerial photographs for seven islands: Barren, Bloodsworth, Hooper, James, Poplar, Smith and South Marsh. Processes of land loss were determined through field surveys and correlated with environmental factors. Future land loss was predicted based on historic trends of land loss and future scenarios of relative sea-level rise in Chesapeake Bay. Two distinct island types exhibited different, long-term patterns of land loss. Upland islands showed rapid land loss along the main stem of the Bay primarily due to wave action against low silt/clay cliffs. Since1848, they have been losing land at an average rate of 1.9 ha/yr. The average erosion rate on the western side of the islands is 4.9 m/yr, compared to 0.7 m/yr on the eastern side of the islands. In contrast, marsh islands experienced more uniform perimeter edge erosion and interior marsh loss. Marsh islands lost land at an average rate of 5.6 ha/yr, with an average rate of marsh edge erosion of 1.2m/yr. Interior marsh loss was not quantified in this study and, except for Bloodsworth Island, is otherwise unavailable; thus, this paper provides a minimum estimate of total land loss of these islands. Regardless of any rise in sea level, the upland islands will totally disappear in less than 20 years (before 2010). The marsh islands have a longer predicted life. Nevertheless, given the likelihood of accelerated sea-level rise and active interior marsh loss, the marsh islands are likely to be greatly reduced in size or totally lost in the coming century.