Relationship between 20th Century Dune Migration and Wetland Formation at Cape Cod National Seashore, Massachusetts

Abstract

Outer Cape Cod (Massachusetts) is dominated by active and stabilizing parabolic and transverse dunes interspersed with numerous inter-dune wetlands. Dune migration has been significantly affected by human activities; conversely, current dune movements are affecting local populations. The objective of the reported research was to assess, using remote sensing and geographic information systems (GIS) technologies, migration of the Cape Cod dunes and the effect of dune movement on distribution of associated wetlands. Aerial photographs from 1938 through 2003 were analyzed to track individual dune movements and subsequent wetland propagation and expansion. Absolute dune movement rates during this period were computed, with a plot of dune movement as a cumulative function. One sub-problem of this study was to quantify ‘white’ areas of active moving sand and ‘dark’ areas of vegetation, in order to quantify changes in vegetative cover with wetland propagation and, conversely, vegetative disappearance with dune movement. Attempts were made to correlate the Palmer Drought Severity Index (PDSI) with dune migration. Based on review of aerial photographs, parabolic dunes have migrated 150 to 250 m since 1938, with 60% of the movement occurring between 1938 and 1977. The relation between absolute parabolic dune migration and corresponding PDSI is approximately logarithmic. Maximum dune migration is associated with PDSI values lower than –2 and reflects moderate drought conditions. Wetlands consistently trailed the dunes, and the distance of wetland movement was related to dune movement distances. Wetland migration was particularly marked from the 1950s to the 1980s. Based on review of georeferenced aerial photographs, it is concluded that marked stabilization of Cape Cod dunes occurred in the 1980s and 1990s, with renewed movement in the 21st Century. This study provides a practical application for assessment of dune migration and vegetative transformations over time using remote sensing and GIS technologies