The twentieth-century migration of parabolic dunes and wetland formation at Cape Cod National Sea Shore, Massachusetts, USA: landscape response to a legacy of environmental disturbance

摘要

Cape Cod, an early North American colony, was covered by mature forest prior to European contact but, with settlement in the late seventeenth century, aeolian processes dominated into the twenty-first century. An aerial photographic time series from ad 1938 to 2003 quantifies dune movement that reflects processes over centuries and documents accelerated parabolic dune movement at ～4 m/yr from 1938 to 1977 during a drier interval. In contrast, dune movement between 1987 and 2003 slowed to ～1 m/yr with wetter conditions. Wetlands expand post dune movement often forming in dune blowouts with seasonally wet conditions. Stratigraphic studies, coupled with optically stimulated luminescence ages, place erosion and burial of the pre-settlement forest soil by migrating dunes at ad 1690 ± 40 yr, with aeolian deposition continuing into the nineteenth and twentieth centuries, consistent with the historic record of land surface conditions. A threshold of landscape stability was exceeded in the late seventeenth to early eighteenth centuries, indicated by dune formation in response to human-induced land-cover changes, concomitant severe droughts and exposure to tropical storm/hurricane windfield. Dune orientation indicates preferential movement during winter with winds dominantly from the W-NW and with reduced vegetation cover. The present high biodiversity in interdunal wetlands is a legacy of aeolian processes from landscape disturbance initiated by European settlers in the seventeenth century.