Remote sensing of geomorphological and ecological change in response to saltmarsh managed realignment, The Wash, UK

An integrated remote sensing approach quantified saltmarsh dynamics in response to a sudden change in surface elevation due to a saltmarsh restoration scheme. The biogeomorphological relationship between surface elevation and saltmarsh presence occurs over the long-term so can be difficult to observe, though the ‘managed realignment’ of coastal defences provides a unique experimental opportunity to study this relationship. Realignment at Freiston Shore, Lincolnshire, UK in August 2002 caused a sudden and high-magnitude sediment input into the local coastal system, significantly increasing the intertidal surface elevation. The resulting impacts on the external, fronting saltmarsh were quantified by aerial photography and airborne multispectral imagery. Algal and pioneer saltmarsh boundary positions were calculated from 1984 to 2006, with the latter zone migrating slowly seaward pre-realignment (3.8 m a−1), but advancing significantly post-realignment (21.3 m a−1). Classification of five-year multispectral imagery accurately showed subtle changes in vegetation community composition within these boundaries. The realignment site was also colonized rapidly compared to other restoration sites, due to its high starting surface elevation. This study shows how, with sufficient sediment input and accommodation space, coastal management decisions can release intertidal surfaces from physical constraints to saltmarsh colonization.

► Integrated remote sensing accurately quantified ecological change in response to coastal management.
► Managed realignment provides a unique mesocosm to study biogeomorphological processes that usually occur over the long-term.
► Rates of saltmarsh migration increased from 3.8 m a−1 to >21 m a−1 post-realignment, once rapid elevation change released vegetation from inundation constraints.
► Internal site colonization was rapid due to high starting elevation.
► Remote sensing is best suited to monitor coastal dynamics over large temporal and spatial scales.