Tidal marsh erosion and accretion trends following invasive species removal, Tamar Estuary, Tasmania

The introduction of Spartina to intertidal marshes last century in many areas of the world transformed estuarine geomorphology, threatened native species and habitats, and impeded coastal access and use. This study investigated erosion/accretion trends of marsh surfaces following removal of invasive Spartina across a substantial intertidal marsh area. Marsh surface changes were monitored within a 0.6 ha experimental site where Spartina anglica cover was removed, and compared with surface changes at a comparable control site. Erosion/accretion rates were measured for over two years using a grid transect network, creek cross sectional profiles, and seaward edge delineation. Results showed that a significant erosion of the marsh surface occurred at the experimental site relative to the control site, using two different statistical analyses. Analysis of mean monthly change found erosion rates at the experimental site to be 13.2 mm a⁻¹ relative to 2.0 mm a⁻¹ at the control site, a rate that was six times greater. Analysis of overall change from the beginning to the end of the study showed that erosion was significantly more pronounced at the experimental site relative to the control site, and increased from the landward edge to the seaward edge at both sites. This study demonstrates the need for consideration of geomorphic processes when managing invasive plants in dynamic environments, and indicates that large scale Spartina removal will cause coastal erosion, bringing potential consequences to adjacent near shore waters and ecosystems.