Physical drivers of saltmarsh change in enclosed microtidal estuaries

Estuaries are among the most biologically productive ecosystems on the planet, per unit area, with intertidal habitats and particularly saltmarshes providing a variety or ecosystem services and supporting large numbers of both primary and secondary producers. These habitats are globally important and are found throughout tropical to temperate climates. Micro-tidal estuaries are found throughout the world and particularly sensitive to sea-level rise, as they are limited in their ability to adjust and are considered vulnerable to future changes .Hence, at a broad scale, understanding the drivers and mechanisms of saltmarsh change in micro-tidal systems is crucial in aiding decision making in future coastal management. This thesis explores the drivers and mechanisms of saltmarsh change through the development of a conceptual model, which is then tested using Poole Harbour, UK as a case study site. The potential drivers of saltmarsh change were investigated using a multidisciplinary approach, combining a GIS historic change analysis utilising aerial photography, charts and maps, a bathymetric analysis of the harbourmorphology and a 2D hydrodynamic TELEMACmodel. Spartina anglicarapidly colonised the Harbourat the end of the 19th Century increasing the saltmarsh area from approximately 120ha to over 900ha during the 1920’s, after which there was a decline in area that has continued to present day However, saltmarsh extent in 2005 was still approximately three times the extent prior to the colonisation of Spartina anglica. Poole Harbouris large and dendritic and spatially within the Harbourseparate tributaries exhibit clearly distinct saltmarsh erosion and accretion trends. Accretion was seen to occur in relatively sheltered locations with short fetches, fronted by high mudflats, in areas that are flood dominant both in terms of hypsometryas well as tidal peak flow and slack duration. Erosion was seen to occur in relatively exposed areas where the marsh top and fringing mudflats are significantly lower and local sediments have a lower shear velocitythan in accretionary regions. Saltmarsh erosion tends to occur in morphologically ebb dominant areas but not exclusively, suggesting multiple drivers are in operation. Poole Harbouris used in this study as an example of a wider global problem. At a broad scale, observations emphasise that saltmarsh changes occurring elsewhere in the UK, and potentially elsewhere in the world, may be more complex than often portrayed. Highlighting the need for detailed case by case studies, that use all the data available over a sufficient time period. Multiple drivers of change controlthe net evolution of saltmarsh in Poole Harbourand this is likely to be a widespread conclusion for other estuaries globally.