A wetland vulnerability assessment : consequences for the avian communities of saltmarshes

Understanding better the consequences of anthropogenic pressure and environmental change is a substantial area of research for modern conservation ecology. This aim of this research is to investigate these consequences for the avian communities of saltmarshes and associated reed beds. The research has four objectives: to classify saltmarsh and reed bed vegetation distribution; to assess the vulnerability of these habitats to sea level rise; to determine the impacts of sea level rise on nesting avifauna; and to derive recommendations for conservation practice. Vegetation classification methods using data from satellites and Unmanned Aerial Vehicles (UAV) for the Upper Mersey Estuary were explored. Satellite data failed to provide adequate classification due to a large spatial resolution. Object-based methods carried out on UAV data produced an accurate vegetation classification. The implications for adopting this method in a vegetation monitoring system are discussed. In 2016 a series of habitat interventions (grazing by cattle, scrape creation, and establishing a reed bed cutting 20-year cycle) on saltmarsh and reedbeds within the Upper Mersey Estuary were commenced. These interventions were maintained during the three years of this study. Changes in the ecology resulting from these interventions were monitored using the Common Bird Census technique between March and July 2015 - 2018, Wetland Bird Survey counts, and wintering bird surveys. These habitat management interventions were associated with increased diversity of wetland species (both feeding and breeding) and therefore, increased habitat connectivity with the Mersey Estuary SPA. Modelling highlighted the moderate sensitivity of saltmarsh habitats in the Upper Mersey Estuary to sea level rise. With lower sea level rise, nesting sites for all avian species were found to be restricted by periodic tidal flooding and under the top-end estimate of tidal increase (between 1.1 – 1.9 metres) the species studied would not be able to breed successfully. The findings reported here have implications for global estuarine saltmarsh management.