Effects of global climate change on coastal salt marshes

A methodology combining ecological modelling with geographical information analysis and remote sensing was employed to determine the effects of sea-le vel rise in estuarine salt marshes, using the Tagus estuary (Portugal) as a case study. The development of salt marsh vegetation was simulated separat ely for C3 and C4 plants, using a combined biogeochemical and demographic m odel. This simulation, which provided small-scale (m(2)) results of annual above-ground primary production, was upscaled to the whole salt marsh area, using bathymetry data, remote sensing and Geographic information System (G IS) for assessing vegetation cover and determining areal distribution of C3 and C4 vegetation. Based on IPCC data, several sea-level rise scenarios we re considered, and the coupled ecological model-GIS were applied to these i n order to determine changes in global salt marsh productivity. The results indicate that the salt marshes of the mesotidal estuaries such as the Tagu s are susceptible to sea-level rise only in a worst case scenario, which is more likely to occur if the terms set out by the Kyoto protocol are not me t by several industrialised nations. The low vulnerability of salt marshes supports the suggestion that areas with high tidal ranges are less vulnerab le to sea level change, due to greater sediment transport and accretion. Ne vertheless, the precautionary principle should always be applied by coastal planners, due to the great uncertainty surrounding forecasts of sea-level rise. (C) 2001 Elsevier Science B.V. All rights reserved.