THE RESPONSE OF COASTAL MARSHES TO SEA-LEVEL RISE - SURVIVAL OR SUBMERGENCE

In order to maintain an elevation in the intertidal zone at which mars h vegetation can survive, vertical accretion of the marsh surface must take place at a rate at least equal to the rate of relative sea-level rise. Net vertical accretion of coastal marshes is a result of intera ctions between tidal imports, vegetation and depositional processes. A ll of these factors are affected, directly or indirectly, by alteratio ns in marsh hydrology which might occur as a result of sea-level rise. The overall response of coastal marshes to relative sea-level rise de pends upon the relative importance of the inorganic and organic compon ents of the marsh soil and the impact of increased hydroperiod on net accumulation. The varied combination of factors contributing to sedime nt supply, and their complexity at the scale of individual marshes, me ans that predicting the response of suspended sediment concentration i n marsh floodwater to any changes which may occur as a result of seale vel rise, at anything other than the local scale is unlikely to be acc urate. The impact of sea-level rise on net below-ground production is also complex. The sensitivity of certain species to waterlogging and s oil chemical changes could result in a change in species composition o r the migration of vegetation zones. Consequently, predicting the net impact of sea-level rise on organic matter accumulation is fraught wit h difficulties and requires improved understanding of interactions bet ween vegetation, soil and hydrologic processes.