Coastal macrophytes contribute to the long term geomorphological stability of Cadiz Bay

Abstract

In the Eastern Gulf of Cadiz, terrestrial sediments are mainly supplied by the large Guadalquivir and smaller Guadalete rivers, both of which are subject to substantial man-made interventions. These rivers are the main sediment source to Cadiz Bay; a shallow, meso-tidal bay with high subtidal macrophyte coverage and extensive salt marshes that appears to act as an effective filter, retaining fine material and ensuring accretion rates that match sea-level rise. Field observations suggest that the relative importance of the different mechanisms by which macrophyte canopies promote accretion is related to their species-specific biometric properties and zonation. Overall, we argue that the key mechanism which enhances long-term accretion in the bay is related to the reduction of erosive forces on the sediment bed cause by the interaction of plant canopies with local hydrodynamics, particularly during high wind events. Considering the importance of coastal macrophytes for long-term accretion, we briefly discuss how different local and regional management strategies in relation to IPCC climate change predictions may influence terrestrial derived-sediment dynamics.