Status and Sustainability of Mediterranean Deltas: The Case of the Ebro, Rhône, and Po Deltas and Venice Lagoon

Abstract

Abstract In this chapter, we describe the Ebro, Rhone, and Po deltas and discuss their sustainability in light of climate change and alternative management scenarios. All of these systems have been strongly modified by human activities, however, each system has a unique combination of impacts that informs management and restoration approaches. The major problem facing the Ebro is a massive reduction of freshwater and sediment input and over 65% of wetlands have been converted to rice fields. Prior to construction of large dams, accretion in the delta plain was maintained by a rice field irrigation network and there was also high deposition at the river mouth during large floods. Sustainable management must include higher freshwater inflow and mobilization of sediment from reservoirs and transport to the delta. Without increased and better managed sediment and freshwater input, the delta will deteriorate despite ongoing wetland restoration in the delta plain. The ongoing conflict between the Spanish government and Catalonia demonstrates how political issues can compromise sustainable management and ecological restoration. The Rhone River has not had a significant decrease in discharge or suspended sediment concentration. The main problem is that almost all river input to the delta plain has been eliminated by dikes but very large floods with high of sediment concentrations still occur regularly. Wetland areas in the lower delta are falling below sea level and without more sediment input, this will continue. Two large floods in 1992 and 1993 demonstrate that river water and sediment can be delivered to extensive areas of the delta and show that managed diversions from the river can be used to sustain the delta. There has been a strong decrease in its sediment load in the Po River but the river has at least five functioning distributaries that distribute water widely on the deltaic wetland fringe. Large areas of the Po delta are up to 5\xa0m below sea level and it is unlikely that these can be maintained to the end of century. Overtime sediment from the Po River could be used to fill in some of these whereas others could be converted to shallow lagoons. For the Venice Lagoon, there is a need for sediment input to marshes if they are to survive sea-level rise. Operation of the MOSE (experimental electromechanical module) flood protection scheme will partly decrease resuspended sediment input to marshes, which can be offset by nourishing marshes with dredged sediment and diverted river water.