Finding the boundary between Eurosiberian and Mediterranean salt marshes

Abstract

In continental Portugal it is generally recognized that the Ria de Aveiro is the coastal limit between Mediterranean and Eurosiberian regions. Considering salt marshes flora and vegetation communities, the Tagus River estuary seems typically Mediterranean, while the Ria de Aveiro lagoon seems typically Eurosiberian, therefore the boundary between the two regions might be found among the smaller salty areas existing between the two referred wetlands (namely the Óbidos Lagoon, the Tornada and Mondego rivers). Although tide height is a sound explanation for the floristic differences between Eurosiberian and Mediterranean saltmarshes, the fact is that the southwest Portuguese Atlantic salt marshes present Mediterranean climate and flora, despite its greater tide heights if compared to the Mediterranean Basin. Conversely, Mediterranean climate by its own is not enough to explain those florisitc differences, as it exits north of Aveiro. We introduced the importance of sea-surface temperature in order to detail the boundary between the two regions. Despite climate and hydrologic regime being Mediterranean between the Tagus and the Ria de Aveiro, the cold Atlantic waters seem to influence the flora and the vegetation of the present salt marshes. It is proposed to classify as Eurosiberian all salt marshes north of the Tagus Basin.