Relationship between groundwater salinity and biodiversity in the Pine forests near Ravenna, Italy

The coastal watershed of Marina Romea in the province of Ravenna is surrounded on all sides by salt water and covered for a large part with a Pine forest, planted in the early 1900’s to prevent salt spray on agricultural land. Monthly monitoring of water table elevation and salinity during a year (March 2007, February 2008) in the Pine forest shows that the water table fluctuates strongly with the seasons and ground water salinity is very high. Using precipitation data, data from the pumping station that keeps the city from flooding and estimates of tree water use based on sap flow measurements published by Teobaldelli et al., (2004), we calculated a simplified monthly water balance. In four monitoring periods out of twelve, the tree water use is larger than the precipitation. In nine out of 12 monitoring periods drainage is larger than precipitation or tree water use. In some months, intense drainage corresponds to large precipitation but in other periods drainage does not correspond to strong precipitations: drainage continues during the summer while precipitations are scarce. These observations suggest that both tree water use and drainage contribute to the salinization of the ground water that is observed in piezometers. The measured changes in water level are used to get an independent estimate of tree water use. The values derived vary between 9 and 34. l/day per tree which are of the same magnitude as the values derived from sap flow measurements (between 10 and 30 l/day/tree). The trees ironically now attract salt intrusion from below in the ground water by taking up so much water and this inhibits their own well being. Analytical calculations based on the Ghyben Herzberg Dupuit formulation suggest that even a small annual recharge of15 mm could stabilize a freshwater lens of 2 m deep in the unconfined aquifer. This freshwater lens is currently not present and this is most likely due to the fact that tree water use and drainage take out a lot of fresh water and also because water table fluctuations may enhance dispersion of salt throughout the aquifer. Forest managers, water managers and hydrologists and hydraulic engineers should work together to find a sustainable furnishing of Marina Romea, that takes into account a drainage and managed aquifer recharge system that prevents flooding of the city but that feeds at the same time a stable freshwater lens that can support in a sustainable way the vegetation that perhaps should exist of fewer Pine trees and of more less water consuming species.