Spring as main groundwater dependent ecosystems.

WATER RESOURCES Springs are peculiar habitats. They are areas were groundwater comes to daylight. Several springs (in particular the perennial ones) show virtually constant water temperature all over the year. Many of the morphological, physical, and chemical characteristics (e.g., hydrological stability) of the spring habitat are determined by the hydrogeological features of the parent aquifer (Van der Kamp 1995). The environmental (physico-chemical) stability of permanent sources can allow the colonization by rare organisms or taxa which are of special interest for biogeographic reasons. The term Hard-Rock Aquifers includes granite, metamorphic or layered sedimentary rocks bearing low permeability intervals, characterized by a medium-low permeability at the scale of each groundwater body. They are characterized by strong discontinuity of the hydrogeological properties with the presence of highly permeable zones or bands due the presence of tectonic structures or alter-detensioning caused for example by deep-seated gravitational deformation (DSGD). This category does not include fractured karst, evaporites and rocks with primary porosity not negligible.