Aquifers provide water, nutrients and energy with various patterns for many aquatic and terrestrial ecosystems (Groundwater-Dependent Ecosystems, GDEs). GDEs are increasingly recognized for their ecological and socio-economic values. At the watershed scale, recharge patterns, geomorphology, internal geometry and geochemistry of aquifers control water availability and nutritive status of groundwater. The local interface structure between the groundwater system and the biocenoses may modify the groundwater features by physicochemical or biological processes, for which biocenoses need to adapt. Based on these considerations, an ecohydrological classification system for GDEs is proposed, as a basis for modelling approaches for GDEs and as a tool for groundwater and landscape management. This conceptual approach reveals the strong importance of the functioning of the aquifer-biocenoses interface.
This aspect was investigated through a case study. The water uptake of 10 alluvial trees in various hydrogeological and ecological situations in the Pfyn Forest (Switzerland) were assessed by analysing 18O and 2H of precipitation, soil water at different depths, surface and groundwater and trees. Isotopic temporal variability of soil layers and trees was strongly linked with seasonal hydrological or ecological processes. Soil humidity is the key factor affecting water uses in the system and trees use water sources opportunistically. Some other temporal different uses of water are consistent with ecological strategies for ensuring reproduction or growth, or conversely to limit competition for water. This strategy appears suitable if water sources (groundwater of soil humidity) are easily available in the system throughout the year, i.e. in locations close to the main stream course. These results permitted to draw a general scheme of the ecohydrological functioning of the system, that could be helpful for its management in a context of local and climate changes.