Groundwater ecology merged during the second part of the 20th century with modern ecological
practice after having adopted the ‘ecosystem concept’. The latter was first applied to karstic systems
and separately for alluvial non-consolidated aquifers along surface running waters. Today groundwater
ecosystems are studied within a multi- and transdisciplinary framework at various spatial and temporal
scales by experts dealing with microbiology, the ecology and systematics of meio- and macro-fauna,
geochemistry, hydrogeology and mathematical modelling. A further paradigmatic change occured with
the recognition that subterranean assemblages of organisms are formed by both hypogean and epigean
taxa. The biological diversity in subterranean ecosystems can be much higher than earlier thought
and may even exceed surface diversity in some taxa. This largely unrecognized biodiversity in many
cases deserves environmental protection. A third phase in the development of groundwater ecology
has occured over the last 15 years with the incorporation of socio-economic research topics within
groundwater ecology (GIBERT et al., 1994a) and in this sense today we have the “New Groundwater
Ecology”.