Round Table 4: Contribution of the groundwater/surface water ecotone concept to our knowledge of river ecosystem functioning

Summary

The aim of this work was to examine the contribution of the groundwater/surface water (GW/SW) ecotone concept towards a better understanding of ecosystem functioning in running water systems. It became clear that a consideration of the differences and similarities between the GW/SW ecotone and the hyporheic zone (HZ) concepts would be helpful. Four major parts could be pointed out. The first part focuses on a comparison between the GW/SW ecotone concepts. The second part emphasizes how the interaction zone between GW and SW influences ecosystem functioning in the two adjacent systems. The third part suggests important topics for future research, and finally recommendations for UNESCO and for managers of river ecosystems are made in the fourth part.

ECOTONE VERSUS HYPORHEIC ZONE

Origin of terms

The hyporheic zone was described in Germany 30 years ago (Orghidan, 1959; Schwoerbel, 1964) but has only recently flourished in the vocabulary of North American stream ecologists (e.g. Williams, 1984; Stanford & Ward, 1988; Triska et al, 1989). Though the term originally associated with a strong biological bias, it is now used in a more general manner to describe the deep sediments of stream beds where GW/SW exchange (see Valett et al, 1993; Hakenkamp et al, 1993).

The ecotone concept is much older since Clements (1904) used this term to describe contact zones between adjacent communities. The ecotone concept also used by Leopold (1933) and Odum (1971), had an initial organismal or community emphasis.