2 - Ecotonal animal assemblages; their interest for groundwater studies

Summary

ABSTRACT In order to better understand the structure of the surface-groundwater organismal assemblages (SGOA), the concept of global aquifer/river system (GARS) of Castany is recalled. The pattern of SGOAs emerges within different space and time scales. Examples of SGOAs and of the processes which form them are presented using case studies from the alluvial sediment fauna of the rivers Rhone, the Danube at Vienna, and the Lachein brook, in southern France. The structure of these assemblages depends on the boundary conditions of the groundwater system, mainly the hydrologic dynamics, and on the initiating conditions offered by the ecological tolerances of each species which contributes in the assemblages. The possible role of the macroorganisms in the functioning of the groundwater ecosystem is discussed. Their role appears less important than was thought earlier. Finally we emphasize the necessity of protecting the diversity of ecotonal assemblages. Scientific, cultural and practical arguments are presented.

INTRODUCTION

The review deals with studies on surface-groundwater organismic assemblages (SGOA) in unconsolidated, porous media, mainly alluvial sediments. These animal assemblages are formed by hypogean dwelling organisms (Hy) and epigean ones (Epi) which live permanently or temporarily in such subsurface habitats. At a first approximation, the SGOA definition agrees with the concept of ecotone, sensu Odum (1971, p. 157): ‘a transition between two or more diverse communities’. The study of such ecotonal animal assemblages represents one of the core aspects of groundwater ecology (GW).