15 - The role of hydrology in defining a groundwater ecosystem

Summary

ABSTRACT Based on two years of observations in a small aquifer in the Danube old arm system (near Vienna), the dynamics of a groundwater ecosystem is analyzed. The results show that differences in the oxygen concentration and the distribution pattern of the meiofauna community are a consequence of seasonal variations of the water level in the old arms. The water level as a boundary condition and also temperature are two important factors that govern the interaction processes between groundwater and surface water. In periods of flood events these interaction processes can achieve greater proportions, giving rise to temporary alterations in the ecosystem. Low water periods inhibit partially the infiltration of surface water into the aquifer.

INTRODUCTION

The delineation of a groundwater (GW) ecosystem within an unconsolidated geological formation is of paramount interest for both basic and applied research (Stanford & Ward, 1992). To perceive the subsurface environment, well defined systems are required. An ecological system consists of both abiotic and biotic components that exchange closely information and/or matter between them (Jordan, 1981). The ecologists dealing with the study of aquatic subsurface environments in porous media had persistent difficulties in defining ecological systems, which should represent more than simple definitions. Danielopol (1980) suggested that beside biological criteria ecologists should also use hydrological ones in order to define an ecological system. Such an approach was pioneered in the 1960s and 1970s by R. Rouch and A. Mangin when they studied the Baget karst system in southern France (see review in Mangin, 1976; Rouch, 1986). Danielopol (1989) showed that for the study of a porous system one of the most appropriate ecological unit should be a well defined aquifer.