SUMMARY Ecological and socioeconomic aspects of subterranean hydrosystems have changed during the past 40–50 years. The major environmental pressures (mainly anthropogenic ones) impact the quantity and quality of groundwater resources and the state of subsurface ecosystems, and it is expected that the environmental pressures on groundwater will continue, at least until 2025, unless new environmental policies change this state of affairs. The world demographic increase and the general rise of water demand constitute one of the major environmental pressures on groundwater ecosystems especially in less developed countries in Africa, Asia and South America. Specific human activities leading to the depletion of groundwater reserves include agricultural practices, landscape alteration, urbanization demand for domestic and public drinking water, various industrial activities such as thermoelectric production and mining, and the rise of tourism in coastal areas. Climate change is contributing to the water crisis too, especially in areas with arid climate and/or in some humid monsoonal countries. The overload of aquifers with pollutants derived from agriculture (fertilizers and pesticides), from industry (release of hydrocarbon chemicals, especially spills), from waste and industrial waters, from domestic and industrial landfills, from the infil- tration of pollutants from surface and from the intrusion of saline water affect groundwater quality. The dangerous increase in contaminated subsurface sites with chemicals and microbial pathogens brings with it health risks to humans. Changes of redox condition in groundwater zones, changes of biological diversity, vegetation changes with modification of agriculture practices and impacts at the biosphere scale, such as the increase in the concentration of nitrous oxides in the atmosphere, all impact ground- water ecosystems. Groundwater ecosystems must be better investigated and understood. Economic, social and ecological lines of thinking have to be combined in order to achieve meaningful policies for the sustain- able development of groundwater reserves and for the protection of subsurface ecosystems. Practical measures and ideas for the development of policies up to the 2025 time-horizon should improve the sustain- able usage of the world’s groundwater resources. Keywords: groundwater ecosystems, environmental manage- ment, ecological sustainability, groundwater depletion, groundwater pollution, groundwater protection, biological diversity INTRODUCTION ‘If nature in the twenty-first century will be a nature that we make, then the guide to action is our knowledge of living systems and our willingness to observe them for what they are, our commitment to conserve natural areas, to recognize the limits of our actions, and to understand the roles of metaphor and myths in our perceptions of our surroundings’ (Daniel Botkin 1990). Groundwater (GW) plays a pivotal role in human life and development. In the past it has offered insurance against drought, a vital factor for human survival. Thought once to be an inexhaustible resource for human needs, a belief reflected in many myths, the availability of GW is now critical in many parts of the world. It has become more and more difficult to supply human needs with sufficient quan- tities of safe and clean water of acceptable quality (see Gleick 1993a, 1996; Postel 1998, 2000; World Water Council 2000). GW is not only important in supporting human welfare, it is also the basis of life for diverse organisms existing below the earth’s surface. The complex relationships between the water and the subsurface organisms generate dynamic ecological systems, which are the topic of the rather young field of GW ecology (Gibert 1992). Quantitative and qualitative aspects of GW were, until recently, mainly studied by hydrologists and hydrochemists, ecologists being less involved in understanding the present or indicating the future status of GW resources. However, during the last 10–15 years, GW problems were analysed increasingly within an integrated hydrological and ecological framework (Nachtnebel & Kovar 1991; Gibert et al. 1994a, Present state and future prospects for groundwater ecosystems DAN L. DANIELOPOL 1 *, CHRISTIAN GRIEBLER 2 , AMARA GUNATILAKA 3 AND JOS NOTENBOOM 4 1 Institute of Limnology, Austrian Academy of Sciences, Mondseestrasse 9, A 5310 Mondsee, Austria, 2 Center for Applied Geosciences, Department of Environmental Mineralogy, University of Tübingen, Wilhelmstrasse 56, D 72074, Tübingen, Germany, 3 Water Resources Management, Verbundplan Ltd, Engineers & Consultants, Parkring 12, A 1010 Vienna, Austria and Institute of Medical Biology, Laboratory of Ecophysiology and Ecotoxicology, University of Vienna, Währingerstraße 10, A 1090 Vienna, Austria, and 4 Netherlands Office for Environmental Assessment, National Institute of Public Health and the Environment (RIVM), Post Box 1, NL 3720 BA Bilthoven, The Netherlands Date submitted: 15 July 2002 Date accepted: 17 December 2002 * Correspondence: Professor Dan L. Danielopol Tel: +43 6232 312527 Fax +43 6232 3578 e-mail: dan.danielopol@oeaw.ac.at Environmental Conservation 30 (2): 1–00 © 2003 Foundation for Environmental Conservation DOI:10.1017/S0376892903000???