Water and Ecology: Linking the Earth's Ecosystems to its Hydrological Cycle

Water is the lifeblood of our planet. It is fundamental to the biochemistry of all living organisms. The planet's ecosystems are linked and maintained by water. It drives plant growth and provides a permanent habitat for many species, including some 8500 species offish, and a breeding ground or temporary home for others, such as most of the world's 4200 species of amphibians and reptiles described so far. Water is also a universal solvent and provides the major pathway for the flow of sediment, nutrients and pollutants. Through erosion, transportation and deposition by rivers, glaciers and ice-sheets, water shapes the landscape and through evaporation and condensation, it drives the energy exchange between land and the atmosphere, thus controlling the Earth's climate. The Bruntland Report, Our Common Future (WCED, 1987), Caring for the Earth (IUCN/UNEP/WWF, 1991) and Agenda 21 from the UNCED Conference in Rio in 1992 marked a turning point in our thinking about water and ecosystems. A central principle that emerged was that the lives of people and the environment are profoundly inter-linked and that ecological processes keep the planet fit for life providing our food, air to breathe, medicines and much of what we call "quality of life". The immense biological, chemical and physical diversity of the Earth forms the essential building blocks of the ecosystem. The sustainable development of water was the focus of the Dublin Conference in 1991 (a preparatory meeting for UNCED). It concluded that "since water sustains all life, effective management of water resources demands a holistic