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FACTS ABOUT WATER AND ENVIRONMENT Water has the pivotal role in mediating global ecosystem processes, linking together the atmosphere, lithosphere and biosphere by moving substances between them and enabling chemical reactions to take place. Not only is it essential for maintaining living organisms, but its physical properties allow it to be used by humans for energy generation, transport and waste disposal, and in a variety of industrial processes. Drinkable water is becoming increasingly scarce. By the year 2025, it is predicted that water abstraction will increase by 50% in developing countries and 18% in developed countries, as population growth and development drive up water demand. Effects on the world’s ecosystems have the potential to dramatically worsen the present situation, and current assessments suggest that existing practices are not adequate to avert this. By some estimates, the expansion of agricultural demand for food by a wealthier and 50% larger global population could drive the conversion of an additional billion hectares of unmodified ecosystems to agriculture by 2050. This could result in nitrogen- and phosphorus-driven eutrophication of freshwater and near-shore marine ecosystems being more than doubled, with comparable increase in pesticide use. Around 50% of the world’s wetlands present in 1900 had been lost by the late 1990s, with conversion of land to agriculture being the main cause of loss. 60% of the world’s 227 largest rivers are strongly to moderately fragmented by dams, diversions and canals, and a high rate of dam construction in the developing world threatens the integrity of remaining free-flowing rivers. 50 out of 69 river stretches in Europe are found to be in poor ecological condition due to the impacts of canalization, dams, pollution and altered flow regimes. Around half of the rivers in the Asia Pacific region have exceedingly high nutrient concentrations; many water bodies, particularly in South-East Asia, contain heavy metals in excess of WHO basic water quality standards. Levels of suspended solids in rivers in Asia have risen by a factor of 4 over the last three decades. At the species level, diversity appears to be high in relation to habitat extent; for example, globally the number of fish species per unit volume of water is more than 5,000 times greater in freshwaters than in the sea. Many extinctions have taken place in inland waters – at least 34 fish species (6 since 1970) and possibly up to 80, from the late 19th century onward – and inland water ecosystems have seen probably the largest known multispecies extinction episodes of the twentieth century. Lake Victoria, shared by Kenya, the United Republic of Tanzania and Uganda, was until recently the home of a species population of up to 500 haplochromine cichlid fish (not all yet formally described), as well as of a number of other fish species. Following introduction of the Nile perch Lates niloticus – and probably also as a result of heavy fishing pressure, increased sedimentation and oxygen depletion due to the increased organic and nutrient loading – about half of the native species are now believed extinct or nearly so, with little chance of recovery. In the Mobile Bay drainage basin in the United States, dam construction has had a catastrophic impact on what was probably the most diverse freshwater snail fauna in the world. 9 families and about 120 species were known from the drainage basin. At least 38 species are believed to have become extinct in the 1930s and 1940s following extensive dam construction in the basin: the system now has 33 major hydroelectric dams and many smaller impoundments, as well as locks and flood-control structures.
Information from: Source: UN World Water Assessment Programme (WWAP), June 2005
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