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Goal 7: Ensure environmental sustainability
Water is a key component of all ecosystems. These provide critical goods and services to people, including materials, food and other organic products, water storage and purification, biogeochemical cycling and waste removal. Most global freshwater is bound up as ice in the Polar regions. Only a small, but varying proportion is active at any one time within the global water cycle (Figure 1).
The world’s ecosystems are under pressure from numerous human
activities and developments, including urbanization, industrialization
and food production. Such activities require freshwater, and to meet
demands, the water cycle is inevitably disrupted. It is also influenced
through land use changes that directly affect water quantity, quality
and water flows. Ecosystems can be damaged, functions lost and vulnerable
plants and animals endangered. Much of the degradation of freshwater
ecosystems results from overexploitation, habitat destruction, pollution
and the introduction of non-native species.
In addition to the negative impacts on aquatic species caused by disrupting the quantity and quality of surface water sources, encroachment of non-native species is also having a major impact on aquatic ecosystems around the world, reducing or eliminating native species in many cases (Heywood and Gardner 1995). Studies of the introduction of non-native fish in Europe, North America, Australia, and New Zealand revealed that 77 per cent of the species introduced led to a drastic reduction or elimination of native fish species (Ross 1991).
Similarly, the introduction in the 1970s of Nile perch and Nile tilapia to Lake Victoria, the world’s largest tropical lake, has fundamentally changed the fish and associated biological communities of the lake. Approximately half the 350 species of cichlids have died out due to the introduction of these two exotic fish species which fed on, and out-competed, the resident populations. Although a new fishery has now been developed based on Nile perch, which currently generates about US$400 million in export income, few within the local community are benefiting, as they have not made the transition to this industry (UNDP and others 2000). The unintended introduction of zebra mussels into the Great Lakes of North America has almost completely displaced native mussel species. This organism has already cost more than US$1 000 million merely to control (Great Lakes Water Quality Board 2001). In African wetlands, countries spend billions of dollars every year to control alien species, such as the water hyacinth, with little success (IUCN 2003).
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