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The first in a series of reports on the world's ecosystems has concluded that freshwater systems are by far the most degraded. "Pilot Analysis of Global Ecosystems (PAGE): Freshwater Systems," released by the World Resources Institute this week, paints a gloomy picture of the degradation suffered by freshwater systems and forecasts problems for the species that depend on them. PAGE reports that half of the world's wetlands were lost in the 20th century, as land was converted to agriculture and urban areas, or filled to combat diseases such as malaria. It says that while many regions of the world have ample freshwater supplies, four out of every 10 people currently live in river basins which are experiencing water scarcity. By 2025, at least 3.5 billion people or nearly 50 percent of the world's population will face water scarcity. In addition, 29 of the world's river basins, with a projected population of 10 million each by 2025, will experience further scarcity. The report pins much of the blame for freshwater degradation on dam construction. It estimates that dams, diversions or canals fragment almost 60 percent of the world's largest 227 rivers. The only remaining large free flowing rivers are found in the tundra regions of North America and Russia, and in parts of Africa and South America. The report recognizes that dams have helped provide drinking water for much of the world's population, increased agricultural output through irrigation, eased transport, and provided flood control and hydropower. But people now withdraw about half of the readily available water in rivers, it says. Between 1900 and 1995, withdrawals increased sixfold, more than twice the rate of population growth. With growing populations, water scarcity is projected to grow dramatically in the next decades. On almost every continent, river modification has affected the natural flow of rivers to a point where many no longer reach the ocean during the dry season, says the report. As examples, the report names the Colorado, Huang-He (Yellow), Indus, Ganges, Nile, Syr Darya, and Amu Darya rivers. It is this construction, plus the introduction of non-native species, pollution, and over-exploitation that has led to more than 20 percent of the world's known 10,000 freshwater fish species becoming extinct, threatened, or endangered in recent decades. The report cites studies of the introduction of non-native fish in Europe, North America, Australia, and New Zealand, that reveal 77 percent of them resulted in the drastic reduction or elimination of native fish species. In North America, 27 species and 13 subspecies of native fish became extinct in the last century largely due to the introduction of non-native fish. "The findings are very disturbing," said World Resources Institute president Jonathan Lash. "We essentially gave the world's freshwater systems a physical exam and found out that it is more imperiled than the other ecosystems we studied." The reports prepare the way for the US$20 million Millennium Ecosystems Assessment, which will be launched next year by the World Resources Institute, the United Nations Environment Program, and other international agencies.
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