The Quiet Crisis

Abstract

Throughout most of human history, freshwater resources have been more than adequate to serve human needs while maintaining the integrity and biological diversity of Earth's ecosystems. However, an exponentially increasing human population is placing ever greater demands on Earth's limited supply of fresh waters. Already more than half of all accessible surface fresh water is put to use by humanity with concomitant degradation or loss of habitat such that Earth's freshwater ecosystems have been altered more profoundly than have terrestrial ecosystems (Allan and Flecker, 1993; Postel et al., 1996; Stiassny, 1996, in press; Pimentai et al., 1997; Vitousek et al., 1997). Some particular examples serve to illustrate the gravity of the situation. In the United States, 98% of an estimated 5.2 million km of streams are sufficiently degraded to be unworthy of federal designation as wild or scenic rivers (Benke, 1990); industrial agriculture around the Aral Sea in the last 30 years has resulted in an approximate halving of the lake's surface area and depth, and a tripling of its salinity (Mainguet and Létolle, 1997; Pimentai et al., 1997); only 2 of Japan's 30,000 rivers are neither dammed nor modified in some way (McAllister et al., 1997). Undoubtedly these types of habitat degradation, often coupled with the deleterious effects of the introduction of exotic species (Courtenay and Moyle, 1992), have profound impacts on the resident biota. Although the precise degree of freshwater impoverishment remains to be fully documented, there can be little doubt that the losses are already great.