FIGURE 1-1 Major rivers and streams of the conterminous United States. SOURCE: Generated from the National Atlas of the United States (available on-line at http://www.nationalatlas.gov).

As noted above, aquatic ecosystems collectively perform numerous interrelated functions and provide a wide range of services. In addition, many aquatic ecosystems support the economic livelihood of local communities through commercial fishing and by serving the recreational sector. To illustrate the importance of these activities, recreational fishing alone generated an estimated $116 billion in total economic output the United States in 2001 (American Sportsfishing Association, 2002). The continuance or growth of these types of economic activities is directly related to the extent and health of these natural ecosystems. However, human activities and rapid population growth (often preferentially in or near aquatic ecosystems), along with historical and ongoing industrial, commercial, and residential development, have led to increased pollution, adverse modification, and destruction of remaining (especially pristine) aquatic ecosystems (Baron et al., 2003; Carpenter et al., 1998; Howarth et al., 2000; NRC, 1992). At the same time, increased human demand for water has reduced the amount available to support these ecosystems (Heinz Center, 2002; Jackson et al., 2001).



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