Special problems of urban river conservation:
the encroaching megalopolis
K.E. Baer and C.M. Pringle
The global landscape is in the midst of an urban transition on a scale that is greater than at any other time in history (Figure 16.1; World Resources Institute – WRI, 1996). Urbanization is playing an increasingly central role in degrading riverine ecosystems, affecting water quantity and quality for both human and nonhuman biota. As recently as 1990, most of the world’s population still lived in rural areas; however, by the year 2025, it is estimated that 60% (or about 5 billion people) will be concentrated in cities (Young et al., 1994).
Riverine ecosystems are extremely vulnerable to the effects of urban development. Many urban areas have been purposefully located near rivers for proximity to transportation, drinking water, irrigation,- food supply and waste disposal. Urban degradation of river systems is an historic problem that can be traced back as far as the establishment of the first cities along the major river systems of the Tigris-Euphrates and Indus Rivers 7000 years ago (Meybeck et al., 1989). Urban drinking water sources have repeatedly been degraded and then abandoned in the course of development (Leslie, 1987). For example, the Roman Tiber was used and then deserted for cleaner sources requiring the construction of aqueducts. Expanding urban populations, associated wastes and old or non-existent waste treatment systems have overtaxed the assimilative capacities of rivers. Urbanization threatens entire catchments; even international water bodies (e.g. the Caribbean, and the Baltic, Black and Mediterranean seas) have been affected, highlighting the critical need for immediate management and conservation efforts to protect water bodies from the impacts of urbanization. This chapter examines global issues surrounding urban river conservation with an emphasis on streams in the USA.
Urban areas occupy only 1% of the earth’s surface (WRI, 1996), but they affect water resources well beyond the scope of a city’s geographical boundaries. With a higher per capita use of natural resources in urban than in non-urban areas (WRI, 1996), urban areas clearly exert a disproportionate effect on the environment relative to non-urban areas.
McDonnell and Pickett (1990) describe urban areas functionally:
‘Urbanization can be characterized as an increase
in human habitation, coupled with increased per
capita energy consumption and extensive
modification of the landscape, creating a system
that does not depend principally on local natural
resources to persist.’
Mumford (1956) likened growing cities to parasitic organisms which consume increasing amounts of