Аннотация:Ubiquitous hydrological alterations—dam construction and associated water diversion, exploitation of groundwater aquifers, stream channelization, and intercatchment water transfer—are producing global-scale effects on the environment. The articles in this special issue of BioScience highlight the cumulative effects of hydrological alterations associated with dam and reservoir development. Such information is critical for deciding whether, when, and where the next major hydrological project will be built; it can also warn us about impending environmental impacts. The study of the cumulative effects of hydrological alterations is a recent endeavor, compared with the study of individual dam and reservoir developments (e.g., Hall 1971, Hecky et al. 1984). The issue of greenhouse gas emissions from reservoirs, for example, is less than a decade old (Rudd et al. 1993). The global significance of reservoirs as sources of greenhouse gases depends on the total surface area of reservoirs and the flux rates from the major types of reservoirs in different geographical locations (Rosenberg et al. 1997). Neither of these quantities is well known, but flux rates have now been measured in 21 locations, enabling the first reasonable estimate of global greenhouse gas emissions from reservoirs (St. Louis et al. 2000). Other recent examples include attempts to determine cumulative environmental effects at hemispheric or global scales. Chao (1991, 1995) reported that worldwide
