Global-Scale Environmental Effects of Hydrological Alterations: Introduction

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.