Rivers in the Anthropocene: The U.S. perspective

Abstract

During the past 50 yr, the number and variety of papers written by U.S. fluvial geomorphologists that examine human alterations of rivers has accelerated substantially. From an initial focus primarily on how human-induced changes in land cover influence sediment yield and river dynamics, the literature has expanded to emphasize the effects of flow regulation, channel engineering, removal of large wood and beavers, and changing climate. These multiple human influences are now widely recognized to have resulted in global-scale cumulative effects including significantly altered fluxes of water, sediment, nitrogen, and carbon, and complete transformation of river networks across much of the planet. One outgrowth of this recognition is the increasing involvement of geomorphologists in diverse forms of river restoration, a form of river management that thus far has largely been dominated by engineers. Acknowledging the ubiquity of human alteration of rivers implies that (i) investigators cannot assume that even the most remote and seemingly pristine river segment has not been affected at least indirectly by people, (ii) the use of reference conditions requires careful consideration with respect to what reference sites indicate about past conditions, as well as their relevance for the future, (iii) detailed geomorphic understanding of the nature and timing of past human alterations of rivers is likely to be critical to effective restoration, and (iv) each scientist must decide how to engage within the context of research and advocacy with the issues of ecosystem degradation and loss of river form and function.