LAUSR

Abstract Evidence for the proposed Anthropocene epoch in fluvial geomorphology hinges on the influence of human activities relative to natural forcing. However, research on cause-effect understanding in river channel evolution has rarely focused on the cumulative impact of multiple drivers for change, limiting insights. Systematic review of 25 recent studies professing to explain reach-scale channel responses to cumulative impacts of human activities and natural forcing over the recent past (ca. 1880–2005) reveals some consistencies in spatio-temporal response across various catchment sizes (median 3000 km2) in mostly industrialized nations. Common drivers for change include changing flood and flow regimes, dam construction, changing land uses and forest cover, bank protection and instream aggregate mining. Recent channel evolution has predominantly involved narrowing, incision and terrace development, reduced bed sediment storage, lower activity rates and simplified channel geometries. Rates of channel change frequently peaked 1955–1990, providing some support for the Anthropocene ‘Great Acceleration’. Evidence here suggests that many river systems are now in morphologically-novel configurations, coinciding temporally with dramatic recent declines in global freshwater aquatic biodiversity. Sustainable approaches to freshwater management must acknowledge these configurations, placing emphasis on process-based approaches to river ecosystem health in which sediment cascades are reconceived to reflect altered longitudinal and lateral connectivity. However, the reviewed studies are driven largely by expert judgment, depicting cause-effect associations through summary conceptual models based on spatial proximity and temporal synchronicity, providing insufficient scientific proof for the Anthropocene based on the ‘overwhelming’ impact of human factors. More conclusive cause-effect statements will require hypothetic-deductive approaches, explicit functional criteria and best-practice environmental model building. Geomorphologists should now move beyond the ‘phase of discovery’ and develop rigorous proofs for cause-effect relationships of cumulative impact; this may be enhanced by developing an avowedly ‘Anthropocene’ perspective in which rivers are viewed critically as socio-biophysical systems co-evolving with human activity.