How large is a river? Conceptualizing river landscape signatures and envelopes in four dimensions

River research often addresses the influence of anthropogenic and natural processes on the ecological, hydrological, and geomorphological dynamics of river systems. However, here we take a river-centered approach and consider how rivers influence their landscapes by developing concepts of river landscape ‘signatures’ and ‘envelopes.’ The influence of a river penetrates well beyond its channel into the atmosphere, across the land surface, and into the subsurface. We define a signature as an emergent property of a set of processes acting on a river landscape, and its envelope as the dynamic penetration of the signature across the landscape. The potential to recognize river signatures and envelopes is driven by unprecedented expansion in data acquisition, processing, and modeling technologies. The spatial envelope of any particular signature will have fuzzy and temporally dynamic edges, may rapidly expand and contract, may differ in its extent from other signatures, and may be highly permeable to many organisms using the river (and broader) landscape. However, an understanding of the approximate dynamic envelope of a signature is crucial to understanding the contribution of rivers at a landscape scale and to informing the sustainable management of these landscapes and their ecosystem services.