Ordering Interfluves: A Simple Proposal for Understanding Critical Zone Evolution

The Earthʹs critical zone (CZ) is the integrated life-supportive system between the atmosphere and the deepest bio-geoweathering front of geologic materials1. When human beings are added to the natural workings of the critical zone, great uncertainty is introduced in understanding the consequences1,2. As we begin our research at our Calhoun Critical Zone Observatory (CCZO) in the Southern Piedmont region of SC, we propose an ordering system for upland interfluves that is to an extent a reciprocal of the widely used Hortonian system that hydrophysically orders stream and river systems. At the Calhoun CZO, interfluve order and corresponding erosion and intra-critical zone regimes inform us about the evolution and functioning of hydrologic, geomorphologic, biogeochemical, and biotic systems; CZ response to historic land use change; and the contemporary functioning and management of the CZ. With LiDAR and DEM mapping enabling new quantitative research of landscape and critical zone structure and function, we propose that many physiographic regions will benefit from a system that orders interfluves.