Soil Production and Transport Perspectives on Critical Zone Studies

Abstract:

Quantifying soil production and transport rates and processes is a key aspect of most critical zone studies. Methodologies range from relatively straightforward, low cost studies like sediment traps and basin volume estimates to sophisticated and expensive studies using chemical and physical tracers and isotope geochemistry. Inherent in all methodologies are assumptions and simplifications that enable any measurement to be translated to a rate and interpreted in terms of process mechanics. For example, quantifying soil production using in situ cosmogenic nuclides measured in the parent material beneath an upland mobile regolith mantle depends on assuming a locally steady state soil thickness (i.e. neither thinning or thickening with time). Similarly, utilizing hillslope-scale sediment traps or landscape-scale basin analyses depends on assumptions of steady state processes and constraining the timescales represented by the captured sediment. As our analyses of landscapes have expanded into the details of how spatial and temporal gradients of all driving variables (lithology, climate, tectonics, distribution of biota, etc.) influence landscape evolution, our adherence to the assumptions and simplifications necessitated by our methods becomes questionable. Here we provide content analyses of recent and ongoing studies quantifying soil production and transport processes across a range of climatic, geologic and tectonic regimes. We code the studies for their inclusion and use of assumptions and simplifications necessary to ensure that the methodologies apply to their intended use. These analyses provide an important perspective on the use of quantitative methods and offer both a complimentary and cautionary views on critical zone studies in general.