Understanding the implications of scale is an important challenge in soil erosion studies. Different soil erosion processes are active or dominant at different spatial scales. Rain splash is relevant at millimetres, sheet flow at metres and concentrated flow up to kilometres. This difference in dominant processes at each scale ensures that soil erosion rates measured at one scale are not (necessarily) representative of sediment yields at larger scales. The different erosion processes result in heterogeneous erosion and sediment transport rates and resultant landforms: from soil microtopography to rills and gullies and ultimately large catchment-scale landscapes. Understanding sediment transport and deposition is crucial for interpretation of erosion rates at different scales. As a scale-dependent process soil erosion is controlled by numerous thresholds and feedbacks. A review of this concept and its contribution to understand the scale effect on erosion processes will be highlighted through papers submitted to the session.
There is also an interaction between spatial and temporal scales of soil erosion processes as the magnitude and frequency of the erosive events interact with the transfer of sediments from the soil particle and aggregate to the pedon, slope and catchment scale. On millennium timescales a Sediment Delivery Ratio (SDR) of one hundred percent is inevitable, though is rarely observed on shorter, observation timescales. Therefore, interpretation and discussion of the SDR concept and how meaningful it is over short timescales will be an important topic in this session.
This session is devoted to illustrate new findings and ideas related to the interpretation and explanation of erosion rates at different spatial and temporal scales as well as ways in which small or single scale observations or predictions can be upscaled to transfer results from the experimental, or reductionist scales to those which are relevant for policy and decision makers. Theoretical, field, laboratory and modelling studies related to the effects of scale are welcome. Studies which integrate different techniques to tackle the scale problem are particularly welcome. Papers that address the interaction of spatial and temporal scale will also be welcome. A critical review of the methods being applied is necessary to allow accurate interpretation and comparison of erosion studies and to develop new research that will contribute to a better understanding of interacting erosion processes at different scales.

Solicited Speakers.

Erik Cammeraat. Universiteit van Amsterdam. The Netherlands.

Waite Osterkamp. U. S. Geological Survey, Tucson, USA.

Olivier Cerdan. INRA SESCPF,Olivet, France

Albert van Dijk. CSIRO Land and Water. Canberra. Australia