We can clearly see here how the increase in bare area that is unavoidable in most forms of agriculture

will, other factors being constant, have a positive effect on the erosion rate per unit area. In practice human activity can also increase erodibility by reducing soil strength. It is therefore clear that human activity can both increase and decrease this natural or ‘potential’ erosion rate at source. It is generally accepted that the dominant GDC-0199 manufacturer spatially and temporally averaged natural driver of weathering and erosion is climate as parameterised by some variant of the T°/P ratio ( Kirkby et al., 2003). Other factors can be dominant such as tectonics but only at extreme temporal scales of millions of years (Ma) or localised over

short timescales Z-VAD-FMK solubility dmso (such as volcanic activity). At the Ma scale tectonics also largely operate through effective-climate as altered by uplift. A major reason for the non-linear relationship of the potential erosion rate with climate, particularly mean annual temperature, is the cover effect of vegetation ( Wainright et al., 2011). So human changes to vegetation cover can both increase and decrease the potential erosion rate. The most common change is the reduction of cover for at least part of the year entailed in arable agriculture, but afforestation, re-vegetation and the paving of surfaces can all reduce the actual erosion rate ( Wolman and Schick, 1967). It is the complexity and non-linearity of the relationship between potential and actual erosion rates that allows seemingly un-reconcilable views concerning the dominant drivers to co-exist. With reference to floodplain alluviation these have varied from the view that it is ‘climatically driven but culturally blurred’ (Macklin, 1999) to ‘largely an artefact of human history’ (Brown, 1997). Can both be right at different times and in different places? Using the above relationships 4��8C we can predict that during an interglacial cycle the erosion and deposition rate would follow the product of changes in rainfall intensity and vegetation quantity, at least after ground-freezing

had ceased. This gives us a geomorphological interglacial cycle (Ig-C) which should have a peak of sedimentation during disequilibrium in the early Ig-C, and most notably a low flux or incision during the main temperate phase as changes in erosivity would not be large enough in most regions to overwhelm the high biomass (Fig. 1), although the role of large herbivores might complicate this locally (Brown and Barber, 1987 and Bradshaw et al., 2003). It follows that widespread alluvial hiatuses should follow the climatic transitions and one would not be expected within the main temperate phase (Bridgland, 2000). What is seen for most temperate phases within either stacked sequences or terrace staircases are either thin overbank units (particularly in the case of interstadials), palaeosols or channel fills incised into cold-stage gravels.