Scale-dependency of sediment yield from badland areas in Mediterranean environments

Abstract

While much attention has been given to erosion processes in badlands, an integrated analysis of sediment production and export rates in badland areas at various spatial scales is currently lacking. This study reviews area-specific sediment yield (SY) from badlands in the Mediterranean measured at different spatial scales, using various measuring techniques, in order to investigate the relationship between size of study area (A) and SY. A database representing 16 571 plot-year and catchment-year data on SY at 87 Mediterranean study sites was compiled. The most commonly reported lithologies associated with badlands are marls, clay rocks and mudstones, and to a lesser extent shales. A high variability of SY from badlands in the Mediterranean region is observed. The relation between A and SY for Mediterranean environments with badlands is significantly different from that reported for Mediterranean environments without badlands. A complex A-SY relationship is identified: for areas < 10 ha, SY is very high (mean SY=475 t ha—1 y—1), whereas for areas > 10 ha, SY decreases non-linearly (power law) with increasing A (mean SY=75 t ha—1 y— 1 and drops from 164.5 t ha—1 y— 1 for 10 ha <A<200 ha to 9.3 t ha— 1 y—1 for A>100 000 ha). This difference is explained by several factors. For A < 10 ha there is little or no sediment storage within badland areas, while for A > 10 ha progressively more sediment can be trapped in different sinks. Further, for A > 10 ha, area-specific erosion rates do not increase (or even decrease) due to decreasing average hillslope gradients and a decreasing fraction of erosion-prone (bare/badland) area. No significant relationships between SY, lithology, and mean air temperature nor mean annual precipitation were observed.