Application of multiple sediment fingerprinting techniques to determine the sediment source contribution of gully erosion: Review and case study from Boushehr province, southwestern Iran

Abstract

Soil erosion by water is one of the most important causes of land degradation in arid and semi-arid regions. Quantitative determination of the relative contributions of sediment sources within catchments is an essential task before developing any appropriate management strategy in order to control soil erosion and sediment transport. In this paper a multi-parameter fingerprinting method is used to determine the sediment contribution of gully erosion (Scg) in three catchments in Iran, with different areas and drainage densities. Tracers including carbon, nitrogen, C/N, phosphorus and 137Cs which provide a clear distinction between subsoil and topsoil were used. The mean value of Scg, the efficiency of the composite tracer, the variation of Scg, and finally the accuracy of model calculations for each tracer are discussed. Although all tracers showed a considerable Scg (between 84 and 99%), the variation and accuracy of mixed models varied noticeably. Furthermore, the residual root mean square error (RRMSE) showed that 137Cs is the most valuable informative tracer while the composite tracers combining organic tracers and 137Cs presented the lowest accuracy. The results also demonstrate that the optimum combination of tracers in each region might be different. Combining the value of Scg with catchment area and geomorphic parameters showed that drainage density and catchment area are the most important factors on Scg variation. However, other physical factors such as gully density and hillslope length should also be taken into account to determine where gully erosion becomes a dominant soil erosion process. Land managers, who rely on results of erosion models which mainly focus on rill and sheet erosion, should consider the results, which demonstrate the importance of gullies as a major sediment source.