Sediment contribution from different geologic formations and land uses in an Iranian small watershed,case study

Many intra and extra problems occurred due to unsustainable human use of natural resources leading to increasing sediment loads in the watersheds.However,few studies have been comprehensively conducted in progressing countries to prioritize sediment sources from different points of views,particularly in some countries like Iran where such valuable information is essential for proper watershed resources management.The present study was therefore planned to assess the importance of potential sediment sources viz.,spatial sources(geologic units) and source types(land use units) in sediment yield in Idelo watershed as one of the important sub-watersheds of Sefidrood large Watershed in Zanjan Province,Iran,using composite fingerprinting.In addition,the results of the sediment fingerprinting approach were compared with those of field measurement data obtained from studying soil erosion types(viz.,sheet,rill and gully erosion).Toward this attempt,16 tracers were detected in different geologic units and land uses and the sediment yielded at the watershed outlet.The results showed that the composite fingerprints of the different geologic units comprising As,N,Cu,Zn,OC and Co tracers could correctly distinguish 86% of the sediment source samples.The red gypsiferous marl contributed 85 percent in sediment yield.In regard to source types,the optimum composite fingerprint encompassed only N and Cu and provided a discriminatory efficiency of 90%.Besides that,the rangelands with 48.8% study area coverage had a significant contribution of 88% in sediment yield.The field measurements confirmed the reliability of results of fingerprinting approach in apportioning watershed scale sediment sources on the base of consistency of the two sets of results.It was also understood from the results,besides successful applicability of composite fingerprinting in assessing the provenance of the sediment yielded at the watershed outlet that the geologic formations and land use types played different roles in sediment yield.Such information helps managers and decision makers to properly regulate appropriate and adaptive management approaches in the study watershed.