Spatio-temporal suspended sediment fingerprinting under different land management practices

Understanding spatio-temporal suspended sediment dynamics is more important in large watersheds due to the decisive role of local source apportionment in sediment transport and yield.The Talar River with a large mountainous watershed in northern Iran,which plays a vital role in water supply for agriculture and drinking,recently has faced quality degradation.The current study explores the relative contribution of suspended sediment sources using geochemical tracers and fingerprinting techniques in high and low flow periods along this river.Soil samples were collected from four major land uses including rangeland,forest,rainfed agriculture,and irrigated agriculture,as well as riverbanks and ri-parian zones along the main river.Furthermore,suspended sediment was sampled at four sampling points along the main river in two seasons.Land use apportionment in suspended sediment yield was calculated using an unmixing model included in a newly developed package(FingerPro)in high flow and low flow,separately.The fingerprinting results showed a highly spatio-temporal dynamic for sediment source contribution along the main river in high and low flow periods.Natural land uses(forest and rangeland)in upstream reaches and agricultural land uses and riverbank sources in downstream reaches showed higher contributions to suspended sediment yield.The mean contribution of various land uses for both high and low flow periods indicated substantial contributions from forest(34％—41％)and riv-erbanks(31％-33％).The significant difference in sediment geochemical properties for the two flow seasons highlights the important role of the prevailing climatic-hydrologic condition on river sediment.Moreover,this issue indicates that sediment source contributions and transfer mechanisms are highly dynamic in Talar River watershed.The current study outcomes provide essential knowledge to create a robust strategy for mitigation of river sediment pollution.