Concentration of heavy metals in the modern flood slackwater deposits along the upper Hanjiang River valley, China

•Heavy metal pollution occurs downstream of Ankang City along the Hanjiang River.•The source of Co, Cr, Ba and V is mainly from anthropogenic inputs.•The source of Cu, Ni, Pb, Zn and Mn is mixed from natural and anthropogenic inputs.

Modern flood slackwater deposits (SWD) were systematically collected after the great flood events which occurred on 19 July, 2010 and on 19 September, 2011 along the upper Hanjiang River valley. Concentrations of heavy metals (Co, Cr, Cu, Ni, Pb, Zn, Ba, Mn and V) in the fresh flood SWD were determined. Enrichment Factor (EF) and Index of Geoaccumulation (Igeo) were employed for heavy metal assessment. These results show that Cu, Ni, Pb, Zn and Mn are defined as only minor enrichment and unpolluted in the upper Hanjiang River basin, whereas Co, Cr, Ba and V are defined as between moderate enrichment and moderately severe enrichment, and moderately polluted in the downstream of Ankang city. Principal component analysis (PCA) and correlation analysis confirm the results of EF and Igeo. Cluster analysis (CA) identifies that Ankang city is the boundary between higher and lower heavy metals in the modern flood SWD. Therefore, we can conclude that the source of Co, Cr, Ba and V is mainly from anthropogenic inputs, but the source of Cu, Ni, Pb, Zn and Mn is mixed from natural and anthropogenic inputs. Concentration of heavy metals in the downstream of Ankang city is higher than that in the upstream. These results would help to establish non-point sources of heavy metal pollution and provide important information for water conservation strategy during the great flood periods in the upper Hanjiang River basin.