Spatial variation and contamination assessment of heavy metals in sediments in the Manwan Reservoir, Lancang River

Due to the construction and operation of Manwan Dam on the Lancang River, sediments were likely to deposit in the impoundment. In this research, sediment samples were collected from 17 sites in the whole reservoir in 2011 to investigate the distribution and sources of heavy metals (Al, As, Cu, Fe, Cd, Cr, Mn, Pb and Zn), as well as to assess the heavy metal contamination status. The results obtained using Principal Component Analysis (PCA) showed that the sources of heavy metals were mainly divided into two groups, natural factors and anthropogenic input. The anthropogenic inputs mainly came from industrial activities of the tributary rivers such as heavy metal mining and smelting, and agricultural practices such as fertilising and pesticide consumption. The sediment quality was assessed according to the sediment guidelines and the enrichment factor (EF). Concentrations of As, Cd, Cr, Cu, Pb and Zn in sediments at some of the sites exceeded either the Threshold Effects Level (TEL) of US National Oceanic and Atmospheric Administration (NOAA) or Effects Range-Low (ERL) of the Canadian Sediment Quality guidelines. The high levels of these heavy metals could cause adverse effects. One-way analysis of variance for spatial analysis revealed that no significant differences were found for most heavy metals at the tail, centre and head of the reservoir except that Cr showed significant differences (P<0.01) at the reservoir centre and the head. Significant variations for some heavy metals were observed in the tributaries and in the mainstream. The comparative EF indices suggested that As, Cd, Pb, Zn and Mn were slightly enriched and Cr, Fe and Cu were not enriched but had different “high–low” orders at the tail, centre and head of the reservoir. We depicted distribution map of enrichment factors for all heavy metals and the potential ecological risk index (RI) was applied to produce the comprehensive risk distribution map.

► Heavy metals in sediments were generally unpolluted but existed variability.
► Manwan Dam did not have significant effects on most of the metals distribution.
► The sites with high comprehensive ecological risk were shown in our study.