Abstract:The surface sediments in wetland along the lower reach of the Dazhang Stream were sampled in July 2018 and the concentrations of six heavy metals (Cr, Ni, Cu, Zn, Pb and Cd) in samples were determined to evaluate their distribution characteristics and ecological risks according to the geoaccumulation index (Igeo) and the potential ecological risk index (RI). Results showed that the average contents of heavy metals in sediments generally followed the sequence of Zn > Pb > Cr > Cu > Ni > Cd and their variations along the lower reach were consistent, which mainly depended on the distributions of grain composition, magnetic parameters, pH, EC, and organic matter along the lower reach. The levels of six heavy metals in sediments of Taohuazhou, Gengjiaoting, Fangzhuangcun and Aolaishidai were very low, which might be due to the sand mining activities at the four sampling sites. The sand mining activities could alter the conditions of flow and sediment in river, resulting in the coarsening of sediments in wetland. Significantly positive correlations were observed among the six metals in sediments (P<0.01), indicating that they might have similar source which represented a combination of sand mining/quarrying wastes and construction/living wastes. The Pb in sediments of most sampling sites was in an unpolluted to moderately polluted status, while Cd was in a moderately polluted status. The average single potential ecological risk indices (Eri) of six heavy metals in sediments generally followed the order of Cd > Pb > Ni > Cu > Cr > Zn, and Cd showed a high ecological risk. The average RI value of heavy metals in all sampling sites was 228.62, implying that the wetland along the lower reach, as a whole, was in a moderately ecological risk. The study found that although the levels of heavy metals in sediments of wetland along the lower reach of the Dazhang Stream were much lower compared with the other branches in the upper reach of the Min River and the main stream of middle and lower reaches of the Min River, the pollution of Pb and Cd (particularly Cd) and their ecological risks were still very serious. Thus, in the next step, more attentions should be especially emphasized to strengthen the management of wetlands along the lower reach of the Dazhang River.