Distribution and contamination assessment of heavy metals in soils from tidal flat, oil exploitation zone and restored wetland in the Yellow River Estuary

Abstract

Metal distributions were monitored along soil profiles and their sources as well as ecological risks were assessed in tidal zone (T), petroleum exploitation zone (P) and restoration zone (R) under different vegetation covers- Phragmites australis (p), Suaeda salsa (s) and bare land (b) in Yellow River estuary (YRE). In the three zones, mean concentrations of metals and mean values of potential ecological risk index (RI) kept the order of P > T > R. For different vegetation covers, the order of mean concentrations and ecological risk factor of all metals was b > s > p in zone P, while it shifted to p > b > s in zone T and p > s > b in zone R, respectively. Principal component analysis inferred that As, Cu, Ni and Zn were derived from natural alluviation and sedimentation, while Cd and Pb were derived from allochthonous inputs and air emissions of oil extraction. Correlation analysis indicated that soil organic matter, moisture, large aggregates as well as electric conductivity were key factors influencing metal distributions in these zones. Although YRE was not heavily polluted by heavy metals, it should be vigilant for metal accumulation in 20–30 cm layer of oil spilled soils, and zones P and T with high RI greatly contributed by Cd.