From the surface to a 90 cm depth, the soils in the whole vertical
profile are contaminated significantly. This phenomenon is a
result of the contaminated sediment. The first step in the tidal flat
reclamation in the PRE is to surround the candidate reclaimed area
with rocks to decrease water flow rate and enhance the deposition
of suspended particles. The current field investigation showed
that the suspended particles could deposit as thick as 15–30 cm in
a single flood season after a water area has been surrounded with
rocks. Therefore, soils at the bottom of the surveyed vertical soil
profiles are actually not much older than the surface soils. Both
the bottom and the surface soils were formed during the recent
industrialization period. Bai et al. [12] also reported that the entire
vertical soil profiles from the wetland of the reclaimed regions in
the PRE were polluted significantly by heavy metals that originated
from anthropogenic sources.