The Distribution and Enrichment of Trace Metals in the Rainfall-Driven Supratidal Wetlands of Tianjin, China

Soil and plant samples are collected from three rainfall-driven supratidal wetlands in Duliujian River Estuary (DRE) and Yongdingxin River Estuary (YRE) of Tianjin, China. Trace metal concentrations (As, Cr, Cu, Ni, Pb, Sr, and Zn) and other soil properties are measured. Results show that rainfall-driven waterlogging has no significant effects on trace metals distribution. However, supratidal wetlands in DRE have higher Ni and Zn, but lower Cr, Pb, and Sr than in YRE. Regardless of initial metal levels in soils, Suaeda salsa in sandy soil has a high bioconcentration factor and translocated more trace metals to the upper parts of plant. The results also show that high salinity in soil is disadvantageous for enrichment and translocation of trace metals in plants. Similarly, soil fertility has diluent effects on trace metal concentrations in plants. Multivariate analysis indicates that Cr, Pb, and Sr might originate from oil pollution and industrial wastewater. However, Zn most probably originates from aquaculture wastewater. Likewise, As and Ni have common sources, which probably originate from parent rocks and atmospheric deposition. Although the ecological risk index for all trace metals are slight, moderate As pollution is found in all habitats according to the sediment quality guideline of China. In addition, enrichment factors of Cr, Pb, and Zn are found to be >1, suggesting slightly polluted for those metals in supratidal regions.