Effects of Tide Dikes on the Distribution and Accumulation Risk of Trace Metals in the Coastal Wetlands of Laizhou Bay, China

Tide dikes play a key role in preventing seawater intrusion in coastal regions; however, their effects on trace metal distribution and accumulation remain unclear. This study explored the distribution and enrichment of trace metals (As, Cr, Cu, Ni, Pb, and Zn) inside and outside tide dikes in Laizhou Bay. The accumulative risk of these metals in the two habitats was analyzed by combining their sources. The results show that the average enrichment factor, geological accumulation index, and potential ecological risk index of As in the outside habitat are significantly higher than those in the inside habitat (p < 0.001), which indicates that the tide dike effectively reduces the migration of As from outside to inside habitats. For other trace metals, no statistical differences were found between the two habitats. Based on principal component analysis and redundancy analysis of trace metals and their correlations with soil physicochemical properties, we speculated that Cr and Zn may derive from soil parent material and rock weathering. Cu, Pb, and Ni may be related to atmospheric nitrogen deposition resulting from nearby agricultural activities, and As may come from industrial wastewater or transport through seagoing rivers. The findings suggest that tide dikes effectively block exogenous trace metals but not those from natural sources.