Effects of planting patterns on heavy metals (Cd, As) in soils following mangrove wetlands restoration

To understand how planting patterns influence As and Cd in soils, the pollution grade release risk and fractions of As and Cd in soils from Jinjiang Estuary wetland were investigated. The geoaccumulation index (I_geo) and risk assessment code (RAC) were used to identify pollution grades and reveal the potential ecological risk of trace metals, respectively. The results showed that the ratios of the acid soluble fraction of Cd in the mangrove area (∼65%) were larger than that of the control group (∼31%). The residual fraction of As in the mangrove area (∼74%) was also larger than that of the control group (∼66%). Therefore, the planting of vegetation increased the mobility of Cd and decreased the mobility of As. Variance analysis showed that the total concentrations and fraction of As and Cd significantly differed among various vegetation types and planting densities. Thus, planting patterns might influence the transformation of trace metal fractions in soil, influencing the total concentrations of As and Cd. Furthermore, mangrove reforestation improved the pollution levels of As and Cd and increased the potential release risk of Cd. The study advances current knowledge on the importance of restoring wetland vegetation, providing suggestions on feasible planting patterns.