[Multiphase Spatial Distribution Characteristics of Cd Morphology in Typical Intertidal Zones in the Guangdong-Hong Kong-Macao Greater Bay Area and Its Influencing Factors].

Simultaneous sampling and observation were conducted at 14 stations in typical intertidal zones of the Guangdong-Hong Kong-Macao greater bay area. The spatial distribution characteristics of Cd morphology in surface water, pore water, suspended matters, and sediments at each sampling site were analyzed, and the influencing factors of Cd morphology changes in each medium were discussed using statistical analyses based on environmental factors. The results showed that the total contents of Cd in surface water, pore water, suspended matters, and sediments in each intertidal zone ranged from 0.41-15.03 μg·L, 0.41-27.54 μg·L, 0.41-4.88 mg·kg, and 0.20-5.30 mg·kg, respectively. The contents of Cd in Shajiao Bay were significantly higher than those in other sampling sites, which should be related to the developed electronics and manufacturing industries in Dongguan. The concentration of Cd in surface water was slightly lower than that in pore water, whereas the content of Cd in suspended matter was comparable to that in sediment at the same sampling site. The results of morphological analysis showed that the ionic-state Cd was dominant in both surface water and pore water, accounting for 67.23%-97.56% and 33.33%-97.16%, respectively. In suspended matter and sediment, Cd was mainly in the residual state, accounting for 45.45%-96.36% and 45.80%-97.27%, respectively. Pearson correlation analysis showed that the complex-state Cd in the aqueous phase was negatively correlated with oxidation reduction potential (ORP) and pH and positively correlated with total organic carbon. The bioavailable Cd in solid sediment was significantly positively correlated with the proportion of clay, ORP, and solid organic carbon and significantly negatively correlated with pH. The single factor linear regression analysis showed that ORP had the greatest effect on the complex-state Cd in the aqueous phase, with regression coefficients of 0.864 and 0.824, respectively. The bioavailable Cd in solid sediment at different depths was significantly affected by the proportion of clay, and the regression coefficients were 0.968, 0.980, 0.977, and 0.877, respectively. The above results indicate that the distribution of total Cd content in the typical intertidal environment of the Greater Bay Area was affected by the characteristics of urban economic development, whereas the allocation of Cd morphology was closely related to environmental factors.