## 3 Results and Discussion
### Influence of Dumping Dredged Materials and the Pollution Status  
To minimize the impact of dumping on the marine ecological environment, the dumping distance, hydrodynamic conditions, water depth, and other factors were comprehensively considered during the selection of the location of the Huangmao Island dumping area. In the case of large amounts of dumping and complex types of dredged materials, benthos was affected even during short-term dumping [3]. HMs in dredged materials enter sediments in different ways, causing changes in the sediment environment and affecting the structure and composition of organisms. [PERSON] et al. [50] found that the concentrations of  
Figure 7: The abundance of taxa, individual density of benthos, and diversity for the benthic fauna (Shannon–Wiener index).  
Cu, Pb, and Cd in sediments had a significant impact on the richness and equity of benthos. [PERSON] et al. [51] found that the correlation coefficient between the HM content in sediments and the community structure was the highest, and the content of HMs in sediments was the main environmental factor affecting the community structure of benthos in this area. The HMs in seawater can enter the sediment in different ways, which can change the sediment environment and affect the structure and composition of organisms.  
The abundance of taxa, density, and diversity have been widely used in the impact assessment of benthos [52]. In this study, there were significant differences in the abundance of taxa and density between the areas inside and outside the dumping area. The abundance of taxa and density outside the dumping area were significantly higher than those inside the dumping area, indicating that dumping dredged materials might affect the benthos. The n-MDS analysis confirmed the observed patterns, separating the S5 stations from the others (S1-S4). Similar to this study, [PERSON] et al. [48] also found that the area with more concentrated dumping had more severe pollution and lower richness of benthos. The Nemerow index showed that the central and northern parts of the Huangmao island dumping area (S1, S2, and S3) were polluted, and the \(RI\) values of HMs in this area were relatively high. [PERSON] et al. [38] investigated the sediments in the Lanshan Port temporary marine dumping area and found that the concentrations of HMs in the dumping area were significantly higher than those outside the dumping area, corroborating the results of this study.  
The results of this study clearly indicate that the source of HMs in the dumping area are mainly from the dumped dredged materials, and dumping had affected the abundance of taxa and the density of benthos, especially in areas with a large dumping quantity and high dumping frequency. Since metal concentrations and evaluation of metal accumulation in benthos were not conducted in this study, the differences in the characteristics of the benthic community between the areas inside and outside the dumping area cannot be directly associated to HM content only. Community structure and composition can also be directly affected by the burial of dumping materials [53]. Other factors, such as dumping amount, dumping frequency, the type of dredged material, and toxicity of the dredged material also change the structure and composition of the benthic community.