## 3 Results and Discussion
### Temporal and Spatial Distribution Characteristics of HMs  
Changes in the concentrations of HMs in the surface sediments in different years are shown in Figure 2. The highest concentrations of Hg, As, Cu, Pb, Cd, and Zn were observed in 2016, 2012, 2013, 2012, 2016, and 2011, respectively. In 2017, the concentrations of all HMs were the lowest, which might be related to the significant reduction in the dumping amount in 2017. From 2011 to 2016, the concentrations of As, Cu, and Pb did not change significantly, that of Zn first decreased and then increased, and those of Hg and Cd increased. Changes in HM concentrations in sediments were affected by multiple factors, such as the pollution level of dumped dredged materials, dumping volume, and hydrodynamic characteristics of the dumping area.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Locate** & **Hg** & **As** & **Cu** & **Pb** & **Cd** & **Zn** & **Reference** \\ \hline Huangmao Island & & & & & & & \\ Dumping Area & 0.03–0.26 & 7.9–19.8 & 13.1–36.3 & 17.4–54.7 & 0.10–0.34 & 50–122 & This study \\ Hulu Island Port & 0.31–0.36 & 6.07–10.5 & 15.6–20.7 & 12–18.5 & 0.17–0.63 & 63.1–126 & \\ Dumping Area & & & & & & \\ Jinzhou Port & 0.10–0.26 & 4.97–8.62 & 0.15–0.45 & 10.7–17.5 & 0.15–0.45 & 22.8–234 & [34] \\ Dumping Area & 0.016–0.023 & 16–25 & 0.112–0.149 & 20.5–23.4 & 0.112–0.149 & 53.9–66.5 & \\ Huangye Port & 0.016–0.019 & 50.9–73.1 & 0.167–0.23 & 17.2–23.7 & 0.156–0.201 & 6.37–7.71 & \\ Dumping Area & & & & & & \\ Marine Dumping Area & & & & & & \\ outside Jiaozhou Bay & & & & & & \\ Fangchenggang & & & & & & \\ Dumping Site & & & & & & \\ at Taiwan Shelf & NA & 12.5–15.6 & 15.6–18.5 & NA & 101.3–124.7 & [37] \\ Lanshan Port & & & & & & \\ Temporary Marine & 0.038–0.082 & NA & 10.32–13.67 & 7–9.15 & 0.15–0.17 & 22.59–28.15 & [38] \\ Dumping Area & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: The concentrations of HMs in sediments from other dumping areas.  
Spatial distribution profiles of the HMs in the sediments from the study area are shown in Figure 3. Concentrations of HMs in surface sediments generally showed a high trend in the north and central areas of the dumping area and a low trend in the south of the dumping area. The concentration of Cd was higher in the dumping area but lower outside the dumping area; it reached its highest value at station S3 (in the center of the dumping area) and the lowest at station S5 (in the south outside the dumping area). The concentration of Pb was higher in the central and south of the dumping area but lower in the northwest; it reached its highest value at station S3 and the lowest at station S2 (at the edge of the dumping area). The concentrations of Hg and As gradually decreased from northwest to southeast, reaching the highest at station S2 and the lowest at station S5. The concentration of Cu gradually decreased from north to south, reaching its highest at station S1 and lowest at station S4. The concentration of Zn gradually decreased from north to south in the dumping area, reaching its highest at station S5 and lowest at station S2.  
Figure 3: Spatial distribution of HMs in sediments.  
Figure 2: Average concentrations of HMs in surface sediments in different years.