*3.2. Variation of Suspended Sediments Concentrations (SSCs) in Overlying Water*

The SSCs in the overlying water under wave actions in Stage II and Stage III were presented in Figure 5. There was a rapid increase in the SSC after loading the 7 cm height wave, and the SSC reached a relatively stable state after approximately 60 min of wave action. During Stage II, the SSC increased significantly, the variation range was 0.118–0.643 g/L. While in Stage III, the SSC first increased slightly, then gradually decreased, and the variation range was 0.357–0.656 g/L. The SSCs at 5 cm above the sediment surface were higher than those at 20 cm above the sediment surface, this agreed well with results in the study of Kong and Zhu [36], which found that SSC increased with water depth under

wave action in a wave flume experiment. Moreover, the SSCs at the two sampling points showed similar variation trend. agreed well with results in the study of Kong and Zhu [36], which found that SSC increased with water depth under wave action in a wave flume experiment. Moreover, the SSCs at the two sampling points showed similar variation trend.

The SSCs in the overlying water under wave actions in Stage II and Stage III were presented in Figure 5. There was a rapid increase in the SSC after loading the 7 cm height wave, and the SSC reached a relatively stable state after approximately 60 min of wave action. During Stage II, the SSC increased significantly, the variation range was 0.118−0.643 g/L. While in Stage III, the SSC first

coarsening and stratification were observed along the edge of the oscillation area.

*3.2. Variation of Suspended Sediments Concentrations (SSCs) in Overlying Water* 

*J. Mar. Sci. Eng.* **2019**, *7*, x 7 of 14

The curve of t = 0 min in Figure 4a represents the initial sediment surface after 40 h consolidation. Fluid oscillation from left to right was observed in the surface layer of sediment immediately after the 7 cm height wave was loaded in the flume, indicating that sediment was liquefied. The liquefaction interface presented an arc shape, and the sediment particles above the interface showed a periodic oscillation along the interface with the same period as the wave, while the particles below the interface stayed still. This phenomenon is considered as the criterion for determining the liquefaction of sediment caused by waves [22]. After 30 min of wave action, the liquefaction depth reached its maximum of about 17 cm. Then the liquefaction interface began to move upwards under continuous wave action, and the range of liquefied sediments retracted until re-stabilization. Obvious

**Figure 5.** Suspended sediments concentration (SSC) variation in the overlying water under wave actions in: (**a**) Stage II and (**b**) Stage III. **Figure 5.** Suspended sediments concentration (SSC) variation in the overlying water under wave actions in: (**a**) Stage II and (**b**) Stage III. action, the dissolved Cu concentration reached a relatively stable state. The dissolved Cu concentration in overlying water variation range of dissolved Cu in overlying water was 0.052−0.146

#### *3.3. Variation of Dissolved Cu Concentration in the Overlying Water 3.3. Variation of Dissolved Cu Concentration in the Overlying Water* mg/L. In Stage III, a rapid increase was observed in the dissolved Cu concentration after the wave was

The variations of dissolved Cu concentrations in overlying water in the three stages were presented in Figure 6. The variations of dissolved Cu concentrations in overlying water in the three stages were presented in Figure 6. loaded, and the concentration kept increasing till the end of the experiment. The variation range was 0.107−0.188 mg/L.

**Figure 6.** Variation of Cu concentration in water during different stages ((**a**): Stage I; (**b**): Stage II; (**c**): Stage III). **Figure 6.** Variation of Cu concentration in water during different stages ((**a**): Stage I; (**b**): Stage II; (**c**): Stage III).

*3.4. Vertical Distribution and Change of Cu Concentration in Sediment*  In Stage I, there was no wave loaded and the sediment was under a consolidation phase for 40 h. The dissolved Cu concentration in the overlying water increased with consolidation time.

In Stage I, the sediment was consolidated for 40 h under hydrostatic pressure. The depth of sediment surface descended by approximately 1 cm during this period. In Stage II, the sediment was liquefied under wave action, and the height of the sediment surface measured from the bottom of the In Stage II, the Cu concentration increased at the beginning of this stage and reached a peak value after 30 min of wave action. A decrease trend was observed afterwards. After 60 min of wave action,

**Figure 7.** Vertical profiles of Cu concentration in the columnar sediment samples at the end of each

stage.

analyzed, and the vertical profiles of Cu contents in the sediment were presented in Figure 7.

mg/L.

0.107−0.188 mg/L.

the dissolved Cu concentration reached a relatively stable state. The dissolved Cu concentration in overlying water variation range of dissolved Cu in overlying water was 0.052–0.146 mg/L.

*J. Mar. Sci. Eng.* **2019**, *7*, x 8 of 14

action, the dissolved Cu concentration reached a relatively stable state. The dissolved Cu concentration in overlying water variation range of dissolved Cu in overlying water was 0.052−0.146

In Stage III, a rapid increase was observed in the dissolved Cu concentration after the wave was loaded, and the concentration kept increasing till the end of the experiment. The variation range was

In Stage III, a rapid increase was observed in the dissolved Cu concentration after the wave was loaded, and the concentration kept increasing till the end of the experiment. The variation range was 0.107–0.188 mg/L. **Figure 6.** Variation of Cu concentration in water during different stages ((**a**): Stage I; (**b**): Stage II; (**c**): Stage III). *3.4. Vertical Distribution and Change of Cu Concentration in Sediment* 

#### *3.4. Vertical Distribution and Change of Cu Concentration in Sediment* In Stage I, the sediment was consolidated for 40 h under hydrostatic pressure. The depth of

In Stage I, the sediment was consolidated for 40 h under hydrostatic pressure. The depth of sediment surface descended by approximately 1 cm during this period. In Stage II, the sediment was liquefied under wave action, and the height of the sediment surface measured from the bottom of the soil tank descended by another 2 cm at the end of this stage. During Stage III, under the 13.5 cm wave action, the height of sediment surface was relatively stable and the it descended by approximately 1 cm comparing with that at the end of stage II. The Cu concentration in the columnar samples were analyzed, and the vertical profiles of Cu contents in the sediment were presented in Figure 7. sediment surface descended by approximately 1 cm during this period. In Stage II, the sediment was liquefied under wave action, and the height of the sediment surface measured from the bottom of the soil tank descended by another 2 cm at the end of this stage. During Stage III, under the 13.5 cm wave action, the height of sediment surface was relatively stable and the it descended by approximately 1 cm comparing with that at the end of stage II. The Cu concentration in the columnar samples were analyzed, and the vertical profiles of Cu contents in the sediment were presented in Figure 7.

**Figure 7.** Vertical profiles of Cu concentration in the columnar sediment samples at the end of each **Figure 7.** Vertical profiles of Cu concentration in the columnar sediment samples at the end of each stage.

stage. At the end of Stage I, the Cu concentrations in the sediment at a depth of 5–10 cm, where the polluted slurry was initially paved, were higher than other parts of the sediment, and the range of Cu concentration was 32–4540 mg/kg. At the end of Stages II and stage III, the layers with higher Cu concentration moved downward. The ranges of Cu concentration at the end of these two stages were 201–4060 mg/kg and 284–3450 mg/kg, respectively. As presented in Figure 7, Cu in the polluted layer diffused into the upper and lower layers, and the amount of upward diffusion was larger than that of downward diffusion.
