**3. Results**

On account of the quality of samples for particulate Cu analysis in overlying water failed to meet the minimum level for digestion analysis, only the dissolved Cu in the overlying water were discussed in this paper.

**3. Results** 

(FAAS).

*2.5. Quality Control* 

#### *3.1. Sediment Liquefaction Process under Wave Action 3.1. Sediment Liquefaction Process under Wave Action*

recovery rates of heavy metals were above 90%.

A layer of electrostatic transparent membrane, on which the liquefaction interfaces were marked, was pasted on the side wall of the sediment tank. The photos of marked interfaces were also taking simultaneously. The marked interfaces were measured every 6 cm at horizontal direction, and a series of curves presenting the variation of liquefaction interfaces was presented in Figure 4. A layer of electrostatic transparent membrane, on which the liquefaction interfaces were marked, was pasted on the side wall of the sediment tank. The photos of marked interfaces were also taking simultaneously. The marked interfaces were measured every 6 cm at horizontal direction, and a series of curves presenting the variation of liquefaction interfaces was presented in Figure 4.

*J. Mar. Sci. Eng.* **2019**, *7*, x 6 of 14

The collected water samples were immediately filtered through 0.45 μm cellulose acetate membranes. The filtrate was then digested by nitric acid followed by Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). The dissolved Cu in sediment samples was pretreated following the instructions in the pretreatment guideline of heavy metals analysis in the marine sediments and organisms-Microwave assisted acid digestion [35] followed by Fire Atomic Absorption Spectroscopy

All reagents used in the analysis were guaranteed reagents, and freshly prepared deionized water was used in the analysis and to rinse all the sampling instruments. Detection limits of FAAS for Cu was 0.0045 mg/L. To guarantee the data accuracy, a blank sample was set and all the samples were determined in triplicate. Average values of these three tests were applied in the present study. Offshore marine sediment (GBW07314) was used as the reference material in the analysis. The

On account of the quality of samples for particulate Cu analysis in overlying water failed to meet

*2.4. Analytical Methods of Cu Concentrations in Water and Sediment Samples* 

**Figure 4. Figure 4.**  Curves presenting the variation of liquefaction interfaces in Stage II ( Curves presenting the variation of liquefaction interfaces in Stage II (**a**) and Stage III (**b**). **a**) and Stage III (**b**).

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