Linwei Dai

A GPU-accelerated shallow water model with a local time-step (LTS) is employed in this work to examine how the Coriolis forces affect the tidal level difference and, consequently, the water–sediment exchange between Hangzhou Bay (HZB) and the Yangtze River Estuary. The model is applied to both idealized and realistic estuary configurations to analyze tidal level gradients between the two neighboring estuaries under different flow conditions and with and without the Coriolis force condition. The model’s accuracy in predicting tidal levels and currents was validated against field data. It is shown that the tidal level gradient is negative during flood tide, indicating a mass transfer trend from south to north, whereas the tidal level gradient is positive during ebb tide, indicating a north-to-south mass transfer. Considering sediment originates mainly from the riverine side, the sediment mass transfer may occur mainly during ebb tide, and the direction is from the Yangtze River to the HZB. This finding provides numerical evidence for previous recognition that sediment in HZB mainly comes from the Yangtze River Estuary. A comparison of the idealized and realistic estuary configurations further indicates that the contrasting bed topography enhances tidal level gradients. The findings show that by causing tidal phase changes and asymmetric tidal range modifications, the Coriolis force increases lateral water level gradients (up to 0.7 m) between the Yangtze Estuary and Hangzhou Bay. Idealized modeling further demonstrates that higher Coriolis coefficients promote sediment exchange and exacerbate water level fluctuations across estuaries. Without the Coriolis effect, the tide level distribution in adjacent estuaries is symmetrical. In the Northern and Southern Hemispheres, the tide level distribution in adjacent estuaries is the opposite. In addition, this study has shown that changes in river flow have a limited effect on water levels at stations farther from the estuary’s flow intake and therefore have a negligible effect on the water level gradient in adjacent estuaries farther away. However, topography differences have a significant effect on water level gradients in neighboring estuaries. These studies emphasize the significance of the Coriolis force in regulating sediment transport pathways in estuaries.

In order to study the impact of artificial reef construction on marine carbon sinks, a one-year monitoring and analysis were carried out in the Sanheng artificial reef areas of Shengsi Island. The main parameters observed were sea surface temperature, salinity, pH, total alkalinity (TA), and dissolved inorganic carbon (DIC). The partial pressure of CO₂ (pCO_2w) in the surface water and the CO₂ flux (FCO₂) across the sea–air interface were calculated and analyzed. The results showed that the annual range of surface water pCO_2w was 34.48~501.53 μatm, and the partial pressure of CO₂ decreases in the following order: winter, spring, autumn, summer. The FCO₂ was significantly negatively correlated with temperature and significantly positively correlated with salinity and TA. The FCO₂ in the four seasons decreases in the following order: winter, spring, autumn, summer. The annual sea–air flux in the survey area ranged from −108.79 to 41.74 mmol m⁻² d⁻¹. In winter, both the reef area and the control area displayed positive FCO₂ values, indicating a source of CO₂, while in the other three seasons, CO₂ flux values were negative, indicating an overall CO₂ sink. Additionally, in autumn, the reef area exhibited a stronger CO₂ sink than the control area. The results indicated that the construction of artificial reefs has a certain carbon sink effect, with no significant difference in effectiveness between different artificial reef construction models.