Joint effect of aquaculture and land reclamation on sediment dynamics

Study region: Sansha Bay, China Study focus: The rapid development of global coastal aquaculture and land reclamation are significantly changing the offshore sediment dynamics system. Based on remote sensing, in-situ observation, digital elevation models and numerical simulation, the research surveyed and simulated changes in aquaculture and land reclamation areas, their effects on sediment dynamics, and the resulting bed erosion/deposition in Sansha Bay from 2005 to 2020. New hydrological insights for the region: From 2005–2020, aquaculture and land reclamation areas increased from 6.2 km² and 16.5 km² to 154 km² and 55.3 km², respectively. In the subtidal area, the sharp increase in aquaculture area dominated the changes in sediment dynamics, altering the vertical velocity profile from a logarithmic to bow shape due to double boundary effect of top aquaculture and bottom bed. This effect shifted maximum velocity layer downward to 0.4–0.6H and the average bottom velocity increased by 10 %, the bottom suspended sediment concentration (SSC) increased 26 %, resulting in a 102 % increase in bed erosion. While in intertidal flat, increased land reclamation dominated the changes in sediment dynamics and weakened the hydrodynamics due to dam reflection effect. This effect decreased bottom velocity by 15 % and SSC by 22 %, resulting in a 153 % increase in bed deposition. This study provides a reference case for the impact of offshore aquaculture and land reclamation on sediment dynamics.