In this study, we sampled the original sediment columns from three points located in the eastern, central, and western areas of Chaohu Lake, and then investigated sediment resuspension under hydraulic disturbances in the laboratory. The results showed that when the hydraulic disturbance is weak and sediment surface shear stress is small (<0.02 N/m²‌), sediment surface layer moves alone. When the hydraulic disturbance is moderate and sediment surface shear stress is within a threshold (3.7 N/m²‌), only a small proportion of the surface sediments begins to move. However, when the hydraulic disturbance is further strengthened and sediment surface shear stress is larger than the threshold value, surface sediments move smoothly. By the experimental results, we found that the plankton layer is about 1 mm (1.56% of the maximum content of suspended matter (SSC_max)), which is the major contribution of individual sediment initiation. The new sediment layer is about 19–22 mm (20.9% of the SSC_max), which considerably affects sediment resuspension in shallow lakes. The consolidated layer is about 22 mm below the bed surface, which requires high shear stress and is hard to be transferred to the water column. The quantified experimental observation results are further verified with the theoretical results.

Shallow water has low depth, and hydrodynamic conditions may change with the effect of wind and waves, resulting in sediment suspension and pollutant release. To investigate the influence of sediment incipient motion on ammonia nitrogen (NH₃-N) release in shallow lakes under hydrodynamic disturbance, we monitored ammonia nitrogen concentration in the overlying water of sediments in Chaohu Lake under static, weak, and strong disturbance conditions and analyzed the ammonia nitrogen release rate based on the these concentrations. In static condition, the sediment particles on the surface moved individually (individual movement), and the ammonia nitrogen release rate was 9.59 mg/m²/day. When the disturbance was weak and a small proportion of sediment particles started to move (small movement), the ammonia nitrogen release rate increased to 34.21 mg/m²/day. When the disturbance was further strengthened, and most of the sediment particles moved (general movement), the ammonia nitrogen release rate was 77.04 mg/m²/day. Distribution showed that the release rate varied the most in the western area followed by the eastern area, and the central area had the lowest release rate. The daily release of ammonia nitrogen in Chaohu Lake ranged from 8742.3 kg to 61,008.59 kg. In this experiment, we combined sediment movement and pollutant release, which provides a new reference for the study of pollutant release in shallow lakes and for ammonia nitrogen management in other shallow lakes.

HIGHLIGHTS. The assessment method of water quality change in the reservoir bay was established.The corresponding relationship between hydrodynamic conditions an